tag:theconversation.com,2011:/global/topics/tides-8620/articlesTides – The Conversation2024-03-12T19:15:29Ztag:theconversation.com,2011:article/2250882024-03-12T19:15:29Z2024-03-12T19:15:29ZPacific Islanders have long drawn wisdom from the Earth, the sky and the waves. Research shows the science is behind them<p>One afternoon last year, we sat in a village hall in Fiji chatting to residents about traditional ways of forecasting tropical cyclones. One man mentioned a black-winged storm bird known as “manumanunicagi” that glides above the land only when a cyclone is forming out to sea. As the conversation continued, residents named at least 11 bird species, the odd behaviour of which signalled imminent changes in the weather. </p>
<p>As we were leaving later that evening, an elder took us aside. He was pleased we had taken their beliefs seriously and said many older Pacific people won’t talk about traditional knowledge for fear of ridicule.</p>
<p>This reflects the dominance of science-based understandings in adapting to climate change and its threats to ways of life. Our <a href="https://wires.onlinelibrary.wiley.com/doi/10.1002/wcc.882">new research</a> suggests this attitude should change. </p>
<p>We reviewed evidence on traditional knowledge in the Pacific for coping with climate change, and found much of it was scientifically plausible. This indicates such knowledge should play a significant role in sustaining Pacific Island communities in future.</p>
<h2>A proven, robust system</h2>
<p>Our research was co-authored with 26 others, most Pacific Islanders with long-standing research interests in traditional knowledge.</p>
<p>People have inhabited the Pacific Islands for 3,000 years or <a href="https://www.routledge.com/Archaeology-of-Pacific-Oceania-Inhabiting-a-Sea-of-Islands/Carson/p/book/9781032486376">more</a> and have experienced many climate-driven challenges to their livelihoods and survival. They have coped not by luck but by design – through robust systems of traditional knowledge built by diverse groups of people over time.</p>
<p>The main short-term climate-related threats to island livelihoods in the Pacific are tropical cyclones which can damage food crops, pollute fresh water and destroy infrastructure. Prolonged droughts – common during El Niño events in the southwest Pacific – <a href="https://doi.org/10.1007/s10584-021-03112-1">also cause</a> widespread damage.</p>
<p>Traditional knowledge in the Pacific explains the causes and manifestations of natural phenomena, and identifies the best ways to respond. It is commonly communicated orally between generations. </p>
<p>Here, we describe such knowledge relating to animals, plants, water and sky – and show how these beliefs make scientific sense.</p>
<p>It’s important to note, however, that traditional knowledge has its own intrinsic value. Scientific explanations are not required to validate it.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/secrets-in-the-canopy-scientists-discover-8-striking-new-bee-species-in-the-pacific-222599">Secrets in the canopy: scientists discover 8 striking new bee species in the Pacific</a>
</strong>
</em>
</p>
<hr>
<h2>Reading the ocean and sky</h2>
<p>Residents of Fiji’s Druadrua Island interpret breaking waves to predict a cyclone as long as one month before it hits. In Vanuatu’s Torres Islands, 13 phrases exist to describe the state of the tide, including anomalies that <a href="https://doi.org/10.1002/j.1834-4461.2004.tb02856.x">herald uncommon events</a>.</p>
<p>These observations make scientific sense. Distant storms can drive ocean swells onto coasts long before the winds and rain arrive, changing the usual patterns of waves.</p>
<p>In Samoa, <a href="https://journals.sagepub.com/doi/abs/10.1177/25148486211047739">ten types of wind</a> are recognised in traditional lore. Winds that blow from the east (matā ‘upolu) indicate the imminent arrival of heavy rain, possibly a tropical cyclone. The south wind (tuā'oloa) is most feared. It will cease to blow, it is said, only when its appetite for death is <a href="https://link.springer.com/article/10.1007/s10584-009-9722-z">sated</a>.</p>
<p>Many Pacific Island communities believe a cloudless, dark blue sky signals the arrival of a tropical cyclone. Other signs include unusually rapid cloud movements and the appearance of “short rainbows”. </p>
<p>These beliefs are supported by science. Rainbows are sometimes “shortened” or partly obscured by a distant rain shower. And Western science has <a href="https://link.springer.com/book/10.1007/978-0-387-71543-8">long recognised</a> changes in clouds and winds can signal the development of cyclones.</p>
<p>In Vanuatu, a halo around a moon signals <a href="https://doi.org/10.1175/wcas-d-13-00053.1">imminent rainfall</a>. Again, this belief is scientifically sound. According to Western science, high thin cirrus clouds signal nearby storms. The clouds contain ice crystals through which moonlight is filtered, creating a halo effect.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/teaching-our-children-from-books-not-the-sea-how-climate-change-is-eroding-human-rights-in-vanuatu-192016">'Teaching our children from books, not the sea': how climate change is eroding human rights in Vanuatu</a>
</strong>
</em>
</p>
<hr>
<h2>The wisdom of animals and plants</h2>
<p>As mentioned above, birds are are said to herald weather changes across the Pacific.</p>
<p>In Tonga, when the frigate bird flies across the land – unusual behaviour for an ocean species – it signals a tropical cyclone is developing. This traditional knowledge is captured in the logo of the <a href="https://met.gov.to">Tonga Meteorological Service</a>. Birds are similarly interpreted in <a href="https://doi.org/10.1080/17477891.2015.1046156">Fiji</a> and <a href="https://doi.org/10.1177/25148486211047739">northern Vanuatu</a>.</p>
<p>This belief stacks up scientifically. One <a href="https://doi.org/10.1016/j.cub.2014.10.079">study</a> in North America, for example, showed golden-winged warblers dodged tornadoes by detecting shifts in infrasound. Another <a href="https://doi.org/10.1038/s41598-019-41481-x">study</a>, which included data on frigate birds in the Pacific, found seabirds appeared to circumvent cyclones, probably by sensing wind strength and direction.</p>
<figure class="align-right ">
<img alt="plantain tree in field" src="https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=799&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=799&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=799&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581159/original/file-20240312-18-84kk3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">When the central shoot of the plantain is curled, people know a cyclone is developing.</span>
<span class="attribution"><span class="source">Patrick Nunn</span></span>
</figcaption>
</figure>
<p>Traditional knowledge about insect behaviour in the Pacific Islands is also used to predict wet weather.</p>
<p>Bees, wasps and hornets usually build nests in tree branches. When nests are built close to the ground, Pacific Islanders know the forthcoming wet season will be wetter than normal, probably due to more tropical cyclones. This type of nest-building may <a href="https://doi.org/10.1080/17477891.2015.1046156">prompt</a> residents to make appropriate preparations such as storing food.</p>
<p>Studies suggest insect behaviour can predict changes in weather. For example, <a href="https://doi.org/10.1016/j.crvi.2009.10.007">a study</a> of wasp nesting in French Guiana found their ability to quickly move nests to more sheltered locations may help them survive wet years.</p>
<p>Across the Pacific, common signs of impending wet weather are found in the <a href="https://doi.org/10.1007/s10113-020-01613-w">behaviours</a> of <a href="https://doi.org/10.5751/ES-08100-210207">some plants</a>. The central shoot of the plantain, for example, will be conspicuously curled instead of straight.</p>
<p>This can be <a href="https://doi.org/10.1093/jxb/eru327">explained</a> scientifically by a process in which plant leaves close to protect their reproductive organs from extreme weather.</p>
<h2>Planning for a warmer future</h2>
<p>Since colonisation imposed Western worldviews around the world, traditional knowledge has been sidelined. This is true of the Pacific Islands, where in some places, traditional knowledge is all but <a href="https://theconversation.com/teaching-our-children-from-books-not-the-sea-how-climate-change-is-eroding-human-rights-in-vanuatu-192016">forgotten</a>. </p>
<p>But both Western and traditional knowledges have their pros and cons. Science-based knowledge, for example, is generic and often can’t realistically be applied <a href="https://theconversation.com/pacific-islands-must-stop-relying-on-foreign-aid-to-adapt-to-climate-change-because-the-money-wont-last-132095">at local scales</a>. </p>
<p>As climate change impacts worsen, optimal planning for island peoples should combine both approaches. This will require open-mindedness and a respect for diverse sources of knowledge.</p><img src="https://counter.theconversation.com/content/225088/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Patrick D. Nunn receives funding from the Department of Foreign Affairs and Trade (DFAT) via the Australia Pacific Climate Partnership (APCP), the Australian Research Council, and the Asia-Pacific Network for Global Change Research.</span></em></p><p class="fine-print"><em><span>Roselyn Kumar receives funding from the Department of Foreign Affairs and Trade (DFAT) via the Australia Pacific Climate Partnership (APCP)</span></em></p>We reviewed evidence on traditional knowledge in the Pacific for coping with climate change, and found much of it was scientifically plausible.Patrick D. Nunn, Professor of Geography, School of Law and Society, University of the Sunshine CoastRoselyn Kumar, Adjunct Research Fellow in Geography and Social Sciences, University of the Sunshine CoastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2182012024-01-19T13:41:44Z2024-01-19T13:41:44ZI’m an artist using scientific data as an artistic medium − here’s how I make meaning<figure><img src="https://images.theconversation.com/files/569152/original/file-20240112-27-8u7iv7.jpeg?ixlib=rb-1.1.0&rect=2%2C0%2C1393%2C932&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sarah Nance at the Bonneville Salt Flats, Utah, 2019.</span> <span class="attribution"><span class="source">Courtesy of Sarah Nance</span></span></figcaption></figure><p>As an <a href="https://www.binghamton.edu/art/profile.html?id=snance">artist working across media</a>, I’ve used everything from thread to my voice to poetically translate and express information. Recently, I’ve been working with another medium – geologic datasets. </p>
<p>While scientists use data visualization to show the results of a dataset in interesting and informative ways, my goal as an artist is a little different. In the studio, I treat geologic data as another material, using it to guide my interactions with Mylar film, knitting patterns or opera. Data, in my work, functions expressively and abstractly. </p>
<p>Two of my projects in particular, “points of rupture” and “tidal arias,” exemplify this way of working. In these pieces, my goal is to offer new ways for people to personally relate to the immense scale of geologic time.</p>
<h2>Points of rupture</h2>
<p>An early project in which I treated data as a medium was my letterpress print series “<a href="https://www.sarahnance.com/shroud/alaska">points of rupture</a>.” In this series, I encoded data from <a href="https://www.britannica.com/science/cryoseism">cryoseismic, or ice quake</a>, events to create knitting patterns. </p>
<p>Working with ice quake data was a continuation of my research into what I call “archived landscapes.” These are places that have had multiple distinct geologic identities over time, like <a href="https://www.nps.gov/gumo/learn/nature/coralreefs.htm">mountains that were once sea reefs</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="silver knitting symbols on black background" src="https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569121/original/file-20240112-17-umjli0.jpg?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"></a>
<figcaption>
<span class="caption">‘points of rupture (alaska glacial event 1999),’ 2020. Letterpress print of knitting pattern coded using cryoseismic data. Edition of 15. 18 x 18 in.</span>
<span class="attribution"><span class="source">Sarah Nance</span></span>
</figcaption>
</figure>
<p>Because knit textiles are made up of many individual stitches, I can use them to encode discrete data points. In a knitting pattern, or chart, each kind of stitch is represented by a specific symbol. I used the open-source program <a href="https://stitch-maps.com">Stitch Maps</a> to write the patterns for this project, translating the peaks and valleys of seismographs into individual stitch symbols. </p>
<p>Knitting charts typically display these symbols in a grid. Instead, Stitch Maps allows them to fall as they would when knitted, so the chart mimics the shape of the final textile. </p>
<p>I was drawn to the expressive possibilities of this feature and how the software allowed me to experiment. I was able to write patterns that worked only in theory and not as physical, handmade structures. This gave me more freedom to design patterns that fully expressed the datasets without having to ensure their viability as textiles.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="graphite drawing of mitten knitting chart on gallery wall" src="https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568495/original/file-20240109-29-ojgmd6.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">‘and when you change the landscape, is it with bare hands or with gloves? (lichen, woodwork, grate),’ 2023. Graphite drawing of selbu mitten knitting chart. 99 x 67 linear inches as installed.</span>
<span class="attribution"><span class="source">Sarah Nance</span></span>
</figcaption>
</figure>
<p><a href="https://nsidc.org/learn/parts-cryosphere/glaciers">Glaciers form</a> incrementally as new snowfall compacts previous layers of snow, crystallizing them into ice. A knitted fabric similarly accumulates in layers, as rows of interlocking loops. Each structure appears stable but could easily be dissolved.</p>
<p>Ice quakes occur in glaciers as a result of <a href="https://www.britannica.com/science/cryoseism">calving events or pooling meltwater</a>. Like melting glaciers, knitting is always in danger of coming apart – but instead of melting, by snagging and unraveling into formlessness. These structural similarities between glaciers and knitting are reflected in the “points of rupture” prints, where disruptive ice quakes translate into unknittable patterns. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="silver knitting symbols on black background" src="https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569080/original/file-20240112-19-758bfo.jpg?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"></a>
<figcaption>
<span class="caption">‘points of rupture (glacier de la plaine morte icequake 2016),’ 2020. Letterpress print of knitting pattern coded using cryoseismic data. Edition of 15. 18 x 18 in.</span>
<span class="attribution"><span class="source">Sarah Nance</span></span>
</figcaption>
</figure>
<h2>The loop</h2>
<p>Repeated, interlocking loops are the base units that compose the structure of a knitted textile. The loop also forms the seed of an in-progress work I pursued during an artist residency with the <a href="https://lunarscience.nasa.gov/sserviteams">NASA</a> <a href="https://www.geodes.umd.edu">GEODES</a> research group. I joined their research team in Flagstaff, Arizona, in August 2023. I assisted in gathering data from sites within the San Francisco volcanic field, while also conducting my own fieldwork: photography, drawing, note-taking and walking.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A digital map showing a crater, with a green circle indicating the path walked, around the lip of the crater." src="https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=629&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=629&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=629&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=790&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=790&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568498/original/file-20240109-21-we196t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=790&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sarah Nance’s walk at S P Crater in Arizona, as recorded in AllTrails.</span>
<span class="attribution"><span class="source">Screenshot of All Trails map</span></span>
</figcaption>
</figure>
<p>One of my walks was a trek around a particularly prominent geologic loop – the rim of the S P cinder cone volcano. This is the second crater walk I’ve completed, the first being a tracing of the subsurface rim of the <a href="https://insider.si.edu/2013/03/iowa-meteorite-crater-confirmed/">Decorah impact structure</a> in Iowa. </p>
<p>I see my paths through these landscapes as stand-ins for yarn. Over time, by taking walks that trace craters, or geologic loops, I will perform a textile. The performance of something as familiar as a textile offers me a new way to think about something that is much more difficult to comprehend – <a href="https://www.britannica.com/science/geologic-time">geologic time</a>. </p>
<hr>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A square box with the words 'Art & Science Collide' and a drawing of a lightbulb with its wire filament in the shape of a brain, surrounded by a circle." src="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567788/original/file-20240103-23-yg479z.png?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"></a>
<figcaption>
<span class="caption">Art & Science Collide series.</span>
<span class="attribution"><span class="source">source</span></span>
</figcaption>
</figure>
<p><em><strong><a href="https://theconversation.com/us/topics/art-in-science-series-2024-149583">This article is part of Art & Science Collide</a></strong>, a series examining the intersections between art and science.</em></p>
<p><em>You may be interested in:</em></p>
<p><a href="https://theconversation.com/literature-inspired-my-medical-career-why-the-humanities-are-needed-in-health-care-217357">Literature inspired my medical career: Why the humanities are needed in health care</a></p>
<p><a href="https://theconversation.com/i-wrote-a-play-for-children-about-integrating-the-arts-into-stem-fields-heres-what-i-learned-about-encouraging-creative-interdisciplinary-thinking-218001">I wrote a play for children about integrating the arts into STEM fields – here’s what I learned about interdisciplinary thinking</a> </p>
<p><a href="https://theconversation.com/art-and-science-entwined-this-course-explores-the-long-interrelated-history-of-two-ways-of-seeing-the-world-210250">Art and science entwined: This course explores the long, interrelated history of two ways of seeing the world </a></p>
<hr>
<h2>Performance and tides</h2>
<p>Performance has been a useful tool in my work, as it can help people understand and relate to geologic processes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="artist's hands holding small chunk of glacial ice" src="https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569102/original/file-20240112-21-spkjsd.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"></a>
<figcaption>
<span class="caption">‘transference,’ 2017. Atlantic sea ice, body heat. Documentation of site-responsive performance on the East Coast Trail, Newfoundland, Canada. Project supported in part by La Soupée, Galerie Diagonale, Montréal, Québec.</span>
<span class="attribution"><span class="source">Sarah Nance</span></span>
</figcaption>
</figure>
<p>The field of geology emerges from a <a href="https://www.upress.umn.edu/book-division/books/a-billion-black-anthropocenes-or-none">long history</a> of extraction and <a href="https://www.dukeupress.edu/geontologies">colonialist ventures</a>. In this context, land is valued for its economic importance – as raw material to be extracted or territory to be claimed. In my performances, I aim to interact with geology as its own active entity, rather than as a consumable resource. </p>
<p>In recent years, I have composed and performed two arias from tidal data. </p>
<p>The first, “<a href="https://www.sarahnance.com/marseille">marseille tidal gauge aria</a>,” sourced 130 years of sea level data collected from a tidal gauge in the Bay of Marseille, France. I converted each yearly average sea level into an individual note within my vocal range. This resulted in a composition that expresses the rising sea levels of the bay as increasingly higher pitches in the aria. </p>
<p>Its lyrics come from a somber poem in Rasu-Yong Tugen’s book “<a href="https://gnomebooks.wordpress.com/2014/02/10/songs-from-the-black-moon/">Songs From the Black Moon</a>.” Each note of the aria communicates not just the measured sea level but also my emotive response to this dataset. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Black flexi disc with gold text and image" src="https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569098/original/file-20240112-23-ffk4lg.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">‘tidal arias,’ 2022. Limited edition flexi disc with vocal performances ‘marseille tidal gauge aria’ and ‘skagway tidal aria.’</span>
<span class="attribution"><span class="source">Sarah Nance</span></span>
</figcaption>
</figure>
<p>Last fall, “marseille tidal gauge aria” was transmitted <a href="https://www.swpc.noaa.gov/phenomena/ionosphere">to the ionosphere</a>, the boundary between Earth’s atmosphere and outer space. This was done as part of artist Amanda Dawn Christie’s project “<a href="https://ghostsintheairglow.space/transmission/august-2023">Ghosts in the Air Glow</a>,” using the <a href="https://haarp.gi.alaska.edu">High-frequency Active Auroral Research Program</a>’s ionospheric research instrument, which is an array of 180 antennas transmitting high-frequency radio waves. </p>
<p>The aria’s transmission reflected off the ionosphere, back to Earth and to shortwave radio listeners around the world.</p>
<p>For the second of these vocal pieces, “skagway tidal aria,” I used predictive as well as recorded tidal data from Skagway, Alaska. With this data, I composed an aria for <a href="https://t2051mcc.com">The 2051 Munich Climate Conference</a>, where speakers presented from the perspective of a climate-altered world 30 years in the future. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="vocal music score" src="https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=388&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=388&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=388&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=488&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=488&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569106/original/file-20240112-25-4mocnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=488&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Score for ‘skagway tidal aria,’ 2021. Recorded and speculative tidal data from Skagway, Alaska (1945-2081), sonified as a vocal composition. Text from ‘Songs From the Black Moon’ by Rasu-Yong Tugen.</span>
<span class="attribution"><span class="source">Sarah Nance</span></span>
</figcaption>
</figure>
<p>I was drawn to this particular dataset because the falling tide levels in Skagway appear to contradict the <a href="https://theconversation.com/what-drives-sea-level-rise-us-report-warns-of-1-foot-rise-within-three-decades-and-more-frequent-flooding-177211">global trend of rising sea levels</a>. However, this is a temporary effect caused by melting glaciers releasing pressure on the land, allowing it to rise faster than water levels. The effect will flatten over the next half-century, and Skagway’s tides will start to rise again.</p>
<p>Over the next few months, I’ll be working with geophysical datasets gathered during the NASA GEODES field expedition to write new arias. I want these pieces to continue blurring the separation between the human and the geologic, inviting listeners to think more deeply about their own relationships with the lands they use and occupy.</p><img src="https://counter.theconversation.com/content/218201/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The author's projects with GEODES and Ghosts in the Air Glow were supported with funding from these organizations.</span></em></p>Sarah Nance uses geologic data and a variety of artistic media to help people think about their place in the landscapes they use and occupy.Sarah Nance, Assistant Professor of Integrated Practice in Art and Design, Binghamton University, State University of New YorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2138772023-09-19T11:52:50Z2023-09-19T11:52:50ZSouth Africa’s destructive storm surges: geoscientist reveals the 3 factors that drove them<figure><img src="https://images.theconversation.com/files/549052/original/file-20230919-27-26ykei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tidal surges can cause enormous damage.</span> <span class="attribution"><span class="source">Martha van der Westhuizen/500px</span></span></figcaption></figure><p><em>A series of powerful tidal surges <a href="https://www.news24.com/news24/southafrica/news/battered-coastal-areas-begin-mop-up-operations-after-spring-tide-damage-20230918">battered</a> coastal areas in South Africa’s Western Cape, Eastern Cape and KwaZulu-Natal provinces over the weekend of 16 September. <a href="https://www.news24.com/news24/southafrica/news/spring-tide-damage-woman-dies-after-waves-crash-into-george-car-park-another-dangerous-surge-expected-20230917">One person died</a>; cars, homes and businesses were damaged. The Conversation Africa asked Jasper Knight, a geoscientist who researches coastal processes, to explain what happened.</em></p>
<h2>What drove the flooding?</h2>
<p>A critical combination of three factors resulted in this significant flooding. First, a storm surge associated with low-pressure weather systems coming onshore. These happen very commonly but often don’t result in high amounts of flooding by themselves. </p>
<p>Second, low-pressure cells often result in strong onshore winds, and these can whip up the sea surface and create big waves which can potentially run further inland, especially when the sea surface is raised.</p>
<p>Third, the coincidence of the storm with the period of high tide (a monthly event) and equinoctial high-high tide (a seasonal event). It is this combination that is the cause here, not these individual factors in isolation.</p>
<h2>What is a storm surge?</h2>
<p>This is where the level of the sea surface near the coast is temporarily raised up and results in flooding along that coastal stretch. Storm surges are caused by a low pressure (cyclone) weather system approaching the coastline from the ocean. Low pressure causes the sea surface to bulge upwards below the centre or eye of the cyclone, and the magnitude of this disturbance is related to the severity of the low pressure system – the deeper the low pressure cell, the higher the elevation of the sea surface. This is usually on the order of tens of centimetres to one metre or so. </p>
<p>As the cyclone approaches land, the water surface along the coast rises.</p>
<h2>What is a spring tide?</h2>
<p>Despite their name, <a href="https://oceanservice.noaa.gov/facts/springtide.html">spring tides</a> are regular occurrences throughout the year. They take place when the sun, Earth and moon are in alignment, and this happens once every (lunar) month. In addition, there are also times of the year, around the <a href="https://education.nationalgeographic.org/resource/equinox/">equinoxes</a>, where spring tides are higher than average. </p>
<p>We are very near the spring (vernal) equinox in the southern hemisphere (which is on or about 22 September). This is a period when the sun is aligned overhead of Earth’s equator and so exerts a bigger tidal force on the oceans. This may have been a contributing factor to the higher water levels around the coast.</p>
<h2>Were people sufficiently warned?</h2>
<p>Tidal patterns are highly predictable and this data is widely available for ports or harbours along the coast. In this case, the South African Weather Service issued <a href="https://www.news24.com/news24/southafrica/news/saturdays-weather-damaging-winds-waves-and-a-storm-surge-warning-for-the-coast-20230915">a warning</a>. This information is particularly useful for boaters, fishermen and other coastal users. Weather patterns are also fairly predictable, which is what weather forecasting is all about, so we know when a big storm may be approaching. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-science-of-weather-forecasting-what-it-takes-and-why-its-so-hard-to-get-right-175740">The science of weather forecasting: what it takes and why it’s so hard to get right</a>
</strong>
</em>
</p>
<hr>
<p>However, the net result of all of these factors in combination is less predictable: although low-lying coastal areas are vulnerable to flooding, forecasters may not know exactly when or how high.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1703707171030962438"}"></div></p>
<p>The other issue here is not just areas being covered by water but also the speed at which the water waves are moving, which is a factor in their destructiveness. </p>
<h2>What kind of emergency measures could be put in place?</h2>
<p>Local communities need to be warned more clearly and effectively if there is a threat of a storm surge and of coastal flooding. People and assets (like cars, anything that is moveable) should be moved from the area or kept inside. People tend to want to go to the sea to watch the waves but this puts them at more risk. Roads should be closed off where possible to keep people safe and away from the area. Floodwater management through using sandbags and similar actions should be undertaken.</p>
<p>Exactly the same measures used in places like <a href="https://www.floridadisaster.org/planprepare/">Florida in the US</a> for reducing hurricane risk should be used in South Africa, such as boarding up windows, keeping assets indoors, evacuating people from high risk areas, and moving furniture in houses to the first floor to reduce flood impacts.</p>
<p>Storm surges – and <a href="https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/">sea levels rising in future</a> – are not going to go away so we need to be prepared for them.</p><img src="https://counter.theconversation.com/content/213877/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jasper Knight 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>Local communities need to be warned more clearly and effectively if there is a threat of a storm surge and of coastal flooding.Jasper Knight, Professor of Physical Geography, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1919792022-10-07T19:11:02Z2022-10-07T19:11:02ZDiscovering the three largest shipwrecks in the St. Lawrence River<figure><img src="https://images.theconversation.com/files/488368/original/file-20221005-25-1kca17.jpg?ixlib=rb-1.1.0&rect=0%2C7%2C1280%2C852&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The SS "Leecliffe Hall" sailing on the Welland Canal, Ontario, shortly before it sank in the St. Lawrence.</span> <span class="attribution"><span class="source">(Matt Miner Collection)</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Of all the rivers in the world, the St. Lawrence River is undeniably one of the most challenging for mariners.</p>
<p>This water highway is at some spots as narrow as a large river and, at others, as wide as a small sea. It has played a vital role over the last three centuries as an important artery for trade, communication, transportation and settlement. And since 1959, the year <a href="https://www.cbc.ca/player/play/1826347537">the St. Lawrence Seaway was inaugurated</a>, it has been a <a href="https://greatlakes-seaway.com/en/the-seaway/">gateway to the heart of the continent</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/rrHHIvywNfE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">On June 26, 1959 Canada and the United States inaugurated the St. Lawrence Seaway with great fanfare.</span></figcaption>
</figure>
<hr>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em>This article is part of our series, <a href="https://theconversation.com/ca-fr/topics/fleuve-saint-laurent-116908">The St. Lawrence River: In depth</a>.
Don’t miss new articles on this mythical river of remarkable beauty. Our experts look at its fauna, flora and history, and the issues it faces. This series is brought to you by <a href="https://theconversation.com/ca-fr">La Conversation</a>.</em></p>
<hr>
<p>The first European explorers who sailed the St. Lawrence discovered it was not easy to master: it was long, but never calm. After crossing the Gulf, mariners would face many difficulties navigating up the river to Québec City, including narrow, sinuous channels, shallow waters, shoal deposits and strong tides. Currents are sometimes unpredictable, there can be very dense fog, and, of course, the river is impossible to navigate in winter. No one ventured on its waters from the end of November to the beginning of May.</p>
<p><a href="https://www.cbc.ca/player/play/2003799619851">Qualified maritime pilots are a must</a> on the capricious and indomitable St. Lawrence, which has the reputation of being one of the most difficult rivers to navigate in the world. The risk of collisions, groundings and shipwrecks is high, which led to tightened navigation safety regulations, particularly in response to the accidents involving large ships that occurred in the 1960s.</p>
<p>It is estimated that there are several thousand wrecks below the surface of the river.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488181/original/file-20221004-12421-ompdb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A window, covered in dense, colourful sea life, shows a view of the interior of the wheelhouse of the SS <em>Leecliffe Hall</em>.</span>
<span class="attribution"><span class="source">(PETQ)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>As a doctoral student in geographic sciences at Laval University and president of the <a href="https://www.facebook.com/PETduQuebec/?ref=page_internal">Technical Wreck Divers of Québec (PETQ)</a>, I propose introducing you to the three most important shipwrecks in terms of size that took place in the river. Our diving activities push the very limits of exploration. Notably, we use diving techniques adapted to the particularly restrictive underwater context of the St. Lawrence, with its strong currents, often reduced visibility and cold, black water, among other hazards.</p>
<p>Our expeditions allow us to share the passion of diving by exposing the results of our research and discoveries, while making the public aware of the history and hidden relics that are just a few steps from the shore of the river.</p>
<h2>The tragedy of the <em>Empress of Ireland</em> (1906-1914)</h2>
<p>Because of its magnitude, one shipwreck in the St. Lawrence River cannot be overlooked: the Royal Mail Ship (RMS) <a href="https://www.pc.gc.ca/apps/dfhd/page_nhs_fra.aspx?id=12391"><em>Empress of Ireland</em></a>. With its 1,012 victims, there is no question this disaster strikes the popular imagination.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=576&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=576&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487866/original/file-20221003-12846-3emxio.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=576&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The RMS <em>Empress of Ireland</em>, on an unspecified date. Its sinking caused the death of over a thousand people.</span>
<span class="attribution"><span class="source">(shmp)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This tragedy was the result of the ship colliding with the Norwegian coal carrier <em>Storstad</em> during the night of May 29, 1914, off Sainte-Luce, east of Rimouski, during foggy weather. In as little as 14 minutes, the liner sank in the cold and inhospitable waters of the St. Lawrence. Unlike the much publicized sinking of the RMS <em>Titanic</em> two years earlier, the worst tragedy in Canadian maritime history was quickly overshadowed by the outbreak of World War I.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=576&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=576&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488180/original/file-20221004-24-u4pqh6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=576&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Windlass on the RMS <em>Empress of Ireland</em>.</span>
<span class="attribution"><span class="source">(Kevin Brown)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It was only 50 years later, in 1964, that the wreck was discovered by a group of divers. Although gigantic, at 173.8 metres in length, this Edwardian liner, built in 1906, was not the largest to have sunk in the waters of the St. Lawrence.</p>
<h2>SS Bulk Carrier <em>Leecliffe Hall</em> (1961-1964)</h2>
<p>At 222.5 metres long and 23 metres wide, the <a href="https://www.boatnerd.com/pictures/historic/perspectives/LeecliffeHall2/default.htm"><em>Leecliffe Hall</em></a> ranks first among the largest wrecks in the St. Lawrence River.</p>
<p>Built by the Scottish shipyard Fairfield Shipbuilding and Engineering Ltd. — the same yard as the RMS <em>Empress of Ireland</em> — and launched in Port Glasgow on May 18, 1961, this colossus was an impressive 18,071 gross registered tons (GRT). The ship’s length from stern to bow is the equivalent of <a href="https://www.aapa-ports.org/advocating/content.aspx?ItemNumber=21500">two American football fields glued together</a>.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=932&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=932&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=932&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1171&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1171&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487865/original/file-20221003-26-6t0vgs.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1171&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">SS <em>Leecliffe Hall</em> sailing upstream over a lock.</span>
<span class="attribution"><span class="source">(Boatnerd.com, Bob Graham collection)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>On Sept. 5, 1964, in the middle of a foggy day, the ship, loaded with 24,500 tons of iron ore, collided with the Greek freighter MV <em>Apollonia</em> off Île aux Coudres, in Québec’s Charlevoix region. The ships remained stuck together and did not sink.</p>
<p>The crew members were evacuated, safe and sound. But some of them, a few hours later, voluntarily returned to the ship, which was drifting alone, to attempt a rescue <em>in extremis</em>. While the men were in the midst of trying to regain control of the ship, the hull suddenly broke apart, killing three brave sailors. Two of the three bodies were never recovered. The <em>Apollonia</em> escaped with a badly damaged bow, but was able to sail again.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=474&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=474&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487869/original/file-20221003-18-4lytdi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=474&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A porthole seen from inside the wheelhouse of the SS <em>Leecliffe Hall</em>.</span>
<span class="attribution"><span class="source">(PETQ)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>On Sept. 9, 2017, a little less than two years after our divers first visited the wreck, a commemorative ceremony was held at the <a href="https://museemaritime.com/Home/">Charlevoix Maritime Museum</a>. In the presence of the widow of one of the missing sailors and some descendants of the other two victims, the ship’s bell and the builder’s plate, which had been recovered the previous year by our team and declared to the Receiver of Wreckage (a federal official whose key role <a href="https://tc.canada.ca/en/marine/receiver-wreck-overview">is to act as the custodian of a wreck in the absence of the rightful owners</a>, were handed over to the museum in an effort to maintain the collective memory of Charlevoix’s subaquatic heritage.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487867/original/file-20221003-16-je5q3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The bell and builder’s plate belonging to the bulk carrier SS <em>Leecliffe Hall</em>, on the day of their recovery.</span>
<span class="attribution"><span class="source">(Sébastien Pelletier)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cloche exposée dans un musée" src="https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=942&fit=crop&dpr=1 600w, https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=942&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=942&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1183&fit=crop&dpr=1 754w, https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1183&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/488807/original/file-20221007-19379-azty39.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1183&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bell and builder’s plate of the SS <em>Leecliffe Hall</em>, on display at the Charlevoix Maritime Museum, in Saint-Joseph-de-la-Rive.</span>
<span class="attribution"><span class="source">(Sébastien Pelletier)</span>, <span class="license">Fourni par l'auteur</span></span>
</figcaption>
</figure>
<h2>The ore carrier MV <em>Tritonica</em> (1956-1963)</h2>
<p>At 161 metres long and 12,863 GRT, the MV <em>Tritonica</em>, built at the English shipyard Laing James & Sons Ltd. was the first ore carrier to use the St. Lawrence Seaway.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=498&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=498&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487864/original/file-20221003-20-cduwyh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=498&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">MV <em>Tritonica</em>, approximately one month before it sank.</span>
<span class="attribution"><span class="source">(René Beauchamp via shipspotting.com)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Sunk on July 20, 1963, off Petite-Rivière-Saint-François, in Charlevoix, following a collision in foggy weather with the SS <em>Roonagh Head</em>, the ship is the third-largest wreck on the St. Lawrence River in Québec waters.</p>
<p>In the silence of the night, locals in the village of Petite-Rivière-Saint-François heard the sounds of engines and sirens, and many, the metallic crash of the two ships colliding. The sinking <a href="https://wrecksite.eu/wreck.aspx?199137">cost the lives of 33 sailors</a>, mostly Chinese. This was the greatest civilian maritime tragedy of the 20th century on the St. Lawrence since that of the <em>Empress of Ireland</em>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=427&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=427&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=427&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487870/original/file-20221003-26-y5p6zj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An anchor of mercy on the foredeck of the MV <em>Tritonica</em>.</span>
<span class="attribution"><span class="source">(PETQ)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In the days following the disaster, <a href="https://www.lesoleil.com/2013/07/20/charlevoix-il-y-a-50-ans-coulait-le-tritonica-056c5f6f597f90417dd1c5adbef4feaf">bodies were recovered from the sea, from the banks of the river and from Île aux Coudres, located a little downstream from the site of the sinking</a>. The wreck posed a danger to navigation so it was subsequently dynamited and moved to a trench dug on the bottom of the river to provide the necessary clearance for the passage of deep draft ships.</p>
<p>The <em>Tritonica</em> only received its first visitors in 2016, aside from the hard-hat divers involved at the time in the post-sinking work. Despite the very limited visibility, exploring the wreck allowed our team to note the absence of its central superstructure, a section removed because it was too high and close to the surface.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/487868/original/file-20221003-20-vw8t3p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A porthole on the foredeck of the MV <em>Tritonica</em>.</span>
<span class="attribution"><span class="source">(PETQ)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>A duty to remember</h2>
<p>Exploring the remains of ships involved in such disasters is particularly exhilarating.</p>
<p>But alongside these tons of rusty steel that fascinate divers so much, there are often human tragedies. We must never forget this.</p>
<p>The privilege of visiting the relics of our past and bringing their stories to the surface must always be carried out with great respect.</p><img src="https://counter.theconversation.com/content/191979/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sébastien Pelletier received funding from the IHQEDS (Institut Environnement, Développement et Société) of Laval University.</span></em></p>The St. Lawrence is one of the most difficult rivers in the world to navigate. It has been the site of collisions, groundings and shipwrecks. Several thousand wrecks lie beneath its surface.Sébastien Pelletier, Doctorant en sciences géographiques, Université LavalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1861602022-07-06T14:43:54Z2022-07-06T14:43:54ZCan scientists predict when the next exceptional high tide will occur along the St. Lawrence River?<figure><img src="https://images.theconversation.com/files/472809/original/file-20220706-25-wedm09.jpeg?ixlib=rb-1.1.0&rect=0%2C4%2C1020%2C677&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Exceptional high tides hit eastern Québec in 2010 and 2016. </span> <span class="attribution"><a class="source" href="https://www.facebook.com/180153525343495/photos/a.180153842010130/180153845343463/">(Groupe Facebook Grandes Marées 2010)</a></span></figcaption></figure><p>Residents of eastern Québec probably remember the exceptional weather conditions and the very high tide of <a href="https://www.cbc.ca/news/canada/montreal/st-lawrence-flood-relief-coming-from-que-1.958433">Dec. 6, 2010</a>. The combination caused flooding along the shores of the St. Lawrence River and millions of dollars in damage to public and private infrastructure.</p>
<p>The water level recorded that day at Rimouski’s tidal gauge (a device used to measure sea level) reached 5.5 metres, <a href="https://www.ledevoir.com/environnement/312622/grandes-marees-reveil-penible-dans-l-est-du-quebec">exceeding the 1914 record by 20 centimetres</a>. Exceptional high tides occur more often than once every 100 years, however. On <a href="https://www.cbc.ca/news/canada/montreal/highway-132-in-gasp%C3%A9-partially-closed-due-to-high-tides-1.3402900">Jan. 11, 2016</a>, strong winds and high tides again caused flooding along the eastern Québec coast.</p>
<p>When might the exceptional high tides of the St. Lawrence River strike next?</p>
<hr>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em>This article is part of our series, <a href="https://theconversation.com/ca-fr/topics/fleuve-saint-laurent-116908">The St. Lawrence River: In depth</a>.
Don’t miss new articles on this mythical river of remarkable beauty. Our experts look at its fauna, flora and history, and the issues it faces. This series is brought to you by <a href="https://theconversation.com/ca-fr">La Conversation</a>.</em></p>
<hr>
<p>As physical oceanography researchers at the <a href="https://www.ismer.ca">Institut des sciences de la mer de Rimouski (ISMER)</a>, we addressed this question in an <a href="https://www.erudit.org/fr/revues/natcan/2016-v140-n1-natcan02274/1034101ar.pdf">article published in 2016</a> in the scientific journal, <em>Le Naturaliste canadien</em>. </p>
<h2>What causes exceptional high tides?</h2>
<p>First, we need to understand which ingredients produce a <a href="https://www.merriam-webster.com/dictionary/high%20tide">high tide</a>. The tide is a daily fluctuation of the sea, with levels alternately rising and falling. Primarily, this oscillation is driven by the gravitational attraction that the moon and the sun exert on the mass of ocean water. This is called an astronomical tide.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tcGEjzt_4is?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What causes tides?</span></figcaption>
</figure>
<p>But changes in sea level can also be caused by variations in air pressure and winds. This is called a meteorological tide. </p>
<p>To generate exceptional high tides, both astronomical and meteorological tides must occur at the same time. Great astronomical tides are predictable decades or even hundreds of years in advance, because the movements of the stars are well known. </p>
<p>In contrast, high meteorological tides are associated with storms, and are only predictable a few days in advance, with considerable uncertainty about their magnitude.</p>
<p>This makes it impossible to anticipate well in advance the next co-occurrence of high astronomical and meteorological tides along the St. Lawrence River. However, it is possible to predict the times of the year when exceptional high tides are most likely to occur. To that end, it is necessary to understand the workings of the astronomical tide.</p>
<h2>Tides at the whim of the stars</h2>
<p>The gravitational pull of the moon is stronger than the sun’s. Although the moon is much smaller than the sun, it is also much closer to the Earth, so its force of attraction outweighs that of the sun. <a href="https://scijinks.gov/tides/">The moon generates two high and two low tides per day</a>, known as a semi-diurnal tide.</p>
<p>The tidal range is the difference between successive high and low tides. In Rimouski, Que., the tidal range of the semi-diurnal tide caused by the moon is <a href="https://www.erudit.org/fr/revues/natcan/2016-v140-n1-natcan02274/1034101ar.pdf">2.54 metres</a>.</p>
<p>Like the moon, the tides caused by the gravitational pull of the sun generate two high and two low tides each day, but with a lower tidal range: 0.81 metres in Rimouski.</p>
<p>When the sun and moon are on the same side of the Earth (new moon) or on opposite sides (full moon), their effects on the tides add up. The high tide caused by the moon arrives at the same time as the high tide caused by the sun. This generates strong tides called spring tides, with a tidal range of 3.35 metres in Rimouski.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Graphic showing how the position of the Earth and moon relative to the sun influences the magnitude of the tide." src="https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/472521/original/file-20220705-16-qopv4q.png?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">Cycles of spring and neap tides. The last quarter moon, which corresponds to neap tides, is not shown, as it is similar to the first quarter, but with the moon on the other side of the Earth.</span>
<span class="attribution"><span class="source">(Cédric Chavanne)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>On the other hand, when the sun and moon are at right angles to the Earth (first and last quarter of the moon), their effects on the tides are offset. The high tide caused by the moon arrives at the same time as the low tide caused by the sun. This generates weak tides called neap tides, with a tidal range of 1.73 metres in Rimouski.</p>
<p>High spring tides are on average 0.8 metres greater than the high neap tides in Rimouski. The spring/neap cycle is about 15 days.</p>
<h2>Solstices and equinoxes</h2>
<p>But to get truly large astronomical tides, you have to consider even longer cycles, some of which are less well known than others. Equinox tides arrive twice a year around March 20 and Sept. 22 (plus or minus a week because of the spring/neap cycle).</p>
<p>During equinox, the sun is above the equator and the <a href="https://oceanservice.noaa.gov/education/tutorial_tides/tides07_cycles.html">semi-diurnal tides are at their highest</a>. On the other hand, during solstice (around June 21 and Dec. 21), the semi-diurnal tides are minimal. However, in Rimouski, the equinox spring tides are only five centimetres higher than those at solstice.</p>
<p>If we are looking at the maximum level of high tides rather than the tidal range, we should also consider the average water level of a tidal cycle, which also has a semiannual cycle: it is almost 10 centimetres higher at solstice than at equinox in Rimouski, and therefore prevails over the semiannual cycle of semi-diurnal tides.</p>
<p>The highest astronomical tides therefore appear close to solstice in Rimouski and not during equinox, but the difference in this semi-annual cycle is only a few centimeters, which does not explain the occurrence of exceptional high tides.</p>
<h2>The role of atmospheric pressure</h2>
<p>The second ingredient needed to produce an exceptionally high tide is the meteorological tide. </p>
<p>During a storm, when air pressure drops, the atmosphere exerts less weight on the sea. Sea level then tends to rise locally. </p>
<p>In addition, winds blowing towards the coast push the water towards the shore and raise the sea level at the coast. The strong waves generated by the wind are then able to surge higher up the shore.</p>
<p>During the storm of Dec. 6, 2010, the maximum water level recorded at the Rimouski tide gauge exceeded the maximum level predicted by the astronomical tide by about one metre. This is much higher than the semi-annual variation of astronomical tides, but it is similar to variations of the spring/neap cycle.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Graphic showing sea level height fluctuating over time." src="https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/472522/original/file-20220705-24-epez07.png?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">Sea level recorded at the Rimouski tide gauge during the Dec. 6, 2010, high tides. Modified from Bourgault et al. (2016).</span>
<span class="attribution"><span class="source">(Cédric Chavanne)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>So, can we predict the occurrence of very large tides? Exceptional high tides in the St. Lawrence River can happen at any time of the year, and not just during solstice or equinox, providing that there is a heavy storm during spring tides.</p>
<p>As storms are generally <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2000JC000686">more intense in winter than in summer along the St. Lawrence River</a>, exceptional high tides are more likely to occur in winter, as shown by the recent events of Dec. 6, 2010, and Jan. 11, 2016. Fortunately, during the winter, sea ice limits wave formation and protects the shore from their impact.</p>
<p>However, given the decreasing presence of sea ice due to <a href="https://www.tandfonline.com/doi/full/10.1080/07055900.2015.1029869">global warming</a>, the risk of high tides flooding the Gulf of St. Lawrence and its estuary during winter will most certainly increase in coming decades.</p><img src="https://counter.theconversation.com/content/186160/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Cédric Chavanne has received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de recherche du Québec - Nature et technologie (FRQNT), the Marine Environmental Observation, Prediction and Response (MEOPAR) network, and of the Quebec Maritime Network (RQM).</span></em></p><p class="fine-print"><em><span>Daniel Bourgault has received funding from the Natural Sciences and Engineering Research Council of Canada, the Fonds de recherche du Québec - Nature et technologie (FRQNT), the Canadian Foundation for Innovation, the Marine Environmental Observation, Prediction and Response (MEOPAR), and the Quebec Maritime Network (RQM).</span></em></p><p class="fine-print"><em><span>Dany Dumont is Executive Director of the Quebec Maritime Network He holds and has received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Quebec Research Fund - Nature and Technology (FRQNT), the Marine Network Environmental Observation, Prediction and Response (MEOPAR), the Quebec Maritime Network (RQM) and several provincial and federal departments (Ministry of Public Security of Quebec, Ministry of Transport of Quebec, Environment and Climate Change Canada, Fisheries and Oceans Canada).</span></em></p>Popular belief suggests the highest tides in the St. Lawrence River are reached around the equinoxes. In truth, they arrive close to the solstices.Cédric Chavanne, Professeur en océanographie physique, Université du Québec à Rimouski (UQAR)Daniel Bourgault, Professeur en océanographie physique, Université du Québec à Rimouski (UQAR)Dany Dumont, Professeur-chercheur en océanographie physique, Université du Québec à Rimouski (UQAR)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1584122021-04-23T12:36:32Z2021-04-23T12:36:32ZThis supermoon has a twist – expect flooding, but a lunar cycle is masking effects of sea level rise<figure><img src="https://images.theconversation.com/files/394314/original/file-20210409-23-1ez8yna.jpg?ixlib=rb-1.1.0&rect=0%2C3%2C2507%2C1477&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">April's super full moon was known as the pink moon because it heralds the arrival of spring flowers.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/man-walks-along-the-huntington-beach-pier-as-a-sea-gull-news-photo/1130794137">Mark Rightmire/MediaNews Group/Orange County Register via Getty Images</a></span></figcaption></figure><p>Another “super full moon” is coming May 26, 2021, and coastal cities like Miami know that means one thing: a heightened risk of tidal flooding.</p>
<p>Exceptionally high tides are common when the moon is closest to the Earth, known as <a href="https://oceanservice.noaa.gov/education/tutorial_tides/tides06_variations.html">perigee</a>, and when it’s either full or new. In the case of what’s informally known as a super full moon, it’s both full and at perigee.</p>
<p>But something else is going on with the way the moon orbits the Earth that people should be aware of. It’s called the lunar nodal cycle, and it’s presently hiding a looming risk that can’t be ignored.</p>
<p>Right now, we’re in the phase of an 18.6-year lunar cycle that lessens the moon’s influence on the oceans. The result can make it seem like the coastal flooding risk has leveled off, and that can make sea level rise less obvious.</p>
<figure class="align-center ">
<img alt="Chart showing how the lunar nodal cycle can mask sea level rise" src="https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/393346/original/file-20210404-23-6jku7d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This simplified chart illustrates how the lunar nodal cycle suppresses and enhances the effects of sea level rise in Miami. The basic model assumes a constant linear increase of sea level, so it doesn’t capture the expected acceleration of sea level rise.</span>
<span class="attribution"><a class="source" href="https://twitter.com/BMcNoldy/status/1351630471487098881">Brian McNoldy</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>But communities shouldn’t get complacent. Global sea level is <a href="https://climate.nasa.gov/news/2680/new-study-finds-sea-level-rise-accelerating/">still rising with the warming planet</a>, and that 18.6-year cycle will soon be working against us.</p>
<p>I am an <a href="https://scholar.google.com/citations?user=CsAY3vUAAAAJ&hl=en">atmospheric scientist</a> at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science who keeps a close eye on sea level rise in Miami. Here’s what you need to know.</p>
<h2>What the moon has to do with coastal flooding</h2>
<p>The moon’s gravitational pull is the dominant reason we have tides on Earth. More specifically, Earth rotating beneath the moon once per day and the moon orbiting around Earth once per month are the big reasons that the ocean is constantly sloshing around.</p>
<p>In the simplest terms, the moon’s <a href="https://oceanservice.noaa.gov/education/tutorial_tides/tides03_gravity.html">gravitational pull</a> creates a bulge in the ocean water that is closest to it. There’s a similar bulge on the opposite side of the planet due to inertia of the water. As Earth rotates through these bulges, high tides appear in each coastal area <a href="https://oceanservice.noaa.gov/education/tutorial_tides/tides05_lunarday.html">every 12 hours and 25 minutes</a>. Some tides are <a href="https://www.youtube.com/watch?v=OP0cpXpw8yk">higher than others</a>, depending on geography.</p>
<p>The sun plays a role too: Earth’s rotation, as well as its elliptic orbit around the sun, generates tides that vary throughout the day and the year. But that impact is less than half of what the moon contributes.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1261617041926090752"}"></div></p>
<p>This gravitational tug-of-war on our water was discovered nearly 450 years ago, though it’s been happening for nearly four billion years. In short, the moon has very strong control over how we experience sea level. It doesn’t affect sea level rise, but it can hide or exaggerate it.</p>
<h2>So, what is the lunar nodal cycle?</h2>
<p>To begin, we need to think about orbits.</p>
<p>Earth orbits the sun in a certain plane – it’s called the ecliptic plane. Let’s imagine that plane being level for simplicity. Now picture the moon orbiting Earth. That orbit also lies on a plane, but it’s slightly tilted, about 5 degrees relative to the ecliptic plane.</p>
<p>That means that the moon’s orbital plane intersects Earth’s orbital plane at two points, called nodes.</p>
<figure class="align-center ">
<img alt="An illustration of the moon's path crossing the ecliptic plane" src="https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=351&fit=crop&dpr=1 600w, https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=351&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=351&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/393351/original/file-20210405-23-1b1r9fq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The lunar nodes are the points where the moon’s path crosses the ecliptic, the plane of Earth’s orbit shown as the view of the sun from Earth over the span of a year.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Lunar_node#/media/File:Lunar_eclipse_diagram-en.svg">Wikimedia</a></span>
</figcaption>
</figure>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Illustration of the Earth and the ecliptic and orbital planes" src="https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/394611/original/file-20210412-13-40jbdy.jpg?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"></a>
<figcaption>
<span class="caption">Earth’s ecliptic and equatorial planes.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/bosf/images/Celestial-Sphere-with-Ecliptic1.jpg">NASA</a></span>
</figcaption>
</figure>
<p>The moon’s orbital plane precesses, or wobbles, to a maximum and minimum of +/- 5 degrees <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/1/3/141/203356/Nodal-Tidal-Cycle-of-18-6-Yr-Its-Importance-in-Sea">over a period of about 18.6 years</a>. This natural cycle of orbits is called the <a href="https://doi.org/10.1029/2010JC006645">lunar nodal cycle</a>. When the lunar plane is more closely <a href="https://solarsystem.nasa.gov/bosf/images/Celestial-Sphere-with-Ecliptic1.jpg">aligned with the plane of Earth’s equator</a>, tides on Earth are exaggerated. Conversely, when the lunar plane tilts further away from the equatorial plane, tides on Earth are muted, relatively.</p>
<p>The lunar nodal cycle was <a href="https://doi.org/10.1098/rstl.1727.0064">first formally documented</a> in 1728 but has been known to keen astronomical observers for thousands of years.</p>
<h2>What effect does that have on sea level?</h2>
<p>The effect of the nodal cycle is gradual – it’s not anything that people would notice unless they pay ridiculously close attention to the precise movement of the moon and the tides for decades.</p>
<p>But when it comes to predictions of tides, dozens of astronomical factors are accounted for, including the lunar nodal cycle.</p>
<p>It’s worth being aware of this influence, and even taking advantage of it. During the most rapid downward phase of the lunar nodal cycle – like we’re in right now – we have a bit of a reprieve in the observed rate of sea level rise, all other things being equal.</p>
<figure class="align-center ">
<img alt="A man wearing flipflops steps onto a **flooded** sidewalk while leaving a hotel." src="https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/394315/original/file-20210409-17-1bow1k2.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">Street flooding has become a common problem during extremely high tides in Miami Beach.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/hotel-guest-steps-out-of-a-hotel-into-a-flooded-street-that-news-photo/490535700">Joe Raedle/Getty Images</a></span>
</figcaption>
</figure>
<p>[<em>You need to understand the coronavirus pandemic, and we can help.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=coronavirus-help">Read The Conversation’s newsletter</a>.]</p>
<p>These are the years to implement <a href="https://theconversation.com/how-to-make-sure-bidens-infrastructure-plan-can-hold-up-to-climate-change-and-save-money-153869">infrastructure plans to protect coastal areas</a> against sea level rise. </p>
<p>Once we reach the bottom of the cycle around 2025 and start the upward phase, the lunar nodal cycle begins to contribute more and more to the perceived rate of sea level rise. During those years, the rate of sea level rise is effectively doubled in places like Miami. The impact varies from place to place since the rate of sea level rise and the details of the lunar nodal cycle’s contribution vary.</p>
<p>Like the “supermoon” in late April, the one on May 26 is a perigean full moon. Even with the lunar nodal cycle in its current phase, cities like Miami should expect some coastal flooding.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><strong><em>This story is part of <a href="https://theconversation.com/uk/topics/oceans-21-96784">Oceans 21</a></em></strong>
<br><em>Our series on the global ocean opened with <a href="https://oceans21.netlify.app/">five in depth profiles</a>. Look out for new articles on the state of our oceans in the lead up to the UN’s next climate conference, COP26. The series is brought to you by The Conversation’s international network.</em></p><img src="https://counter.theconversation.com/content/158412/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian McNoldy serves as a volunteer science advisor for Coastal Risk Consulting. </span></em></p>Sea level is still rising, and when that lunar cycle starts upward again, it will mean double trouble for places like Miami.Brian McNoldy, Senior Research Associate, University of MiamiLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1149302019-04-25T10:13:57Z2019-04-25T10:13:57ZHow did the moon end up where it is?<figure><img src="https://images.theconversation.com/files/269958/original/file-20190418-28106-jo3vox.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/night-sky-moon-clouds-141449116">Suppakij1017/Shutterstock</a></span></figcaption></figure><p>Nearly 50 years since man first walked on the moon, the human race is once more pushing forward with attempts to land on the Earth’s satellite. This year alone, China has landed a robotic spacecraft <a href="https://www.bbc.co.uk/news/science-environment-46724727">on the far side of the moon</a>, while India is close to <a href="https://www.techradar.com/news/first-china-then-israel-now-india-is-landing-on-the-moon-in-2019">landing a lunar vehicle</a>, and Israel <a href="https://www.bloomberg.com/opinion/articles/2019-04-17/why-israel-won-t-give-up-on-a-moon-landing">continues its mission</a> to touch down on the surface, <a href="https://theconversation.com/beresheet-first-privately-funded-mission-crashes-on-moon-but-its-significance-is-huge-115404">despite the crash</a> of its recent venture. NASA meanwhile has announced it wants to send astronauts <a href="https://theconversation.com/us-wants-a-crewed-mission-to-the-moon-in-five-years-but-can-and-should-that-be-done-114951">to the moon’s south pole</a> by 2024.</p>
<p>But while these missions seek to further our knowledge of the moon, we are still working to answer a fundamental question about it: how did it end up where it is?</p>
<p>On July 21, 1969, the Apollo 11 crew installed the first set of mirrors <a href="https://ilrs.cddis.eosdis.nasa.gov/science/scienceContributions/lunar.html">to reflect lasers</a> targeted at the moon from Earth. The subsequent experiments carried out using these arrays have helped scientists to work out the distance between the Earth and moon for the past 50 years. We now know that the moon’s orbit has been getting larger <a href="http://curious.astro.cornell.edu/about-us/37-our-solar-system/the-moon/the-moon-and-the-earth/111-is-the-moon-moving-away-from-the-earth-when-was-this-discovered-intermediate">by 3.8cm per year</a> – it is moving away from the Earth. </p>
<p>This distance, and the use of moon rocks to date the moon’s formation to <a href="https://theconversation.com/how-old-is-our-moon-71036">to 4.51 billion years ago</a>, are the basis for the <a href="https://www.space.com/19275-moon-formation.html">giant impact hypothesis</a> (the theory that the moon formed from debris after a collision early in Earth’s history). But if we assume that lunar recession has always been 3.8cm/year, we have to go back 13 billion years to find a time when the Earth and moon were close together (for the moon to form). This is much too long ago – but the mismatch is not surprising, and it might be explained by the world’s ancient continents and tides. </p>
<h2>Tides and recession</h2>
<p>The distance to the moon <a href="https://www.forbes.com/sites/brucedorminey/2017/01/31/earth-and-moon-may-be-on-long-term-collision-course/">can be linked to</a> the history of Earth’s continental configurations. The loss of tidal energy (due to friction between the moving ocean and the seabed) slows the planet’s spin, which forces the moon to move away from it – the moon recedes. The tides are largely controlled by the shape and size of the Earth’s ocean basins. When the Earth’s tectonic plates move around, the ocean geometry changes, and so does the tide. This affects the moon’s retreat, so it appears smaller in the sky. </p>
<p>This means that if we know how Earth’s tectonic plates have changed position, we can work out where the moon was in relation to our planet at a given point in time. </p>
<p>We know that the strength of the tide (and so the recession rate) also depends on the distance between Earth and the moon. So we can assume that the tides were stronger when the moon was young and closer to the planet. As the moon rapidly receded early in its history, the tides will have become weaker and the recession slower. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UIKmSQqp8wY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The detailed mathematics that describe this evolution were first developed by George Darwin, son of the great Charles Darwin, in 1880. But his formula produces the opposite problem when we input our modern figures. It predicts that Earth and the moon were close together only 1.5 billion years ago. Darwin’s formula can only be reconciled with modern estimates of the moon’s age and distance if its typical recent recession rate is reduced to about one centimetre per year. </p>
<p>The implication is that today’s tides must be abnormally large, causing the 3.8cm recession rate. The reason for these large tides is that the present-day North Atlantic Ocean is just the right width and depth to be in resonance with the tide, so the natural period of oscillation is close to that of the tide, allowing them to get very large. This is much like a child on a swing who moves higher if pushed with the right timing. </p>
<p>But go back in time – a few million years is enough – and the North Atlantic is sufficiently different in shape that this resonance disappears, and so the moon’s recession rate will have been slower. As plate tectonics moved the continents around, and as the slowing of Earth’s rotation changed the length of days and the period of tides, the planet would have slipped in and out of similar strong-tide states. But we don’t know the details of the tides over long periods of time and, as a result, we cannot say where the moon was in the distant past.</p>
<h2>Sediment solution</h2>
<p>One promising approach to resolve this is to try to detect <a href="https://www.livescience.com/64813-milankovitch-cycles.html">Milankovitch cycles</a> from physical and chemical changes in ancient sediments. These cycles come about because of variations in the shape and orientation of Earth’s orbit, and variations in the orientation of Earth’s axis. These produced climate cycles, such as the ice ages of the last few million years. </p>
<p>Most Milankovitch cycles don’t change their periods over Earth’s history but some are affected by the rate of Earth’s spin and the distance to the moon. If we can detect and quantify those particular periods, we can use them to estimate day-length and Earth-moon distance at the time the sediments were deposited. So far, this has only been attempted for a single point in the distant past. <a href="https://www.pnas.org/content/115/25/6363.abstract">Sediments from China suggest that</a> 1.4 billion years ago the Earth-moon distance was 341,000km (its current distance is 384,000km).</p>
<p>Now we are aiming to repeat these calculations for sediments in hundreds of locations laid down at different time periods. This will provide a robust and near-continuous record of lunar recession over the past few billion years, and give us a better appreciation of how tides changed in the past. Together, these interrelated studies will produce a consistent picture of how the Earth-moon system has evolved through time.</p><img src="https://counter.theconversation.com/content/114930/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mattias Green receives funding from The Natural Environmental Research Council. </span></em></p><p class="fine-print"><em><span>David Waltham receives funding from NERC</span></em></p>Though it’s fairly straightforward to locate the Earth’s moon in space today, there is a fundamental gap in our understanding of how it got there.Mattias Green, Reader in Physical Oceanography, Bangor UniversityDavid Waltham, Professor of Geophysics, Royal Holloway University of LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1053712018-12-11T23:30:28Z2018-12-11T23:30:28ZCurious Kids: How does the Moon, being so far away, affect the tides on Earth?<figure><img src="https://images.theconversation.com/files/244951/original/file-20181111-116841-10bxw8f.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4224%2C3168&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When the sea level rises to its highest point, we call that high tide. When it falls to its lowest point, that's called low tide.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/bpinzini/4811517787/in/photolist-8kbhBe-t6Wqu-V9E4Rj-bwPoqJ-oY6DQ2-poSVN-8HEPDt-8zzY37-dgfS7Y-5ZWhDN-ooeRhw-oFjni7-drDheu-pgUnWK-7Efezw-WjLGdD-hGrGu4-2cMqEer-cLPprS-275aF2W-4LApJD-o9n4S1-P5NfW-Y9UcXm-oBbG-5a5jJr-VJTPAi-4RMFK7-8zwUKg-nFiY7-o9Fk99-39kKrk-dDYxAm-9pjmWu-qeQwN6-6p9dyV-dNkyY6-23gFUAK-kEBNt4-dNbvbU-NgC4KX-rg8Pyu-4T846v-5jZTGg-fEBa7u-nXAhnv-4r9o1w-7PHt5p-hfyc7-8zwNNn">Flickr/bpinzini</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</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. You can send your question to curiouskids@theconversation.edu.au. You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>How does the Moon, being so far away, affect the tides on Earth? – Lachie, age 8, Doreen, Melbourne.</strong></p>
</blockquote>
<hr>
<p>Great question Lachie!</p>
<p>The short answer is that the Moon’s gravity pulls the oceans (and us) towards it. Even though the Moon is so far away, it is large enough that its force of gravity is strong enough to do that.</p>
<p>But before we get into how the Moon affects tides, let’s look at what tides are.</p>
<p>Tides are the rise and fall of water level in the oceans (and lakes, and even in your cup of water, but they’re very small). </p>
<p>When the sea level rises to its highest point, we call that high tide. When it falls to its lowest point, that’s called low tide.</p>
<p>The rise and fall of the tides is known as the tide cycle. If there’s one high tide and one low tide a day, like you would see if you went on holiday to Perth, it’s called a diurnal tide cycle. If there are two high tides and two low tides, like you see in Victoria, it’s called a semi-diurnal tide cycle. </p>
<p>The Moon has the most effect on the tides, but it’s not the only factor that affects them. The Sun and the Earth can also affect the tides. We’ll start with the Moon. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-are-there-living-things-on-different-galaxies-98562">Curious Kids: Are there living things on different galaxies?</a>
</strong>
</em>
</p>
<hr>
<h2>Tides and the Moon</h2>
<p>The Moon affects the tides because of gravity. You will have noticed that every time you jump, you always land back on the ground. This is because the Earth’s gravity is pulling you back down. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&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 Earth’s spinning means that another high tide occurs on the opposite side of the Earth to the Moon.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>The Moon has gravity of its own, which pulls the oceans (and us) towards it. The Moon’s gravitational pull on us is much weaker than Earth’s, so we don’t really notice it, but we can see the Moon’s effect on the liquid water of the oceans. The oceans are pulled towards the Moon’s gravity slightly, causing a bulge or high tide on the side of the Earth closest to the Moon. </p>
<h2>The Earth’s effect</h2>
<p>If the Moon causes a high tide on one side of the Earth, what causes the high tide on the other side?</p>
<p>The Earth is spinning, which is why we have night and day. The Earth’s spinning means that another high tide occurs on the opposite side of the Earth to the Moon. </p>
<p>These two high tides draw water away from the rest of the oceans, causing two low tides between the high tides. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/4UZxzyOVJ8Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Why do we have tides? - Forces of Nature with Brian Cox: Episode 2 - BBC One.</span></figcaption>
</figure>
<h2>The Sun</h2>
<p>The Sun, just like the Moon and the Earth, also has its own gravity which can affect the tides. Although the Sun is much larger than the Moon and has more gravity, it’s also much further away, meaning its pull on the tides is less than half as strong as the Moon’s. </p>
<p>It still does have an effect, though. When the Sun and Moon are in line with the Earth (when a full moon or new moon occur), their combined gravity cause very high tides (and very low tides), known as “spring tides.”</p>
<p>When the Sun and Moon are at right angles to each other (during a waxing or waning moon), the Sun helps to cancel out the pull of gravity from the Moon, causing lower high tides and higher than average low tides, known as “neap tides”. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.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">Lunar and Solar tides diagram.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>So the Moon affects the tides because of gravity, but gravity from the Sun and the spinning of the Earth also change how the tides behave.</p>
<p>Best wishes,</p>
<p>Mark Hemer.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-is-there-anything-hotter-than-the-sun-105748">Curious Kids: Is there anything hotter than the Sun?</a>
</strong>
</em>
</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
<br>
* 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
<br>
* Tell us on <a href="http://www.facebook.com/conversationEDU">Facebook</a></em></p>
<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/105371/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Hemer receives funding from the National Environmental Science Program Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.</span></em></p>The Moon has gravity of its own, which pulls the oceans (and us) towards it.Mark Hemer, Senior Research Scientist, Oceans and Atmosphere, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/949292018-04-12T13:29:16Z2018-04-12T13:29:16ZSupercontinent formation may be linked to a cycle of supertides<figure><img src="https://images.theconversation.com/files/214513/original/file-20180412-566-149cjla.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/breaking-waves-rising-storm-336142628?src=LfGVumZo48UIqrUBUA4a0A-1-2">Oskari Porkka/Shutterstock</a></span></figcaption></figure><p>Earth’s crust is made up of fractured slabs of rock, like a broken shell on an egg. These plates move around at speeds of about 5cm per year – and eventually this movement brings all the continents together and form what is known as a supercontinent. The last supercontinent on Earth was <a href="https://www.livescience.com/38218-facts-about-pangaea.html">Pangaea</a>, which existed between 300-180m years ago.</p>
<p>This collection and dispersion of the continents is known as a supercontinent cycle, and the world now is 180m years into the current cycle. It is predicted that the next supercontinent <a href="https://www.cambridge.org/core/journals/geological-magazine/article/future-of-earths-oceans-consequences-of-subduction-initiation-in-the-atlantic-and-implications-for-supercontinent-formation/5F0C1733CB5994BAB1A04979EE59C768">will form</a> in about 250m years, when the Atlantic and Pacific oceans both close and a new ocean forms where the large Asian plate splits. Because the plates move around, ocean basins change their shape and size. For example, the Atlantic is currently expanding at about the rate your fingernails grow (a couple of centimetres per year), whereas the Pacific is slowly closing. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214508/original/file-20180412-570-138r0n0.jpg?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"></a>
<figcaption>
<span class="caption">A vision of Earth 200m years ago.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/earth-planet-200-million-years-ago-525778483?src=mIc8sl4YaLaqakiUOnLDKA-1-2">Rashevskyi Viacheslav/Shutterstock</a></span>
</figcaption>
</figure>
<p>These changes in the ocean basins can have a very large impact on the tides over millions of years. This is because the tide moves around the oceans like a very long wave, with more than 1,000km between two peaks. The way this wave moves is largely controlled by the shape of the ocean basin and its depth, and if the ocean has the right size – if the length of a basin is half that of the wave, or “resonant” – the tides can become very large. </p>
<p>Resonance can happen in any system that swings or oscillates if you force it at its natural period. For example, if you give a child on a swing a small push at the right time, they will swing higher and higher, because you are forcing them at the natural period of the swing. The period of the tide is set by the motions of the Earth, moon and sun – and the natural period of an ocean basin is set by its geometry. For example, today, the north Atlantic is very near resonance because these two periods are almost the same. This is why the tides in the Atlantic are much larger than those in the Pacific or Indian Oceans. </p>
<p>But this has not always been the case. From <a href="https://www.sciencedirect.com/science/article/pii/S0012821X16307518">experiments with computer models</a> which can simulate the tides with great accuracy, we know that the tides were weak for long periods of the current supercontinent cycle, because the shape and size of the basins couldn’t support large tides. In fact, of the past 250m years, it is only the last 2m years or so that have seen large tides on Earth. Since we are approaching the halfway point of the supercontinent cycle, we asked ourselves a question: what will happen to the tides as the next supercontinent assembles in 250m years or so? Is it possible that there is a supertidal cycle linked to the supercontinent cycle?</p>
<p>Using the computer model, we <a href="https://bit.ly/2qraeO5">have now found</a> that there is indeed a supertidal cycle linked to the supercontinent cycle. In fact, there are two: we are currently at the start of one “tidal maximum”, a period of time when the tides are very large. They will then weaken significantly, before briefly becoming large again in around 150m years from now. After that, the tides will again drop down to less than half of the energy levels they have at present as the next supercontinent forms. This will happen because the basins go in and out of resonance as their shape changes. The tidal maxima are brief in geological terms and only last 20m years or so. For most of the time, the tides are less energetic than they are today and, over the 400-600m years between the formations of the two supercontinents, the tides are only large for 50m years in total. </p>
<p>Tides are a major energy source for the ocean: the energy pumped into the tide by the sun and the moon is lost, or dissipates, within the ocean. This energy helps stir the ocean – much like a spoon stirs a cup of coffee. In the same way as the spoon moves sugar and milk around in the cup, the tide can drive movements of nutrients, heat and salt between the deep ocean and the surface. Fluxes of heat and salt are key to the large-scale climate controlling ocean circulation and fluxes of nutrients help sustain biological production, especially in shallow seas. </p>
<p>Changes in tides on any timescale can have large effects on the whole Earth system. While the changes described here may not have impact on us in the immediate future, it adds to our understanding of how the tides interact within various disciplines – including plate tectonics, the climate system, nutrient recycling and, eventually, the ocean’s ability to evolve and host life.</p><img src="https://counter.theconversation.com/content/94929/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mattias Green receives funding from The Natural Environmental Research Council (grants NE/F014821/1 and NE/I030224/1). </span></em></p>Tides are the largest they have been for 250m years.Mattias Green, Reader in Physical Oceanography, Bangor UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/913182018-02-11T19:08:31Z2018-02-11T19:08:31ZKing tides and rising seas are predictable, and we’re not doing enough about it<p>Recent <a href="https://www.ausmarinescience.com/marine-science-basics/tides/#King">king tides</a> have again caused significant damage to coastal assets in Australia and New Zealand. This time the combination of large tides and coastal storms damaged properties on <a href="https://www.theguardian.com/australia-news/2018/feb/01/king-tide-driven-by-super-blue-blood-moon-inundates-torres-strait-island">Torres Strait islands</a> and in <a href="https://www.weatherwatch.co.nz/content/perfect-storm-caused-nelson-flooding-metocean">Nelson and other coastal areas of New Zealand</a>. It is <a href="https://www.sciencedirect.com/science/article/pii/S0964569116301119">increasingly recognised</a> worldwide that, despite many coastal adaptation plans being developed, the implementation of these plans is lagging. </p>
<p>King tides occur several times a year when the Moon is slightly closer to the Earth (so they’re sometimes called <a href="https://oceanservice.noaa.gov/facts/perigean-spring-tide.html">perigean spring tides</a>). This means king tides are predictable, as are rising sea levels. The combination, along with sporadic storm events, will lead to increasing flooding of our coastal cities. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/hurt-by-sea-how-storm-surges-and-sea-level-rise-make-coastal-life-risky-68348">Hurt by sea: how storm surges and sea-level rise make coastal life risky</a>
</strong>
</em>
</p>
<hr>
<p>Higher sea levels, whether creeping (associated with anthropogenic climate change) or transient (episodic storm events), have impacts on both private and public property and assets. What is now mostly nuisance flooding will become more problematic, and the ever-increasing global damage bill from disaster will continue to mount. </p>
<p>According to the global re-insurer Munich Re, losses from natural disasters in 2017 totalled <a href="https://www.munichre.com/en/media-relations/publications/press-releases/2018/2018-01-04-press-release/index.html">US$330 billion</a>, the second highest on record. Almost half of these losses (41%) were uninsured.</p>
<h2>Who’s responsible for adaptation plans?</h2>
<p>In keeping with the theory that risk is best managed by those closest to the risk, local government in Australia is the level of government best suited to managing such local risks. In <a href="https://theconversation.com/coastal-communities-including-24-federal-seats-at-risk-demand-action-on-climate-threats-58764">response to the increasing threat from rising sea levels</a>, many local government councils around Australia have developed coastal climate adaptation plans.</p>
<p>Federal and state governments clearly also have roles to play in managing coastal inundation. The federal government is often the insurer of last resort, especially for public infrastructure.</p>
<hr>
<p><em><strong>Read more:</strong> <a href="https://theconversation.com/coastal-communities-including-24-federal-seats-at-risk-demand-action-on-climate-threats-58764">Coastal communities, including 24 federal seats at risk, demand action on climate threats</a></em></p>
<p><em><strong>Read more:</strong> <a href="https://theconversation.com/coastal-law-shift-from-property-rights-to-climate-adaptation-is-a-landmark-reform-59083">Coastal law shift from property rights to climate adaptation is a landmark reform</a></em></p>
<hr>
<p>In Queensland, the state government has implemented the successful <a href="http://www.qcoast2100.com.au/program-purpose">QCoast2100</a> program. This is helping local governments to develop adaptation plans all along the state’s coastline.</p>
<p>It is <a href="https://www.sciencedirect.com/science/article/pii/S2212096315000169">increasingly recognised</a> that many of the plans developed in the past contain overcomplicated analyses of oversimplified adaptation options. Instead, we need less complicated ways of determining the most suitable adaptation option and assessments that consider more tailored and considered options, which will then be more readily implementable.</p>
<h2>What are the options?</h2>
<p>Coastal climate adaptation options tend to fall into one of three categories:</p>
<ul>
<li><strong>retreat</strong> – relocate assets and structures inland or to higher ground</li>
<li><strong>protect</strong> – mostly by building engineered seawalls, although green infrastructure can also be implemented</li>
<li><strong>accommodate</strong> – live with the hazard but reduce the vulnerability of structures and assets.</li>
</ul>
<p>Retreat makes intuitive sense: relocating assets out of harm’s way reduces their vulnerability. However, this approach has <a href="https://theconversation.com/coastal-law-shift-from-property-rights-to-climate-adaptation-is-a-landmark-reform-59083">proved politically problematic</a>, <a href="https://www.sciencedirect.com/science/article/pii/S0964569113000926">especially for private buildings</a>.</p>
<p>Most communities are familiar with seawalls and other forms of coastal protection. Others fundamentally disagree with the principle of hard coastal protection measures.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/contested-spaces-conflict-behind-the-sand-dunes-takes-a-new-turn-74239">Contested spaces: conflict behind the sand dunes takes a new turn</a>
</strong>
</em>
</p>
<hr>
<p>The third adaptation option, accommodating sea-level rise, is becoming the most popular approach in many nations, <a href="http://www.nytimes.com/2013/02/17/arts/design/flood-control-in-the-netherlands-now-allows-sea-water-in.html">including the low-lying Netherlands</a>. However, this approach is probably the least understood in Australia and rarely appears as the preferred option in Australian coastal adaptation plans. </p>
<p>This option includes making existing structures less vulnerable. This might involve relocating electrical and air-conditioning services and switchboards higher in existing buildings. Over time, vulnerable sites can be repurposed with less vulnerable land uses and structures. </p>
<p>This is different from pre-emptively evicting and relocating entire communities from vulnerable locations – the retreat option. The retreat option is most easily implemented immediately after major flooding that has led to significant damage. </p>
<h2>Plans must consider the politics</h2>
<p>Early coastal adaptation plans commonly advocated mass pre-emptive coastal retreat, but local government often ended up shelving or rejecting such recommendations. Instead, councils simply commissioned the construction of small local seawalls in areas at risk of erosion.</p>
<p>More developed and recent coastal adaptation plans consider finer spatial scales. What they still often don’t do is consider more sophisticated and politically informed adaptation options and approaches. </p>
<p>Hence adaptation planning is still often best characterised as the “plan and forget” approach. These plans typically lack monitoring and evaluation and a realistic implementation strategy.</p>
<p>Increased flooding of our coastline is inevitable and happening. Therefore, adaptation planning needs to consider more nuanced options that are likely to be more politically palatable and implementable.</p><img src="https://counter.theconversation.com/content/91318/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Gibbs is a Director of Green Cross Australia and Coastal Adaptation Solutions. Mark is also the Chair of the Queensland Government Climate Adaptation Strategy Partners group.</span></em></p>King tides and rising seas are an increasing and predictable threat, but adaptation plans to limit the damage to coastal property are still not managing the political obstacles.Mark Gibbs, Director, Knowledge to Innovation; Chair, Green Cross Australia, Queensland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/826282018-01-02T01:14:29Z2018-01-02T01:14:29ZAn X-factor in coastal flooding: Natural climate patterns create hot spots of rapid sea level rise<figure><img src="https://images.theconversation.com/files/200216/original/file-20171220-4948-1fce2q6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A motorist drives through "nuisance flooding" in Charleston, SC, Oct. 1, 2015.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Climate-Countdown-A-City-Acts/95b8b400b2fc42ac8f5b247eb81e1b35/3/0">AP Photo/Stephen B. Morton</a></span></figcaption></figure><p>For Americans who live along the east and Gulf of Mexico coasts, the end of the <a href="http://www.noaa.gov/media-release/extremely-active-2017-atlantic-hurricane-season-finally-ends">2017 Atlantic hurricane season</a> on Nov. 30 was a relief. This year forecasters recorded 17 named storms, 10 of which became hurricanes. Six were major hurricanes (Category 3 or stronger), and three made landfall: Harvey in Texas, Irma in the Caribbean and Florida, and Maria in the Caribbean and Puerto Rico. It was the most costly season ever, inflicting <a href="https://www.insurancejournal.com/news/national/2017/11/28/472368.htm">more than US$200 billion in damages</a>.</p>
<p>Many scientists have found evidence that climate change is amplifying the impacts of hurricanes. For example, several <a href="https://news.agu.org/press-release/agu-fall-meeting-human-caused-warming-likely-intensified-hurricane-harveys-rains/">studies</a> just published this month conclude that human-induced climate change made rainfall during Hurricane Harvey more intense. But climate change is not the only factor making hurricanes more damaging.</p>
<p>In a <a href="http://dx.doi.org/10.1002/2017GL073926">study</a> we co-authored with our colleague <a href="http://users.clas.ufl.edu/jbmartin/website/jmartin.html">Jon Martin</a>, we showed that two converging natural climate processes created a “hot spot” from Cape Hatteras, North Carolina to Miami where sea levels rose six times faster than the global average between 2011 and 2015. We also showed that such hot spots have occurred at other points along the Eastern Seaboard over the past century. Now we see indications that one is developing in Texas and Louisiana, where it likely amplified flooding during Harvey – and could make future coastal storms more damaging.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=970&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=970&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=970&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1219&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1219&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200221/original/file-20171220-4965-cyi9de.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1219&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nearly every site measured has experienced an increase in coastal flooding since the 1950s. The rate is accelerating in many locations along the east and Gulf coasts.</span>
<span class="attribution"><a class="source" href="https://www.epa.gov/climate-indicators/climate-change-indicators-coastal-flooding">USEPA</a></span>
</figcaption>
</figure>
<h2>Solving a salinity puzzle</h2>
<p>Our work started when Jon Martin showed one of us (Arnoldo) salinity data from water trapped between sediments lining the floor of the <a href="http://www.irlcouncil.com/">Indian River Lagoon</a> in east Central Florida. Here groundwater with zero salinity pools along the coast behind several barrier islands. Jon and his research team were analyzing changes in water chemistry and found that salinity had increased dramatically over the preceding decade. This suggested that saltwater was rapidly intruding into the lagoon. </p>
<p>This process is typically driven either by sea level rise or humans pumping fresh water from underground, or some combination of the two. Arnoldo consulted <a href="https://tidesandcurrents.noaa.gov/">online data</a> from the National Oceanic and Atmospheric Administration, and found that sea level rise had accelerated rapidly at nearby Trident Pier between 2011 and 2015. While global sea level has been rising at an average pace of about 1 foot per century, this site had recorded an increase of about 5 inches in a mere five years. </p>
<p>When Arnoldo shared this finding with Andrea, an international expert in past sea level rise, she was floored. These rates were ten times higher than the long-term rates of sea level rise along the Florida coastline. Further investigation showed that all tide gauges south of Cape Hatteras showed a similar uptick over the same period. This raised two questions: Had similar rates of rapid sea level rise previously been observed in the southeast United States? And what was causing this temporary acceleration?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=582&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=582&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200225/original/file-20171220-4980-rmpu90.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=582&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stations with positive sea level trends (yellow-to-red) are experiencing both global sea level rise and lowering or sinking of the local land. Stations illustrated with negative trends (blue-to-purple) are experiencing global sea level rise and a greater vertical rise in the local land, causing an apparent decrease in relative sea level.</span>
<span class="attribution"><a class="source" href="https://tidesandcurrents.noaa.gov/sltrends/slrmap.htm">NOAA</a></span>
</figcaption>
</figure>
<h2>Converging climate patterns</h2>
<p><a href="http://dx.doi.org/10.1038/nclimate1597">Previous work</a> along the Atlantic coast had identified the area north of Cape Hatteras as vulnerable to accelerated rates of sea level rise, particularly in the context of climate change. Warming of the planet is expected to weaken the Gulf Stream, a powerful Atlantic Ocean current that pulls water away from the east coast and carries it northward. Slowing down the Gulf Stream leaves more water in place along the coastline, raising sea levels. </p>
<p>But this mechanism could not explain a jump of this magnitude in sea levels south of the Cape. <a href="http://dx.doi.org/10.1038/nature14491">Another previous study</a> offered an additional clue. It proposed that the <a href="https://www.climate.gov/news-features/understanding-climate/climate-variability-north-atlantic-oscillation">North Atlantic Oscillation (NAO)</a>, a seesaw pattern in air pressure over different regions of the North Atlantic Ocean, could explain the shift in the position of short-term variations in sea level rise. </p>
<p>Shifts in the NAO alter the position of the jet stream, wind patterns and storm tracks, all of which affect the distribution of water in the North Atlantic basin. Ultimately, the cumulative effects of NAO on the ocean determine whether water will pile up to the north or south of Cape Hatteras. Thus, water piled up preferentially to the north of Cape Hatteras in the period 2009-2010, and to the south from 2011 to 2015.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/200250/original/file-20171220-4968-w29rzm.jpg?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>
<figcaption>
<span class="caption">When the NAO is in its positive phase (left), the contrast between high pressure over the Azores and low pressure in the far north Atlantic is stronger than normal, which leads to mild storms over northern Europe and drying over the Mediterranean. But when the contrast is lower than normal, the NAO enters its negative phase (right), leading to cold, dry weather in northern Europe and wet conditions across the south.</span>
<span class="attribution"><a class="source" href="https://www2.ucar.edu/atmosnews/just-published/16205/revealing-europes-winter-weather-history">UCAR</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This NAO-related mechanism explained where sea level accelerations might occur along the Atlantic coast, but did not seem to explain their timing. We filled in the blanks by examining tide gauge records over the last century along the entire U.S. Atlantic coast. This review showed that the timing of short-term sea level accelerations, lasting one to several years, was correlated with the accumulated signal of another recurring climate pattern: The <a href="https://oceanservice.noaa.gov/facts/ninonina.html">El Niño Southern Oscillation</a>, or ENSO, which is the result of an oscillation of atmospheric pressure in the Tropical Pacific Ocean basin.</p>
<p>Although ENSO occurs in the Pacific, its effects <a href="https://theconversation.com/what-north-america-can-expect-from-el-nino-51959">propagate across North America</a>, altering air temperatures and wind regimes in the eastern United States. These changes in wind distributions can affect water transport in the North Atlantic Ocean, causing it to build up along the U.S. Eastern Seaboard at times. Other scientists have <a href="http://dx.doi.org/10.1002/2014JC009999">shown</a> that this transport ultimately determines the timing of short-term accelerations in sea-level rise along the U.S. Atlantic coast.</p>
<p>In summary, we found that short-term accelerations in sea level rise have repeatedly occurred over the last century, sometimes occurring south of Cape Hatteras and sometimes focused north of the Cape. These hot spots can exceed rates of 4 inches in five years, and can occur anywhere along the U.S. Atlantic coast. They form when the accumulated signals of ENSO and the NAO converge, displacing seawater toward the coastline.</p>
<h2>A wild card for coastal flooding</h2>
<p>Our research has serious implications for coastal planners. Global warming is raising sea levels along the entire Atlantic coast, and communities should be preparing for it. In addition, our findings show that sea level can rise and fall around this level by more than 4 inches over a five-year period, due to variability in ocean-atmosphere interactions in the Pacific and Atlantic ocean basins. This variability can occur over the course of five to 10 years.</p>
<p>These hot spots amplify the severity of coastal flooding that is <a href="https://www.nytimes.com/2016/09/04/science/flooding-of-coast-caused-by-global-warming-has-already-begun.html?mcubz=0&_r=0">already occurring</a> from storms and king tides. Residents between Charleston, South Carolina and Jacksonville, Florida – a stretch where sea levels are at least 4 inches (10 centimeters) higher now then they were in 2010 – have found this out the hard way.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Ne41XSZKTuA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Miami Beach residents are coping with dramatic increases in flooding driven by sea level rise.</span></figcaption>
</figure>
<p>Now we are looking at data from the Gulf of Mexico, where tide stations are also showing water levels which are typically higher than predicted. The increase along Florida’s Gulf coast is past its peak, but Texas and Louisiana are still seeing an acceleration in sea level rise. Accelerations in sea level rise are hard to predict, and it is unclear whether they will become more serious over time. But they make it even more urgent for coastal communities to take sea level rise seriously today.</p><img src="https://counter.theconversation.com/content/82628/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arnoldo Valle-Levinson receives funding from the National Science Foundation. </span></em></p><p class="fine-print"><em><span>Andrea Dutton receives funding from the National Science Foundation. </span></em></p>Climate change is raising global sea levels. Now research shows that ‘hot spots’ where seas rise another 4 to 5 inches in five years can occur along the Atlantic and Gulf coasts, further magnifying floods.Arnoldo Valle-Levinson, Professor of Civil and Coastal Engineering, University of FloridaAndrea Dutton, Assistant Professor of Geology, University of FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/838772017-09-13T04:10:49Z2017-09-13T04:10:49ZExplainer: how does the sea ‘disappear’ when a hurricane passes by?<p>You may have seen the <a href="https://twitter.com/WeatherKait/status/906952050755428352">media images</a> of bays and coastlines along Hurricane Irma’s track, in which the ocean has eerily “disappeared”, leaving locals amazed and <a href="http://www.npr.org/sections/thetwo-way/2017/09/11/550164459/manatees-rescued-after-irma-leaves-them-high-and-dry-in-sarasota-bay">wildlife stranded</a>. What exactly was happening?</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"906579283950403585"}"></div></p>
<p>These coastlines were experiencing a “negative storm surge” – one in which the storm pushes water away from the land, rather than towards it. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/irma-and-harvey-very-different-storms-but-both-affected-by-climate-change-83800">Irma and Harvey: very different storms, but both affected by climate change</a>
</strong>
</em>
</p>
<hr>
<p>Most people are familiar with the idea that the sea is not at the same level everywhere at the same time. It is an uneven surface, pulled around by gravity, such as the tidal effects of the Moon and Sun. This is why we see tides rise and fall at any given location.</p>
<p>At the same time, Earth’s atmosphere has regions where the air pressure is higher or lower than average, in ever-shifting patterns as weather systems move around. Areas of high atmospheric pressure actually push down on the ocean surface, lowering sea level, while low pressure allows the sea to rise slightly. </p>
<p>This is known as the “<a href="http://onlinelibrary.wiley.com/store/10.1029/96RG03037/asset/rog1470.pdf?v=1&t=j7ifd6ap&s=d428b3957528e720df55a5de3884cde68d051309">inverse barometer effect</a>”. Roughly speaking, a 1 hectopascal change in atmospheric pressure (the global average pressure is 1,010hPa) causes the sea level to move by 1cm.</p>
<p>When a low-pressure system forms over warm tropical oceans <a href="https://www.nasa.gov/vision/earth/environment/HURRICANE_RECIPE.html">under the right conditions</a>, it can intensify to become a tropical depression, then a tropical storm, and ultimately a tropical cyclone – known as a hurricane in the North Atlantic or a typhoon in the northwest Pacific. </p>
<p>As this process unfolds, the atmospheric pressure drops ever lower and wind strength increases, because the pressure difference with surrounding areas causes more air to flow towards the storm.</p>
<p>In the northern hemisphere tropical cyclones rotate anticlockwise and officially become hurricanes once they reach a maximum sustained wind speed of around 120km per hour. If sustained wind speeds reach 178km per hour the storm is classed as a major hurricane. </p>
<h2>Surging waters</h2>
<p>A “normal” storm surge happens when a tropical cyclone reaches shallow coastal waters. In places where the wind is blowing onshore, water is pushed up against the land. At the same time the cyclone’s incredibly low air pressure allows the water to rise higher than normal. On top of all this, the high waves whipped up by the wind mean that even more water inundates the coast. </p>
<p>The anticlockwise rotation of Atlantic hurricanes means that the storm’s northern side produces winds blowing from the east, and its southern side brings westerly winds. In the case of Hurricane Irma, which tracked almost directly up the Florida panhandle, this meant that as it approached, the east coast of the Florida peninsula experienced easterly onshore winds and suffered a storm surge that caused severe inundation and flooding in areas such as <a href="http://www.npr.org/2017/09/11/550058360/hurricane-irma-hits-miami-causing-major-flooding">Miami</a>.</p>
<h2>The negative surge</h2>
<p>In contrast, these same easterly winds had the opposite effect on Florida’s west coast (the Gulf Coast), where water was pushed offshore, leading to a negative storm surge. This was most pronounced in areas such as Fort Myers and Tampa Bay, which normally has a relatively low tide range of less than 1m. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"906996604326092801"}"></div></p>
<p>The negative surge developed over a period of about 12 hours and resulted in a water level up to 1.5m below the predicted low tide level. Combined with the fact that the sea is shallow in these areas anyway, it looked as if the sea had simply disappeared. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/predicting-disaster-better-hurricane-forecasts-buy-vital-time-for-residents-83810">Predicting disaster: better hurricane forecasts buy vital time for residents</a>
</strong>
</em>
</p>
<hr>
<p>As tropical cyclones rapidly lose energy when moving over land, the unusually low water level was expected to rapidly rise, which prompted authorities to issue a <a href="http://www.baynews9.com/content/news/baynews9/news/article.html/content/news/articles/bn9/2017/9/9/irma_hurricane_warni.html">flash flood warning</a> to alert onlookers to the potential danger. The negative surge was replaced by a storm surge of a similar magnitude within about 6 hours at Fort Myers and 12 hours later at Tampa Bay.</p>
<p>Rising waters are the deadliest aspect of hurricanes – even more than the ferocious winds. So while it may be tempting to explore the uncovered seabed, it’s certainly not wise to be there when the sea comes rushing back.</p><img src="https://counter.theconversation.com/content/83877/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Darrell Strauss receives funding from an Advance Queensland Research Fellowship in partnership with Griffith University and the City of Gold Coast.</span></em></p>Pictures of ocean bays emptied of water as Hurricane Irma moved through the Caribbean and Florida show that storm surges can move away from the coast, as well as onto it.Darrell Strauss, Senior Research Fellow, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/775032017-05-10T15:52:32Z2017-05-10T15:52:32ZWhy beaches lose their sand – and then suddenly reappear<figure><img src="https://images.theconversation.com/files/168756/original/file-20170510-21610-11mujiq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Dooagh beach, Ireland.</span> <span class="attribution"><span class="source">Handout</span></span></figcaption></figure><p>In spring 1984 a whole beach disappeared. Over just two days, the golden sands of Dooagh on the island of Achill, off the west coast of Ireland, were stripped away to reveal bare rocks. </p>
<p>This occurred during a series of southwesterly storms and, importantly, during peak equinox – short periods in spring and autumn when tides are particularly strong due to the nature of the Earth’s movement around the sun. Jutting out into the Atlantic, Achill is exposed to the worst the ocean can throw at it and southwesterly winds (from the south west) can generate substantive waves. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"432194198180089856"}"></div></p>
<p>Thirty-three years later, in April 2017, <a href="http://edition.cnn.com/2017/05/08/travel/dooagh-beach-achill-island-ireland/">the beach returned</a> and the rocks were covered with sand once again. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"862246037288869888"}"></div></p>
<p>Though it may seem baffling to most people, there’s nothing miraculous about what happened in Achill. This “magical reappearing beach” is simply a great example of a process that happens in coastal seas more regularly that you might think.</p>
<h2>Bye bye beach</h2>
<p>First, let’s consider how Dooagh beach disappeared in the first place. The movement of pebbles, sand and sediment around the coast is caused by a mixture of waves, tides, and what is growing on the seafloor. Waves not only have the ability to stir up the sea bed and to wash beach sand into the ocean, but they can also create <a href="http://www.alevelgeography.com/transportation/">longshore drift</a> as they strike a coast at an angle, gradually shifting sediment along the coast. </p>
<p>Rip-currents are created in certain circumstances where water piles up close to the shore and can only exit the beach in narrow and intense flows. <a href="https://theconversation.com/rip-currents-are-a-natural-hazard-along-coasts-heres-how-to-spot-them-63081">These strong currents</a> are best known to humans for causing many fatal swimming accidents, but they can also carry sand and pebbles far offshore. Seaweed can help stabilise those fragile sediments, but its growth is limited in the early months of the year. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=325&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=325&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=325&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=409&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=409&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168765/original/file-20170510-21615-1739due.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=409&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Achill Island faces the full force of the Atlantic Ocean.</span>
<span class="attribution"><span class="source">Val Payne / shutterstock</span></span>
</figcaption>
</figure>
<p>When a beach gets unlucky and all of these factors come together – strong tides and abnormally high sea levels, a lack of seaweed – it can suddenly disappear. This is what happened to Dooagh in spring 1984, and had previously happened in a similar incident there in 1890.</p>
<h2>Enter sand</h2>
<p>So, what brought the beach back in 2017 (and in 1927)? Almost the same processes that stole it in the first place. Some of the conditions were identical: April has the highest tides of the year and low algal growth. However this time the beach replenishment occurred during northerly winds.</p>
<p>It’s hard to say for sure where the sand had been for the past 33 years but likely it was simply sitting on the seafloor some miles offshore and also in adjoining bays. The strong tides lifted the sand from the seafloor (and from the neighbouring bays that had benefited from the loan), unhindered by algae, and the northerly winds meant the waves carried it onshore. </p>
<p>This didn’t happen overnight. Over the past two years surfers had reported <a href="http://www.independent.co.uk/news/world/europe/sandy-beach-ireland-reappears-30-years-washed-away-winds-a7724801.html">seeing sand offshore</a>. By March 2017 (the second highest tide of the year) local fishermen reported the appearance of a sand bar offshore and a small amount of sand was deposited at the low water mark. The continued northerly winds followed by the exceptional April tides gave the final push and returned sand to Dooagh, depositing it well above the mean water level mark on the beach.</p>
<h2>Changing coastlines</h2>
<p>People in Achill shouldn’t get too complacent as there’s no doubt Dooagh beach will disappear again at some point in future. It just needs to experience similar conditions to those of 1890 and 1984. </p>
<p>A beach disappearing so quickly is rare but not unheard of. In January 2015, for instance, the residents of Porthleven in Cornwall woke to a rocky shore after a strong southwesterly storm stripped the sand from their beach, again overnight. The bay has the same southwards orientation as Dooagh. It occurred during a spring tide, which is a fortnightly high tidal flow (not to be confused with spring the season). However in this case a shift of the wind (and hence waves) to southeasterly <a href="http://www.telegraph.co.uk/news/newstopics/howaboutthat/11363263/Cornish-beach-is-washed-away-overnight...-then-reappears.html">returned the sand</a> just one day later.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"563449499339591681"}"></div></p>
<p>In 1995 I was involved in deploying some equipment to measure flows on a pebble beach near the town of Southsea on the English Channel. Overnight a strong storm hit, and on returning the following day the beach and all of our scientific equipment had gone, leaving behind a soft, sandy beach with an entirely different shape. Great for tourism, not so for science. In fact, the only science we achieved was through recovering some of our battered and heavy equipment – much of it ten miles to the east – which is presumably where most of the pebble beach had gone (though where the sand had come from is still a bit of a mystery, perhaps it was beneath the pebbles all along).</p>
<p>These are just a few examples; I could cite many others. The coastline of the British Isles is constantly in flux for good reason. Each cubic metre of seawater weighs a tonne and Britain and Ireland are exposed to the pounding of Atlantic storms as well as some of the strongest tides on the planet. Predicting where and when the coast will erode is far from simple. There is also the issue that one coastal area’s loss is another’s gain. If beaches are overprotected without careful planning, retention of the beach-line in one location could mean that there is no longer replenishment sand further along the coast, causing a new problem. </p>
<p>The sea has shaped and re-shaped our coastlines since the Earth first had oceans, and will continue to do so for many more years yet. Ireland’s “reappearing beach” is just a tiny snapshot of this process.</p><img src="https://counter.theconversation.com/content/77503/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Boxall receives funding from the University of Southampton, NERC and in the past the EU Framework programme. </span></em></p>A entire beach in Ireland has returned 33 years after being washed away.Simon Boxall, Lecturer in Ocean and Earth Science, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/749282017-04-05T03:10:24Z2017-04-05T03:10:24ZSqueezed by gravity: how tides affect the groundwater under our feet<figure><img src="https://images.theconversation.com/files/163078/original/image-20170329-1670-1vvhett.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There's a lot of water beneath our feet.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>When returning from a swim in the ocean, sometimes it seems as though your towel has moved. Of course, it’s just that the water line has shifted. </p>
<p>The natural rise and fall of the ocean at the beach is an excellent demonstration of gravitational forces exerted by the Sun and the Moon. Although the tidal force is small, it is strong enough to pull regularly on the ocean, making an enormous volume of water rise and fall.</p>
<p>What you might not know is that tidal forces from the Sun and Moon also influence the air we breathe and the solid ground we stand on. These effects are referred to as atmospheric and Earth tides.</p>
<p>While we don’t tend to notice Earth and atmospheric tides, they do affect both the land and the world’s largest freshwater resource located underneath our feet: <a href="http://www.connectedwaters.unsw.edu.au/sites/all/files/UNSW-CWI_groundwater-facts_2017.pdf">groundwater</a>. This occupies the pores that exist in geological materials such as sand or soil, much like water in a kitchen sponge.</p>
<p>We have <a href="http://onlinelibrary.wiley.com/doi/10.1002/2016GL071328/abstract">developed a method</a> that incorporates tidal influences to monitor our precious groundwater resources without the need for pumping, drilling or coring. </p>
<h2>Water beneath our feet</h2>
<p>It has been estimated that groundwater makes up 99% of the usable freshwater on Earth. If all of Earth’s groundwater were extracted and pooled across the world’s land surface, it would be <a href="http://www.nature.com/ngeo/journal/v9/n2/full/ngeo2590.html">enough to create a lake 180 metres deep</a>. </p>
<p>While this sounds like a lot of water, it is important to remember that not all groundwater is available for use. In fact, groundwater is currently <a href="http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/abstract">mined on a global scale</a>, especially in drier parts of the world, where groundwater <a href="https://theconversation.com/the-worlds-biggest-source-of-freshwater-is-beneath-your-feet-53874">underpins human activities</a> during times of drought.</p>
<p>Groundwater extraction can lead to a downward shift in the land surface level (known as “subsidence”), particularly if groundwater is removed from underground zones that contain soft clays. This is a significant global problem, especially in coastal areas, due to <a href="http://www.sciencedirect.com/science/article/pii/S0959378014000880">urbanisation and associated water demand</a>.</p>
<p>Alternatively, a long wet period with excess rainfall can cause the groundwater to rise up and cause flooding. </p>
<h2>Effect of tides on groundwater</h2>
<p>Deeper groundwater buried underneath layers of different types of sediments is under great pressure (in groundwater terminology this is called “<a href="https://en.wikipedia.org/wiki/Aquifer#Confined_versus_unconfined">confined</a>”). The gravity change from Earth tides squeezes the sediment, and therefore changes the pressure of the water in the pores. </p>
<p>The atmospheric tides add to the weight that is sitting on top of the groundwater and cause a change in stress that results in a downward squeezing.</p>
<p>Groundwater at that depth responds to these stress changes, which can be measured as tiny water level fluctuations inside a groundwater borehole.</p>
<p>We have developed a new approach that exploits these tidal influences to <a href="http://onlinelibrary.wiley.com/doi/10.1002/2016GL071328/abstract">calculate important subsurface properties</a>. For example, this can predict how the pressure is lowered when groundwater is pumped, and by how much the land surface would sink as a result of shrinking subsurface material (just like squeezing a kitchen sponge). </p>
<p>The method basically allows accurate calculation of the compressible subsurface properties from the groundwater response to Earth and atmospheric tides.</p>
<p>This development is significant because it will allow analyses of a subsurface water reservoir (called an aquifer) without human-induced stresses such as pumping or taking physical samples of the material through drilling or coring in addition to constructing a borehole.</p>
<p>All that’s needed for this analysis is a roughly 16-day period of continuous measurements of groundwater levels and atmospheric pressure at hourly intervals. </p>
<p>Groundwater levels are routinely recorded as part of water monitoring programs around the world and in <a href="http://groundwater.anu.edu.au/">Australia</a>, as funded by the Federal Government <a href="http://www.connectedwaters.unsw.edu.au/ncris">groundwater NCRIS</a> scheme. Atmospheric pressure is a standard parameter measured by weather stations, such as operated by the <a href="http://www.bom.gov.au/">Bureau of Meteorology</a>.</p>
<p>The effects of tidal forces on groundwater might be less apparent to us than their effects on the ocean, but they’re just as important. Our new method of understanding the influence of tides on groundwater significantly reduces the effort to predict the response to groundwater pumping and the potential for land subsidence. </p>
<p><a href="http://onlinelibrary.wiley.com/doi/10.1002/2016WR020311/abstract">This technique can make passive use of existing boreholes</a> and could be applied to the global archive of groundwater levels to inform more sustainable groundwater resource development in the future.</p><img src="https://counter.theconversation.com/content/74928/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gabriel C Rau received funding from the NSW Government Research Acceleration and Attraction Program in 2016 to support the federally funded NCRIS Groundwater Infrastructure.</span></em></p><p class="fine-print"><em><span>Ian ACWORTH receives funding from the ARC NCGRT program</span></em></p><p class="fine-print"><em><span>Landon J.S. Halloran and Mark O. Cuthbert 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>We know the tides affect the oceans, but it also affects groundwater. If we can understand how, then we can better protect this precious resource.Gabriel C Rau, Lecturer, School of Civil and Environmental Engineering (CVEN) & Connected Waters Initiative Research Centre (CWI), UNSW SydneyIan Acworth, Emeritus Professor: Groundwater resources, UNSW SydneyLandon J.S. Halloran, Postdoctoral Researcher in Hydrogeology/Geophysics, UNSW SydneyMark O. Cuthbert, Research Fellow in Groundwater Science, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/683482016-11-14T22:43:27Z2016-11-14T22:43:27ZHurt by sea: how storm surges and sea-level rise make coastal life risky<p><em>The journal <a href="http://link.springer.com/journal/10584">Climatic Change</a> has published a <a href="http://link.springer.com/journal/10584/139/1/page/1">special edition</a> of review papers discussing major natural hazards in Australia. This article is one of a <a href="https://theconversation.com/au/topics/australian-natural-hazards-series-32987">series</a> looking at those threats.</em></p>
<hr>
<p>Australia is a huge continent, but a coastal nation. About 80% of Australians live within 50km of the coast, and a sea-level rise of 1.1 metres (a high-end scenario for 2100) would put about A$63 billion (in 2008 dollars) worth of residential buildings at risk. </p>
<p>Anyone who lives along Sydney’s northern beaches, especially in <a href="http://www.abc.net.au/news/2016-06-16/engineers-waiting-for-collaroy-residents-to-have-houses-cleared/7516184">Collaroy</a>, saw at first hand the damage the ocean can wreak on coastal properties when the coastline was hit by a severe <a href="https://theconversation.com/explainer-the-wild-storms-that-lash-australias-east-coast-40564">east coast low</a> during a king tide in June.</p>
<p>There are many different factors that determine which coastal homes or suburbs are most at risk of inundation or erosion, either now or in the future. In a <a href="http://link.springer.com/article/10.1007/s10584-016-1647-8">review</a> published as part of a series produced by the <a href="http://ozewex.org">Australian Energy and Water Exchange</a> initiative, we investigated the causes of extreme sea levels and coastal impacts in Australia, how they have changed, and how they might change even more. While significant progress has been made over recent decades, many questions remain.</p>
<p>The first factor to consider is the average sea level, relative to the land elevation. This “background” sea level varies, both from year to year and season to season. Depending on where you live and what the climate is doing, background sea level can fluctuate by up to about 1m. Around Australia’s northern coastline, for example, El Niño and La Niña can cause large variations in year-to-year sea levels. </p>
<p>On top of this are the tides, which rise and fall predictably, and whose range varies by location and phase of the moon. Most places have two tides a day, but curiously <a href="http://link.springer.com/article/10.1007/s10584-016-1647-8">some only have one - including Perth</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145701/original/image-20161114-9065-mho9m6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Map of tide pattern variations. Red: one high and low tide daily (diurnal); blue: two high and low tides per day (semi-diurnal) with a mixed tidal regime between.</span>
<span class="attribution"><span class="source">OZEWEX</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>On top of that again is the effect of the weather, the most notable short-term effects being storm surges and storm waves. During a surge, the storm pushes extra water onto the coast through a combination of wind pressure, wave buildup, and atmospheric pressure changes. Obviously these factors are much more localised than tides.</p>
<p>Extreme sea-level events, such as the one that hit Sydney in June, can arise from isolated events such as a storm surge. But more often they are due to a combination of natural phenomena that on their own may not be considered extreme. In Sydney, several factors aligned: a storm surge driven by an <a href="https://theconversation.com/explainer-the-wild-storms-that-lash-australias-east-coast-40564">east coast low</a>, an uncommon wave direction, a king tide, and a higher-than-average background sea level.</p>
<p>These processes already have the capacity to destroy coastal homes and infrastructure. But for the future, we also need to factor in climate change, which will raise the background sea level and may also change the frequency and intensity of storms.</p>
<h2>Long-term trends</h2>
<p>Average sea levels in Australian waters have been rising at rates similar to (but just below) the global average. Since 1993, <a href="http://www.bom.gov.au/oceanography/projects/abslmp/abslmp.shtml">Australian tide gauges</a> show an average rise of 2.1mm per year, whereas <a href="http://www.cmar.csiro.au/sealevel/sl_hist_last_decades.html">satellite observations</a> reveal a global average rise of 3.4mm per year. </p>
<p>What really counts is extreme sea levels, and these have been rising at <a href="http://onlinelibrary.wiley.com/doi/10.1029/2009JC005997/full">roughly the same rate</a>, meaning that the rising background sea level is a fairly good guide to how extremes are increasing. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=936&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=936&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=936&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145527/original/image-20161111-25066-n4i4j3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1176&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 effects of a king tide on Queensland’s Gold Coast.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File%3ACSIRO_ScienceImage_10726_The_effects_of_a_king_tide_on_Queenslands_Gold_Coast.jpg">Bruce Miller/CSIRO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This trend will continue in the future, although more energetic storm systems may also cause larger storm surges and hence higher rates of extreme sea levels in some places. More frequent storms are also set to make extreme sea-level events more common.</p>
<p>By 2100, global average sea level is <a href="http://www.ipcc.ch/report/ar5/wg1/">projected</a> to rise by 0.28-0.61m, relative to the period 1986-2005, if this century’s global warming can be held to about 1°C. But if greenhouse emissions continue to increase at their current rate, the world is in line for sea-level rises of 0.52-0.98m. </p>
<p>This rise will not be uniform around Australia’s coastline. The east coast is likely to experience up to 6cm more sea-level rise than the global average by 2100, because of the expected warming and strengthening of the East Australian Current.</p>
<p>Trends in Australia’s weather and waves are harder to predict. <a href="http://science.sciencemag.org/content/332/6028/451">Satellite measurements</a> over the past 30 years suggest that waves are getting slightly higher in the Southern Ocean, and climate models suggest that <a href="http://www.nature.com/nclimate/journal/v3/n5/full/nclimate1791.html">this may continue</a>. As the tropics continue to expand with climate change, the band of westerly winds over the Southern Ocean will retreat further south and strengthen, whipping up higher waves that will travel to Australia’s southern coast as swell. On the other hand, weakening winds nearer to Australia may help to dampen down wave heights. On Australia’s eastern coast, climate models suggest fewer large wave events <a href="http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2142.html">due to decreasing storminess in the Tasman Sea in the future</a>. </p>
<p>A significant challenge we face is not having the data available to monitor the changes along our southern coastline. Australia has the longest east-west continental shelf in the world, but we have only a handful of wave buoys to measure these processes; much of the coastline is not monitored despite widespread coastal management concerns.</p>
<p>Our understanding of extreme sea-level change in Australia is also limited by available tide gauge coverage. Only two digital tide gauge records (in <a href="http://www.psmsl.org/data/obtaining/stations/111.php">Fremantle</a> and <a href="http://www.psmsl.org/data/obtaining/stations/65.php">Fort Denison</a>) extend back to at least the early 20th century, and records elsewhere around the coast typically span less than 50 years. </p>
<p>However, our investigation discovered that there is an opportunity to increase the length of available records by digitising old paper tide gauge charts. This could extend several records along our southern and tropical coastlines.</p>
<p>We also have major gaps in our knowledge about how our coastlines will be changed by flooding and erosion. The simple methods used to predict coastal erosion may <a href="http://www.nature.com/nclimate/journal/v3/n1/abs/nclimate1664.html">underestimate erosion significantly, particularly in estuaries</a>. </p>
<p>Given the considerable urban infrastructure located within estuaries, and the fact that they are vulnerable both to coastal storms and river floods, this is one of the many crucial questions about life on the coast that we still need to answer.</p><img src="https://counter.theconversation.com/content/68348/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kathleen McInnes works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.</span></em></p><p class="fine-print"><em><span>Mark Hemer works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency. </span></em></p><p class="fine-print"><em><span>Ron Hoeke works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.</span></em></p>Many Australians live on the coast, but how much do we know about the risks? While average sea levels are relatively easy to gauge, the risk of flooding also depends on weather, landscape, and climate.Kathleen McInnes, Senior research scientist, CSIROMark Hemer, Senior Research Scientist, Oceans and Atmosphere, CSIRORon Hoeke, Littoral oceanographer, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/582322016-05-10T10:51:18Z2016-05-10T10:51:18ZRaging seas: going local to understand ocean extremes of the future<figure><img src="https://images.theconversation.com/files/121214/original/image-20160504-6918-1pw3s6a.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">Shutterstock</span></span></figcaption></figure><p>The world’s sea level is expected to rise by up <a href="http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WGIAR5_SPM_brochure_en.pdf%20Table%20SPM.2">to 82cm</a> by the end of the century. Some areas of the world, <a href="http://www.climatechange2013.org/images/report/WG1AR5_ALL_FINAL.pdf">such as</a> the north-east coast of North America and the Western Pacific, will be more affected than others. But in many places this will mean floods are more likely, the cost of coastal protection will rise, and coastal ecosystems will be put in danger.</p>
<p>Yet it isn’t just the average sea level that will rise. The biggest risks will come from the fact that the highest sea levels (caused by high tides and weather) will also increase by at least as much as the mean. This is what are seeing so far in <a href="http://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%282004%29017%3C1190%3AEFSCIE%3E2.0.CO%3B2">many parts of the world</a>. A potential increase in the frequency and <a href="https://theconversation.com/earthquakes-superstorms-and-other-little-known-perils-of-climate-change-49761">severity of storms</a> could make higher sea-level extremes and their impact even worse. More violent storms could also produce more energetic and higher waves, testing the resilience of ships and offshore structures like oil rigs and disrupting trade. But how serious will these problems be?</p>
<p>Computer models of climate change caused by greenhouse warming indicate that the most devastating tropical cyclones will be between 2% and 11% <a href="http://www.nature.com/ngeo/journal/v3/n3/full/ngeo779.html">more intense by 2100</a>. The same models also indicate there will be fewer tropical cyclones overall but more high-intensity cyclones. This leaves us with a rather unclear picture that is <a href="http://www.nature.com/ngeo/journal/v3/n3/full/ngeo779.html">further complicated</a> because <a href="http://onlinelibrary.wiley.com/doi/10.1002/qj.2364/full">scientists disagree</a> on whether and how tropical cyclones have been changing over the past 30 or 40 years. </p>
<p>The role of regional climate patterns like the <a href="https://theconversation.com/explainer-el-nino-and-la-nina-27719">El Niño</a> cycle of wind and sea temperature changes in the Pacific and the monsoons in the Indian Ocean also add to this complexity. Although we expect climate change to influence these phenomena, they also vary significantly from year to year naturally, making it very challenging to say if any particular extreme event is driven by climate change.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jMQ31n4eBbQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p><a href="http://nat-hazards-earth-syst-sci.net/10/1457/2010/nhess-10-1457-2010.pdf">Research we conduct with several collaborators</a> involves examining changes in extreme waves and sea-level records to identify factors that contribute to changes in extremes. This information can then be used to improve computer models of sea level in the hope of making this picture clearer.</p>
<p>As mentioned, sea level extremes have generally been found to change in line with the observed mean sea level trends. But changes in extremes are also caused by changes in the tides, in the seasonal cycle, in currents in the ocean, and the number of the typhoons impacting on land.</p>
<h2>More than just climate change</h2>
<p>We found that each of these factors affected the areas studied (<a href="http://onlinelibrary.wiley.com/doi/10.1002/2014JC010360/abstract">the Mediterranean Sea</a>, the Caribbean Sea, and <a href="http://onlinelibrary.wiley.com/doi/10.1029/2008JC004912/full">the North Sea</a>) by a different degree. We also found that these factors were not all related to climate change or natural variability. For example, significant changes in the extremes at the <a href="http://onlinelibrary.wiley.com/doi/10.1002/2013JC009607/abstract">Chinese coasts</a> are linked to changes in regional tides thought to be related to the extensive land reclamation going on to create more space for building. This kind of human influence is distinct from climate change but just as important to the local environment.</p>
<p>Other partners worked on improving the parameters of models of <a href="http://onlinelibrary.wiley.com/doi/10.1002/2013JC009160/abstract">tropical cyclones</a>. This confirmed that previous models underestimated sea level extremes. But what this also means is that climate models that are much less detailed aren’t good enough to produce firm conclusions on whether climate change will increase extreme ocean activity.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/121771/original/image-20160509-20577-71tync.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">Cyclones could become less frequent but more intense.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>For example, we know that wave heights in the North Atlantic have increased, partly due to changes in regional atmospheric patterns. But for the <a href="http://www.sciencedirect.com/science/article/pii/S0921818113002816">Norwegian Sea</a>, the increase has been much smaller since 2000 than previously recorded.</p>
<p>If we want to understand how marine extremes will change in the future, we need to look at each location individually and take into account the specific factors that will affect its extreme ocean activity. We also need more detailed global and regional climate models and a clearer understanding of cyclonic systems to be able to predict changes in the severity and the pathways of cyclones and how they affect extreme activity.</p>
<p>Other environmental factors that could become more extreme, such as temperature, salt levels, oxygen content, acidity and current speeds will also be important in determining the impacts of climate change on the marine environment. But the data we have now doesn’t allow us to do such comprehensive analyses. Until we have a clearer picture, we won’t know just how extreme our oceans will become as the climate changes.</p><img src="https://counter.theconversation.com/content/58232/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Prof. Michael Tsimplis has received funding for this work from the Lloyd's Register Foundation. I am a member of the steering group of the Mediterranean Climate Variability initiative (MEDCLIVAR), the deputy director of the Southampton Marine and Maritime Institute.
</span></em></p>Climate change isn’t the only thing making sea levels higher and cyclones more intense.Mikis Tsimplis, Professor of law and ocean sciences, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/482602015-09-29T05:23:48Z2015-09-29T05:23:48ZAfter the supermoon, comes the supertide<figure><img src="https://images.theconversation.com/files/96472/original/image-20150928-30964-awi6ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">..and high tides.</span> <span class="attribution"><span class="source">Paul J Martin / Shutterstock.com</span></span></figcaption></figure><p>The city of Plymouth, on England’s south coast, normally has fairly moderate tides. However this week it will have <a href="http://www.ntslf.org/tides/hilo?port=Plymouth">a 6m “supertide”</a> – the highest tide <a href="http://www.plymouthherald.co.uk/Flood-alert-highest-supertide-18-years-come/story-26210483-detail/story.html">in 18 years</a>. This comes just days after the celebrated <a href="https://theconversation.com/fact-over-fiction-on-the-apocalyptic-super-blood-moon-47916">“supermoon”</a>.</p>
<p>In fact, many locations along the UK, US and Australian coasts will experience their highest tides for tens of years around September 29 or 30. Coastal roads in Miami, for instance, have already <a href="http://www.miamiherald.com/news/local/community/miami-dade/miami-beach/article36784707.html">been closed</a> in anticipation of exceptional tides.</p>
<p>These high tides may bring water levels uncomfortably close to the tops of harbour walks and flood defences, emphasising the threat of rising sea levels. In the UK they are unlikely to be a major problem on their own unless they coincide with storms (a <a href="https://theconversation.com/been-flooded-recently-these-scientists-want-to-hear-from-you-41716">strong storm surge</a> has a greater impact than even the most exotic of tides). However in other areas, like in parts of America and the Pacific, no storms are necessary: these high tides on their own can lead to <a href="http://oceanservice.noaa.gov/facts/nuisance-flooding.html">nuisance flooding</a>.</p>
<h2>Why do we expect such extreme tides?</h2>
<p>Tides are controlled by changes in the position and alignment of the moon and sun relative to Earth. Every fortnight – at new moon or full moon – the Earth, sun and moon are in an approximately straight line as seen from space and the additional gravitational pull of the sun causes stronger tides, known as spring tides.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/budXQlGL8Dc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Bay of Fundy on Canada’s Atlantic coast has the world’s highest tides.</span></figcaption>
</figure>
<p>Yet each month one set of spring tides is higher than the other. This is because tidal forces are strengthened when the moon is at “<a href="http://www.moonconnection.com/apogee_perigee.phtml">perigee</a>” and its elliptical orbit takes it closest to Earth. Tide-generating forces are also enhanced when the moon is directly overhead at the equator, part of a cycle lasting 27.2 days – a so-called “<a href="http://www.britannica.com/science/draconic-month">draconic month</a>”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=416&fit=crop&dpr=1 600w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=416&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=416&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=523&fit=crop&dpr=1 754w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=523&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=523&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Elliptical orbits of: (A) the moon around the Earth; and (B) the Earth around the sun.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Tides can differ over the course of a year, as the Earth moves from its <a href="http://www.windows2universe.org/physical_science/physics/mechanics/orbit/perihelion_aphelion.html">closest (perihelion) to furthest (aphelion)</a> point from the sun and back. More important is the variation in the sun’s position north or south of the equator, which causes the seasons. The tide-generating forces are greatest at the equinoxes in March and September when the sun is directly overhead at the equator. Spring tides are always higher at these times of year. </p>
<h2>A perfect tide?</h2>
<p>Over periods longer than a year, very large spring tides occur when all the astronomical factors we have mentioned earlier coincide. </p>
<p>Two longer-term motions of the moon’s orbit around the Earth are important. These motions (<a href="http://csep10.phys.utk.edu/astr161/lect/time/precession.html">astronomers call them precessions</a>) are the reason we are seeing unusually large spring tides this year. </p>
<p>The first precession is known as the cycle of lunar perigee, and influences tides about every four to five years. The elliptical orbit of the moon around the Earth slowly moves in relation to the sun, completing a full circuit every 8.8 years. This means at either the March or September equinox approximately every 4.5 years the moon is both at its closest point to the Earth, and is also overhead at the equator.</p>
<p>The second precession is known as the <a href="http://onlinelibrary.wiley.com/doi/10.1029/2010JC006645/abstract">lunar nodal cycle</a> and is due to a very slow change in the moon’s orbit. Imagine the Earth’s orbit around the sun took place on an enormous sheet of glass – what astronomers call the ecliptic plane. The moon’s orbit cuts this surface at an angle of approximately 5 degrees. Over 18.6 years the moon’s orbit slowly rotates around so it cuts through the ecliptic plane in a different place. </p>
<p>One effect of this is to change how far above or below the equator the moon can reach in its orbit. In 2015 the moon is at the point where it deviates the least from the equator. This slightly increases the chances of the moon being directly overhead at the equator at any given point, and thus coinciding with the other factors that contribute to extreme tidal forces.</p>
<p>A lot of things have to fall in place at once to generate record-breaking tides and this year the cycle of lunar perigee and the lunar nodal cycle nearly perfectly coincide, resulting in some of the highest spring tides for decades. </p>
<hr>
<p><em>The authors help run the <a href="http://www.surgewatch.org/contribute-photos/">SurgeWatch</a> website and would welcome any photos of high tides during this period.</em></p><img src="https://counter.theconversation.com/content/48260/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ivan Haigh has received funding from the Natural Environment Research Council and the Engineering and Physical Sciences Research Council.</span></em></p><p class="fine-print"><em><span>Kevin Horsburgh receives funding from The Natural Environment Research Council and the Environment Agency.</span></em></p>This is what you get when a full moon, a perigee moon and the September equinox all happen at once.Ivan Haigh, Lecturer in Coastal Oceanography, University of SouthamptonKevin Horsburgh, Head of Marine Physics and Ocean Climate, National Oceanography CentreLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/238622014-03-03T11:58:59Z2014-03-03T11:58:59ZExplainer: what are tidal bores?<p>Surfers and spectators <a href="http://www.gloucestercitizen.co.uk/star-Severn-bore-sweeps-Gloucestershire/story-20738035-detail/story.html">gathered along the Severn Bore</a> in Gloucestershire, England, in recent days to take advantage of the tidal wave that swept upstream. What’s known as a tidal bore – a wave of up to 2.8 metres – came in from the Atlantic on Sunday and a five-star bore (the largest waves that occur) coursed up the river on Monday morning. </p>
<p>Tidal bores are one of the most famous tidal effects where rising water from the ocean creates tidal waves which wash inland, up rivers. They take place on the Amazon and the Qiantang River in Southeast China, where the event is held to be sacred and marked by temples and large crowds. On the Severn Estuary in Southwest England the all-important sea level can rise and fall as much as 14 metres in the space of 12 hours. That’s the height of three double decker buses.</p>
<p>All around the world the sea level rises and falls every day with the tides. They vary from month to month, season to season and place to place. In the Mediterranean the tides are small. Along parts of the Atlantic and Pacific coasts their rise and fall can be extreme.</p>
<h2>Pull of the moon</h2>
<p>Tides are caused by the combining gravitational pull of the sun and the moon in relation to forces created by the spin of the earth. The gravity of the moon pulls at the earths surface, as water is “loose” it moves in response. Sometimes the gravitational pull of the sun (which is weaker on the earth as the sun is so far away) counteracts that of the moon and tides are lower. Sometimes the pull of moon and sun are in line (at new and full moon) and the highest, spring tides occur. </p>
<p>Before gravity was understood the tides were a great mystery to science and religion. The 8th Century British scholar and theologian, The Venerable Bede, wrote that the tides were somehow created by the breath of the moon. This is because the complex rhythm of the tides broadly follows the rhythm of the waxing and waning moon.</p>
<p>The Severn Estuary has the second highest tides in the world – after the Bay of Fundy in Canada – and the highest in Europe. The estuary is basically funnel shaped, going from west to east. This means that, as the Atlantic tide rises, a vast volume of water gets pushed up the estuary and, as the channel narrows, the depth of the river changes rapidly too into the lower reaches of the Severn River. As a result, the advancing top level of the water picks up speed and becomes a fully-fledged tidal wave followed by a surge of water.</p>
<p>On certain days of the year very high tides occur and these lead to what are called four or even five star bores – the biggest and most spectacular. The tidal wave gathers speed and height and crashes up the river channel making the Severn <a href="http://saveoursevern.org/">“the river that sometimes flows backward”</a>. </p>
<p>The record rainfall this winter threatened to hinder the height of the bore, which gains height from the river being shallow. But the river levels were able to drop back down as the rain subsided over the last couple of weeks, allowing for better bore forming over the weekend.</p>
<h2>Gathering spectacle</h2>
<p>Crowds gather to watch, websites show the best viewing areas and surfers and kayak canoeists come to ride the waves, adding to the drama and spectacle. The <a href="http://news.bbc.co.uk/1/hi/england/gloucestershire/4899262.stm">world record</a> for the longest distance travelled in one go on a surfboard has been held on the Severn Bore by surfer Steve King. He rode the wave for a one hour and 16 minutes, travelling more than seven miles upstream.</p>
<p>Because of the way they are created the tides don’t fit our normal day-night sequence in a simple way. High tides, and low tides – they always follow each other – can take place at any time, throughout the day or night. So they bring distinctive and special senses of time and rhythms to the places they affect. Both nature (such as wading birds) and society (sailors, farmers, fisher folk, walkers) must plan their day not by the clock of the sun, but by the clock of the moon.</p>
<p>Their unique timetable and the spectacular nature of tidal landscapes and phenomena such as the bore has been the inspiration for many artists and writers over the years. But tidal landscapes, despite being culturally and ecologically rich and unique, are under severe pressure nationally and internationally. Development, flood defences and land reclamation are serving to alter the often desolate and lonely – but very beautiful – landscapes of tidal areas. </p><img src="https://counter.theconversation.com/content/23862/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Owain Jones receives funding from NWO-HARC for research on tidal landscapes including the Severn Estuary.</span></em></p>Surfers and spectators gathered along the Severn Bore in Gloucestershire, England, in recent days to take advantage of the tidal wave that swept upstream. What’s known as a tidal bore – a wave of up to…Owain Jones, Reader in Cultural Geography, University of GloucestershireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/220332014-01-17T14:42:31Z2014-01-17T14:42:31ZMoon’s gravity alone cannot create the world’s largest tides<figure><img src="https://images.theconversation.com/files/39311/original/9k7849wm-1389962708.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">How long can you stay there depends on practice and physics.</span> <span class="attribution"><span class="source">elisfanclub</span></span></figcaption></figure><p>“Tide goes in, tide goes out…you can’t explain that.” So claimed US talkshow anchor Bill O’Reilly, in a baffling attempt to discredit atheism which <a href="http://www.youtube.com/watch?v=wb3AFMe2OQY&t=1m50s">became something of a YouTube sensation</a>.</p>
<p>I have been on holiday to Brittany a few times and I was aware the tides there were enormous – but, when I looked into why, I discovered that the reality is even more fascinating and complex than O’Reilly failed to grasp. </p>
<p>Tides around the world can range from almost nothing to over ten metres – so how can the Moon’s gravity alone give rise to such a diversity of tides?</p>
<p>Well, it can’t – at least, not on its own. The Moon’s gravity is strong enough to cause Earth’s oceans to oscillate, but it can’t account for the the variety of tidal ranges observed. These variations are caused in large part by the physics of waves.</p>
<p>You can think of tides as enormous waves rolling around the circumference of the Earth. The interplay between these gargantuan oscillations, rebounding from continents and interacting with one-another, can allow for huge differences between local tides. The large tidal range in Brittany, for example, is due to a tidal resonance – the cumulative effect of adjacent tidal waves perfectly in sync. If you want to learn more, it’s explained in this video:</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/vv6RPcGSKXQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption"><em>Lab, Camera, Action!</em> explains how tidal resonance bestows the Bay of Saint Brieuc in Brittany with one of the world’s largest tides.</span></figcaption>
</figure>
<p>Tides are also responsible for a host of excellent epiphenomena. For example, the Severn estuary in the UK plays host to the inaptly named <a href="http://en.wikipedia.org/wiki/Severn_bore">Severn bore</a>, which is anything but: a solitary two-metre-high shock wave which glides with an eerie smoothness for twenty miles up the river. Or there is Bodø in Norway, home of <a href="http://en.wikipedia.org/wiki/Saltstraumen">the world’s largest tidal maelstrom</a>, where the tide rushing through a narrow channel forms tumultuous whirlpools.</p>
<p>“Time and tide wait for no man”, or so the saying goes – and there are few more potent everyday examples of the power and indifference of nature. The advance of a spring tide up the Plage Bonaparte (the beach featured in the video) has often left me in awe. And, occasionally, sprinting with armfuls of cricket stuff and deck chairs to avoid them being claimed by the sea.</p>
<p>And if you want to experience the power of tides, I recommend standing in the sea and letting the tide rise up from your feet to your neck. Just make sure you know your physics – pick the biggest tide of the year on a beach with one of the world’s largest tides – or you may find yourself waiting for quite some time.</p>
<p><em><a href="http://www.youtube.com/watch?v=vv6RPcGSKXQ">Tides</a> is part of the science video series <a href="http://www.youtube.com/labcameraaction">Lab, Camera, Action!</a></em></p><img src="https://counter.theconversation.com/content/22033/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Steele 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>“Tide goes in, tide goes out…you can’t explain that.” So claimed US talkshow anchor Bill O’Reilly, in a baffling attempt to discredit atheism which became something of a YouTube sensation. I have been…Andrew Steele, Bioinformatician, King's College LondonLicensed as Creative Commons – attribution, no derivatives.