tag:theconversation.com,2011:/nz/topics/geophysics-12335/articlesGeophysics – The Conversation2023-11-29T23:11:39Ztag:theconversation.com,2011:article/2172862023-11-29T23:11:39Z2023-11-29T23:11:39ZNew unified theory shows how past landscapes drove the evolution of Earth’s rich diversity of life<p>Earth’s surface is the living skin of our planet – it connects the physical, chemical and biological systems.</p>
<p>Over geological time, this surface evolves. Rivers fragment the landscape into an environmentally diverse range of habitats. These rivers also transfer sediments from the mountains to the continental plains and ultimately the oceans. </p>
<p>The idea that landscapes have influenced the trajectory of life on our planet has a long history, dating back to the early 19th century scientific narratives of German polymath <a href="https://learningfromlandscapes.com/2019/06/11/humboldt-the-invention-of-nature/">Alexander von Humboldt</a>. While we’ve learnt more since then, many aspects of biodiversity evolution remain enigmatic. For example, it’s still unclear why there is a 100-million-year gap between the explosion of marine life and the development of plants on continents.</p>
<p>In research <a href="https://www.nature.com/articles/s41586-023-06777-z">published in Nature</a> today, we propose a new theory that relates the evolution of biodiversity over the past 540 million years to sediment “pulses” controlled by past landscapes.</p>
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<h2>10 years of computational time</h2>
<p>Our simulations are based on an open-source code released as part of a <a href="https://theconversation.com/scientists-just-revealed-the-most-detailed-geological-model-of-earths-past-100-million-years-200898">Science paper</a> published earlier this year.</p>
<p>To drive the evolution of the landscape through space and time in our computer model, we used a series of reconstructions for what the climate and tectonics were like in the past.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two colourful computer simulated Earth globes side by side" src="https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=291&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=291&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=291&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=365&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=365&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558304/original/file-20231108-27-yqmk6n.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=365&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">These two globes from our simulation show landscapes 200 million years ago (just before the Pangea supercontinent broke up, left) and 15 million years ago (right), after the formation of the Andes, Alps and Himalayas.</span>
<span class="attribution"><span class="source">Author provided</span></span>
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<p>We then compared the results of our global simulations with reconstructions of marine and continental biodiversity over the past 540 million years.</p>
<p>To perform our computer simulations, we took advantage of Australia’s <a href="https://nci.org.au/">National Computational Infrastructure</a> running on several hundreds of processors. The combined simulations presented in our study are equivalent to ten years of computational time.</p>
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Read more:
<a href="https://theconversation.com/how-the-earths-last-supercontinent-broke-apart-to-form-the-world-we-have-today-131632">How the Earth's last supercontinent broke apart to form the world we have today</a>
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<h2>Marine life and river sediment were closely linked</h2>
<p>In our model, we discovered that the more sediment rivers carried into the oceans, the more the sea life diversified (a positive correlation). You can see this tracked by the red line in the chart below. </p>
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<a href="https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=222&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=222&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=222&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=279&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=279&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560720/original/file-20231121-3914-t01a3j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=279&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Reconstructed sediment fluxes to the oceans (red line) versus diversity of marine animals (black line, adapted from C. Bentley using Sepkoski’s compendium) from the Cambrian through to the Neogene.</span>
<span class="attribution"><span class="source">Author provided</span></span>
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<p>As the continents weather, rivers don’t just carry sediment into the oceans, they also bring a large quantity of nutrients. These nutrients, such as carbon, nitrogen and phosphorus, are essential to the <a href="https://www.britannica.com/science/biogeochemical-cycle">biological cycles</a> that move vital elements through all living things.</p>
<p>This is why we think rivers delivering more or less nutrients to the ocean – on a geological timescale of millions of years – is related to the diversification of marine life.</p>
<p>Perhaps even more surprisingly, we found that episodes of mass extinctions in the oceans happened shortly after significant decreases in sedimentary flow. This suggests that a lack or deficiency of nutrients can destabilise biodiversity and make it vulnerable to catastrophic events (like asteroid impacts or volcanic eruptions).</p>
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Read more:
<a href="https://theconversation.com/what-is-a-mass-extinction-and-are-we-in-one-now-122535">What is a 'mass extinction' and are we in one now?</a>
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<h2>Landscapes also drove the diversity of plants</h2>
<p>On the continents, we designed a variable that integrates sediment cover and landscape ruggedness to describe the continents’ capacity to host diverse species. </p>
<p>Here we also found a striking correlation (see below) between our variable and plant diversification for the past 400 million years. This highlights how changes in landscape also have a strong influence on species diversifying on land. </p>
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<a href="https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=232&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=232&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=232&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=291&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=291&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560719/original/file-20231121-27-hlx0p3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=291&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Sediment cover in continental regions (black line) versus the long-term trend in land-plant diversity. Illustrations from Rebecca Horwitt.</span>
<span class="attribution"><span class="source">Author provided</span></span>
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<p>We hypothesise that as Earth’s surface was gradually covered with thicker soil, richer in nutrients deposited by rivers, plants could develop and diversify with more elaborate root systems. </p>
<p>As plants slowly expanded across the land, the planet ended up hosting varied environments and habitats with favourable conditions for plant evolution, such as the emergence of flowering plants some 100 million years ago.</p>
<h2>A living planet</h2>
<p>Overall, our findings suggest the diversity of life on our planet is strongly influenced by landscape dynamics. At any given moment, Earth’s landscapes determine the maximum number of different species continents and oceans can support.</p>
<p>This shows it’s not just tectonics or climates, but their interactions that determine the long-term evolution of biodiversity. They do this through sediment flows and changes to the landscapes at large.</p>
<p>Our findings also show that biodiversity has always evolved at the pace of plate tectonics. That’s a pace incomparably slower than the current rate of extinction caused by human activity.</p>
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Read more:
<a href="https://theconversation.com/five-ways-you-can-help-stop-biodiversity-loss-in-your-area-and-around-the-world-196746">Five ways you can help stop biodiversity loss in your area – and around the world</a>
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<img src="https://counter.theconversation.com/content/217286/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This research was undertaken with resources from the National Computational Infrastructure supported by the Australian Government and from Artemis HPC supported by the University of Sydney. This work was supported by an Australian Research Council grant.</span></em></p><p class="fine-print"><em><span>Beatriz Hadler Boggiani, Laurent Husson, and Manon Lorcery do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>For decades, scientists have tried to uncover the cause of long-term changes in Earth’s biodiversity. New simulations point at geography playing a critical role.Tristan Salles, Senior Lecturer, University of SydneyBeatriz Hadler Boggiani, PhD Candidate, University of SydneyLaurent Husson, Earth sciences researcher, Université Grenoble Alpes (UGA)Manon Lorcery, PhD Candidate, Université Grenoble Alpes (UGA)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2095932023-08-10T03:24:09Z2023-08-10T03:24:09ZNew evidence suggests the world’s largest known asteroid impact structure is buried deep in southeast Australia<figure><img src="https://images.theconversation.com/files/542059/original/file-20230810-25-7n4kt.png?ixlib=rb-1.1.0&rect=43%2C0%2C2600%2C1005&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Google Maps</span></span></figcaption></figure><p><em>Acknowledgment: I’d like to thank my colleague Tony Yeates, who originated the view of the Deniliquin multi-ring structure as an impact structure – and who was instrumental to this work.</em></p>
<p>In <a href="https://www.sciencedirect.com/science/article/abs/pii/S0040195122002487">recent research</a> published by myself and my colleague Tony Yeates in the journal Tectonophysics, we investigate what we believe – based on many years of experience in asteroid impact research – is the world’s largest known impact structure, buried deep in the earth in southern New South Wales.</p>
<p>The Deniliquin structure, yet to be further tested by drilling, spans up to 520 kilometres in diameter. This exceeds the size of the near-300km-wide <a href="https://en.wikipedia.org/wiki/Vredefort_impact_structure">Vredefort</a> impact structure in South Africa, which to date has been considered the world’s largest.</p>
<h2>Hidden traces of Earth’s early history</h2>
<p>The history of Earth’s bombardment by asteroids is largely concealed. There are a few reasons for this. The first is erosion: the process by which gravity, wind and water slowly wear away land materials through time. </p>
<p>When an asteroid strikes, it creates a crater with an uplifted core. This is similar to how a drop of water splashes upward from a transient crater when you drop a pebble in a pool. </p>
<p>This central uplifted dome is a key characteristic of large impact structures. However, it can erode over thousands to millions of years, making the structure difficult to identify.</p>
<p>Structures can also be buried by sediment through time. Or they might disappear as a result of subduction, wherein tectonic plates can collide and slide below one another into Earth’s mantle layer.</p>
<p>Nonetheless, new geophysical discoveries are unearthing signatures of impact structures formed by asteroids that may have reached tens of kilometres across – heralding a paradigm shift in our understanding of how Earth evolved over eons. These include pioneering discoveries of impact “ejecta”, which are the materials thrown out of a crater during an impact. </p>
<p><a href="https://www.sciencedirect.com/science/article/abs/pii/S1387647317300714">Researchers think</a> the oldest layers of these ejecta, found in sediments in early terrains around the world, might signify the tail end of the Late Heavy Bombardment of Earth. The <a href="https://www.sciencedirect.com/science/article/abs/pii/S1387647317300714">latest evidence</a> suggests Earth and the other planets in the Solar System were subject to intense asteroid bombardments until about 3.2 billion years ago, and sporadically since.</p>
<p>Some large impacts are correlated with mass extinction events. For example, the <a href="https://en.wikipedia.org/wiki/Alvarez_hypothesis">Alvarez hypothesis</a>, named after father and son scientists Luis and Walter Alvarez, explains how non-avian dinosaurs were wiped out as a result of a large asteroid strike some 66 million years ago.</p>
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Read more:
<a href="https://theconversation.com/we-found-the-worlds-oldest-asteroid-strike-in-western-australia-it-might-have-triggered-a-global-thaw-130192">We found the world's oldest asteroid strike in Western Australia. It might have triggered a global thaw</a>
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<h2>Uncovering the Deniliquin structure</h2>
<p>The Australian continent and its predecessor continent, <a href="https://en.wikipedia.org/wiki/Gondwana">Gondwana</a>, have been the target of numerous asteroid impacts. These have resulted in at least 38 confirmed and 43 potential impact structures, ranging from relatively small craters to large and completely buried structures.</p>
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<a href="https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=516&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=516&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=516&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=649&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=649&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541853/original/file-20230809-24-hpgo51.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=649&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">This map shows the distribution of circular structures of uncertain, possible or probable impact origin on the Australian continent and offshore. Green dots represent confirmed impact craters. Red dots represent confirmed impact structures that are more than 100km wide, whereas red dots inside white circles are more than 50km wide. Yellow dots represent likely impact structures.</span>
<span class="attribution"><span class="source">Andrew Glikson and Franco Pirajno</span></span>
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<p>As you’ll recall with the pool and pebble analogy, when a large asteroid hits Earth, the underlying crust responds with a transient elastic rebound that produces <a href="https://www.lpi.usra.edu/publications/books/CB-954/CB-954.pdf">a central dome</a>. </p>
<p>Such domes, which can slowly erode and/or become buried through time, may be all that’s preserved from the original impact structure. They represent the deep-seated “root zone” of an impact. Famous examples are found in the Vredefort impact structure and the 170km-wide <a href="https://en.wikipedia.org/wiki/Chicxulub_crater">Chicxulub crater</a> in Mexico. The latter represents the impact that caused the extinction of the dinosaurs.</p>
<p>Between 1995 and 2000, Tony Yeates suggested magnetic patterns beneath the Murray Basin in New South Wales <a href="https://www.aseg.org.au/publications/preview-old">likely represented</a> a massive, buried impact structure. An analysis of the region’s updated geophysical data between 2015 and 2020 confirmed the existence of a 520km diameter structure with a seismically defined dome at its centre.</p>
<p>The Deniliquin structure has all the features that would be expected from a large-scale impact structure. For instance, magnetic readings of the area reveal a symmetrical rippling pattern in the crust around the structure’s core. This was likely produced during the impact as extremely high temperatures created intense magnetic forces.</p>
<p>A central low magnetic zone corresponds to 30km-deep deformation above a seismically defined mantle dome. The top of this dome is about 10km <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GL065345">shallower than the top</a> of the regional mantle.</p>
<p>Magnetic measurements also show evidence of “radial faults”: fractures that radiate from the centre of a large impact structure. This is further accompanied by small magnetic anomalies which may represent igneous “dikes”, which are sheets of magma injected into fractures in a pre-existing body of rock. </p>
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<figcaption>
<span class="caption">This ‘total magnetic intensity’ image of the Deniliquin impact structure portrays its 520km-diameter multi-ring pattern, the central core, radial faults and the location of shallow drill holes.</span>
<span class="attribution"><a class="source" href="https://www.sciencedirect.com/science/article/abs/pii/S0040195122002487">Data from Geoscience Australia, published in Glikson and Yeates, 2022</a></span>
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<p>Radial faults, and igneous sheets of rocks that form within them, are typical of large impact structures and can be found in the Vredefort structure and the <a href="https://journals.uair.arizona.edu/index.php/maps/article/viewFile/14921/14892">Sudbury impact structure</a> in Canada.</p>
<p>Currently, the bulk of the evidence for the Deniliquin impact is based on geophysical data obtained from the surface. For proof of impact, we’ll need to collect physical evidence of shock, which can only come from drilling deep into the structure.</p>
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Read more:
<a href="https://theconversation.com/these-5-spectacular-impact-craters-on-earth-highlight-our-planets-wild-history-197618">These 5 spectacular impact craters on Earth highlight our planet's wild history</a>
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<h2>When did the Deniliquin impact happen?</h2>
<p>The Deniliquin structure was likely located on the eastern part of the Gondwana continent, prior to it splitting off into several continents (including the Australian continent) much later.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=344&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=344&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=344&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=432&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=432&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541858/original/file-20230809-21-qpfxif.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=432&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Deniliquin structure was likely created in eastern Gondwana during the Late Ordovician.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41598-022-08941-3#rightslink">Zhen Qiu et al, 2022</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The impact that caused it may have occurred during what’s known as the Late Ordovician mass extinction event. Specifically, I think it may have triggered what’s called the <a href="https://www.britannica.com/science/Ordovician-Silurian-extinction">Hirnantian glaciation stage</a>, which lasted between 445.2 and 443.8 million years ago, and is also defined as the <a href="https://www.sciencedirect.com/science/article/abs/pii/S1342937X23000655">Ordovician-Silurian extinction event</a>. </p>
<p>This huge glaciation and mass extinction event <a href="https://www.britannica.com/science/Ordovician-Silurian-extinction">eliminated</a> about 85% of the planet’s species. It was more than double the scale of the <a href="https://en.wikipedia.org/wiki/Alvarez_hypothesis">Chicxulub impact</a> that killed off the dinosaurs. </p>
<p>It is also possible the Deniliquin structure is older than the Hirnantian event, and may be of an early Cambrian origin (about 514 million years ago). The next step will be to gather samples to determine the structure’s exact age. This will require drilling a deep hole into its magnetic centre and dating the extracted material. </p>
<p>It’s hoped further studies of the Deniliquin impact structure will shed new light on the nature of early <a href="https://www.livescience.com/37584-paleozoic-era.html">Paleozoic</a> Earth.</p><img src="https://counter.theconversation.com/content/209593/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Glikson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Research on the Deniliquin structure points to an asteroid impact that would have been more than double the scale of the one that killed the dinosaurs.Andrew Glikson, Adjunct professor, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2049052023-05-08T20:11:01Z2023-05-08T20:11:01ZSupercomputers have revealed the giant ‘pillars of heat’ funnelling diamonds upwards from deep within Earth<figure><img src="https://images.theconversation.com/files/524817/original/file-20230508-27-u0wox4.jpg?ixlib=rb-1.1.0&rect=32%2C24%2C5359%2C3564&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Most diamonds are formed deep inside Earth and brought close to the surface in small yet powerful volcanic eruptions of a kind of rock called “kimberlite”. </p>
<p>Our <a href="https://www.nature.com/articles/s41561-023-01181-8">supercomputer modelling</a>, published in Nature Geoscience, shows these eruptions are fuelled by giant “pillars of heat” rooted 2,900 kilometres below ground, just above our planet’s core.</p>
<p>Understanding Earth’s internal history can be used to target mineral reserves – not only diamonds, but also crucial minerals such as nickel and rare earth elements. </p>
<h2>Kimberlite and hot blobs</h2>
<p>Kimberlite eruptions leave behind a characteristic deep, carrot-shaped “pipe” of kimberlite rock, which often contains diamonds. <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X17307124">Hundreds of these eruptions</a> that occurred over the past 200 million years have been discovered around the world. Most of them were found in Canada (178 eruptions), South Africa (158), Angola (71) and Brazil (70).</p>
<p><iframe id="FbdgL" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/FbdgL/3/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Between Earth’s solid crust and molten core is the mantle, a thick layer of slightly goopy hot rock. For decades, geophysicists have used computers to study how the mantle slowly flows over long periods of time. </p>
<p>In the 1980s, <a href="https://www.sciencedirect.com/science/article/pii/0012821X84900438">one study showed</a> that kimberlite eruptions might be linked to small thermal plumes in the mantle – feather-like upward jets of hot mantle rising due to their higher buoyancy – beneath slowly moving continents. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/volcanoes-diamonds-and-blobs-a-billion-year-history-of-earths-interior-shows-its-more-mobile-than-we-thought-179673">Volcanoes, diamonds, and blobs: a billion-year history of Earth's interior shows it's more mobile than we thought</a>
</strong>
</em>
</p>
<hr>
<p>It had <a href="https://www.nature.com/articles/230042a0">already been argued</a>, in the 1970s, that these plumes might originate from the boundary between the mantle and the core, at a depth of 2,900km.</p>
<p>Then, in 2010, <a href="https://www.nature.com/articles/nature09216">geologists proposed</a> that kimberlite eruptions could be explained by thermal plumes arising from the edges of two deep, hot blobs anchored under Africa and the Pacific Ocean.</p>
<p>And last year, <a href="https://theconversation.com/volcanoes-diamonds-and-blobs-a-billion-year-history-of-earths-interior-shows-its-more-mobile-than-we-thought-179673">we reported that</a> these anchored blobs are more mobile than we thought.</p>
<p>However, we still didn’t know exactly how activity deep in the mantle was driving kimberlite eruptions.</p>
<h2>Pillars of heat</h2>
<p>Geologists assumed that mantle plumes could be responsible for igniting kimberlite eruptions. However, there was still a big question remaining: how was heat being transported from the deep Earth up to the kimberlites?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=494&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=494&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=494&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=621&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=621&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524728/original/file-20230506-35349-epn7ao.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=621&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A snapshot of the global mantle convection model centred on subduction underneath the South American plate.</span>
<span class="attribution"><span class="source">Ömer F. Bodur</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>To address this question, we used <a href="https://nci.org.au">supercomputers</a> in Canberra, Australia to create three-dimensional geodynamic models of Earth’s mantle. Our models account for the movement of continents on the surface and into the mantle over the past one billion years. </p>
<p>We calculated the movements of heat upward from the core and discovered that broad mantle upwellings, or “pillars of heat”, connect the very deep Earth to the surface. Our modelling shows these pillars supply heat underneath kimberlites, and they explain most kimberlite eruptions over the past 200 million years. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=303&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=303&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=303&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=381&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=381&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524816/original/file-20230508-23-g6oon7.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=381&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A schematic representation of Earth’s heat pillars and how they bring heat to kimberlites, based on output from our geodynamic model.</span>
<span class="attribution"><span class="source">Ömer F. Bodur</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The model successfully captured kimberlite eruptions in Africa, Brazil, Russia and partly in the United States and Canada. Our models also predict previously undiscovered kimberlite eruptions occurred in East Antarctica and the Yilgarn Craton of Western Australia. </p>
<figure>
<iframe src="https://player.vimeo.com/video/824007338" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s “pillars of heat” in a global mantle convection model can be used to predict kimberlite eruptions. Credit: Ömer F. Bodur.</span></figcaption>
</figure>
<p>Towards the centre of the pillars, mantle plumes rise much faster and carry dense material across the mantle, which may explain chemical differences between kimberlites in <a href="https://www.nature.com/articles/s41561-023-01181-8">different continents</a>.</p>
<p>Our models do not explain some of the kimberlites in Canada, which might be related to a different geological process called “plate subduction”. We have so far predicted kimberlites back to one billion years ago, which is the current limit of <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012825220305237">reconstructions of tectonic plate movements</a>.</p><img src="https://counter.theconversation.com/content/204905/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ömer Bodur was supported by funding from the Australian Research Council and from De Beers.</span></em></p><p class="fine-print"><em><span>Nicolas Flament receives funding from the Australian Research Council and from De Beers.</span></em></p>The volcanic eruptions that bring diamonds to Earth’s surface are driven by ‘pillars of heat’ stretching deep inside the planet.Ömer F. Bodur, Honorary Fellow, University of WollongongNicolas Flament, Associate Professor, University of WollongongLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2013942023-05-04T20:03:03Z2023-05-04T20:03:03ZRemarkable new tech has revealed the ancient landscape of Arnhem Land that greeted Australia’s First Peoples<figure><img src="https://images.theconversation.com/files/519170/original/file-20230404-21-omaerx.jpg?ixlib=rb-1.1.0&rect=793%2C0%2C4626%2C3794&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The view from the Arnhem Land escarpment over the floodplains that contain a hidden landscape.</span> <span class="attribution"><span class="source">Ian Moffat</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Many visitors to Arnhem Land in the Northern Territory are struck by the magnificent cliffs, stunning bird life and extraordinary rock art. Some may know this landscape includes the earliest evidence of human occupation in what is now Australia, at Madjedbebe, where signs of habitation have been dated to 65,000 years ago.</p>
<p>Most people, however, ignore the expansive floodplains surrounding these sites, especially when they are covered by water during the wet season.</p>
<p>Our research, recently published in <a href="https://doi.org/10.1371/journal.pone.0283006">PLOS One</a>, shows these floodplains hide a complex landscape buried deep underground critical to understanding the deep history of the region. We have mapped the cliffs and rivers, more than 15 metres below the current surface, which would have greeted the first people to arrive here.</p>
<h2>Red Lily Lagoon</h2>
<p>This landscape has been transformed by a sea-level rise of more than 120 metres, which brought the coastline from more than 200 kilometres away to lap directly on the cliffs in the Red Lily Lagoon area in Western Arnhem Land. </p>
<p>Since then, the East Alligator River has filled this region with sediment and the coast has retreated 60 kilometres to the northeast, leaving the current landscape of jagged sandstone cliffs surrounded by flat floodplains, which are seasonally flooded.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519171/original/file-20230404-17-14454r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Arnhem Land is home to an extraordinary array of rock art.</span>
<span class="attribution"><span class="source">Ian Moffat</span></span>
</figcaption>
</figure>
<p>The buried landscape we have mapped contains a sandstone escarpment, now buried underground, which has great potential to contain archaeological sites. This overlooked a deep valley that contained a river system, which is now buried by more than 15 metres of sediment. </p>
<p>Eventually, around 8,000 years ago, this river system was flooded by sea-level rise, leading to mangroves filling the valley and levelling it with marine sediments built up between the roots of the mangrove trees.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two photos: the top one shows a flat plain with a rocky escarpment in the background, the bottom shows the same view but with the foreground filled with brackish water and mangrove trees." src="https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=698&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=698&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=698&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=877&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=877&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524276/original/file-20230504-20-my8xg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=877&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A digital reconstruction shows a view of the Red Lily Lagoon area today (top) and the same view around 7,000 years ago (bottom), when the ocean lapped against the rocky escarpment.</span>
<span class="attribution"><span class="source">Jarrad Kowlessar</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>These major changes in the local environments are also visible through materials excavated from Madjedbebe and other sites in the area. </p>
<p>The excavations show people in the area ate land animals and freshwater fish before the valley flooded. But afterwards, diets changed to take advantage of the ample supply of shellfish.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/buried-tools-and-pigments-tell-a-new-history-of-humans-in-australia-for-65-000-years-81021">Buried tools and pigments tell a new history of humans in Australia for 65,000 years</a>
</strong>
</em>
</p>
<hr>
<h2>Modern maps of an ancient landscape</h2>
<p>Previous work in Arnhem Land using drilling has provided some information about the history of the landscape, but our research achieves much greater detail.</p>
<p>Our work used a technique called electrical resistivity tomography. This is when we pass an electrical current through the ground to measure the nature of the sediments and rocks beneath the surface. This method can map more than 50 metres below the surface, and because it doesn’t involve digging or drilling, we could work right up to existing archaeological sites.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519167/original/file-20230404-27-qweuse.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Electrical resistivity tomography equipment used to image the subsurface of the floodplains near Red Lily Lagoon, Arnhem Land.</span>
<span class="attribution"><span class="source">Ian Moffat</span></span>
</figcaption>
</figure>
<p>We combined this data with aerial mapping of the modern landscape undertaken with a drone and an airborne laser. This allows us to compare the subsurface results to the contemporary land surface and get a good understanding for just how much change has occurred up to the present day.</p>
<p>While geophysics techniques like these are often used to find and map archaeological sites, we instead focused on reconstructing the ancient landscape itself. Knowing how landscapes have changed provides important context for understanding choices people may have made about where to live, what to eat and how to move around.</p>
<h2>What lies beneath?</h2>
<p>This research paints a new picture of the landscape that greeted the First Peoples on their arrival. This older buried landscape, which is so different to the modern one, was occupied for most of the history of human activity in the area – starting over 60,000 years ago and lasting until just 8,000 years ago. </p>
<p>The past 8,000 years have seen dramatic changes, from a dry river valley to a mangrove forest to today’s seasonally inundated flood plains. These changes would have had important implications for people, including in terms of what they could eat and drink, and where they could live.</p>
<p>Some archaeologists have questioned the accuracy of the dates of occupation determined from the Madjebebe site. Criticism has focused on possible disturbance to the site by <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/gea.21822">termite activity</a>, and also the <a href="https://www.pnas.org/doi/full/10.1073/pnas.1808385115">lack of other sites of a similar age</a> in the region.</p>
<p>Our research shows why a lack of other sites may not be surprising: the most likely places for people to have lived when they first occupied this area are now buried more than 10 metres beneath the floodplain. </p>
<h2>‘We want people to see’</h2>
<p>Beyond Red Lily Lagoon, the methods we have used will give archaeologists a low cost, non-invasive way to understand ancient landscapes on a broad scale. Better models of how the environment has changed let us ask new questions about how people lived. </p>
<p>This is useful, not just as a tool for understanding why sites are where they are but also how people may have responded to the landscape around them. For example, we may have a different view of a rock art panel if we can understand what the artist could see around them when they painted it.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519168/original/file-20230404-26-dp02ls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The research provides a new perspective on the history of the Arnhem Land region, which is important for First Nations people.</span>
<span class="attribution"><span class="source">Ian Moffat</span></span>
</figcaption>
</figure>
<p>This research also has important implications for First Nations people. Alfred Nayinggul, a senior Erre Traditional Owner from Arnhem Land and co-author of this research, said: </p>
<blockquote>
<p>We want people to see and want people to know what’s been happening many thousand years ago in the past. We need to know where those other places in Australia are, and that it was different before, and how it was formed, and we didn’t know what it was. We need to know, us Bininj, and everyone in the world with this new technology, bringing that up to our country. I need to know, and the rest of the world would see, what was in the past.</p>
</blockquote><img src="https://counter.theconversation.com/content/201394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jarrad Kowlessar receives funding from Flinders University. </span></em></p><p class="fine-print"><em><span>Daryl Wesley receives funding from the Australian Research Council, the Australian Nuclear Science and Technology Organisation, the Museum and Art Gallery of the Northern Territory, National Geographic Research Scheme and Flinders University. </span></em></p><p class="fine-print"><em><span>Ian Moffat receives funding from the Australian Research Council, the Australian Nuclear Science and Technology Organisation, the Museum and Art Gallery of the Northern Territory and Flinders University. </span></em></p><p class="fine-print"><em><span>Alfred Nayinggul does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Beneath the floodplains of Arnhem Land lies a hidden landscape that has been transformed over millennia as seas rose and fell.Jarrad Daniel Kowlessar, Associate Lecturer, Flinders UniversityAlfred Nayinggul, Senior Erre Traditional Owner, Indigenous KnowledgeDaryl Wesley, Senior research fellow, Flinders UniversityIan Moffat, Associate Professor of Archaeological Science, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1978162023-03-22T17:18:31Z2023-03-22T17:18:31ZHow a local community helped us make incredible prehistoric discoveries<figure><img src="https://images.theconversation.com/files/516900/original/file-20230322-22-l769gr.jpg?ixlib=rb-1.1.0&rect=0%2C18%2C4160%2C3095&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Around 400 local children have been involved in this archaeological project in Cardiff, Wales.</span> <span class="attribution"><span class="source">Vivian Paul Thomas</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The knowledge and control of bronze gave some people who lived between 2200BC and 700BC enormous wealth and power. Their lives and deeds were immortalised by their burial mounds, known as barrows and cairns, which still litter our landscape today. Incredibly though, finding the places where <a href="https://www.britannica.com/event/Bronze-Age">bronze age</a> people lived has proven to be very difficult. </p>
<p>In south Wales, for example, only a handful of settlements are <a href="https://museum.wales/articles/1339/Prehistoric-feasting-in-south-Wales/">known</a> about. Typically, all that remain are the ruins of a flimsy roundhouse or two. We have little else to tell us about the lives of the inhabitants. Maybe that’s because bronze age people had mobile lifestyles, moving around the landscape with their herds from season to season but never staying in the same place too long. That’s one argument, anyway. </p>
<p>However, in the summer of 2022, a collaborative, <a href="https://www.researchgate.net/publication/335914255_The_Caerau_and_Ely_Rediscovering_Heritage_Project_legacies_of_co-produced_research">community-led archaeological excavation</a> on the outskirts of Cardiff began to challenge those assumptions. </p>
<figure class="align-center ">
<img alt="An illustration depicts a prehistoric bearded man pouring liquid into a mould. Two men in the background are gathered around a fire." src="https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516899/original/file-20230322-399-mcbkan.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The bronze age is the name given to the period of time between 2200BC and 700BC.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/foundry-workshop-on-outskirts-lake-town-1122922061">Morphart Creation</a></span>
</figcaption>
</figure>
<p>It’s hard to imagine how our prehistoric ancestors would have reacted when they first began to make and use metal. They took rocks that sparkled with green and silver, crushed and heated them until they became liquid. They then poured this elixir into moulds before cooling and breaking them open to reveal the dark golden-coloured metallic objects inside. It must have appeared like magic. </p>
<p>Since 2011, our <a href="https://www.caerheritage.org">CAER Heritage Project</a> has mobilised people in the Cardiff suburbs of Caerau and Ely to imagine and explore such history and archaeology. Both areas face challenges such as high unemployment and poor educational attainment. But they are also home to a host of extremely friendly and talented people, not to mention some outstanding heritage too.</p>
<p>Until recently, much of our archaeological investigation had focused on the <a href="https://orca.cardiff.ac.uk/id/eprint/130880/1/Davis_and_Sharples_Glamorgan_Hillforts_Caerau.pdf">Caerau hillfort</a>. This is the largest and most impressive iron age (700BC) hillfort in the region and is almost entirely surrounded by houses. </p>
<figure class="align-center ">
<img alt="A group of school children stand in a field with their backs towards the camera. A man stands in front of them pointing towards something." src="https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2048%2C1532&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516749/original/file-20230321-2560-3ljuag.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Local schoolchildren gather near the Caerau hillfort.</span>
<span class="attribution"><span class="source">Vivian Paul Thomas</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p><a href="https://caerheritageproject.com/discover/">We discovered</a> that the hilltop was used as a gathering place during the stone age (3600BC), before the hillfort was built around 600BC. </p>
<p>Over the last couple of years, we have taken archaeology into the housing estates themselves. During the COVID lockdowns between 2020 and 2021, local residents did “<a href="https://www.bbc.co.uk/news/uk-wales-53234395">mini-digs</a>” in their gardens. Many <a href="https://caerheritageproject.com/2020/07/16/caer-big-dig-the-big-discoveries-so-far/">discovered</a> prehistoric items such as flints and pottery shards. </p>
<p>The best chance of finding the places where prehistoric people lived was in a large area of open ground known as Trelai Park, which is around 1,500 metres east of the Caerau hillfort. The park is today used for sport but in its centre are the remains of a <a href="http://www.cardiffparks.org.uk/otheropenspaces/trelaipark/info/romanvilla.shtml">Roman villa</a>, which was excavated in 1922 by the renowned archaeologist, <a href="https://www.britannica.com/biography/Mortimer-Wheeler">Sir Mortimer Wheeler</a>. </p>
<p>A century later, in April 2022, we completed a “geophysical survey” of the park with local school children and adults. Geophysics is a process using a machine called a <a href="https://www.britannica.com/technology/magnetometer">magnetometer</a>, which allows archaeologists to “see” under the ground without removing the soil and helps us work out where to dig.</p>
<p>We had expected to find more Roman remains, but around 200 metres south of the villa, we discovered an intriguing square enclosure.</p>
<figure class="align-left ">
<img alt="Looking over the shoulder of a man wearing a baseball cap who is using a tool to carve out a section of earth." src="https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=901&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=901&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=901&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1132&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1132&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516908/original/file-20230322-26-zw4oej.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1132&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Vivian Paul Thomas</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Digging beneath one of the football pitches last summer, we revealed the <a href="https://the-past.com/news/remains-of-a-bronze-age-roundhouse-unearthed-in-near-cardiff/">remains of a substantial roundhouse</a>. It was made from timber and thatch which had long since rotted away, but the big post holes that held up its circular wall still survived. </p>
<p>A radiocarbon date from a piece of burnt wood indicated it was built around 1500BC, which is the middle of the bronze age. That makes it the <a href="https://www.bbc.co.uk/news/uk-wales-62155069">oldest known house in the Welsh capital</a>. </p>
<p>Even more amazingly, the floor surface that its occupants had walked, worked and slept on was still there. Trampled into this floor were finds of flint and stone tools, pottery and burnt bones which gave us a glimpse into bronze age daily life. </p>
<p>Surrounding the roundhouse was a large ditch and bank which was the square enclosure we had discovered through geophysics. Placed into the ditch was an <a href="https://www.bbc.co.uk/news/uk-wales-62155069">extraordinary complete pot</a>, beautifully decorated in bronze age “<a href="https://archaeologydataservice.ac.uk/library/browse/details.xhtml?recordId=3246094&recordType=MonographSeries">Trevisker</a>” style. This type of decoration is common in Devon and Cornwall but this pot was made from local Welsh clay. Perhaps it was a copy made by bronze age travellers 3,500 years ago. </p>
<figure class="align-center ">
<img alt="A pair of hands wearing rubber gloves holds up a muddy object." src="https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516909/original/file-20230322-1452-pa1ljw.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Was this clay pot made by bronze age travellers?</span>
<span class="attribution"><span class="source">Vivian Paul Thomas</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>No other bronze age settlement like this has been discovered in south Wales and we have plenty of questions as a result, which, so far, remain unanswered.</p>
<p>One thing we do know is that none of these discoveries could have been made without the passion and participation of local people. Almost 400 children were involved in the dig as well as hundreds of volunteers, who gave more than 3,000 hours of their time to help out. </p>
<p>What sets CAER apart from many other community archaeology projects is that the people have remained involved in the work way beyond just the excavation process. Children and adults have sieved, cleaned and analysed our finds and continue to research the bronze age in their spare time. </p>
<figure class="align-center ">
<img alt="An aerial shot of a green field with three separate archaeological excavations taking place. There are precise holes in the ground and a blue tent set up." src="https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516922/original/file-20230322-18-qmmcss.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The archaeological dig in Trelai Park took place on the football pitch.</span>
<span class="attribution"><span class="source">Crown Copyright RCAHMW</span></span>
</figcaption>
</figure>
<p>Buoyed by such enthusiasm, we will be back digging in Trelai Park this summer, where once again we will be working alongside our passionate citizen archaeologist colleagues. We’re excited at the prospect of what we may uncover.</p><img src="https://counter.theconversation.com/content/197816/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Oliver Davis receives funding from AHRC, National Lottery Heritage Fund, Arts Council Wales, Royal Archaeological Institute, Prehistoric Society, Cambrian Archaeological Association. </span></em></p>Since 2011, professional and amateur archaeologists in Cardiff have been unearthing prehistoric artefacts. But last summer, they began to discover something even more extraordinary.Oliver Davis, Senior lecturer, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2002582023-02-21T19:04:05Z2023-02-21T19:04:05ZIn a new study, we’ve observed clues that distinguish the very deepest part of Earth’s core<figure><img src="https://images.theconversation.com/files/511009/original/file-20230220-2192-e5uwge.png?ixlib=rb-1.1.0&rect=263%2C17%2C3544%2C1952&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Rost9/Shutterstock</span></span></figcaption></figure><p>Not so long ago, Earth’s interior was thought to be made up of four layers: the crust, mantle, (liquid) outer core and (solid) inner core.</p>
<p>In a new study <a href="https://doi.org/10.1038/s41467-023-36074-2">published today in Nature Communications</a>, we provide further evidence for the existence of an “innermost inner core” – a distinct internal metallic ball embedded in the inner core like the most petite Russian nesting doll. </p>
<p>Studying Earth’s centre is not just a topic of academic curiosity, but something that sheds light on the very evolution of life on our planet’s surface. </p>
<p>This is because the inner core grows outwards by solidifying materials from the liquid outer core. As these materials solidify, heat is released and causes upward movement in the liquid layer – what’s known as a convection current. In turn, this convection generates our planet’s geomagnetic field.</p>
<p>The magnetic field protects life on Earth from <a href="https://climate.nasa.gov/news/3105/earths-magnetosphere-protecting-our-planet-from-harmful-space-energy/">harmful cosmic radiation</a>. Without the shield it provides, life on Earth would not be possible in the form we know today. </p>
<p>So, understanding the evolutionary history of our planet’s inner core and its connection with the geomagnetic field is relevant to understanding the timeline of life’s evolution on Earth’s surface.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-makes-one-earth-like-planet-more-habitable-than-another-33479">What makes one Earth-like planet more habitable than another?</a>
</strong>
</em>
</p>
<hr>
<h2>Studying the insides of the planet</h2>
<p>Like radiologists imaging a patient’s internal organs, seismologists use seismic waves from large earthquakes to study the deep interior of Earth. Earthquakes are our sources, and seismometers recording ground motions or vibrations that move through Earth are our receivers.</p>
<p>However, unlike medical imaging, we do not have the luxury of having sources and receivers equally distributed around the body. Large earthquakes useful for our probes are confined near tectonic margins, such as <a href="https://theconversation.com/five-active-volcanoes-on-my-asia-pacific-ring-of-fire-watch-list-right-now-90618">the Ring of Fire</a> surrounding the Pacific. Meanwhile, seismometers mainly exist on land. </p>
<p>Furthermore, the inner core, which is <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.1995.tb03540.x/abstract">one-fifth of Earth’s radius</a>, accounts for less than 1% of Earth’s volume. To target this relatively small volume in the planet’s centre, seismometers often need to be positioned on the opposite side of the globe, the so-called antipode of an earthquake.</p>
<p>But that’s unlikely in practice because the antipodes of active earthquake zones are often in the ocean, where seismometers are expensive to install. </p>
<p>With the limited data we do have from such antipode measurements, an internal metallic ball within the inner core – the innermost inner core – <a href="http://www.pnas.org/content/99/22/14026">was hypothesised</a> about 20 years ago, with an estimated radius of about 300km.</p>
<p>Several <a href="http://www.sciencedirect.com/science/article/pii/S0031920118302395">lines of evidence</a> have confirmed its <a href="https://www.science.org/doi/10.1126/science.1078159">existence</a>, including <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB020545">recent</a> <a href="https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB023540">studies</a> from our research group. </p>
<h2>Bouncing seismic waves</h2>
<p>Now, for the first time, we report observations of seismic waves originating from powerful earthquakes travelling back and forth from one side of the globe to the other up to five times like a ricochet. These new observations are exciting because they provide new probes from different angles of the centremost part of our planet. </p>
<p>A critical advantage of our study was getting data from dense continental-scale networks (consisting of several hundred seismometers) installed around some of the largest quakes.</p>
<p>It differs from previous studies because it uses seismic waves that bounce multiple times within Earth, along its diameter and through its centre. By capturing them, we obtain an unparalleled sampling of the innermost inner core.</p>
<h2>A ball in the centre</h2>
<p>The potential difference between the innermost metallic ball and the outer shell of the inner core is not in its chemical composition, like with some other Earth layers. Both are likely made of an iron-nickel alloy with small amounts of lighter chemical elements.</p>
<p>Additionally, the transition from the innermost (solid) ball to the outer shell of the inner core (also solid) seems gradual rather than sharp. That is why we can’t observe it via direct reflections of seismic waves from it. This differs from previous studies documenting sharp boundaries between the other layers inside Earth – from crust to mantle, for example.</p>
<p>So, what precisely did we observe that gives us clues about this innermost inner core?</p>
<p>The observed difference is in anisotropy – a material’s property to let (or propagate) seismic waves faster or slower through it depending on the direction in which they travel.</p>
<p>Different speeds could be caused by different arrangements of iron atoms at high temperatures and pressures, or by the arrangements of atoms when crystals grow.</p>
<p>There is <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB020545">strong evidence</a> that the outer shell of the inner core is anisotropic. The slowest direction of seismic waves is in the equatorial plane (and the fastest is parallel to Earth’s spin axis).</p>
<p>By contrast, in the innermost part of the inner core – as our study of the ricochet waves shows – the slowest direction of propagation forms an oblique angle with the equatorial plane. This is critical, and this is why we can say we’ve detected “distinct” anisotropy in the innermost inner core. </p>
<p>Excitingly, while shallow structures within Earth’s crust and upper mantle are being mapped in incredible detail, we are still at the discovery stage regarding its deepest structures.</p>
<p>However, the image of Earth’s deep interior is getting sharper with the expansion of the dense continental networks, advanced data analysing techniques, and computational capacities.</p>
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Read more:
<a href="https://theconversation.com/just-add-mantle-water-new-research-cracks-the-mystery-of-how-the-first-continents-formed-156845">Just add (mantle) water: new research cracks the mystery of how the first continents formed</a>
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<img src="https://counter.theconversation.com/content/200258/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hrvoje Tkalčić receives funding from The Australian Research Council. </span></em></p><p class="fine-print"><em><span>Thanh-Son Pham does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Earth doesn’t just have an inner core. It also has an innermost inner core, a solid ball within the solid ball in the very middle of the planet.Thanh-Son Pham, Postdoctoral Fellow in Geophysics, Australian National UniversityHrvoje Tkalčić, Professor, Head of Geophysics, Director of Warramunga Array, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1799852022-03-29T15:27:27Z2022-03-29T15:27:27ZPluto: ‘recent’ volcanism raises puzzle – how can such a cold body power eruptions?<figure><img src="https://images.theconversation.com/files/454165/original/file-20220324-27-whdwz1.png?ixlib=rb-1.1.0&rect=50%2C44%2C1900%2C919&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Simulated image of Pluto's Wright Mons volcano.</span> <span class="attribution"><span class="source">Nature Communications</span></span></figcaption></figure><p>Pluto, the Solar System’s largest dwarf planet, just became even more interesting with a <a href="https://www.nature.com/articles/s41467-022-29056-3">report</a> that icy lava flows have recently covered substantial tracts of its surface. In this context, “recently” means probably no more than a billion years ago. That’s old, of course – and there is no suggestion that volcanoes are still active – but it’s only a quarter the age of the Solar System and no one knows how Pluto brewed up the heat needed to power these eruptions.</p>
<p>The news, coming nearly seven years after NASA’s New Horizons probe made its spectacular <a href="https://theconversation.com/stunning-crystal-clear-images-of-pluto-but-what-do-they-mean-47517">flyby of Pluto on July 14, 2015</a>, is thanks to analysis of images and other data by a team led by Kelsi Singer of the Southwest Research Institute in Boulder, Colorado.</p>
<p>Singer’s team draw particular attention to a mountainous feature named Wright Mons, which rises 4-5km above its surroundings. It is about 150km across its base and has a central depression (a hole) 40-50km wide, with a floor at least as low as the surrounding terrain.</p>
<p>The team claims that Wright Mons is a volcano, and cite the lack of impact craters as evidence that it is not likely to be older than 1-2 billion years. Many other areas of Pluto have been around long enough to accumulate large numbers of impact craters – no recent icy lava flows have covered them.</p>
<p>As volcanoes go, Wright Mons is a big one. Its volume exceeds 20 thousand cubic kilometres. Although considerably less than the volume of Mars’s biggest volcanoes, this is similar to the total volume of Hawaii’s <a href="https://www.usgs.gov/volcanoes/mauna-loa">Mauna Loa</a>, and much greater than the volume of its above sea-level portion. This is particularly impressive given Pluto’s small size, with a diameter about a third that of Mars and a sixth that of Earth.</p>
<figure class="align-center ">
<img alt="Figure of volcano height profiles." src="https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=135&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=135&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=135&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=170&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=170&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454368/original/file-20220325-27-1l1wx7y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=170&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Height profile of Wright Mons (blue line), compared with the above sea-level part of Hawaii’s Mauna Loa (blue line) and the biggest volcanoes on Mars (red lines).</span>
<span class="attribution"><span class="source">Singer et al. (2022)</span></span>
</figcaption>
</figure>
<h2>The Wright stuff</h2>
<p>In detail, the slopes of Wright Mons and much of its surroundings are seen to be crowded with hummocks up to 1km high and mostly 6-12km across. The team conclude that these hummocks are made primarily of water-ice, rather than nitrogen- or methane-ice that covers some other young regions on Pluto. They argue that this is consistent with the material strength necessary to form and preserve these domes, but they do recognise small patches of much weaker nitrogen-ice, mainly in the central depression.</p>
<p>The hummocks were likely created by some sort of ice volcanism, known by the technical term “cryovolcanism” – erupting icy water rather than molten rock. Pluto’s bulk density shows that it must have rock in its interior, but its outer regions are a mixture of ices (water, methane, nitrogen and probably ammonia and carbon monoxide, too, all of which are less than a third as dense as rock) in the same way that the crust of the Earth and other rocky planets is a mixture of several silicate minerals.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of Wright Mons" src="https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=501&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=501&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=501&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=630&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=630&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454162/original/file-20220324-25-1n8g0ai.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=630&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">250km wide image centred on Wright Mons.</span>
<span class="attribution"><span class="source">NASA/JHUAPL/SwRI</span></span>
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</figure>
<p>At Pluto’s surface temperature of well below -200°C, ice made of frozen water is immensely strong. It can (and on Pluto, does) form steep mountains that will last for eternity without sagging downhill like a glacier on the much less frigid Earth, where water-ice is weaker.</p>
<h2>What melts the ice?</h2>
<p>Ice, of course, melts at much lower temperatures than rock. And when there is a mixture of two ices, melting can begin at a lower temperature than for either of the pure ices (the same principle applies in silicate rock made of different minerals). This makes melting even easier. Despite this, it is a surprise to find evidence of relatively young water-rich cryovolcanic eruptions on Pluto, because there is no known heat source to power them. </p>
<p>There is only very limited scope for Pluto’s interior to be heated by tidal forces – a gravitational effect between orbiting bodies, such as a moon and a planet – which warm the interiors of some of the moons of Jupiter and Saturn. And the amount of rock inside Pluto is not enough to produce much heat from radioactivity.</p>
<p>Singer and her coworkers speculate that Pluto somehow held on to heat from its birth, which was unable to leak out until late in the body’s history. This would be consistent with Pluto having a deep <a href="https://theconversation.com/life-inside-pluto-hot-birth-may-have-created-internal-ocean-on-dwarf-planet-140976">internal liquid water ocean</a>, suggested based on other evidence. </p>
<p>If the hummocks from which Wright Mons is built do represent water-ice eruptions, this stuff clearly was not flowing freely like liquid water, but must have been some kind of gooey crystal-rich “mush”, maybe within a completely frozen, but still pliable, outer skin that confined each effusion of fluid into a dome-like hummock.</p>
<h2>A hole in the argument?</h2>
<p>The team cite the depth and volume of the central depression of Wright Mons to dismiss earlier suggestions that this is a volcanic crater (a caldera) or that it has been excavated by explosive eruptions. Instead, they regard it as a gap that somehow avoided being covered by erupted hummocks.</p>
<p>I have my doubts about that, because there is an even bigger probable volcano, Piccard Mons, to the south of Wright Mons that also has a large central depression. It strikes me as too much of a coincidence for there to be two adjacent volcanoes <em>both</em> with fortuitous holes in their middles. I think it is more likely that these central depressions are somehow integral to how these volcanoes grew or erupted.</p>
<figure class="align-center ">
<img alt="Height map showing the ring-like Wright Mons in the northern half and the even larger Piccard Mons in the southern half." src="https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1145&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1145&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1145&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454364/original/file-20220325-25-1c7p6gt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1439&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Height map showing the ring-like Wright Mons in the northern half and the even larger Piccard Mons in the southern half.</span>
<span class="attribution"><span class="source">NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute</span></span>
</figcaption>
</figure>
<p>Piccard Mons is less well characterised than Wright Mons because, by the time New Horizons made its closest approach, Pluto’s rotation had carried Piccard Mons into darkness. The flyby was so fast that only the side of Pluto facing the Sun at the right time could be seen in detail. However, New Horizons was able to image Piccard Mons thanks to sunlight weakly reflected onto the ground by haze in Pluto’s atmosphere.</p>
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Read more:
<a href="https://theconversation.com/nasa-mission-brings-pluto-into-sharp-focus-but-its-still-not-a-planet-40495">NASA mission brings Pluto into sharp focus – but it's still not a planet</a>
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<p>That was a remarkable achievement, but it leaves us wanting to know more. What extra details are lurking in the poorly imaged half of Pluto? It will probably be decades before we find out, or learn much more about how these icy volcanoes formed.</p><img src="https://counter.theconversation.com/content/179985/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is Professor of Planetary Geosciences at the Open University. He is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury and BepiColombo, and from the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He is Educator on the Open University's free learning Badged Open Course (BOC) on Moons and its equivalent FutureLearn Moons MOOC, and chair of the Open University's level 2 course on Planetary Science and the Search for Life.</span></em></p>Pluto has recently active icy volcanoes, that have erupted water ice.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1746002022-01-13T11:25:05Z2022-01-13T11:25:05ZThe science that is helping researchers find the ‘disappeared’ in Latin America<p>In most Latin American countries where there has been a high level of civil conflict over the past few decades, there are still <a href="http://www.desaparecidos.org">huge numbers</a> of missing people due to forced disappearances. In Colombia alone this number is estimated to be more than <a href="https://www.icmp.int/press-releases/profiles-of-the-missing-from-colombia-perspectives-and-priorities-of-families-of-the-disappeared/#:%7E:text=As%20many%20as%20120%2C000%20people,guerrilla%20groups%2C%20and%20organized%20crime.">120,000 people</a> after five decades of bitter insurgency. Many thousands of others have been disappeared across Mexico, Argentina, Chile, El Salvador and Guatemala. </p>
<p>Searching for human remains in South America is hugely challenging, which is often a consequence of the remote locations used, inhospitable search terrain, and the time that has elapsed since the person disappeared, which can be over 40 years. </p>
<figure class="align-center ">
<img alt="Scientists trekking with horses through tropical rainforest" src="https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/439897/original/file-20220109-33062-1niw9i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The authors horse trekking (with equipment) through tropical rainforest to a suspected 1980s mass burial site in the grounds of a derelict mountain school.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Trying to locate victims is a very case-specific process – it largely depends on how, when, where and why each victim was killed and who killed them. Since governments are often unwilling to look for bodies, it has often fallen to researchers like us to do it instead.</p>
<p>The generally accepted strategy for searching for remains either <a href="http://dx.doi.org/10.1016/j.earscirev.2012.05.006">on land</a> or <a href="http://dx.doi.org/10.1016/j.earscirev.2017.04.012">under water</a> is a phased investigation of an area that is suspected of having been used for burials. These are often places where it’s not possible just to go in and start digging – first it’s necessary to build up the evidence that would give a strong legal case for securing official permission. </p>
<p>The investigation starts from available background information and satellite information to look for clues as to where bodies might be buried. Ground teams then do controlled studies which usually involve burying pig cadavers as proxies for humans, which over long periods of time allows them to gain insights into how the soil in that area might have responded to human burials. This then allows them to identify places in the suspected burial area that have similar ground characteristics, at which point they can make full ground surveys followed by more intrusive investigations. </p>
<p>Research by the Keele co-authors, with Spanish colleagues at Oviedo University, has used these techniques to <a href="https://doi.org/10.1016/j.forsciint.2018.03.034">successfully locate</a> in 2016 the remains of 26 victims who had been buried in the 1930s in a mountainous region of Asturias province in northern Spain during the <a href="https://en.wikipedia.org/wiki/Spanish_Civil_War">Spanish civil war</a>. More recently an organisation called the <a href="https://en.wikipedia.org/wiki/Argentine_Forensic_Anthropology_Team">Argentine Forensic Anthropology Team</a>, originally set up to search for disappeared victims in that country, has investigated other South American conflicts and recovered the remains of victims of a mass killing in 1981 in <a href="https://www.bbc.co.uk/news/av/stories-59587051">El Salvador</a> using similar techniques. </p>
<h2>Gathering evidence</h2>
<p>In a controlled study, researchers identify test sites that may be similar to those encountered by forensic investigators during the hunt for murder victims. They then replicate what might be encountered by search teams, for example, they simulate murder victims in various burial scenarios. </p>
<p>Though most researchers use pigs as proxies for human cadavers, some use donated bodies where laws allow <a href="https://theconversation.com/coming-to-a-field-near-you-the-body-farms-where-human-remains-decompose-in-the-name-of-science-50561">(not in the UK</a> at present). Pigs are usually used because they are of a similar size to humans and have comparable body tissue-fat ratios, organ sizes and skin types. </p>
<p>These test sites are then surveyed to find out the best method for detecting bodies in that type of environment. This relates to the fact that over time, bodies decompose and release fluids. They become skeletons and the overlying soil compacts. </p>
<p>The diagram below shows different stages of a clandestine grave of a murder victim, with a) showing a fresh burial that simply walking over the site could identify, b) early-stage decomposition that releases gases detectable by search dogs, c) late-stage decomposition that releases conductive fluids detectable by an electrical resistivity survey and, d) skeletonised stage, best detected by ground-penetrating radar (GPR).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=219&fit=crop&dpr=1 600w, https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=219&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=219&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=276&fit=crop&dpr=1 754w, https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=276&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/440256/original/file-20220111-19-15beer8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=276&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p>Our research team set up controlled test sites in the campus grounds of Los Llanos and Antonio Nariňo universities in Colombia, which have different tropical, rural and field environments. We simulated burials using pig carcasses in various different burial types. Some were dismembered, some were clothed, some unclothed. These, sadly, are all common burial scenarios in Colombia. </p>
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Read more:
<a href="https://theconversation.com/coming-to-a-field-near-you-the-body-farms-where-human-remains-decompose-in-the-name-of-science-50561">Coming to a field near you? The 'body farms' where human remains decompose in the name of science</a>
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<p>Once created, the simulated graves containing the pig carcasses were refilled and monitored for over two years. Monitoring included aerial surveys using cameras and specialist detector equipment on unmanned drones. We also performed ground geophysical surveys using <a href="https://archive.epa.gov/esd/archive-geophysics/web/html/resistivity_methods.html#:%7E:text=Surface%20electrical%20resistivity%20surveying%20is,the%20surrounding%20soils%20and%20rocks.">electrical resistivity</a>, which measures current resistances in the ground with decompositional fluids being an excellent geophysical target – shown below – and GPR which detects buried objects.</p>
<figure class="align-center ">
<img alt="Burial site in Colombia showing electrical equipment being used to detect remains" src="https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=510&fit=crop&dpr=1 600w, https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=510&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=510&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=641&fit=crop&dpr=1 754w, https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=641&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/439898/original/file-20220109-13-4a4va.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=641&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Controlled Colombian site photograph showing geophysical electrical resistivity equipment being used to collect data over the simulated clandestine burials of murder victims (blue and yellow wooden stakes).</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>From <a href="http://doi.org.uk/10.1111/1556-4029.14962">drone results</a>, we found vegetation changes that indicated recent grave positions if they weren’t under dense forest canopies. Different plants <a href="http://dx.doi.org/10.1016/j.jappgeo.2016.10.002">also grew</a> over the burials when compared to typical forest plants, so these could indicate where bodies are located if search teams knew what they were looking for. </p>
<p>Geophysical results for the test site showed that electrical resistivity surveys could best detect burial positions. But as time passed since burial, this technique got progressively less effective as a grave detection technique (this has been demonstrated in various <a href="https://doi.org/10.1038/s41598-020-64262-3">published European controlled studies</a>). Interestingly, a relatively small survey grid pattern was judged best, due to the smaller burial sizes of dismembered victims. </p>
<h2>Mountain searches</h2>
<p>One recently <a href="https://dx.doi.org/10.1111/1556-4029.14168">published case study</a> by the co-authors on finding missing persons in Colombia from the 1980s illustrates the difficulties in both finding and surveying burial sites in difficult search terrains.</p>
<p>The mountainous study site, in a derelict training school in Casanare province in central Colombia, was identified as a potential burial site. Researchers used a combination of known criminal and paramilitary training locations, military base locations, past police reports and search information as well as contemporary witness testimonies and the missing individual’s social media activities with tagged locations. </p>
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<a href="https://theconversation.com/the-science-of-finding-buried-bodies-77803">The science of finding buried bodies</a>
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<p>Ground geophysical electrical resistivity and GPR surveys, with subsequent intrusive investigations of the targeted geophysical anomalies, successfully located burials containing remains, but these were found to be animal not human.</p>
<p>This ongoing collaborative research of both controlled test sites and forensic searches will be crucial, not only for Latin American countries, but also for forensic investigators searching for victim remains globally.</p><img src="https://counter.theconversation.com/content/174600/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Pringle receives funding from the HLF, the Nuffield Foundation, Royal Society, NERC, EPSRC and EU Horizon2020. He is affiliated with the Geological Society of London. Jamie works for Keele University.</span></em></p><p class="fine-print"><em><span>Alejandra Baena receives funding from American Academy of Forensic Science. She is affiliated with International Net of Forensic Researchers (Red Iberoamérica de Investigadores Forenses - RIIF). Alejandra works for Universidad Antonio Nariño, Colombia, South America.</span></em></p><p class="fine-print"><em><span>Carlos Martín Molina Gallego receives funding from:
American Academy of Forensic Sciences.
International Union of Geological Sciences - Initiative on Forensic Geology (IUGS-IFG), which linked him as "Official for Latin America".
International Net of Forensics Resarchers (Red Iberoamericana de Investigadores Forenses)
Carlos works for Universidad Antono Nariño, Colombia, Sur América.
</span></em></p><p class="fine-print"><em><span>Kristopher Wisniewski is affiliated with the Geological Society of London.</span></em></p><p class="fine-print"><em><span>Vivienne Heaton does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Researchers are using modern forensic techniques to find the bodies of victims of civil conflict in Latin America.Jamie Pringle, Senior Lecturer in Geosciences, Keele UniversityAlejandra Baena, Researcher in Materials Physics, Geophysics and Materials Science., Universidad Antonio NariñoCarlos Martín Molina, Researcher Professor, Universidad Antonio NariñoKristopher Wisniewski, Lecturer in Forensic Science, Keele UniversityVivienne Heaton, Lecturer in Forensic Anthropology and Biology, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1632482021-07-26T02:15:35Z2021-07-26T02:15:35ZAustralia badly needs earth science skills, but universities are cutting the supply<p>Earth science is vital to Australia’s economic and environmental future but we are dramatically decreasing our earth science capability. Earth scientists work not only in mining and mineral exploration (which contribute <a href="https://www.rba.gov.au/education/resources/snapshots/economy-composition-snapshot/">11% of Australia’s GDP</a>) but also in fields such as environmental science, groundwater monitoring for the agricultural and environmental sectors, geotechnical work for the construction industry, and <a href="https://earthdata.nasa.gov/learn/backgrounders/remote-sensing">satellite remote sensing</a>. These skills will be increasingly important to meet the challenges of climate change, particularly as renewable energy sources require <a href="https://www.bbc.com/news/science-environment-57234610">new discoveries of minerals</a> for batteries, electric cars and wind turbines. </p>
<p>Already in short supply, geologists, geophysicists and earth science technicians are on the <a href="https://immi.homeaffairs.gov.au/visas/working-in-australia/skill-occupation-list">skilled occupation list</a> for immigration. Despite this need, Australian universities have recently made huge cuts to earth science teaching. In the past year, the <a href="https://coastcommunitynews.com.au/central-coast/news/2020/08/decision-by-university-to-drop-geology-labelled-as-plain-dumb/">University of Newcastle</a> and <a href="https://campusmorningmail.com.au/news/earth-sciences-erode-at-macquarie-u/">Macquarie University</a> have closed entire earth science departments. </p>
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Read more:
<a href="https://theconversation.com/devastating-the-morrison-government-cuts-uni-funding-for-environment-courses-by-almost-30-147852">'Devastating': The Morrison government cuts uni funding for environment courses by almost 30%</a>
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<p>Earth science jobs have also been lost at other universities including <a href="https://www.canberratimes.com.au/story/7043826/anu-college-of-science-set-to-lose-103-jobs/">ANU</a>, <a href="https://honisoit.com/2021/07/yet-more-redundancies-at-macquarie/">UNSW</a>, <a href="https://www.examiner.com.au/story/6962820/fears-of-big-job-losses-at-university-of-tasmania/">Tasmania</a> and <a href="https://www.theage.com.au/national/victoria/melbourne-uni-cuts-threaten-to-make-us-the-bogans-of-the-pacific-20210326-p57ehg.html">Melbourne</a>. Almost every university in the eastern states has cut undergraduate courses in earth sciences. </p>
<p>Federal government policies bear significant responsibility for this loss of earth science capability. The <a href="https://t.co/2du37iBi3s?amp=1">lack of JobKeeper support</a> for universities during the pandemic has been widely discussed, but the unhelpful policies run much deeper. </p>
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<h2>Funding changes hit earth science teaching hard</h2>
<p>Despite its importance, earth science undergraduate enrolments in Australia are modest. Most years only about <a href="https://www.agc.org.au/resources/reports/australian-geoscience-council-report/">200 students graduate with an honours degree</a> (the minimum generally required to be employed in the field), while <a href="https://www.ato.gov.au/About-ATO/Research-and-statistics/In-detail/Taxation-statistics/Taxation-statistics-2018-19/">over 15,000 people</a> work as geoscientists in Australia. Commonwealth funding for university teaching is based on student numbers, so earth science departments receive little teaching income. </p>
<p>The <a href="https://ministers.dese.gov.au/tehan/job-ready-graduates-power-economic-recovery">stated aim</a> of the 2020 <a href="https://www.dese.gov.au/job-ready">Job-Ready Graduates Package</a> was to address this by “better preparing students for jobs that reflect Australia’s expected economic, industry and employment growth”. The package did reduce fees for earth science students. However, it did not increase funding to cover the resulting fee shortfall.</p>
<p>As a result, university income was reduced by <a href="https://www.afr.com/work-and-careers/education/crippling-loss-scientists-warn-of-damage-to-uni-research-20200821-p55nya">16% for science students</a> and <a href="https://www.theguardian.com/australia-news/2020/oct/14/environmental-science-hit-with-severe-funding-cuts-in-coalition-universities-overhaul">29% for environmental science students</a>. At a time when universities are deciding which courses to cut, these suddenly less profitable courses have risen to the top of the list.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/the-government-is-making-job-ready-degrees-cheaper-for-students-but-cutting-funding-to-the-same-courses-141280">The government is making ‘job-ready’ degrees cheaper for students – but cutting funding to the same courses</a>
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<h2>Research lacks funding too</h2>
<p>Australia excels in earth science research. In the <a href="https://www.topuniversities.com/university-rankings/world-university-rankings/2020">2020 QS World University Rankings</a>, nine Australian earth science institutions were in the top 100 in the world, compared to five in biology, three in physics, one in chemistry and none in mathematics. However, research funding policies have hit earth science departments particularly hard.</p>
<p>Most Australian government research funding <a href="https://andrewnorton.net.au/2020/06/05/why-did-universities-become-reliant-on-international-students-part-4-trying-to-maintain-a-teaching-research-academic-workforce/">does not cover the full costs of doing research</a>, including academic salaries and university overheads. This funding system essentially punishes earth science departments for their research excellence because there is no money to cover the required laboratory facilities or academic <a href="https://link.springer.com/article/10.1007/s11192-021-04073-z">salaries that come with research success</a>. </p>
<p>Universities had <a href="https://andrewnorton.net.au/2020/06/04/why-did-universities-become-reliant-on-international-students-part-3-the-rise-of-research-project-grants/">increasingly used international student fees</a> to bridge the research funding gap. But <a href="https://theconversation.com/as-hopes-of-international-students-return-fade-closed-borders-could-cost-20bn-a-year-in-2022-half-the-sectors-value-159328">revenue from those fees has been falling</a> since our borders closed to these students. Earth science departments and academics are again on university chopping blocks. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/big-spending-recovery-budget-leaves-universities-out-in-the-cold-160439">Big-spending 'recovery budget' leaves universities out in the cold</a>
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<h2>Research excellence offers little protection</h2>
<p>Responsibility also lies with the universities that ultimately decided to cut earth science departments and jobs. Not all these cuts were made in response to COVID-19. For instance, Macquarie University <a href="https://campusmorningmail.com.au/news/earth-sciences-erode-at-macquarie-u/">began earth science redundancies in 2019</a>, well before any COVID-19 budgetary crisis. </p>
<p>However, the pandemic has accelerated the loss of earth science teaching. With Macquarie again as an example, in the past year the university has made <a href="https://honisoit.com/2021/07/yet-more-redundancies-at-macquarie/">most academic positions in earth science</a> redundant, while announcing plans to build a <a href="https://www.theurbandeveloper.com/articles/macquarie-university-development-applcation-law-school">A$60 million law school</a>. </p>
<p>Earth science had been an area of research strength at Macquarie University. The department hosted an <a href="http://ccfs.mq.edu.au/">Australian Research Council (ARC) Centre of Excellence</a> and produced six ARC Future Fellows in the past ten years. The university is clearly making strategic decisions <a href="https://www.smh.com.au/national/nsw/macquarie-university-courses-must-soon-meet-viability-scores-to-survive-20200930-p560qb.html">on the basis of undergraduate enrolments</a> rather than research excellence or Australian skills needs. </p>
<h2>How can these problems be solved?</h2>
<p>A solution to this problem requires Commonwealth funding to be restructured. For a start, research funding should cover the costs of research. </p>
<p>If the Australian government is serious about producing graduates for jobs in areas of need, it should design policies that encourage universities to invest in those areas rather than punishing them for doing so. Universities, as public institutions that seek the support of the public, should commit to supporting areas of importance to Australia, even if these are not the most profitable for the universities themselves. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-government-linked-the-cost-of-university-teaching-to-funding-and-student-fees-but-the-numbers-dont-add-up-161345">The government linked the cost of university teaching to funding and student fees, but the numbers don't add up</a>
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<p>The immediate problem that must be solved to protect our remaining earth science teaching is low undergraduate student numbers. An easy step for the Australian government would be to boost the small amount of earth science content in the school curriculum. Yet <a href="https://www.australiancurriculum.edu.au/consultation">current proposals are to reduce it</a>. </p>
<p>The government should also mount campaigns to show school students the variety of exciting, important and impactful careers they could have as geoscientists. Without immediate changes, the future of earth sciences in Australia looks grim.</p><img src="https://counter.theconversation.com/content/163248/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kate Selway receives funding from the Australian Research Council and is on the Federal Executive of the Australian Society of Exploration Geophysicists. Kate took a voluntary redundancy from Macquarie University in February 2021 and currently works at the University of South Australia.</span></em></p>Earth scientists are on the skilled occupation list for immigration even as universities cut back in this area. The problem lies with a funding model that offers no incentive to lift graduate numbers.Kate Selway, Senior Research Fellow, Future Industries Institute, University of South AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1648782021-07-22T18:16:16Z2021-07-22T18:16:16ZMars InSight: mission unveils surprising secrets of red planet’s interior – new research<figure><img src="https://images.theconversation.com/files/412734/original/file-20210722-25-4hl9a2.jpg?ixlib=rb-1.1.0&rect=122%2C114%2C4906%2C2280&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Mars InSight lander.</span> <span class="attribution"><span class="source">NASA/JPL-Caltech</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>We may have walked on the Moon and sent probes across the solar system, but we know very little about what’s going on inside other planets. Now, for the first time, we have been able to view the interior of one, thanks to Nasa’s Mars InSight probe. The probe, which <a href="https://theconversation.com/mars-insight-here-is-whats-next-after-the-tricky-landing-107749">landed in 2018</a>, is equipped with a solar-powered lander bristling with equipment, including a seismometer (a very sensitive vibration detector).</p>
<p>The results, <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abj8914">published in three studies in Science</a>, throw up some unexpected findings about Mars’s interior, including a very large core. </p>
<p>Though Mars has no tectonic plates, <a href="https://theconversation.com/mars-quakes-the-insight-lander-shows-active-faults-in-the-planets-crust-132315">the first “marsquakes” were detected</a> within months of the probe landing. These may result from vibrations caused by meteorites hitting the surface or from processes inside the planet. </p>
<p>It is difficult to detect quakes on Mars, partly because the seismometer is subject to the extremes of Martian weather, with seasonally changing windy periods obscuring the data. The signals used to probe the Martian interior all come from relatively small quakes, the best among the <a href="https://www.sciencedirect.com/science/article/pii/S0031920120302739">hundreds detected so far</a>.</p>
<p>Planets grow by accumulating material (accretion) early in the life of a solar system. But their interiors are not a uniform mix of these initial ingredients – they also undergo differentiation, where some lighter minerals “float” towards the surface, while heavier components like iron sink towards the planet’s centre. We expect rocky planets like Mars to have an iron-rich core, followed by a <a href="https://www.britannica.com/science/mineral-chemical-compound/Silicates">silicate</a> layer called the mantle and an outermost skin known as the crust. Until now, how much of Mars each of these layers occupied was unknown.</p>
<h2>Metallic heart</h2>
<p>It’s impossible to get a sample of Mars’s core. Instead, to estimate its size, we used seismic waves (created by marsquakes). On Earth, the core’s radius was first estimated by finding its “shadow” – an area where the core disrupts the arrival of seismic waves from distant earthquakes. <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abi7730">Our study</a> had to rely on a particular kind of slow, sideways-travelling waves called S-waves which have been reflected back to the surface by the interface between the core and the mantle. </p>
<p>Careful seismic processing by seismologists from around the world revealed signals from six marsquakes relatively close to the probe. Combined with information from mineral physics and from seismic waves travelling through the mantle, we were able to estimate the size and density of the Martian core. This suggests that the radius is a whopping 1,830km (give or take 40km) – just over half of the planet’s radius, which is bigger than we thought. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/412612/original/file-20210722-21-c8ynpz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Shear waves travel from a marsquake and reflect off the iron-nickel core.</span>
<span class="attribution"><span class="source">Chris Bickel/Science</span></span>
</figcaption>
</figure>
<p>The larger than expected core requires that a relatively large proportion of lighter elements must be mixing with its iron. From our work, we now know that the Martian core should contain a high fraction of sulphur and other light elements. Experiments show that liquid iron compounds containing this much sulphur are unlikely to solidify at the pressures and temperatures we expect at the centre of Mars, so it is unlikely that it has an inner solid core as Earth does. This may help us understand why there is no planet-wide magnetic field on Mars today, unlike on Earth.</p>
<h2>Layers and layers</h2>
<p>A planet’s crust comprises a tiny fraction of its mass. But the Martian crust’s chemical and thermal interactions with the atmosphere, and with any water or ice present, helps set the conditions that determine whether life can exist there.</p>
<p>In the <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abf8966">second new study</a>, another team investigated seismic waves which converted from P-waves, which are rapid, compressional waves, to S-waves (or vice versa) when they encountered different rocky material, and an assessment of background vibrations and gravity, to probe the Martian crust. This suggested the possible average Martian crust thickness is between 24km to 72km. This means we can rule out earlier estimates of up to about 100km. </p>
<p>From over 100 years of seismology on Earth, we know that beneath the thin crust lies the mantle, but the mantle itself is not uniform all the way to the core. The upper mantle and the crust, collectively known as the lithosphere, are rigid, while the lower mantle is a solid that can flow. On Earth, it is the lithospheric plates that move as part of plate tectonics, but on Mars, it is unclear what role the lithosphere plays.</p>
<p>To sample different depths of the mantle we can use both direct and reflected seismic waves. Direct P- or S-waves dive deep into the mantle and then return to the surface. The depth they travel down to depends on the structure of the planet and the distance from the quake to the seismometer. Reflected waves return to the surface and then dive again two or three times. <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abf2966">A third study</a> identified eight low-frequency marsquakes that produced both direct and reflected waves, and used these to create and test different models of the Martian crust and mantle. </p>
<p>By comparing the data and the models, they found that Mars’s lithosphere is between 400km and 600km thick. This is considerably thicker than any rigid layer seen in the Earth and implies that the Martian crust has a higher concentration of radioactive heat-producing elements than previously thought.</p>
<p>We now know more about the ingredients that went into building Mars, and that it has a very thick lithosphere, allowing our smaller sister planet to retain its internal heat. Though future astronauts won’t have to worry about the small marsquakes we used to probe the red planet, the lack of a magnetic field generated by the sulphur-rich core will mean they and their equipment will need to be more careful of the harsh <a href="https://science.nasa.gov/science-news/news-articles/earths-magnetosphere">solar wind</a>. </p>
<p>Our new understanding of the Martian interior is part of a new era of planetary seismology, more than fifty years since the <a href="https://link.springer.com/article/10.1007/s11214-020-00709-3">Apollo missions</a> landed seismometers on the Moon. New seismometers will be deployed to the Moon as part of the <a href="https://www.nasa.gov/artemisprogram">Artemis mission</a>, while the <a href="https://dragonfly.jhuapl.edu">Dragonfly</a> mission will place a seismometer on Saturn’s moon Titan in the mid-2030s. These experiments will help us understand more about how planets form and evolve – seeing deep into Mars is just one piece of a solar-system sized puzzle.</p><img src="https://counter.theconversation.com/content/164878/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jessica Irving receives funding from the UK Space Agency and has previously received funding from NASA.
</span></em></p><p class="fine-print"><em><span>Anna Horleston receives funding from UK Space Agency.</span></em></p>Mars’ core is larger and less dense than we thought.Jessica Irving, Senior Lecturer in Geophysics, University of BristolAnna Horleston, Senior Research Associate in Planetary Seismology, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1561042021-02-26T10:56:15Z2021-02-26T10:56:15ZMelting ocean mud helps prevent major earthquakes — and may show where quake risk is highest<figure><img src="https://images.theconversation.com/files/386609/original/file-20210226-19-1rdefw2.jpg?ixlib=rb-1.1.0&rect=0%2C4%2C2731%2C1814&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The largest and most destructive earthquakes on the planet happen in places where two tectonic plates collide. In our <a href="https://www.nature.com/articles/s41467-021-21657-8">new research</a>, published today in Nature Communications, we have produced new models of where and how rocks melt in these collision zones in the deep Earth. </p>
<p>This improved knowledge about the distribution of melted rock will help us to understand where to expect destructive earthquakes to occur. </p>
<h2>What causes earthquakes?</h2>
<p>Giant earthquakes, such as the magnitude-9.0 quake in 2011 that caused the Fukushima nuclear disaster, or the magnitude-9.1 event in 2004 that caused the Boxing Day tsunami, occur at the collision zones between two tectonic plates. In these so-called subduction zones, one plate slides beneath the other. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-fukushima-quake-may-be-an-echo-of-the-2011-disaster-and-a-warning-for-the-future-155293">The Fukushima quake may be an echo of the 2011 disaster — and a warning for the future</a>
</strong>
</em>
</p>
<hr>
<p>The sinking plate acts as an enormous conveyor belt, carrying material from the surface down into the deep Earth. Earthquakes occur where the sinking plate gets stuck; strain builds up until it eventually quickly releases. Fluids and molten rocks in the system lubricate the plates, helping them slide past each other and stopping big earthquakes from happening. </p>
<h2>When happens when ocean mud ends up inside Earth?</h2>
<p>My colleague Michael Förster and I were interested in what happens to sediments when they are carried down into the deep Earth at a subduction zone. These sediments start out as thick layers of mud on the ocean floor but get carried down into the deep Earth as part of the sinking plate. </p>
<p>Michael took a sample of mud collected from the ocean floor and heated it up to the high temperatures and pressures it would experience in a subduction zone. He found the sediments melt and then react with the surrounding rocks, forming the mineral phlogopite and also saline fluids. </p>
<h2>A puzzle solved</h2>
<p>Geophysical models of subduction zones allow us to map out exactly where the molten rocks and fluids are. These measurements are like x-rays of Earth’s interior, helping us peer into places we cannot otherwise see. </p>
<p>We were particularly interested in models of the electrical conductivity of subduction zones. This is because the fluids and molten rock we were looking at are more electrically conductive than the surrounding rock. Models of subduction zones have long been enigmatic, because they show Earth is very conductive in regions where people did not expect to see a lot of fluids and molten rock. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/386607/original/file-20210226-17-1qah4kx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Melting sediment from the seafloor helps tectonic plates slide over one another without creating major earthquakes.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1038/s41467-021-21657-8">Selway & Forster</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>I calculated the electrical conductivity of the phlogopite, molten sediments and fluids that were produced in the experiments and found they matched extremely well with the geophysical models. This provides good evidence that what we see in the experiments is happening in the real Earth, and allows us to calculate where the molten rock and fluids are in subduction zones around the world. </p>
<h2>Understanding where big earthquakes are likely to occur</h2>
<p>Giant earthquakes are not likely to occur in the parts of the subduction zone where the sediments melt. All of the products of the melting — the molten rock itself, the saline fluids, and even the mineral phlogopite — help the two plates slide past each other easily without causing large earthquakes. </p>
<p>We compared our models with locations of earthquakes in subduction zones along the west coast of the United States. We found there were no large earthquakes where sediments were melting, but the movement of fluids from the melted sediments could explain some small, non-destructive earthquakes and very faint signals of tremor where the two plates easily slide past each other.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/breaking-new-ground-the-rise-of-plate-tectonics-7514">Breaking new ground – the rise of plate tectonics</a>
</strong>
</em>
</p>
<hr>
<p>Earthquakes are a tangible reminder that we live on an active planet and that, deep beneath our feet, huge forces are making rocks flow and melt and collide. Accurately predicting earthquakes will be an ongoing goal of geoscientists for decades to come. </p>
<p>It requires intricate detective work to weave together all the tiny threads of information we have about processes that occur so deep in the Earth that we will never be able to see or sample them. Our results are one new thread in this puzzle. We hope it will contribute to one day being able to keep people safe from the risk of earthquakes. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/underground-sounds-why-we-should-listen-to-earthquakes-5798">Underground sounds: why we should listen to earthquakes</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/156104/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kate Selway receives funding from the Australian Research Council. </span></em></p>When sea sediment melts inside the Earth, it helps tectonic plates slide over one another smoothly.Kate Selway, Macquarie UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1517882020-12-15T19:16:52Z2020-12-15T19:16:52ZWhere does the Earth’s heat come from?<figure><img src="https://images.theconversation.com/files/373907/original/file-20201209-15-1i85cih.jpg?ixlib=rb-1.1.0&rect=3%2C79%2C2040%2C1311&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Piton de la Fournaise in eruption, 2015.</span> <span class="attribution"><span class="source">Greg de Serra/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Earth generates heat. The deeper you go, the higher the temperature. At 25km down, temperatures rise as high as 750°C; at the core, it is said to be 4,000°C. Humans have been making use of hot springs as far back as antiquity, and today we use geothermal technology to heat our apartments. Volcanic eruptions, geysers and earthquakes are all signs of the Earth’s internal powerhouse.</p>
<p>The average heat flow from the earth’s surface is 87mW/m<sup>2</sup> – that is, 1/10,000th of the energy received from the sun, meaning the earth emits a total of <a href="https://unt.univ-cotedazur.fr/uved/bouillante/cours/i.-la-geothermie-manifestations-quantification-origine-et-utilisations-de-la-chaleur-interne-du-globe/2.-comprendre-et-modeliser-les-transferts-de-chaleur-pour-determiner-l2019origine-de-la-chaleur-interne-du-globe/2.3-origine-de-la-chaleur-interne-du-globe.html">47 terawatts</a>, the equivalent of several thousand nuclear power plants. The source of the earth’s heat has long remained a mystery, but we now know that most of it is the result of radioactivity.</p>
<h2>The birth of atoms</h2>
<p>To understand where all this heat is coming from, we have to go back to the birth of the atomic elements.</p>
<p>The <a href="https://theconversation.com/us/topics/big-bang-470">Big Bang</a> produced matter in the form of protons, neutrons, electrons, and neutrinos. It took around 370,000 years for the first atoms to form – protons attracted electrons, producing hydrogen. Other, heavier nuclei, like deuterium and helium, formed at the same time, in a process called <a href="https://fr.wikipedia.org/wiki/Nucl%C3%A9osynth%C3%A8se_primordiale">Big Bang nucleosynthesis</a>.</p>
<p>The creation of heavy elements was far more arduous. First, stars were born and heavy nuclei formed via accretion in their fiery crucible. This process, called <a href="https://fr.wikipedia.org/wiki/Nucl%C3%A9osynth%C3%A8se_stellaire">stellar nucleosynthesis</a>, took billions of years. Then, when the stars died, these elements spread out across space to be captured in the form of planets.</p>
<p>The earth’s composition is therefore highly complex. Luckily for us, and our existence, it includes all the natural elements, from the simplest atom, hydrogen, to heavy atoms such as uranium, and everything in between, carbon, iron – the entire periodic table. Inside the bowels of the earth is an entire panoply of elements, arranged within various onion-like layers.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374908/original/file-20201214-15-1ylfnmj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Our planet contains all the elements of the periodic table.</span>
<span class="attribution"><span class="source">Sandbh/Wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We know little about the inside of our planet. The deepest mines reach down 10km at the most, while the earth has a radius of 6,500km. Scientific knowledge of deeper levels has been obtained through seismic measurements. Using this data, geologist divided the earth’s structure into various strata, with the core at the center, solid on the inside and liquid on the outside, followed by the lower and upper mantles and, finally, the crust. The earth is made up of heavy, unstable elements and is therefore radioactive, meaning there is another way to find out about its depths and understand the source of its heat.</p>
<h2>What is radioactivity?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371006/original/file-20201124-21-6w5mly.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=755&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Drugs and cosmetics containing a small dose of radium, early 20th century.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Tho-Radia-IMG_1228.JPG/1023px-Tho-Radia-IMG_1228.JPG">Rama/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Radioactivity is a common and inescapable natural phenomenon. Everything on earth is radioactive – that is to say, everything spontaneously produces elementary particles (humans emit a few thousand per second). In Marie Curie’s day, no one was afraid of radioactivity. </p>
<p>On the contrary, it was said to have beneficial effects: beauty creams were certified radioactive and contemporary literature extolled the radioactive properties of mineral water. Maurice Leblanc wrote of a thermal spring saving his protagonist Arsène Lupin during one of his adventures:</p>
<blockquote>
<p>“The water contained such energy and power as to make it a veritable fountain of youth, properties arising from its incredible radioactivity.” (Maurice Leblanc, <a href="https://fr.wikipedia.org/wiki/La_Demoiselle_aux_yeux_verts">“La demoiselle aux yeux verts”</a>, 1927)</p>
</blockquote>
<p>There are various kinds of radioactivity, each involving the spontaneous release of particles and emitting energy that can be detected in the form of heat deposits. Here, we will be talking about “beta” decay, where an election and a neutrino are emitted. The electron is absorbed as soon as it is produced, but the neutrino has the surprising ability to penetrate a wide range of materials. The whole of the Earth is transparent to neutrinos, so detecting neutrinos generated by radioactive decay within the Earth should give us an idea of what is happening at its deepest levels.</p>
<p>These kinds of particles are called <a href="https://neutrino-history.in2p3.fr/the-earth-seen-through-neutrinos/">geoneutrinos</a>, and they provide an original way to investigate the depths of the Earth. Although detecting them is no easy matter, since neutrinos interact little with matter, some detectors are substantial enough to perform this kind of research.</p>
<p>Geoneutrinos mainly arise from heavy elements with very long half-lives, whose properties are now thoroughly understood through lab studies: chiefly uranium, thorium and potassium. The decay of one uranium-238 nucleus, for example, releases an average of 6 neutrinos, and 52 megaelectronvolts of energy carried by the released particles that then lodge in matter and deposit heat. Each neutrino carries around two megaelectronvolts of energy. According to standardized measures, one megaelectronvolt is equivalent to 1.6 10<sup>-13</sup> joules, so it would take around 10<sup>25</sup> decays per second to reach the earth’s total heat. The question is, can these neutrinos be detected?</p>
<h2>Detecting geoneutrinos</h2>
<p>In practice, we have to take aggregate measurements at the detection site of flows coming from all directions. It is difficult to ascertain the exact source of the flows, since we cannot measure their direction. We have to use models to create computer simulations. Knowing the energy spectrum of each decay mode and modeling the density and position of the various geological strata affecting the final result, we get an overall spectrum of expected neutrinos which we then deduct from the number of events predicted for a given detector. This number is always very low – only a handful of events per kiloton of detector per year.</p>
<p>Two recent experiments have added to the research: <a href="https://www.sciencedirect.com/science/article/pii/S0550321316300529">KamLAND</a>, a detector weighing 1,000 metric tons underneath a Japanese mountain, and <a href="https://physicsworld.com/a/borexino-spots-solar-neutrinos-from-elusive-fusion-cycle/">Borexino</a>, which is located in a tunnel under the Gran Sasso mountain in Italy and weighs 280 metric tons. Both use “liquid scintillators”. To detect neutrinos from the earth or <a href="https://www.futura-sciences.com/sciences/actualites/physique-neutrinos-cosmiques-naissent-eruptions-quasars-50447/">the cosmos</a>, you need a detection method that is effective at low energies; this means exciting atoms in a scintillating liquid. Neutrinos interact with protons, and the resulting particles emitted produce observable light.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/371009/original/file-20201124-23-cplwt9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Sno+ experiment uses the SnoLab detector in Canada, to detect geoneutrinos, among other things.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/138424555@N03/23753317224/in/photolist-CbZXE9-CGoBWC-D9vPxZ-Cc82tr-D2dSae-Cc82va-CGoBSj-D2dSct-CYWVvC">SNOLAB</a></span>
</figcaption>
</figure>
<p>KamLAND has announced more than 100 events and Borexino around 20 that could be attributed to geoneutrinos, with an uncertainty factor of 20-30%. We cannot pinpoint their source, but this overall measurement – while fairly rough – is in line with the predictions of the simulations, within the limits of the low statistics obtained.</p>
<p>Therefore, the <a href="https://link.springer.com/chapter/10.1007/978-0-387-70771-6_4">traditional hypothesis</a> of a kind of nuclear reactor at the center of the earth, consisting of a ball of fissioning uranium like those in nuclear power plants, has now been excluded. Fission is not a spontaneous radioactivity but is stimulated by slow neutrons in a chain reaction.</p>
<p>There are now new, more effective detectors being developed: <a href="https://en.wikipedia.org/wiki/SNO%2B">Canada's SNO+</a>, and <a href="https://www.scmp.com/news/china-insider/article/1456878/guangdong-races-ahead-global-effort-measure-elusive-neutrinos">China's Juno</a>, which will improve our knowledge of geoneutrinos.</p>
<blockquote>
<p>“Far from diminishing it, adding the invisible to the visible only enriches the latter, gives it meaning, completes it.” (Paul Claudel, <a href="http://www.gallimard.fr/Catalogue/GALLIMARD/Blanche/Positions-et-propositions">“Positions et propositions”</a>, 1928)</p>
</blockquote>
<hr>
<p><em>Translated from the French by Alice Heathwood for <a href="http://www.fastforword.fr/en">Fast ForWord</a>.</em></p><img src="https://counter.theconversation.com/content/151788/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>François Vannucci ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>The study of neutrinos produced within the Earth’s interior provides a better understanding of the radioactivity of our planet.François Vannucci, Professeur émérite, chercheur en physique des particules, spécialiste des neutrinos, Université Paris CitéLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1427522020-07-20T11:52:47Z2020-07-20T11:52:47ZEarth’s magnetic field may change faster than we thought – new research<figure><img src="https://images.theconversation.com/files/348116/original/file-20200717-33-1cc38wb.jpg?ixlib=rb-1.1.0&rect=47%2C61%2C4475%2C2420&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's long been a mystery how fast the Earth's magnetic field changes.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/abstract-earth-magnetic-fields-250125172">Andrey VP/Shutterstock</a></span></figcaption></figure><p>The Earth’s magnetic field, generated 3,000km below our feet in the liquid iron core, is crucially important to life on our planet. It extends out into space, wrapping us in an electromagnetic blanket that shields the atmosphere and satellites from solar radiation.</p>
<p>Yet the magnetic field is <a href="https://theconversation.com/the-earths-magnetic-north-pole-is-shifting-rapidly-so-what-will-happen-to-the-northern-lights-117237">constantly changing</a> in both its strength and direction and has undergone some dramatic shifts in the past. This includes <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">enigmatic reversals of the magnetic poles</a>, with the south pole becoming the north pole and vice versa. </p>
<p>A long-standing question has been how fast the field can change. Our new study, <a href="https://www.nature.com/articles/s41467-020-16888-0">published in Nature Communications</a>, has uncovered some answers.</p>
<p>Rapid changes of the magnetic field are of great interest because they represent the most extreme behaviour of the ocean of molten iron in the liquid core. By tying the observed changes to core processes, we can learn important information about an otherwise inaccessible region of our planet. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">Why the Earth's magnetic poles could be about to swap places – and how it would affect us</a>
</strong>
</em>
</p>
<hr>
<p>Historically, the fastest changes in Earth’s magnetic field have been <a href="https://theconversation.com/the-earths-magnetic-field-reverses-more-often-now-we-know-why-96957">associated with reversals</a>, which occur at irregular intervals a few times every million years. But we discovered field changes that are much faster and more recent than any of the data associated with actual reversals. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Magnetic reversal.</span>
<span class="attribution"><span class="source">NASA.</span></span>
</figcaption>
</figure>
<p>Nowadays satellites help monitor changes in the field in both space and time, complemented by navigational records and ground-based observatories. This information reveals that changes in the modern field are rather ponderous, around a tenth of a degree per year. But, while we know that the field has existed <a href="https://science.sciencemag.org/content/327/5970/1238.abstract?casa_token=QREHDyVnFUUAAAAA:tHfGEiP4L3NrRO-TnbT73JpMhjiNdZXqZDMAuW6RyhdJO9NMBMVdJUBSl6dpvBvasC-uNGzTaGuEYJA">for at least 3.5 billion years</a>, we don’t know much about its behaviour prior to 400 years ago. </p>
<p>To track the ancient field, scientists analyse the magnetism recorded by sediments, lava flows and human-made artefacts. That’s because these materials contain microscopic magnetic grains that record the signature of Earth’s field at the time they cooled (for lavas) or were added to the landmass (for sediments). Sediment records from central Italy around the time of the last polarity reversal almost 800,000 years ago <a href="https://academic.oup.com/gji/article/199/2/1110/618671">suggest relatively rapid field changes</a> reaching one degree per year.</p>
<p>Such measurements, however, are extremely challenging, with results <a href="https://academic.oup.com/gji/article-abstract/213/3/1744/4944226?redirectedFrom=fulltext">still being debated</a>. For example, there are uncertainties in the process by which sediments acquire their magnetism. </p>
<h2>Improved measurements</h2>
<p>Our research takes a different approach by using computer models based on the physics of the field generation process. This is combined with a recently published reconstruction of global variations in Earth’s magnetic field spanning the last 100,000 years, based on a compilation of measurements from sediments, lavas and artefacts. </p>
<p>This shows that changes in the direction of Earth’s magnetic field reached rates that are up to ten degrees per year – ten times larger than the fastest currently reported variations. </p>
<p>The fastest observed changes in the geomagnetic field direction occurred around 39,000 years ago. This shift was associated with a locally weak field in a confined region just off the west coast of central America. The event followed the global “<a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X12003421">Laschamp excursion</a>” – a “failed reversal” of the Earth’s magnetic field around 41,000 years ago in which the magnetic poles briefly moved far from the geographic poles before returning. </p>
<p>The fastest changes appear to be associated with local weakening of the magnetic field. Our model suggests this is caused by movement of patches of intense magnetic field across the surface of the liquid core. These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.</p>
<h2>The impact on society</h2>
<p>Changes in the magnetic field, such as reversals, probably don’t pose a threat to life. Humans did manage to live through the dramatic Laschamp excursion. Today, the threat is mainly down to our reliance on electronic infrastructure. Space weather events such as geomagnetic storms, arising from the interaction between the magnetic field and incoming solar radiation, could disrupt satellite communications, GPS and power grids. </p>
<figure class="align-center ">
<img alt="Picture of a satellite orbiting Earth." src="https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellites are at risk from space weather.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/space-satellite-orbiting-earth-elements-this-363654452">Andrey Armyagov/Shutterstock</a></span>
</figcaption>
</figure>
<p>This is troubling – the economic cost of a collapse of the US power grid due to a space-weather event <a href="https://www.swpc.noaa.gov/content/space-weather-faq-frequently-asked-questions">has been estimated at</a> around one trillion dollars. The threat is serious enough for space weather to appear as a <a href="https://www.gov.uk/government/collections/national-risk-register-of-civil-emergencies">high priority</a> on the UK national risk register. </p>
<p>Space weather events tend to be more prevalent in regions where the magnetic field is weak – something we know can happen when the field is changing rapidly. Unfortunately, computer simulations suggest that directional changes arise after the field strength begins to weaken, meaning we cannot predict dips in field strength by just monitoring the field direction. Future work using more advanced simulations can shed more light on this issue. </p>
<p>Is another rapid change in the magnetic field on its way? This is very hard to answer. The fastest changes are also the rarest events: for example, the changes identified around the Laschamp excursion are over two times faster than any other changes occurring over the last 100,000 years. </p>
<p>This makes it difficult for scientists to predict rapid changes – they are “black swan events” that come as a surprise and have a big impact. One possible route forward is to use physics-based models of how the field behaves as part of the forecast. </p>
<p>We still have a lot to learn about the “speed limit” of Earth’s magnetic field. Rapid changes have not yet been directly observed during a polarity reversal, but they should be expected since the field is thought to become globally weak at these times.</p><img src="https://counter.theconversation.com/content/142752/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Davies receives funding from NERC. </span></em></p>Changes in the Earth’s magnetic field pose a great risk to electronic infrastructure.Christopher Davies, Associate professor, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1427172020-07-17T01:19:18Z2020-07-17T01:19:18ZAustralian cities are quiet during lockdown. Earthquake scientists are making the most of it<p>Our responses to the COVID-19 pandemic have dramatically changed human activity all over the world. People are working from home, schools are closed in many places, travel is restricted, and in some cases only essential shops and businesses are open. </p>
<p>Scientists see signs of these changes wherever they look. Carbon dioxide emissions are down, air quality has improved, and there is less traffic. </p>
<p>The drop in activity has also been a surprising boon for earthquake scientists like us. Our sensitive instruments are detecting far less of the noise and vibration produced by humans in motion — which means we have a unique opportunity to listen in on tiny earthquakes we might never have detected otherwise.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/underground-sounds-why-we-should-listen-to-earthquakes-5798">Underground sounds: why we should listen to earthquakes</a>
</strong>
</em>
</p>
<hr>
<h2>The seismic hum of humans</h2>
<p>Seismometers are sensitive scientific instruments used to detect earthquakes, volcanic eruptions and nuclear tests, by recording the movement of the ground. They often detect mining activity and can even pick out crowds responding to football games — so-called “footyquakes”. </p>
<p>On top of this, everyday human activity creates a high-frequency seismic “hum” that is stronger during the day and weaker at night. This is particularly evident in urban environments, but is also observed in rural or unpopulated areas. </p>
<p>The decrease in this noise signature was first identified in March by Belgian scientists as lockdown measures were introduced in Europe. These early results, computer codes and data were widely shared on Twitter, sparking an enthusiastic collaboration of seismologists around the world who found this change in signal everywhere they looked.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1240952099887865856"}"></div></p>
<h2>Schoolyard sounds</h2>
<p>In Australia, the change in human behaviour was most dramatically observed in the data recorded by the <a href="https://www.auscope.org.au/geophysical-observatory">Australian Seismometers in Schools (AuSiS) network</a>. These instruments are research-quality seismometers that are maintained by school students — our next generation of geophysicists.</p>
<p>The usual happy schoolyard sounds and hubbub disappeared at many schools, as they shut and most or all students stayed home. The usual hum of the children (and teachers) during the school day, observed in the movement between classrooms, and during lunchtimes or Saturday morning sports, abruptly stopped at locations such as Ulladulla High School on the south coast of New South Wales and Keysborough Secondary College in suburban Melbourne. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1714&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1714&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347848/original/file-20200716-17-1xkxswe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1714&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The heartbeat of four schools from December 1 2019 to July 15 2020. The summer holiday and the school closedown period are eerily quiet.</span>
<span class="attribution"><span class="source">AuSiS</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>At other schools, such as Daramalan College in Canberra, there was only a small decrease in human noise, with the school seismometer recording people commuting to work in essential public services and government offices that continued to operate throughout the initial lockdown. The seismometer at North Rockhampton State High School in Queensland also saw less of the effect, as the students were still able to attend classes.</p>
<p>The level of noise recorded across Australia during lockdown compares to the Christmas week. When restrictions began easing, the signal was similar to the annual January pattern when schools are closed, most businesses are open but many people are away on holiday. As schools reopened across Australia in mid to late May, noise levels were mostly back to “normal” except for what is usually observed for Saturday morning sports.</p>
<h2>Lockdown 2.0</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=692&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=692&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=692&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=869&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=869&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347517/original/file-20200715-31-1f0ixal.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=869&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At Keysborough Secondary College in Victoria, school hours, especially between lessons, are bustling and noisy. Weekends and night-times are quiet enough to use these instruments for seismological research.</span>
<span class="attribution"><a class="source" href="https://raw.githubusercontent.com/ANU-RSES-Education/SeismicNoise_AuSIS_KSC/master/results/latest-hourly.png">AuSiS</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>However, regional differences became even more pronounced as metropolitan Melbourne reinstated stay-at-home restrictions on July 8. As a second spike of COVID-19 cases was detected in Victoria and then ramped up in late June, the level of movement began to drop again. </p>
<p>In the seismic noise signal from Keysborough Secondary College, we can see the school holiday quiet period becoming quieter still as further restrictions to school activity were enforced.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-victorian-earthquake-didnt-do-much-damage-but-the-next-one-might-7787">The Victorian earthquake didn't do much damage ... but the next one might</a>
</strong>
</em>
</p>
<hr>
<h2>Earthquake detection</h2>
<p>The low level of background noise from humans recorded in the seismic data during lockdown gives us a window of opportunity to study smaller earthquakes. Detection of small earthquakes or motion on fault lines is essential for seismic hazard assessment. </p>
<p>Small events are typically identified by looking at changes in amplitudes of signals, but very small events have small amplitude signals and these cannot be observed because they are drowned out by the background noise. </p>
<p>This time of quiescence in seismic noise due to the COVID-19 emergency provides a unique opportunity to learn more about small earthquakes occurring in previously unidentified locations.</p><img src="https://counter.theconversation.com/content/142717/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Meghan S. Miller receives funding from the Australian Research Council and from AuScope which is part of the National Collaborative Research Infrastructure Strategy (NCRIS). </span></em></p><p class="fine-print"><em><span>Louis Moresi receives funding from the Australian Research Council and from AuScope which is part of the National Collaborative Research Infrastructure Strategy (NCRIS).</span></em></p>A network of sensitive instruments in schools around Australia is recording the eerie silence of the coronavirus pandemic — and tiny earthquakes that would otherwise be undetectable.Meghan S. Miller, Associate Professor; Program Director AuScope Earth Imaging, Australian National UniversityLouis Moresi, Professor of Geophysics, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1234282020-01-06T12:06:32Z2020-01-06T12:06:32ZA new way to identify a rare type of earthquake in time to issue lifesaving tsunami warnings<figure><img src="https://images.theconversation.com/files/308024/original/file-20191219-11946-1t4d9ok.jpg?ixlib=rb-1.1.0&rect=350%2C0%2C5065%2C3700&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This unusual earthquake type generates an outsized tsunami. </span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/1fEYDfuGli0">camila castillo/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Just a few times in a century, somewhere on the globe, a rare “tsunami earthquake” occurs. These are mysterious because, while they’re just medium-sized as earthquakes go, they cause disproportionately large and devastating tsunamis. This type of midsized earthquake is very different than an event like the <a href="http://www.tectonics.caltech.edu/outreach/highlights/sumatra/what.html">2004 earthquake in Sumatra</a> – a very big magnitude 9.2 event which unsurprisingly produced a huge tsunami.</p>
<p>The most recent tsunami earthquake happened in 2010. <a href="https://doi.org/10.1029/2010GL046552">A magnitude 7.8 earthquake</a> <a href="http://itic.ioc-unesco.org/index.php?option=com_content&view=article&id=1673:301&catid=1444&Itemid=1444">off the Mentawai Islands in Indonesia</a> <a href="https://doi.org/10.1029/2010GL046498">set off a tsunami</a> that was <a href="https://doi.org/10.1029/2012JB009159">over 50 feet in height</a> in some places – much greater than seismologists would predict based just on the earthquake’s size. <a href="https://earthobservatory.sg/outreach/natural-hazard-outreach/west-sumatra-tectonics-and-tsunami-hazard">509 people were killed</a>, and 15,000 more were displaced or left homeless. </p>
<p>Tsunami earthquakes are particularly destructive and dangerous because the massive tsunami waves can hit local coastal communities within just five to 15 minutes – before officials can issue a warning. But <a href="https://doi.org/10.1029/2019GL083989">based on our analysis</a> of previously unavailable closeup observations of the 2010 Mentawai event, my colleagues <a href="https://scholar.google.com/citations?user=8YD_3R8AAAAJ&hl=en&oi=ao">and I</a> think there is a way to determine that an event is a tsunami earthquake in time to warn people that an unexpectedly large wave is on the way.</p>
<h2>Earthquakes under the ocean</h2>
<p>The Earth’s surface is made up of <a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">floating tectonic plates</a> that fit together like a slightly imperfect jigsaw puzzle. These plates are moving next to, under or away from each other.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An earthquake along a subduction zone happens when the leading edge of the overriding plate breaks free and springs seaward, raising the seafloor and the water above it. This uplift starts a tsunami.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/earthquake-starts-tsunami">USGS</a></span>
</figcaption>
</figure>
<p>In <a href="https://www.livescience.com/43220-subduction-zone-definition.html">a subduction zone</a>, one tectonic plate is sinking beneath another. This builds up stresses over time and will eventually create an earthquake. Most typical subduction-zone earthquakes occur roughly 10 to 30 miles down, in an area where the rocks are rigid and strong on the fault between the two tectonic plates.</p>
<p>Meanwhile, the shallowest area of a subduction zone, closest to the seafloor, is made up of soft sediments that are not very strong. Earthquakes rarely occur only here, because stresses mostly don’t build up in these soft, weak rocks.</p>
<p>Geoscientists define an earthquake’s overall size with its magnitude. Earthquake magnitude describes how much “work” is accomplished by the earthquake moving the fault – more work for either more movement, or for moving more rigid rock.</p>
<p>Very large earthquakes, like the magnitude 9 Tohoku earthquake in Japan in 2011, are so big that they break the deeper part of the subduction zone, but also continue upwards to break the shallow part of a subduction zone. This rapid earthquake motion moves the seafloor and <a href="https://www.iris.edu/hq/inclass/animation/subduction_zone_tsunamis_generated_by_megathrust_earthquakes">creates a tsunami</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cartoon depicting the amount of movement in five earthquakes. The 2010 Mentawai tsunami earthquake moved the fault much more – over 65 feet compared to about 15 feet for the others – and the movement occurred much closer to the seafloor than in any of the other earthquakes.</span>
<span class="attribution"><span class="source">Sahakian et al. (2019), GRL</span></span>
</figcaption>
</figure>
<h2>What sets tsunami quakes apart</h2>
<p>“Tsunami earthquakes” are strange in that they happen almost entirely in the soft, weak section of the fault.</p>
<p>Because tsunami earthquakes break such soft rock, they happen slower, and create much more movement on or near the seafloor in comparison to a normal subduction-zone earthquake of the same size that happens in rigid rock. This in turn creates a much larger tsunami than expected. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=314&fit=crop&dpr=1 600w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=314&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=314&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=395&fit=crop&dpr=1 754w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=395&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=395&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Seismograms showing how much the ground shook from six similarly sized earthquakes, at seismometers all about the same distance from their earthquake. You’d expect the shaking to be comparable. The 2010 Mentawai earthquake seismogram is at the bottom in orange, and shows significantly less shaking than any of the others.</span>
<span class="attribution"><span class="source">Modified from Sahakian et al. (2019), GRL.</span></span>
</figcaption>
</figure>
<p>A tsunami earthquake might have the same magnitude as an earthquake that occurs in rigid rock but produces much less of what seismologists call high-frequency energy. </p>
<p>Think of breaking a thick slab of concrete – which is strong and would produce an audible bang with both low and high-pitched noise – versus breaking a loaf of bread, which makes almost no sound at all. In the Earth, “sound” is the shaking you feel under your feet. The soft bread break is like a tsunami earthquake that doesn’t release a lot of high-frequency energy, and thus doesn’t create as much shaking as we would expect for its magnitude.</p>
<h2>Sensing quakes in time to warn</h2>
<p>Currently, officials rely on knowing an earthquake’s magnitude and location to issue tsunami warnings within tens of minutes. But this doesn’t work in the case of tsunami earthquakes, because the earthquake’s magnitude doesn’t match up with the size of the tsunami it produces.</p>
<p>Instead, to figure out whether an earthquake is in fact a tsunami earthquake, scientists compare its seismic magnitude measured from afar with the amount of high frequency radiated energy it produced, as recorded by far away stations.</p>
<p>If the ratio of energy to magnitude is very low, it’s a tsunami earthquake – basically, its shaking was far too weak for its magnitude because it was breaking soft rock. Instead, its energy is of the low-frequency type: Rather than strong shaking, its energy goes into large slow movement of the seafloor and the ensuing tsunami.</p>
<p>The problem is that in the past, scientists had never recorded one of these elusive earthquakes closeup in what we call the near-field – within about 180 miles (300 kilometers) or so. Instead, scientists have had to find an earthquake’s energy-to-magnitude ratio using seismic waves that have traveled all the way from the epicenter of the earthquake across the world to where researchers can measure them. This process is relatively slow, so we haven’t been able to identify tsunami earthquakes quickly enough to warn people in time, before the wave hits the coast.</p>
<p>Now my colleagues and I have for the first time analyzed data recorded by seismic stations that happened to be near the epicenter of the 2010 Mentawai earthquake. We think we have figured out a new way to identify the danger of a future tsunami earthquake, faster.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tsunamis can take a terrible toll, as for this Indonesian family that lost their father and their home in the Mentawai disaster.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Indonesia-Disasters/77a6343c59ee46199456933fc238e848/4/0">AP Photo/Tundra Laksamana</a></span>
</figcaption>
</figure>
<h2>Closer and quicker proxies</h2>
<p>Our new study used the same concept of comparing the energy released by an earthquake to its seismic magnitude – but based on data from geographically close to the event. Instead of looking at energy measurements recorded at a distance, we used two proxies.</p>
<p>To look directly at how much the ground shook, we used seismic stations onshore near the epicenters of 16 earthquakes, including the Mentawai one in 2010. Because the amount the ground accelerates when seismic waves pass through illustrates how much high frequency energy is in the earthquake, this information was a stand-in for the data we would traditionally get from the far-flung teleseismic stations. Low accelerations mean little high frequency energy.</p>
<p>For the normal earthquakes we looked at, the accelerations from near-field seismometers were close to what we’d expect for each earthquake’s magnitude. In comparison, the 2010 Mentawai earthquake’s accelerations were closer to what we would expect for a magnitude 6.3 earthquake – whereas the earthquake was actually a magnitude 7.8, and produced a tsunami we’d expect for an event of greater than magnitude 8.</p>
<p>We also looked at GPS stations close to the earthquakes. They can show us how much the ground actually moved or was displaced, and measure the earthquake magnitude itself.</p>
<p>Using these measurements together allowed us to compare the amount of energy in the earthquake with respect to its magnitude – without waiting for the seismic waves to travel across the globe. Instead, we would have been able to identify a tsunami earthquake immediately by looking at how low the accelerations were on local seismometers in comparison to the magnitude of the earthquake based on GPS readings.</p>
<p>We think our finding is really promising because these near-field measurements are available immediately – even while an earthquake is happening. Seismologists could use this approach in the future, to identify a tsunami earthquake right after it happens, and provide warning to the nearby coast before the tsunami wave arrives.</p>
<p>[ <em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/123428/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Valerie Sahakian does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A tricky kind of earthquake that happens in the soft rock of the ocean floor causes much larger tsunamis than their magnitude would predict. New research pinpoints a way to identify the danger fast.Valerie Sahakian, Assistant Professor of Geophysics, University of OregonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1232652019-09-16T20:35:31Z2019-09-16T20:35:31ZExplainer: what happens when magnetic north and true north align?<figure><img src="https://images.theconversation.com/files/292338/original/file-20190913-190002-1sm4kgi.jpg?ixlib=rb-1.1.0&rect=42%2C16%2C5615%2C3638&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Very rarely, depending on where you are in the world, your compass can actually point to true north.
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/1393250468?src=vKUFR7i2pguMpY8BD0TNHg-1-62&size=huge_jpg">https://www.shutterstock.com</a></span></figcaption></figure><p>At some point in recent weeks, a once-in-a-lifetime event happened for people at Greenwich in the United Kingdom.</p>
<p>Magnetic compasses at the historic London area, known as the <a href="https://www.rmg.co.uk/discover/explore/prime-meridian-greenwich">home of the Prime Meridian</a>, were said to have pointed directly at the north geographic pole for the <a href="https://www.sciencealert.com/compasses-are-about-to-do-something-that-hasn-t-happened-in-over-300-years">first time in 360 years</a>. </p>
<p>This means that, for someone at Greenwich, magnetic north (the direction in which a compass needle points) would have been in exact alignment with geographic north. </p>
<p>Geographic north (also called “true north”) is the direction towards the fixed point we call the North Pole. </p>
<p>Magnetic north is the direction towards the north magnetic pole, which is a wandering point where the Earth’s magnetic field goes vertically down into the planet. </p>
<p>The north magnetic pole is currently about 400km south of the north geographic pole, but can move to about 1,000km away.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=648&fit=crop&dpr=1 754w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=648&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=648&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The lines of the Earth’s magnetic field come vertically out of the Earth at the south magnetic pole and go vertically down into the Earth at the north magnetic pole.</span>
<span class="attribution"><span class="source">Nasky/Shutterstock</span></span>
</figcaption>
</figure>
<h2>How do the norths align?</h2>
<p>Magnetic north and geographic north align when the so-called “angle of declination”, the difference between the two norths at a particular location, is 0°. </p>
<p>Declination is the angle in the horizontal plane between magnetic north and geographic north. It changes with time and geographic location.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The declination angle varies between -90° and +90°.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>On a map of the Earth, lines along which there is zero declination are called agonic lines. Agonic lines follow variable paths depending on time variation in the Earth’s magnetic field.</p>
<p>Currently, zero declination is occurring in some parts of Western Australia, and will likely move westward in coming years.</p>
<p>That said, it’s hard to predict exactly when an area will have zero declination. This is because the rate of change is slow and current models of the Earth’s magnetic field only cover a few years, and are updated at roughly five-year intervals. </p>
<p>At some locations, alignment between magnetic north and geographic north is very unlikely at any time, based on predictions.</p>
<h2>The ever-changing magnetic poles</h2>
<p>Most compasses point towards Earth’s north magnetic pole, which is usually in a different place to the north geographic pole. The location of the magnetic poles is constantly changing.</p>
<p>Earth’s magnetic poles exist because of its magnetic field, which is produced by electric currents in the liquid part of its core. This magnetic field is defined by intensity and two angles, inclination and declination.</p>
<p>The relationship between geographic location and declination is something people using magnetic compasses have to consider. Declination is the reason a compass reading for north in one location is different to a reading for north in another, especially if there is considerable distance between both locations.</p>
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<strong>
Read more:
<a href="https://theconversation.com/new-evidence-for-a-human-magnetic-sense-that-lets-your-brain-detect-the-earths-magnetic-field-113536">New evidence for a human magnetic sense that lets your brain detect the Earth's magnetic field</a>
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<p>Bush walkers have to be mindful of declination. In Perth, declination is currently close to 0° but in eastern Australia it can be up to 12°. This difference can be significant. If a bush walker following a magnetic compass disregards the local value of declination, they may walk in the wrong direction.</p>
<p>The polarity of Earth’s magnetic poles has also changed over time and has undergone <a href="https://www.nasa.gov/topics/earth/features/2012-poleReversal.html">pole reversals</a>. This was significant as we learnt more about plate tectonics in the 1960s, because it <a href="https://divediscover.whoi.edu/mid-ocean-ridges/magnetics-polarity/">linked the idea</a> of seafloor spreading from mid-ocean ridges to magnetic pole reversals. </p>
<h2>Geographic north</h2>
<p>Geographic north, perhaps the more straightforward of the two, is the direction that points straight at the North Pole from any location on Earth. </p>
<p>When flying an aircraft from A to B, we use directions based on geographic north. This is because we have accurate geographic locations for places and need to follow precise routes between them, usually trying to minimise fuel use by taking the shortest route. All GPS navigation uses geographic location.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/five-maps-that-will-change-how-you-see-the-world-74967">Five maps that will change how you see the world</a>
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<p>Geographic coordinates, latitude and longitude, are defined relative to Earth’s <a href="https://www.scientificamerican.com/article/earth-is-not-round/">spheroidal</a> shape. The geographic poles are at latitudes of 90°N (North Pole) and 90°S (South Pole), whereas the Equator is at 0°.</p>
<h2>An alignment at Greenwich</h2>
<p>For hundreds of years, declination at Greenwich was negative, meaning compass needles were pointing west of true north.</p>
<p>At the time of writing this article I used an <a href="https://ngdc.noaa.gov/geomag/calculators/magcalc.shtml#declination">online calculator</a> to discover that, at the Greenwich Observatory, the Earth’s magnetic field currently has a declination just above zero, about +0.011°. </p>
<p>The average rate of change in the area is about 0.19° per year, which at Greenwich’s latitude represents about 20km per year. This means next year, locations about 20km west of Greenwich will have zero declination.</p>
<p>It’s impossible to say how long compasses at Greenwich will now point east of true north. </p>
<p>Regardless, an alignment after 360 years at the home of the Prime Meridian is undoubtedly a once-in-a-lifetime occurrence.</p><img src="https://counter.theconversation.com/content/123265/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Wilkes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Recently, magnetic compasses at Greenwich pointed directly at true north for the first time in 360 years. This is currently happening in Western Australia too. But what does it mean?Paul Wilkes, Senior Research Geophysicist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1146962019-06-24T12:47:41Z2019-06-24T12:47:41ZWe probed Santorini’s volcano with sound to learn what’s going on beneath the surface<figure><img src="https://images.theconversation.com/files/273695/original/file-20190509-183083-li2utt.jpg?ixlib=rb-1.1.0&rect=0%2C9%2C2285%2C1358&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sound waves let researchers visualize what's happening below the surface.</span> <span class="attribution"><span class="source">Emilie Hooft</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The island of Santorini in the Mediterranean has attracted people for millennia. Today, it feels magical to watch the sun set from cliffs over the deep bay, surrounded by cobalt blue churches and whitewashed houses. This mystical place attracts about 2 million tourists per year, making it one of the <a href="https://www.planetware.com/tourist-attractions/greece-gr.htm">top destinations in Greece</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=620&fit=crop&dpr=1 600w, https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=620&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=620&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=779&fit=crop&dpr=1 754w, https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=779&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/280752/original/file-20190621-61751-g0nt87.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=779&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Greek islands of Santorini form the perimeter of a volcano whose last major explosion happened about 3,400 years ago. Now the center of the crater-like caldera is filled with seawater.</span>
<span class="attribution"><a class="source" href="https://photojournal.jpl.nasa.gov/catalog/PIA02673">NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Not all those visitors recognize that Santorini is an active volcano. In 1630 B.C., the volcano exploded and collapsed leaving behind an almost circular hole. This is the caldera – visible today as a bay filled with seawater and lined by cliffs. The large explosion <a href="https://archaeology-travel.com/greece/south-aegean/santorini/akrotiri/">covered a Bronze Age town</a>, burying buildings in volcanic ash two stories deep. </p>
<p>The <a href="https://www.arcgis.com/apps/MapJournal/index.html?appid=007b8ebcbfe34bfabf17c486b2445637">latest lava flows erupted in 1950</a> and <a href="https://www.volcanodiscovery.com/santorini/1950-eruption.html">expanded the islands that have grown at the center of the caldera</a>. Recently, in 2011-2012, the volcano went through a period of unrest. The ground bulged up and out, and many small earthquakes occurred. <a href="https://news.nationalgeographic.com/news/2012/09/120912-magma-balloon-lava-santorini-volcano-science/">Scientists concluded</a> that a small amount of magma was injected about 2.5 miles (4 kilometers) under the northern portion of the caldera.</p>
<p>What attracted me to this iconic place is that most of the volcano is submerged under water. <a href="https://scholar.google.com/citations?user=GoO8Z7oAAAAJ&hl=en&oi=ao">I am a geophysicist</a> interested in how magma moves deep in the Earth. Over the past decade, I’ve been <a href="https://youtu.be/LXh8lZK55VE">using advanced technology</a> to improve how we “see” magma’s otherwise hidden pathways below volcanoes around the world.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sygEQzn0BP4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Get a glimpse of how researchers conducted their seismic experiment to understand the volcano of Santorini.</span></figcaption>
</figure>
<h2>Using sound to see what’s beneath the surface</h2>
<p>In the 1780s, French scientist Ferdinand Fouquet traveled to Santorini to view an ongoing eruption. He was the first to realize how the volcanic <a href="https://www.nationalgeographic.org/encyclopedia/caldera/">surface depression known as a caldera was formed</a>. As magma emptied out of its underground reservoir during the eruption, the roof of rock that had been covering it collapsed. The flanks of the volcano that remained form the ring of islands visible above water today.</p>
<p>My research project aimed to delve deeper, literally, than <a href="https://doi.org/10.1016/j.tecto.2017.06.005">what we can see from the surface</a> to figure out what’s going on within this still active volcano. A blanket of water over everything except the very top of the Santorini volcano meant I could use deep-penetrating marine sound sources to “illuminate” the subsurface structures. My international collaborators and I wanted to find the location and depth where magma was collecting and how much magma there is right now.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=268&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=268&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=268&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=337&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=337&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273678/original/file-20190509-183086-5rgr4p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=337&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">R/V Marcus Langseth within the Santorini caldera with an ocean-bottom seismometer floating in front of the ship.</span>
<span class="attribution"><span class="source">Doug Toomey</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We conducted our work from the R/V Marcus Langseth, an American marine seismic ship. It is the only academic ship with a sound source capable of imaging the deep insides of a volcano. This technology is controversial because of the <a href="https://doi.org/10.1038/460939b">potential impact of loud sounds</a> on marine wildlife and its intensive use by oil exploration companies.</p>
<p>We spent months doing environmental permitting and finding the optimal design for the experiment. <a href="https://santorini.uoregon.edu">The ship carried a team</a> of experienced biological observers who surveyed the sea both above and below water for sound-sensitive or endangered species. If any were observed at a distance, we were to follow a prescribed set of actions to ensure they wouldn’t be disturbed. After all this preparation, though, we saw almost no wildlife during the expedition.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=459&fit=crop&dpr=1 600w, https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=459&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=459&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=577&fit=crop&dpr=1 754w, https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=577&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/280802/original/file-20190621-61747-175xtok.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=577&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the airguns. It has a volume of 180 cubic inches and is about 18 inches long.</span>
<span class="attribution"><span class="source">Emilie Hooft</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Our “active source seismic imaging” method is like making a CAT-scan picture of the inside of the Earth. Instead of building an image using X-rays, though, we use sound waves generated by 36 heavy, metal canisters – called airguns – that are towed deep in the water behind the ship. When the airguns open, compressed air pushes on the seawater, creating a sound wave that travels through the Earth.</p>
<p>In this instance, the sound travels through the rocks beneath the volcano. Then seismic sensors resting on the seafloor on the other side of the volcano record when the sound reaches them. The team installed 65 of these stations on land, across Santorini and the nearby islands, and dropped another 90 stations to the seafloor. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273702/original/file-20190509-183109-l65l0a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The team installing one of the land seismometers on Anafi.</span>
<span class="attribution"><span class="source">Joanna Morgan, Imperial College London</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We have to use very accurate timing to measure how long it takes the sound energy to go through the different parts of the volcano. The energy from the sound source will travel more slowly through rocks that are broken or that are hot and contain magma. When we probe the structure from many different directions and at many different depths, we can recover a detailed picture of the interior of the Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=311&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=311&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=311&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=391&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=391&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273681/original/file-20190509-183106-3expvj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=391&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">University of Oregon graduate student Brandon VanderBeek capturing an ocean-bottom seismometer after it resurfaces. The caldera cliffs of Santorini are in the distance. The black fresh lavas of the island inside the caldera are in front, on the left.</span>
<span class="attribution"><span class="source">Emilie Hooft</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To get the data back from the seafloor, we send a special sound signal to the sensor – like a bird call – that commands the instrument to drop its anchor. Then everyone scans the sea looking for the instrument. During the day we search for a cheerful orange flag, at night a strobe light makes this task easier. Our ship maneuvers alongside the instrument and a crew member leans over the side, hooks the instrument on a long pole and pulls it back on board. The data is in hand. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273696/original/file-20190509-183112-yzuwdz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Scientists gather around the map table in the R/V Langseth’s main laboratory.</span>
<span class="attribution"><span class="source">PROTEUS Science Team</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Filling out the subsurface picture</h2>
<p>Analysis of the seismic data is an enormous task. It required experienced inspection by Ph.D. student Ben Heath and master’s student Brennah McVey. We then used seismic tomography to make the first detailed “photographs” of Santorini’s subsurface structure. The term tomography comes from the Greek words “tomos” for slice and “graphos” for draw. Basically sophisticated computer code makes a three-dimensional digital model of the object of interest based on the speed sound waves traveled through it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/280795/original/file-20190621-61733-1wgf0d7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The grey volume is the column of porous rock beneath the northern caldera. This is the zone of the initial collapse during the Bronze age eruption. As the plumbing system refills, magma (red in this schematic) accumulates directly beneath this region.</span>
<span class="attribution"><span class="source">Brennah McVey, University of Oregon</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Surprisingly, <a href="https://doi.org/10.1016/j.epsl.2019.02.033">we found a narrow zone of collapsed rock</a> hiding within the broad caldera at Santorini. <a href="http://elementsmagazine.org/2019/06/11/late-bronze-age-eruption-santorini-volcano-impact-ancient-mediterranean-world/">Geological studies</a> of the eruptions at Santorini hadn’t led us to expect there would be a confined volume of rocks in the northern part of the caldera that sound traveled through more slowly. Rather we thought the entire caldera would be filled with this type of broken rock at shallow depths. Our finding meant that the collapsed portion of the caldera was much narrower and deeper than it appears from the surface. </p>
<p>This column of disrupted rock is less than 2 miles (3 km) across – small compared to the size of the 6-mile-wide (10 km) caldera. The structure goes down into the ground 2 miles (3 km) below the bottom of the bay. These rocks must contain lots of water-filled gaps to have sufficiently slowed the seismic energy we recorded.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/vJqmypD17mU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">3D visualization of Santorini’s caldera and magma plumbing system.</span></figcaption>
</figure>
<p>To figure out how this unique volume of disrupted rock formed, we drew on existing knowledge of <a href="https://nom.maps.arcgis.com/apps/Cascade/index.html?appid=2a6c54875bf743dd8143786a55dcb2b1">Santorini’s most recent large explosion</a>, the Late Bronze Age eruption in 1630 B.C. As magma erupted from the subsurface, it caused the overlying rocks to break up. At the same time, underground explosions fractured the rocks when magma and water came into contact. Then, above this collapsing column, the seafloor depression filled with porous volcanic deposits from the eruption itself. Finally, the entire bay dropped down and <a href="https://doi.org/10.1038/ncomms13332">rapid flooding formed a tsunami wave</a>.</p>
<p>What is particularly interesting about our findings is that magma continues to accumulate directly beneath the column of disrupted rock – thousands of years after the explosion that originally created the caldera. My colleagues and I think the rising magma comes to a halt beneath the reduced weight of the broken rock in the collapsed column.</p>
<p>Our research helps explain how magma systems are reset and regrow after major volcanic episodes.</p><img src="https://counter.theconversation.com/content/114696/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emilie Hooft receives funding from the U.S. National Science Foundation. The experiment and analysis were supported by National Science Foundation grant number OCE-1459794 to the University of Oregon and Leverhulme Grant RPG-2015-363 to Imperial College London. Data used in this research were provided by instruments from the Ocean Bottom Seismograph Instrument Pool, which is funded by the National Science Foundation. The Geophysical Instrument Pool Potsdam provided 60 land seismometers. The Aristotle University of Thessaloniki contributed 5 land seismometers and the Greek military donated helicopter time for installations on the smaller islands. This work benefited from access to the University of Oregon high performance computer, Talapas. </span></em></p>Geophysicists use sound waves to build a picture of the magma and rock beneath this active volcano, most of which is underwater. It’s like CT scanning the Earth.Emilie Hooft, Associate Professor of Earth Sciences, Volcanology Cluster of Excellence, & Oregon Hazards Lab, University of OregonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1006312018-08-01T10:38:21Z2018-08-01T10:38:21ZParts of the Pacific Northwest’s Cascadia fault are more seismically active than others – imaging data suggests why<figure><img src="https://images.theconversation.com/files/229901/original/file-20180730-106514-1rqf4bf.jpg?ixlib=rb-1.1.0&rect=114%2C2%2C1652%2C1092&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's going on 150 kilometers below the Earth's surface?</span> <span class="attribution"><a class="source" href="https://www.goodfreephotos.com">Good Free Photos</a></span></figcaption></figure><p>The Pacific Northwest is known for many things – its beer, its music, its mythical large-footed creatures. Most people don’t associate it with earthquakes, but they should. It’s home to the <a href="http://discovermagazine.com/2012/extreme-earth/01-big-one-earthquake-could-devastate-pacific-northwest">Cascadia megathrust fault</a> that runs 600 miles from Northern California up to Vancouver Island in Canada, spanning several major metropolitan areas including Seattle and Portland, Oregon.</p>
<p>This geologic fault has been relatively quiet in recent memory. There haven’t been many widely felt quakes along the Cascadia megathrust, certainly nothing that would rival a catastrophic event like the 1989 <a href="https://earthquake.usgs.gov/earthquakes/events/1989lomaprieta/">Loma Prieta earthquake</a> along the active San Andreas in California. That doesn’t mean it will stay quiet, though. Scientists know it has the potential for large earthquakes – as big as <a href="https://www.newyorker.com/magazine/2015/07/20/the-really-big-one">magnitude 9</a>.</p>
<p>Geophysicists have known for over a decade that not all portions of the Cascadia megathrust fault behave the same. The northern and southern sections are much more seismically active than the central section – with frequent small earthquakes and ground deformations that residents don’t often notice. But why do these variations exist and what gives rise to them?</p>
<p><a href="https://scholar.google.com/citations?user=67KN5e4AAAAJ&hl=en&oi=ao">Our</a> <a href="https://scholar.google.com/citations?user=SXGw77gAAAAJ&hl=en&oi=sra">research</a> tries to answer these questions by <a href="https://doi.org/10.1029/2018GL078700">constructing images of what’s happening deep within the Earth</a>, more than 100 kilometers below the fault. We’ve identified regions that are rising up beneath these active sections which we think are leading to the observable differences along the Cascadia fault.</p>
<h2>Cascadia and the ‘Really Big One’</h2>
<p>The Cascadia <a href="https://www.livescience.com/43220-subduction-zone-definition.html">subduction zone</a> is a region where two tectonic plates are colliding. The <a href="https://americastectonics.weebly.com/juan-de-fuca-explorer-and-gorda-plates.html">Juan de Fuca</a>, a small oceanic plate, is being driven under the North American plate, atop which the continental U.S. sits.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229912/original/file-20180731-102467-1oh0x8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Juan de Fuca plate meets the North American plate beneath the Cascadia fault.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Cascadia_earthquake_sources.png">USGS</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Subduction systems – where one tectonic plate slides over another – are capable of producing the world’s largest known earthquakes. A prime example is the <a href="https://www.livescience.com/39110-japan-2011-earthquake-tsunami-facts.html">2011 Tohoku earthquake</a> that rocked Japan.</p>
<p>Cascadia is seismically very quiet compared to other subduction zones – but it’s not completely inactive. Research indicates the fault ruptured in a <a href="https://www.opb.org/news/series/unprepared/jan-26-1700-how-scientists-know-when-the-last-big-earthquake-happened-here/">magnitude 9.0 event in 1700</a>. That’s roughly 30 times more powerful than the largest predicted San Andreas earthquake. Researchers suggest that we are within the roughly <a href="https://projects.oregonlive.com/maps/earthquakes/timeline">300- to 500-year window</a> during which <a href="https://www.newyorker.com/magazine/2015/07/20/the-really-big-one">another large Cascadia event may occur</a>.</p>
<p>Many smaller undamaging and unfelt events take place in northern and southern Cascadia every year. However, in central Cascadia, underlying most of Oregon, there is very little seismicity. Why would the same fault behave differently in different regions? </p>
<p>Over the last decade, scientists have made several additional observations that highlight variations along the fault.</p>
<p>One has to do with <a href="https://www.ldeo.columbia.edu/%7Edjs/aleut/info_for_public.html">plate locking</a>, which tells us where stress is accumulating along the fault. If the tectonic plates are locked – that is, really stuck together and unable to move past each other – stress builds. Eventually that stress can be released rapidly as an earthquake, with the magnitude depending on how large the patch of fault that ruptures is.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=769&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=769&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=769&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=966&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=966&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229900/original/file-20180730-106521-cc0xx3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=966&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A GPS geosensor in Washington.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:EarthScope-geosensor.jpg">Bdelisle</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Geologists have recently been able to deploy <a href="https://www.unavco.org/projects/major-projects/pbo/pbo.html">hundreds of GPS</a> monitors across Cascadia to record the subtle ground deformations that result from the plates’ inability to slide past each other. Just like historic seismicity, plate locking is more common in the <a href="http://geodesygina.com/Cascadia.html">northern and southern parts of Cascadia</a>.</p>
<p>Geologists are also now able to observe difficult-to-detect seismic rumblings known as <a href="https://pnsn.org/tremor">tremor</a>. These events occur over the time span of several minutes up to weeks, taking much longer than a typical earthquake. They don’t cause large ground motions even though they can release significant amounts of energy. Researchers <a href="https://doi.org/10.1126/science.1084783">have only discovered</a> <a href="https://doi.org/10.1126/science.1060152">these signals</a> in the <a href="https://doi.org/10.1126/science.1070378">last 15 years</a>, but permanent seismic stations have helped build a robust catalog of events. Tremor, too, seems to be more concentrated along the <a href="https://doi.org/10.1130/G23740A.1">northern and southern parts</a> of the fault. </p>
<p>What would cause this situation, with the area beneath Oregon relatively less active by all these measures? To explain we had to look deep, over 100 kilometers below the surface, into the Earth’s mantle.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=588&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=588&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=588&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=738&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=738&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229896/original/file-20180730-106524-1kc0lc8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=738&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Green dots and blue triangles show locations of seismic monitoring stations.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1029/2018GL078700">Bodmer et al., 2018, Geophysical Research Letters</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Imaging the Earth using distant quakes</h2>
<p>Physicians use electromagnetic waves to “see” internal structures like bones without needing to open up a human patient to view them directly. Geologists <a href="https://www.iris.edu/hq/inclass/animation/seismic_tomography_ct_scan_as_analogy">image the Earth</a> in much the same way. Instead of X-rays, we use seismic energy radiating out from distant magnitude 6.0-plus earthquakes to help us “see” features we physically just can’t get to. This energy travels like sound waves through the structures of the Earth. When rock is hotter or partially molten by even a tiny amount, seismic waves slow down. By measuring the arrival times of seismic waves, we create 3D images showing how fast or slow the seismic waves travel through specific parts of the Earth. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=557&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=557&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=557&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=699&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=699&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229895/original/file-20180730-106499-xy3gha.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=699&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ocean bottom seismometers waiting to be deployed during the Cascadia Inititive.</span>
<span class="attribution"><span class="source">Emilie Hooft</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To see these signals, we need records from seismic monitoring stations. More sensors provide better resolution and a clearer image – but gathering more data can be problematic when half the area you’re interested in is underwater. To address this challenge, we were part of a team of scientists that deployed hundreds of seismometers on the ocean floor off the western U.S. over the span of four years, starting in 2011. This experiment, the <a href="https://cascadia.uoregon.edu/">Cascadia Initiative</a>, was the first ever to cover an entire tectonic plate with instruments at a spacing of roughly 50 kilometers.</p>
<p><a href="https://doi.org/10.1029/2018GL078700">What we found are two anomalous regions</a> beneath the fault where seismic waves travel slower than expected. These anomalies are large, about 150 kilometers in diameter, and show up beneath the northern and southern sections of the fault. Remember, that’s where researchers have already observed increased activity: the seismicity, locking, and tremor. Interestingly, the anomalies are not present beneath the central part of the fault, under Oregon, where we see a decrease in activity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=446&fit=crop&dpr=1 600w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=446&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=446&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=561&fit=crop&dpr=1 754w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=561&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/229899/original/file-20180730-106505-ah3ah8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=561&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Regions where seismic waves moved more slowly, on average, are redder, while the areas where they moved more quickly are bluer. The slower anomalous areas 150 km beneath the Earth’s surface corresponded to where the colliding plates are more locked and where tremor is more common.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1029/2018GL078700">Bodmer et al., 2018, Geophysical Research Letters</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>So what exactly are these anomalies?</p>
<p>The tectonic plates float on the Earth’s rocky mantle layer. Where the mantle is slowly rising over millions of years, the rock decompresses. Since it’s at such high temperatures, nearly 1500 degrees Celsius at 100 km depth, it can <a href="https://www.wired.com/2012/12/why-do-rocks-melt-volcano/">melt ever so slightly</a>.</p>
<p>These physical changes cause the anomalous regions to be more buoyant – melted hot rock is less dense than solid cooler rock. It’s this buoyancy that we believe is affecting how the fault above behaves. The hot, partially molten region pushes upwards on what’s above, similar to how a helium balloon might rise up against a sheet draped over it. We believe this increases the forces between the two plates, causing them to be more strongly coupled and thus more fully locked.</p>
<h2>A general prediction for where, but not when</h2>
<p>Our results provide new insights into how this subduction zone, and possibly others, behaves over geologic time frames of millions of years. Unfortunately our results can’t predict when the next large Cascadia megathrust earthquake will occur. This will require more research and dense active monitoring of the subduction zone, both onshore and offshore, using seismic and GPS-like stations to capture short-term phenomena. </p>
<p>Our work does suggest that a large event is more likely to start in either the northern or southern sections of the fault, where the plates are more fully locked, and gives a possible reason for why that may be the case.</p>
<p>It remains important for the public and policymakers to stay informed about the potential risk involved in <a href="https://www.seattletimes.com/seattle-news/science/californias-celeb-quake-expert-says-preventing-damage-is-key-to-quick-recovery/">cohabiting with a subduction zone fault</a> and to support programs such as <a href="https://earthquake.usgs.gov/research/earlywarning/">Earthquake Early Warning</a> that seek to expand our monitoring capabilities and mitigate loss in the event of a large rupture.</p><img src="https://counter.theconversation.com/content/100631/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Doug Toomey receives funding from National Science Foundation and the United States Geological Survey. </span></em></p><p class="fine-print"><em><span>Miles Bodmer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new array of seismometers provides a glimpse of what’s happening deep beneath this geologic fault. New data help explain why the north and south of the region are more seismically active than the middle.Miles Bodmer, PhD Student in Earth Sciences, University of OregonDoug Toomey, Professor of Earth Sciences, University of OregonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/906872018-02-06T07:14:11Z2018-02-06T07:14:11ZHow we’re developing underground mapping technologies - lessons from the Beaumont case<figure><img src="https://images.theconversation.com/files/204783/original/file-20180205-19915-4szzwy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An ERT survey line on the New Castalloy site: the metal pegs allow electricity to be injected into the ground and the orange cable carries the current to the pegs. </span> <span class="attribution"><span class="source">Ian Moffat </span>, <span class="license">Author provided</span></span></figcaption></figure><p>It’s difficult to look on the bright side when <a href="http://www.abc.net.au/news/2018-02-02/enduring-mystery-of-adelaides-missing-beaumont-children/9352254">children missing for 52 years</a> still aren’t found. </p>
<p>However my recent work with the South Australian police in identifying a potential burial site of Jane, Arnna and Grant Beaumont (not seen since Australia Day 1966) has advanced a method for identifying disturbed soil, archaeological material and unmarked grave sites. </p>
<p>Known as electrical resistivity tomography (ERT), this technique maps underground features in 3D. </p>
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Read more:
<a href="https://theconversation.com/australia-has-2-000-missing-persons-and-500-unidentified-human-remains-a-dedicated-lab-could-find-matches-90620">Australia has 2,000 missing persons and 500 unidentified human remains – a dedicated lab could find matches</a>
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<p>This recent survey took place on the grounds of the New Castalloy factory in South Australia. The land became a renewed site of interest in the Beaumont case when two new witnesses came forward and said that they had dug, as teenagers, a large hole at the site on the same weekend as the Beaumont children disappeared. </p>
<p>Unfortunately, following excavation on the site, we now know the new area of focus contained nothing but animal bones and other debris. While this was not the result that was hoped for, ERT was critical in narrowing down a large block of land to find a smaller zone that was feasible for excavation. Without this technology it is likely that police investigation would have been unable to proceed and that this area of the Castalloy site could not have been ruled out as being of interest.</p>
<h2>How does geophysics find graves?</h2>
<p>My background is in geology and geophysics, but my research for the past fifteen years has focused on <a href="https://www.antiquity.ac.uk/projgall/516">archaeological targets</a> and, in particular, the <a href="https://theconversation.com/pilot-study-on-why-academics-should-engage-with-others-in-the-community-76707">location of unmarked graves</a>. </p>
<p>Unfortunately, the techniques we use don’t work as “bone detectors” directly: instead, they map soil disturbance caused by the mixing and repacking of soil layers during the back filling of graves. Obviously finding disturbance alone is not enough to identify a grave, it needs to have appropriate dimensions and should reflect historical information or witness statements about the site.</p>
<p>Ground Penetrating Radar (GPR) is a forensic approach commonly used to explore underground features, which sends pulses of radar energy into the ground and measures the response. This creates 2D profiles which show the soil structure and composition, in an image which is something like digging a trench and looking at the wall.</p>
<p>However GPR was not suited to investigate the New Castalloy site - mainly due to the depth of the potential burials (up to four metres below ground level). The radar signal rapidly decreases with depth for GPR surveys in areas with electrically conductive soils, such as the shallow areas of this site. I did trial GPR at the New Castalloy factory however the results show nothing below around 1m depth.</p>
<p>On that basis, I decided to use Electrical Resistivity Tomography (ERT). To my knowledge, this was the first time this technique has been applied to a forensic case in Australia.</p>
<p>However, an ERT survey takes time. My team and I worked for 14 hours a day for three consecutive days to image the site. This time requirement may explain why ERT, while widely used in the mineral exploration industry, has not been extensively used in forensic investigations in Australia before.</p>
<p>ERT works by injecting electricity into the ground and then measuring how well (or poorly) it travels to a series of receiving electrodes. The electrodes are connected to the ground with metal pegs that are watered to ensure the current can travel easily into the ground. </p>
<p>On the New Castalloy site I was able to image to a maximum depth of 10m, with a resolution along the lines of 0.5m. </p>
<h2>What we found</h2>
<p>The ERT data was processed into a series of 2D profiles, depth slices and a 3D cube with the assistance of <a href="https://www.researchgate.net/profile/Kleanthis_Simyrdanis">Kleanthis Simyrdanis</a>, an expert in the archaeological use of ERT, from the Institute for Mediterranean Studies in Crete. </p>
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Read more:
<a href="https://theconversation.com/pilot-study-on-why-academics-should-engage-with-others-in-the-community-76707">Pilot study on why academics should engage with others in the community</a>
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<p>I reviewed this data to look for areas of soil disturbance with dimensions and a location that reflected witness accounts of a potential grave site. Two connected features immediately stood out. They were approximately 2 x 1 m and 2 x 2 m, and did not continue all the way to the surface; instead they appeared to start underneath a thin resistive layer that was interpreted as the fill added to the site after the hole was dug.</p>
<p>Even though we could see from the data that a hole had been dug at this location, there was no way of knowing whether this feature was a grave. I passed on my findings to detectives from the Major Crime Investigation Section at SA Police, and they made the decision to excavate the site. </p>
<p>The excavation took place on February 2nd. It uncovered fill brought on to the site to aid construction of the nearby building, and then a sandy layer which was found to contain a feature made up of a variety of rubbish including broken ceramic, shell and animal bone. The feature was also wetter than the surrounding sand. This feature corresponded almost exactly in size and shape to the feature found during the ERT survey. No human remains were discovered and the clay layer underneath the feature we found was clearly not disturbed. </p>
<h2>Can geophysics help solve crime?</h2>
<p>In this case, the close correspondence between buried materials found in the subsurface of the New Castalloy site and the feature shown using ERT validate the use of this technique for finding disturbances underground. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=470&fit=crop&dpr=1 600w, https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=470&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=470&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=591&fit=crop&dpr=1 754w, https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=591&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/204521/original/file-20180202-123846-1jnht58.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=591&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Beaumont children who went missing in 1966.</span>
<span class="attribution"><span class="source">Supplied by South Australia Police</span></span>
</figcaption>
</figure>
<p>It sadly did not find Jane, Arnna and Grant Beaumont on this occasion, but is now established as an appropriate technique for other sites with complicated sub-surface conditions.</p><img src="https://counter.theconversation.com/content/90687/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The geophysical survey of the New Castalloy site was funded by Channel 7. Dr Moffat receives research funding from the Australian Research Council.</span></em></p>How can we find buried bodies? Ground penetrating radar is one solution - but it’s not always effective. Electrical resistivity tomography (ERT) offers a very sensitive alternative.Ian Moffat, ARC DECRA Research Fellow in Archaeological Science, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/803112017-09-19T19:41:02Z2017-09-19T19:41:02ZCurious Kids: Why is the Earth round?<figure><img src="https://images.theconversation.com/files/180163/original/file-20170728-23788-1z0m3og.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The mass of the Earth is big enough that the gravitational force it creates can pull the hard shape of ice, rock and metal into a sphere.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/2017/new-night-lights-maps-open-up-possible-real-time-applications">NASA Earth Observatory images by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA's Goddard Space Flight Center</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!</em> </p>
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<blockquote>
<p><strong>Why is the Earth round? – Zoe, age 3, Sydney.</strong></p>
</blockquote>
<p>Thank you, Zoe, for your great question. Asking questions like this is a really important part of being a scientist.</p>
<p>Imagine the Earth pulling everything it is made up of, all of its mass, towards its centre. This happens evenly all over the Earth, causing it to take on a round shape. Let me explain what I mean by that.</p>
<p>To understand why the Earth is round we need to look at two things - mass and gravity. </p>
<p>Every single thing in the universe has mass - from the biggest star to a tiny grain of sand. People, too, have mass. The more big and dense something is, the more mass it has. So an elephant would have more mass than a mouse, for example.</p>
<h2>More mass means more gravity</h2>
<p>While you might not be able to see it, all objects with mass are actually being pulled towards each other by a force called gravity. The bigger the mass of something, the stronger its pull.</p>
<p>Have you ever wondered why if you drop something, it falls towards the Earth and not up into the sky? Or the reason why we’re all stuck to the ground? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180458/original/file-20170801-2341-1tvg9xi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">From the moment water is flung upwards, gravity is working to pull it back down.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/davidwithacamera/32520273400/in/photolist-RxGUhY-9itKGb-axJt8E-AtYxsD-5gh6L2-4rpofz-h6FC2E-81VdTs-jSQ2xp-ogD97x-sugELC-e3Az52-3HDYJE-qicgYj-o1Ac7w-4YUs1Y-UoCRJQ-dAhboR-TKivXi-TKeb8X-BGhh5f-SgeSqp-Wag2jn-TGiTJy-ef63pa-akvk22-GLiQb-6LzFvm-VUsdJb-qnzpeB-W6NZLy-fJ1kig-qE9EDw-VBJiNu-VUsF8d-oW6oWb-W6PfRJ-frCJ1-jzDbYy-gHFxcE-5u7hZZ-hUq4nj-dMmz2n-6fHHFc-9bWN4e-Ba9949-ehrQ4j-UYHBH4-ebPnWn-dfKHb1">David Simmonds/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>That’s because of gravity. Because the mass of the Earth is so much bigger than the mass of people (or spoons, or vases, or water), we’re all strongly pulled towards it, which is why it feels like we’re stuck to the earth’s surface.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-plants-could-grow-in-the-goldilocks-zone-of-space-76918">Curious Kids: What plants could grow in the Goldilocks zone of space?</a>
</strong>
</em>
</p>
<hr>
<h2>Not everything in space is round</h2>
<p>Part of what makes a planet a planet is its round shape. But most things in space are not perfectly round at all! In fact, some things are very lumpy. The reason for this is the way planets are made.</p>
<p>Planets are made of rock, ice, and gas. Before becoming a planet, the rocky and icy parts are small lumps, no bigger than sand grains, moving around the young Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=281&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=281&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=281&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=353&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=353&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180451/original/file-20170801-22140-1sorxcu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=353&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An accretion disk, made from gas rock and ice, similar to the one that formed our Solar system billions of years ago.</span>
<span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/news/239/8-planets-that-make-you-think-star-wars-is-real/">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<p>Over millions of years, gravity pulled the small rocky and icy parts towards each other until they started to stick together. Eventually these small parts grew from the size of sand into the size of mountains.</p>
<p>These mountains of rock and ice are fluffy, like giant dirty snowballs. So the small mass - and weak gravity - of the whole mountain is unable to overcome the hard shape of the rock and ice lumps to become round. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-do-stars-twinkle-81188">Curious Kids: Why do stars twinkle?</a>
</strong>
</em>
</p>
<hr>
<p>Fluffy mountains like these got swept together billions of years ago to make the planets we recognise today. But some of them are still minor objects in the Solar system. These bits of leftover planet-building material, called asteroids and comets, have very lumpy shapes. Some are shaped like potatoes and others like eggs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=470&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=470&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=470&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=590&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=590&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180447/original/file-20170801-22136-15k0b50.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=590&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A comparison of asteroid sizes, including Ceres and Vesta, the two largest objects in the asteroid belt.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Asteroid_size_comparison.jpg">NASA/ESA/STScI</a></span>
</figcaption>
</figure>
<p>The largest of these minor bodies, such as Ceres and Pluto, have enough gravity to look round like a planet. They are called dwarf planets. Some, like Haumea, spin very fast, giving them an stretched shape, like this:</p>
<iframe src="https://giphy.com/embed/3oEhmHt60uQY4Y4mLC" width="100%" height="480" frameborder="0" class="giphy-embed" allowfullscreen=""></iframe>
<p><a href="https://giphy.com/gifs/3oEhmHt60uQY4Y4mLC"></a></p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:</em></p>
<p><em>* Email your question to curiouskids@theconversation.edu.au
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* Tell us on <a href="https://twitter.com/ConversationEDU">Twitter</a> by tagging <a href="https://twitter.com/ConversationEDU">@ConversationEDU</a> with the hashtag #curiouskids, or
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/80311/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan P. Marshall does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Imagine the Earth pulling everything it is made up of, all of its mass, towards its centre. This happens evenly all over the Earth, causing it to take on a round shape.Jonathan P. Marshall, Vice Chancellor's Post-doctoral Research Fellow, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/820422017-08-09T11:27:32Z2017-08-09T11:27:32ZThe German Great Escape: the science of how 83 military officers tunnelled out of a Welsh prison camp in 1945<figure><img src="https://images.theconversation.com/files/181526/original/file-20170809-26064-1vt9372.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Plotting a route out? German prisoners in Britain during WWII.</span> <span class="attribution"><span class="source">Ministry of Information Photo Division Photographe</span></span></figcaption></figure><p>It only takes the opening notes of the theme tune to 1963 classic film <a href="http://www.imdb.com/title/tt0057115/">The Great Escape</a> for most people to conjure up images of the lives of prisoners of wars – and their escapes – during World War II. The film, based on the best-selling book of the same name, tells the story of how British Commonwealth prisoners escaped from Stalag Luft III in Sagan (now Żagań, Poland), in Nazi Germany.</p>
<p>This escape was not unique – there were an estimated 69 other mass escapes of prisoners of war during the war. In seven of these it was by German prisoners escaping. Now our new scientific investigation, <a href="http://dx.doi.org/10.1080/15740773.2017.1357900">published in the Journal of Conflict Archaeology</a>, reveals a hidden tunnel that allowed 83 German prisoners to escape from <a href="http://www.islandfarm.wales/">Camp 198</a> in Bridgend, South Wales, in March 1945.</p>
<p>Camp 198 had been established in 1944 in Bridgend to house 1,600 German officers. With the allies now squeezing the Germans on two fronts, the war had turned a corner, and prisoners were flooding in. In the UK alone, camps sprung up everywhere, numbered in a consecutive sequence that reached <a href="http://discovery.nationalarchives.gov.uk/details/r/C1367149">Camp 1026</a>, in order to house an estimated 400,000 prisoners. And with the <a href="http://hrlibrary.umn.edu/instree/y3gctpw.htm">Geneva Convention</a> specifying that officers could not be put to work in the fields, or anywhere else for that matter, there were undoubtedly many escape plans made.</p>
<p>Yet camp security measures at Bridgend were generally poor. Perhaps overwhelmed by the huge influx of enemy personnel, protocols for anti-escape measures took some time to develop. The lack of sentry towers and perimeter lighting on the fences meant that escape attempts were extremely likely. Tunnels had already proven to be the most common means of escape in the Great War – wherever ground conditions permitted it. The clay soils at Bridgend made it harder to dig tunnels than the sandy soils underlying the Stalag Luft III camp. However the Bridgend tunnels did not need as much shoring support to keep the tunnel intact, a bit of wood salvaged from huts did the trick.</p>
<p>We know the prisoners actually once started a tunnel that was discovered by the guards, perhaps breeding complacency among them. Whatever the case, it did not deter the would-be escapers, and it was a second tunnel, started in “Hut 9”, that finally allowed them to escape.</p>
<h2>Scientific investigation</h2>
<p>Left derelict when closed in 1948, Camp 198 was mostly demolished in the 1990s. However, Hut 9 was preserved by the local authorities, and remains in remarkable condition for scientists to investigate.</p>
<p>Hut 9 provides much evidence of the lives of the officer occupants, filling their days in captivity. Hand-drawn prisoner graffiti still adorns the prison walls. Much of it is poetry, referring to the “heimat” – home – or of loved ones. One of the graffitied walls in Hut 9 was false, constructed to hide the soil that was placed behind it and never discovered.</p>
<p>But what of the tunnel itself? Just as we did to locate <a href="http://dx.doi.org/10.1002/gea.20184">the missing tunnel “Dick”</a> near Hut 122 at the site of the Great Escape, Stalag Luft III, in 2003, we used geophysical investigations outside of Hut 9 at Bridgend to successfully detect the tunnel’s subsurface position. </p>
<p>We started the investigation by using <a href="http://onlinelibrary.wiley.com/doi/10.1002/9781118786352.wbieg0297/abstract">ground-based surface scanning</a> to create a surface model of the site. This helped us <a href="https://doi.org/10.1016/j.geomorph.2013.12.020">identify variations in the surface</a>, such as depressions which could indicate a collapsed tunnel. We then used ground penetrating radar surveys, which uses radar pulses to image the subsurface, to find the specific tunnel location (as well as plenty of tree roots).</p>
<p>At this point, we still weren’t ready to start digging. Measurements of electrical resistivity – how strongly a material opposes the flow of an electric current – helped us determine which parts of the tunnel were filled. Magnetic surveys, used to locate metallic objects, turned out to be less successful, as there was little metal within the tunnel.</p>
<p>While the escape tunnel at Stalag Luft III was dug some ten metres below ground – requiring some prodigious archaeological effort to reach it – at Bridgend, we discovered that the tunnel was at a relatively shallow level of 1.5 metres below ground level. Careful excavations by hand eventually helped us reach this tunnel, which was found to still be remarkably intact. Sawn-off wooden bed legs and materials from the prisoners’ huts, used to support the tunnel walls and roof, were still present, just as they had been left in 1945.</p>
<iframe src="https://drive.google.com/file/d/0B44anbUFlDinbmh3YzhxMmF0TlU/preview" width="100%" height="480"></iframe>
<p>Following the German escape, the local police, home guard, army and air force were all mobilised. While one group of prisoners stole a car and got as far as Birmingham, none managed to successfully make their way back to Germany. </p>
<p>By comparison, in the “Great Escape”, three people managed to return home. Of course, the Germans had to travel through the small, densely-populated island of the UK. The allied escapers achieved a much greater travel distance (470km versus 44km on average) than the Germans before being captured. They also had more sophisticated forged documents and escape material that would have significantly aided their escapes. </p>
<p>Given their comparatively simple plan, it is remarkable that so many Camp 198 prisoners managed to get out. And with the tunnel and the surrounding area destined to become a listed national monument and conserved for future generations, it may soon become as well remembered as the events described in the Great Escape.</p><img src="https://counter.theconversation.com/content/82042/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Pringle receives funding from the HLF, the Nuffield Foundation, Royal Society, NERC, EPSRC and EU Horizon2020. He is affiliated with the Geological Society of London.</span></em></p><p class="fine-print"><em><span>Peter Doyle does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists have uncovered a hidden tunnel left in remarkable condition at a now derelict prison in Bridgend, South Wales.Jamie Pringle, Senior Lecturer in Engineering & Environmental Geosciences, Keele UniversityPeter Doyle, Head of Research Environment, London South Bank UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/815242017-08-04T10:31:16Z2017-08-04T10:31:16ZThe source of up to half of the Earth’s internal heat is completely unknown – here’s how to hunt for it<figure><img src="https://images.theconversation.com/files/180610/original/file-20170801-29610-1o62xaa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">pixabay</span></span></figcaption></figure><p>It may not be obvious while lying in the sun on a hot summer’s day, but a considerable amount of heat is also coming from below you – emanating from deep within the Earth. This heat is equivalent to more than three times the total power consumption of the entire world and drives important geological processes, such as the movement of tectonic plates and the flow of magma near the surface of the Earth. But despite this, where exactly up to half of this heat actually comes from is a mystery.</p>
<p>It is thought that a type of neutrinos – <a href="https://theconversation.com/how-the-neutrino-could-solve-great-cosmic-mysteries-and-win-its-next-nobel-prize-48789">particles</a> with extremely low mass – emitted by radioactive processes in the Earth’s interior may provide important clues to solving this mystery. The problem is that they are nearly impossible to catch. But in a new paper, <a href="https://www.nature.com/articles/ncomms15989">published in the journal Nature Communications</a>, we have set out a way to do just that.</p>
<p>The known sources of heat from the Earth’s interior are radioactive decays, and residual heat from when our planet was first formed. The amount of heating from radioactivity, estimated based on measurements of the composition of rock samples, is highly uncertain – accounting for anywhere from 25-90% of the total heat flow. </p>
<h2>Elusive particles</h2>
<p>Atoms in radioactive materials have unstable nuclei, meaning they can split up (decay to a stable state) by giving off nuclear radiation – some of which gets converted to heat. This radiation consists of various particles with specific energies – depending on what material emitted them – including neutrinos. When the radioactive elements decay within the Earth’s crust and mantle, they emit “geo-neutrinos”. In fact, each second, the Earth radiates more than a trillion trillion such particles to space. Measuring their energy can tell researchers about what material produced them and therefore the composition of the Earth’s hidden interior.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180913/original/file-20170803-7693-a3e55b.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Earth’s core.</span>
</figcaption>
</figure>
<p>The main known sources of radioactivity within the Earth are unstable types of uranium, thorium and potassium – something we know based on samples of rock up to 200km below the surface. What lurks beneath that depth is uncertain. We know that the geo-neutrinos emitted when uranium decays have more energy than those emitted when potassium splits up. So by measuring the energy of geo-neutrinos, we can know what type of radioactive material they come from. In fact, this is a much easier way to figure out what’s inside the Earth than drilling tens of kilometres down below the surface. </p>
<p>Unfortunately, geo-neutrinos are notoriously difficult to detect. Rather than interacting with ordinary matter such as that inside detectors, they tend to just whizz right through them. That’s why it took a huge underground detector filled with with about 1,000 tonnes of liquid <a href="https://www.nature.com/nature/journal/v436/n7050/full/nature03980.html">to make the first observation of geo-neutrinos</a>, in 2003. These detectors measure neutrinos by registering their collision with atoms in the liquid.</p>
<p>Since then, only one other experiment has managed <a href="http://www.sciencedirect.com/science/article/pii/S0370269310003722?via%3Dihub">to observe geo-neutrinos</a>, using a similar technology. Both measurements imply that approximately half of the Earth’s heat caused by radioactivity (20 terawatts) can be explained by decays of uranium and thorium. The source of the remaining 50% is an open question. </p>
<p>However, measurements so far have been unable to measure the contribution from potassium decays – the neutrinos emitted in this process have too low an energy. So it could be that the rest of the heat comes from potassium decay.</p>
<h2>New technology</h2>
<p>Our new research suggests we can make a map of the heat flow from inside the Earth by measuring the direction the geo-neutrino comes from, as well as its energy. This sounds simple, but the technological challenge is formidable, requiring new particle detection technology. </p>
<p>We propose using gas-filled “time projection chamber detectors”. Such detectors work by making a 3D picture of a geo-neutrino colliding with the gas inside it – knocking off an electron from a gas atom. The movement of this electron can then be tracked over time to reconstruct one dimension of the process (time). High-resolution imaging technology can then reconstruct the two spatial dimensions of its movement. In the liquid detectors currently used, the particles that get knocked off in collisions travel such a short distance (because they are in a liquid) that the direction is impossible to resolve. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180903/original/file-20170803-17289-1o0gxw3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Earth heat flow map.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget#/media/File:Earth_heat_flow.jpg">wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Similar detectors, on a smaller scale, are currently used to make precision measurements of neutrino interactions, and to search for dark matter. We calculated that the size of the detector needed to discover the geo-neutrinos from radioactive potassium would be 20 tonnes. To properly map the mantle composition for the first time, it would need to be 10 times more massive. We have built a <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.95.122002">prototype</a> for such a detector, and are working on scaling up.</p>
<p>Measuring geo-neutrinos in this way could help map the heat flow in the Earth’s interior. This would help us to understand the evolution of the inner core by assessing the concentration of radioactive elements. It could also help unravel the longstanding mystery of what source of heat powers the convection (transfer of heat by movement of fluids) in the outer core that generates the Earth’s geomagnetic field. This field is vital for retaining our atmosphere which protects life on Earth from the sun’s harmful radiation. </p>
<p>It’s strange that we know so little about what’s going on under the ground that we walk on. That makes it exciting to think about how these measurements could finally allow the pioneering exploration of the veiled inner workings of the Earth.</p><img src="https://counter.theconversation.com/content/81524/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors of this work are Jocelyn Monroe, Michael Leyton and Stephen Dye. Jocelyn Monroe receives funding from the European Research Council and the UK Science and Technology Facilities Council. Stephen Dye appreciates past support from the Cooperative Studies of the Earth’s Deep Interior (CSEDI) and the Cooperative Institute for Dynamic Earth Research (CIDER) programs funded by the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Michael Leyton receives funding from the Marie Skłodowska-Curie Fellowship program, Ministerio de Economia, Industria y Competitividad (MINECO), Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER).</span></em></p>A new detector could work out what’s causing a heat flow from the Earth’s interior. It may even solve the mystery of what powers the Earth’s magnetic field.Jocelyn Monroe, Professor of Physics, Royal Holloway University of LondonMichael Leyton, Postdoctoral Researcher in Physics, Royal Holloway University of LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/799462017-06-28T09:15:07Z2017-06-28T09:15:07ZIt’s nonsense to say fracking can be made safe, whatever guidelines we come up with<figure><img src="https://images.theconversation.com/files/175798/original/file-20170627-27176-1og9b1w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Can we mitigate the risks associated with fracking?</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/justinwoolford/6254818029/">Justin Woolford/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>Can fracking be safe? A new study suggests how fracking – the process of extracting oil and gas trapped in rocks deep underground by blasting water into the rock at high pressure – can be conducted without causing earthquakes, which is one of the <a href="https://theconversation.com/can-fracking-cause-bigger-more-frequent-earthquakes-16056?sr=3">most well known concerns</a>. While this kind of research can help produce guidelines to reduce the risks associated with fracking, ultimately, it makes no sense to talk of fracking being entirely “safe”.</p>
<p>You might as well ask whether you can ensure your journey to work is safe. There are rules designed to reduce the risks, such as speed limits and the highway code, but there will always be the chance of human error or equipment failure. Venturing onto the roads is an inherently unsafe business. Of course, that doesn’t mean we should never do it. The risks involved in any industrial activity mean that we need to think carefully about how to manage them, rather than trying to claim it is safe or not.</p>
<p>Fracking or hydraulic fracturing involves pumping up to <a href="http://www.refine.org.uk/research/whatisfracking/">16 Olympic swimming pools’ worth of water</a>, chemical additives and sand into shale rocks lying between 2km and 3km underground. This creates a dense network of small fractures in the rocks, releasing gas or oil that moves into the water stream and is pumped or carried to the surface.</p>
<p>Earthquakes can occur when fracking takes place near a geological fault. It’s a bit like <a href="https://www.scientificamerican.com/article/bring-science-home-hovercraft/">how a hovercraft works</a>, by pumping air to produce a cushion so it can slip more easily over the land surface. If frack fluid is pumped into a geological fault, it can also slip more easily. Fracking can also change the stress on the fault, causing it to release, and a big enough fault shift will be felt as an earthquake.</p>
<p>The <a href="https://link.springer.com/article/10.1007/s40948-017-0065-3">new paper</a>, published in Geomechanics and Geophysics for Geo-Energy and Geo-Resources, tries to predict how far from a geological fault it is safe to frack a well without causing an earthquake. Such research is important as it could lead to areas of land being ruled out for fracking, prevent earthquakes and, of course, save the fracking industry from a PR disaster.</p>
<p>To make this prediction, the researchers from Keele and Birmingham universities ran 50 models of a fracking operation based loosely on a site in north-west England and modelled the extent of the expected change in underground stresses. They combined this with an estimation of the smallest stress change that geoscientists think could trigger an earthquake. The results show any fracking site needs to be at least 63 metres away laterally from any fault, and perhaps as far as 433 metres. They haven’t estimated by how much this would reduce the chance of an earthquake.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175664/original/file-20170626-29060-z5xeb1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The process of fracking for shale gas.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/fracking-shale-gas-info-graphic-209800900?src=mQ-RjdLL7NNMwHw8Ik2bjA-1-7">jaddingt/Shutterstock</a></span>
</figcaption>
</figure>
<p>Fracking has been going on since the 1950s and on a large commercial scale in the US for the last 15 years, so it might seem surprising that there aren’t already guidelines that cover this kind of risk. But it partly reflects our limited knowledge of the complex underground landscape and how fracking interacts with it. Because of the complexity and variability, a detailed understanding of the geology of what’s below the Earth’s surface is very incomplete.</p>
<h2>The unknown underground</h2>
<p>We know the layers of rock beneath the Earth’s surface are extremely complex because we can see this in the rock outcrops at surface level. In the 1970s, exploration firms started to use soundwaves that bounce off underground rock layers to create <a href="http://www.seismicatlas.org/">acoustic images of the subsurface</a>. A borehole can then verify what the images correspond to and the properties of the rock layers. But the resolution of a seismic reflection is low, each at best representing ten metres of rock.</p>
<p>This variability and complexity in the rock – and our blurred understanding of it – means that when fracking is carried out for the first time in any location there are uncertainties and risks. How far do the rock layers continue for? What will actually happen to the fracking fluid? Could it travel further than expected into a fault?</p>
<p>To try to get answers to these questions, geoscientists carry out experiments in laboratories, build computer models and examine empirical evidence from the thousands of fracking operations that have been carried out in the US. But, even then, we cannot be sure of the answers.</p>
<h2>Making sense of fracking risks</h2>
<p>For example, in 2012 <a href="http://www.sciencedirect.com/science/article/pii/S0264817212000852">I led a study</a> into how tall fractures become and so how close to the surface they can get. We used thousands of measurements of fractures from the US. An obvious uncertainty is whether the full extent of the fractures was detected using the well-established method of deploying microphones in a nearby well and detecting the cracks as they grow. We found fractures caused by fracking are unlikely to extend beyond 600 metres vertically. This evidence is now the basis for the UK law that <a href="http://researchbriefings.files.parliament.uk/documents/SN06073/SN06073.pdf">prohibits fracking within 1km of the earth’s surface</a>.</p>
<p>Similarly, the new research on earthquakes could one day inform a law on where exactly drilling can take place. But all these results are preliminary, using empirical data, modelling and various assumptions. Only by drilling and closely monitoring more wells will we learn whether the science is robust. </p>
<p>There are <a href="http://www.nerc.ac.uk/latest/news/nerc/fracking-monitoring/">plans for monitoring</a> the first fracking sites in the UK. This will give us data we can use to put more accurate parameters into our models and learn if the existing guidelines are too lax or too conservative. One day we could stream live environmental data from many sites and automatically detect abnormalities, potentially allowing us to spot environmental damage early.</p>
<p>The more we learn about fracking, the more we will be able to manage and reduce its risks. The debate around fracking needs to start with some honesty. Very little of our everyday lives are completely “safe”, and fracking is no exception.</p><img src="https://counter.theconversation.com/content/79946/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Davies leads the ReFINE (Researching Fracking in Europe) consortium, which
has been funded by Ineos, Shell, Chevron, Total, GDF Suez, Centrica and Natural Environment Research Council (UK). He formerly worked in the oil and gas industry and is a Professor and Pro-Vice Chancellor at Newcastle University, UK.</span></em></p>From crossing a road to fracking for oil, everything has inherent risks. At best, we can only aim to agree that, on balance, they are contained and justified.Richard Davies, Pro-Vice Chancellor for Engagement and Internationalisation, Newcastle UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/778032017-05-17T12:12:27Z2017-05-17T12:12:27ZThe science of finding buried bodies<figure><img src="https://images.theconversation.com/files/169750/original/file-20170517-24725-1n168qw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Saddleworth moor, where the victims of the Moors Murders were buried.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/staceycav/9387252510/in/photolist-fiw88d-figTdt-RvGfjA-QRqiLZ-RRQfum-RRQe1E-carW3G-jPvgVt-fiw8p1-mwPBFt-figUhP-cVDhtL-pb9dh2-7Ffpmg-oTH3Ev-5C286Y-5BWMF2-4gtzSU-5WJs2T-5C27p1-e73VG-4gtz4L-bL7jqk-5WsB21-Q1ZQzF-8ikS3i-aw7ifj-aw4Chn-e73VK-8ikS38-4gpyKR-oRFajE-aiWKCD-5WyDnQ-4gtBjj-aw4CPT-aw7hTs-EASdAX-EASJrt-aw7jnQ-7UNpRb-4gtGcs-dEhjA-4gtE7y-q81iS1-qBHTW-5UpoUG-aiZxrY-aCkYxT-HdZg4">blogsession.co.uk/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Ian Brady, who tortured and killed five children in the UK in the 1960s with his accomplice Myra Hindley, <a href="https://www.theguardian.com/uk-news/2017/may/15/ian-brady-the-moors-murderer-dies-aged-79">died in prison on May 15</a>. Jailed in 1966, Brady buried four of his victims in shallow graves on Saddleworth Moor outside Manchester – and the remains have since been found. Sadly, the body of one his victims, Keith Bennett, however, is still missing.</p>
<p>Brady’s death has left Bennett’s family feeling like the final chance to find his remains <a href="http://www.bbc.co.uk/news/uk-england-manchester-39933184">has been lost</a>. The police, however, insist that the search will go on. But how do you go about finding a lost body after so many years?</p>
<p>UK Home Office statistics show that <a href="https://www.gov.uk/government/publications/missing-children-and-adults-strategy">around 2,000</a> of the 200,000 people who are reported missing each year are still not found after 12 months. Some want to start a new life, but an unknown number become victims of crime. Some are murdered. Most of these cases are solved fairly rapidly, but some – so-called cold cases – are harder to crack.</p>
<p>Luckily, science can help. In many homicide cases, bodies end up getting buried in the ground. There are various scientific methods that can help locate such victims, with one of the most important being to <a href="https://doi.org/10.1016/j.geomorph.2013.12.020">identify variations in the surface</a>, such as depressions or small hills, which could indicate that a body has been buried underneath. Search teams can also use specialist “cadaver dogs” to sniff for remains or geophysical methods to scan identified areas. The latter include ground penetrating radar, which uses radar pulses to image the subsurface.</p>
<p>We recently <a href="http://dx.doi.org/10.1016/j.earscirev.2012.05.006">published a review</a> which set out best practice when it comes to finding bodies on land. We discovered that a phased approach usually yields the best results. This involves starting with analysis of large-scale satellite data to locate potential burial areas – for example where soil has been recently disturbed. You then proceed with initial site investigations, looking at suspect areas to find out the soil type and other environmental data. The last stage involves carrying out focused site searches and digging.</p>
<h2>Control studies with animal and human bodies</h2>
<p>But despite this knowledge, the current detection rate of cold cases is low – perhaps only one in 100 cases are successful. As each case is unique, control studies using purpose-built clandestine graves are helping us further work out which detection techniques work best in which cases. In the UK, we currently use pigs as human analogues, although the US, Australia and, since January, the Netherlands, <a href="https://theconversation.com/coming-to-a-field-near-you-the-body-farms-where-human-remains-decompose-in-the-name-of-science-50561">use donated human cadavers</a>. </p>
<p>The approach needed will change as a body decomposes (see figure below) – with the local soil type, burial style and the types of rock in the ground also being important variables. A 50-year-old body buried in a shallow grave in the moors may be relatively intact in wet peatland, whereas a recently buried body in dry sand will rapidly decay. </p>
<p>Ground penetrating radar is best to locate bodies that have been wrapped in something (wrapping provides a good reflective surface). In other cases, where the body is still decomposing, fluids such as blood from the cadaver can be detected by machines that measure electrical resistivity – how strongly a material opposes the flow of an electric current. In a recent study, we showed that conductivity in grave soil water rapidly increases up to two years after burial – data which we can use to <a href="https://dx.doi.org/10.1111/1556-4029.12802">estimate the time since death</a>. </p>
<p>Control studies can only go as far back in time as experiments last, so researchers have also been looking at real graves that are much older to assist with more ancient missing persons cases. </p>
<p>Graveyards and cemeteries are an obvious choice for this. These can be geophysically surveyed, most commonly with ground penetrating radar and electrical resistivity to look for bodies buried without a grave stone. These can be exhumed, both for research purposes and to confirm the identity of the remains. We did this recently when <a href="http://www.fsijournal.org/article/S0379-0738(14)00033-4/fulltext">new church community halls were being built on old graveyards</a>. Exhumation regulations differ across the world, but in the UK you are allowed to do this if burials are over 100 years old.</p>
<p>An issue with this, however, is that graveyard burials are in coffins, often along with preservatives. Few accidental burials or homicide graves use coffins or chemicals. Nonetheless, ongoing geophysical research of graveyard burials is extending our knowledge of how long bodies are detectable for. This can certainly feed into cold case searches. </p>
<p>This kind of research has also improved our understanding of how well different survey methods work in different environments. For example, electrical resistivity surveys tend to work best in clay-rich soils whereas radar is best in sandy soils. We’ve also learned that gravestones are often not exactly in the correct position, and that graves containing many bodies <a href="http://dx.doi.org/10.1016/j.forsciint.2014.01.009">are often not vertically aligned</a>. This may occur due to coffins subsiding in soft ground, or in more extreme examples, due to “coffin slip”, where in inclined ground, burials move down the slope over time. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/169752/original/file-20170517-9937-191uxcc.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Search for a missing person in woodland in the Midlands with a magnetic gradiometer.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Clearly more research needs to be done to improve detection rates of cold cases. In fact, the key is to combine collaborative academic control studies with input from search practitioners and experts. Advances in technology – such as <a href="http://dx.doi.org/10.1016/j.forsciint.2013.12.036">drones</a> that can help locate surveys in real time and more sensitive geophysical devices – are also allowing us to integrate both simple observations and advanced geophysical searches into one system. </p>
<p>There’s certainly good reason to believe that Bennett was also buried somewhere on the moor. Initial searches, mainly using police manpower and volunteers looking for physical signs of ground disturbance, were unsuccessful. Many other methods have since been used, including specialist search dogs and metal detectors (should there be metal in Keith’s clothing). Soil sampling and other tests have also been used to look for decomposition of fluids, but it is probably too late for this now. Ground penetrating radar has also been used to search for a skeleton.</p>
<p>However, these methods are time consuming and only a relatively small area can be surveyed each time. But, as long we continue looking – and use the latest technology and research to inform the search – there is every chance that we could one day find Bennett’s body.</p><img src="https://counter.theconversation.com/content/77803/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Pringle receives funding from the HLF, the Nuffield Foundation, Royal Society, NERC, EPSRC and EU Horizon2020. He is affiliated with the Geological Society of London. </span></em></p><p class="fine-print"><em><span>Alastair Ruffell receives funding from ERC, EPSRC.</span></em></p>50 years after the Moors Murders, UK police are still hoping to find a missing body. And scientists are working hard to help.Jamie Pringle, Senior Lecturer in Engineering & Environmental Geosciences, Keele UniversityAlastair Ruffell, Research associate in Geoforensics, Queen's University BelfastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/475282017-02-06T04:52:22Z2017-02-06T04:52:22ZDoes an anomaly in the Earth’s magnetic field portend a coming pole reversal?<figure><img src="https://images.theconversation.com/files/155051/original/image-20170131-3248-1n8ah.jpg?ixlib=rb-1.1.0&rect=382%2C12%2C3873%2C2707&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's north would become south.</span> <span class="attribution"><a class="source" href="https://spaceflight.nasa.gov/gallery/images/station/crew-23/html/iss023e058455.html">NASA </a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The Earth is blanketed by a magnetic field. It’s what makes compasses point north, and protects our atmosphere from continual bombardment from space by charged particles such as protons. Without a magnetic field, our atmosphere would slowly be stripped away by harmful radiation, and life would almost certainly not exist as it does today.</p>
<p>You might imagine the magnetic field is a timeless, constant aspect of life on Earth, and to some extent you would be right. But Earth’s magnetic field actually does change. Every so often – on the order of several hundred thousand years or so – the magnetic field has flipped. North has pointed south, and vice versa. And when the field flips it also tends to become very weak.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">On the left, the Earth’s magnetic field we’re used to. On the right, a model of what the magnetic field might be like during a reversal.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:NASA_54559main_comparison1_strip.gif">NASA/Gary Glazmaier</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>What currently has geophysicists like us abuzz is the realization that the strength of Earth’s magnetic field has been decreasing for the last 160 years at an alarming rate. This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly. The magnetic field strength is so weak there that it’s a hazard for satellites that orbit above the region – the field no longer protects them from <a href="http://scitechdaily.com/new-hubblecast-video-explores-south-atlantic-anomaly/">radiation which interferes</a> with satellite electronics.</p>
<p>And the field is continuing to grow weaker, potentially portending even more dramatic events, including a global reversal of the magnetic poles. Such a major change would affect our navigation systems, as well as the transmission of electricity. The spectacle of the northern lights might appear at different latitudes. And because more radiation would reach Earth’s surface under very low field strengths during a global reversal, it also might affect rates of cancer.</p>
<p>We still don’t fully understand what the extent of these effects would be, adding urgency to our investigation. We’re turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to puzzle it out.</p>
<h2>Genesis of the geomagnetic field</h2>
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<a href="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Cutaway image of the Earth’s interior.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Earth_poster.svg">Kelvinsong</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>Earth’s magnetic field is created by <a href="http://www.geomag.bgs.ac.uk/education/earthmag.html#_Toc2075563">convecting iron in our planet’s liquid outer core</a>. From the wealth of <a href="https://www.ngdc.noaa.gov/geomag/geomag.shtml">observatory and satellite data</a> that document the magnetic field of recent times, we can model what the field would look like if we had a compass immediately above the Earth’s swirling liquid iron core. </p>
<p>These analyses reveal an astounding feature: There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior. In this area, the polarity of the field is opposite to the average global magnetic field. If we were able to use a compass deep under southern Africa, we would see that in this unusual patch north actually points south.</p>
<p>This patch is the main culprit creating the South Atlantic Anomaly. In numerical simulations, unusual patches similar to the one beneath southern Africa appear immediately prior to geomagnetic reversals.</p>
<p>The poles have reversed frequently over the history of the planet, but the <a href="http://doi.org/10.1002/ggge.20263">last reversal is in the distant past</a>, some 780,000 years ago. The rapid decay of the recent magnetic field, and its pattern of decay, naturally raises the question of what was happening prior to the last 160 years.</p>
<h2>Archaeomagnetism takes us further back in time</h2>
<p>In archaeomagnetic studies, geophysicists team with archaeologists to learn about the past magnetic field. For example, clay used to make pottery contains small amounts of magnetic minerals, such as magnetite. When the clay is heated to make a pot, its magnetic minerals lose any magnetism they may have held. Upon cooling, the magnetic minerals record the direction and intensity of the magnetic field at that time. If one can determine the age of the pot, or the archaeological site from which it came (using radiocarbon dating, for instance), then an archaeomagnetic history can be recovered. </p>
<p>Using this kind of data, we have a partial history of archaeomagnetism for the Northern Hemisphere. In contrast, the Southern Hemisphere archaeomagnetic record is scant. In particular, there have been virtually no data from southern Africa – and that’s the region, <a href="http://dx.doi.org/10.1016/j.epsl.2011.03.030">along with South America</a>, that might provide the most insight into the history of the reversed core patch creating today’s South Atlantic Anomaly.</p>
<p>But the ancestors of today’s southern Africans, Bantu-speaking metallurgists and farmers who began to migrate into the region between 2,000 and 1,500 years ago, unintentionally left us some clues. <a href="http://doi.org/10.1146/annurev.an.11.100182.001025">These Iron Age people</a> lived in huts built of clay, and stored their grain in hardened clay bins. As the <a href="http://www.sahistory.org.za/article/pre-1500">first agriculturists of the Iron Age of southern Africa</a>, they relied heavily on rainfall. </p>
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<a href="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Grain bins of the style used centuries ago.</span>
<span class="attribution"><span class="source">John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>The communities often responded to times of drought with rituals of cleansing that involved burning mud granaries. This somewhat tragic series of events for these people was ultimately a boon many hundreds of years later for archaeomagnetism. Just as in the case of the firing and cooling of a pot, the clay in these structures recorded Earth’s magnetic field as they cooled. Because the floors of these ancient huts and grain bins can sometimes be found intact, we can sample them to obtain a record of both the direction and strength of their contemporary magnetic field. Each floor is a small magnetic observatory, with its compass frozen in time immediately after burning.</p>
<p><a href="http://dx.doi.org/10.1038/ncomms8865">With our colleagues, we’ve focused our sampling</a> on Iron Age village sites that dot the Limpopo River Valley, bordered today by Zimbabwe to the north, Botswana to the west and South Africa to the south.</p>
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<a href="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=196&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=196&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=196&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=246&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=246&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=246&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">What’s happening deep within the Earth, beneath the Limpopo River Valley?</span>
<span class="attribution"><span class="source">John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Magnetic field in flux</h2>
<p>Sampling at Limpopo River Valley locations has yielded the first archaeomagnetic history for southern Africa between A.D. 1000 and 1600. What we found reveals a period in the past, near A.D. 1300, when the field in that area was decreasing as rapidly as it is today. Then the intensity increased, albeit at a much slower rate.</p>
<p>The occurrence of two intervals of rapid field decay – one 700 years ago and one today – suggests a recurrent phenomenon. Could the reversed flux patch presently under South Africa have happened regularly, further back in time than our records have shown? If so, why would it occur again in this location?</p>
<p>Over the last decade, researchers have accumulated <a href="http://dx.doi.org/10.1016/j.epsl.2005.01.037">images from the analyses of earthquakes’ seismic waves</a>. As seismic shear waves move through the Earth’s layers, the speed with which they travel is an indication of the density of the layer. Now we know that a large area of slow seismic shear waves characterizes the core mantle boundary beneath southern Africa.</p>
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<a href="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Location of the South Atlantic Anomaly.</span>
<span class="attribution"><span class="source">Michael Osadicw/John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>This particular region underneath southern Africa has the somewhat wordy title of the African Large Low Shear Velocity Province. While many wince at the descriptive but jargon-rich name, it is a profound feature that must be tens of millions of years old. While thousands of kilometers across, its boundaries are sharp. Interestingly, the reversed core flux patch is nearly coincident with its eastern edge.</p>
<p>The fact that the present-day reversed core patch and the edge of the African Large Low Shear Velocity Province are physically so close got us thinking. We’ve come up with a <a href="http://dx.doi.org/10.1038/ncomms8865">model linking the two phenomena</a>. We suggest that the unusual African mantle changes the flow of iron in the core underneath, which in turn changes the way the magnetic field behaves at the edge of the seismic province, and leads to the reversed flux patches. </p>
<p>We speculate that these reversed core patches grow rapidly and then wane more slowly. Occasionally one patch may grow large enough to dominate the magnetic field of the Southern Hemisphere – and the poles reverse.</p>
<p>The conventional idea of reversals is that they can start anywhere in the core. Our conceptual model suggests there may be special places at the core-mantle boundary that promote reversals. We do not yet know if the current field is going to reverse in the next few thousand years, or simply continue to <a href="https://doi.org/10.3389/feart.2015.00061">weaken over the next couple of centuries</a>.</p>
<p>But the clues provided by the ancestors of modern-day southern Africans will undoubtedly help us to further develop our proposed mechanism for reversals. If correct, pole reversals may be “Out of Africa.”</p>
<hr>
<p><em>This story was updated to correct the units used in the last figure; magnetic field strength is depicted in tens of nanoTesla.</em></p><img src="https://counter.theconversation.com/content/47528/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Tarduno receives funding from the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Vincent Hare receives funding from the US National Science Foundation and !Khure Africa, a dual South Africa/France collaborative Earth System programme. </span></em></p>Are we headed to a magnetic reversal and all the global disruption that would bring? Enter archaeomagnetism. A look at the archaeological record in southern Africa provides some clues.John Tarduno, Professor of Geophysics, University of RochesterVincent Hare, Postdoctoral Associate in Earth and Environmental Sciences, University of RochesterLicensed as Creative Commons – attribution, no derivatives.