tag:theconversation.com,2011:/ca/topics/landslides-3173/articles
Landslides – The Conversation
2023-11-17T17:18:21Z
tag:theconversation.com,2011:article/207090
2023-11-17T17:18:21Z
2023-11-17T17:18:21Z
‘Many sleepless nights’: why scientists who predict landslides are under enormous pressure
<p>In June 2023, in the eastern part of Switzerland, the small picturesque village of Brienz/Brinzauls narrowly avoided being wiped out by a <a href="https://www.theguardian.com/world/2023/jun/16/huge-landslide-misses-swiss-mountain-village-of-brienz-by-a-hair">huge landslide</a>. The community sits at the foot of a steep slope that was on the move and eventually around 1.2 million cubic metres of rock collapsed, stopping just a few metres short of the village. </p>
<p>The landslide was predicted well in advance. The village had already been <a href="https://www.bbc.co.uk/news/world-europe-65580427">evacuated</a> and there was intense media interest. The slope even had a <a href="https://www.youtube.com/watch?v=3N80eDCnqaM">YouTube live stream</a>. As an expert in landslides who has been involved in these sorts of tough evacuation decisions before, I know those involved in the monitoring of the site, and making decisions around keeping the population safe, will have endured many sleepless nights. </p>
<p>Back in 2010 I was involved in the management of a landslide crisis in <a href="https://www.nation.com.pk/18-May-2010/evacuations-start-amid-fears-of-hunza-lake-burst">northern Pakistan</a>. Here, 14,000 people were relocated from the path of a potential flood after a landslide blocked a river and created a new lake. The day to day pressures of decisions like these are enormous.</p>
<p>The situation in Brienz/Brinzauls was not new (the double name is because the village has a mix of speakers of German and Romansh, Switzerland’s fourth native language). Villagers first noticed the slopes around the village were moving a century ago, and more modern monitoring has indicated that the slope had been moving at a rate of <a href="http://www.albula-alvra.ch/files/BXMediaPlusDocument8589file.pdf">seven metres per year or more</a>. The deforming slope even extends beneath the village, which has already been damaged by the movement, although the crisis this year did not affect that part of the slope.</p>
<p>In 2022 the speed abruptly increased, and parts of the slope above the village started moving at over 25 cm per day, while individual rocks started <a href="https://www.nau.ch/news/schweiz/brienz-gr-felsbrocken-donnert-ins-tal-polizei-erwischt-velofahrer-66506327">detaching</a> and falling down on the fields below. The steepness of the slope meant that a collapse seemed likely.</p>
<p>The challenge in these situations is in knowing when this might actually occur. And whether it will happen in a series of smaller landslides over weeks or even months, or as a single, more catastrophic event, that would be over quickly but would destroy the village. </p>
<h2>Movement monitoring in detail</h2>
<p>Over the past two decades, earth scientists have developed ways to monitor ground movement much more closely. This has allowed accurate assessment of the tectonic movement of continental plates, subsidence above coal mines, damage caused by tunnelling beneath cities, or the collapse of coastal cliffs.</p>
<p>Technologies include ultra-high-resolution GPS measurements, data from radar satellites and the use of robotic surveying instruments. The <a href="https://www.science.org/content/article/fleets-radar-satellites-are-measuring-movements-earth-never">precision can be extraordinary</a> – satellites located 800 km from the surface of the earth can detect movement of less than 3mm.</p>
<p>All these techniques mean the behaviour of slopes can be analysed in real time and scientists can quantify how they respond to external factors such as rainfall and earthquakes. It has even been discovered that some slopes respond to <a href="https://nhess.copernicus.org/articles/22/3125/2022/">changes in air pressure</a> as weather systems pass across the landscape. Usefully, these systems allow us to detect when a slope is moving dangerously fast, so that people can be warned and evacuated.</p>
<p>In the case of Brienz/Brinzauls, the slope had been accelerating through early 2023, although the exact causes were unclear. While short-term accelerations are common, sustained accelerations like this are a good indication that a collapse could be starting. In such circumstances, evacuation is prudent.</p>
<h2>No one wants unnecessary evacuations</h2>
<p>But relocating people, temporarily or permanently, is a huge issue. Understandably, many people struggle to cope, and there is ample evidence that relocated people often suffer from <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/286994/12-1297-mental-health-impacts-of-disasters.pdf">poor mental health and wellbeing</a>.</p>
<p>Where the population is moved into a camp for displaced people, which often happens in less affluent countries (but fortunately not in Switzerland), the evacuees are prone to <a href="https://blogs.worldbank.org/latinamerica/women-girls-gender-based-violence-aftermath-disasters-haiti">abuse, trafficking and destitution</a>. Experience tells us that women and children are particularly vulnerable in such circumstances.</p>
<p>So there are good reasons to avoid evacuating people unnecessarily, or too early, while also ensuring that the potentially affected population is kept safe. Thus, evacuating at the right time is critical.</p>
<p>Unfortunately, it is very hard to predict exactly how and when a big rock slope will collapse. Big rock slopes that are accelerating towards a full landslide typically move in patterns that can be modelled mathematically, allowing predictions that can be remarkably accurate in some circumstances. But complexities in the ground conditions mean that many slopes deviate from this, often slowing down unexpectedly. In some cases, movement returns to a crawl, or even stops altogether for a while. </p>
<p>We do not have enough information about the ground at any site to be able to know what a change in movement rate means for future behaviour (in the case of Brienz/Brinzauls, the “active slope” was about three million tonnes of rock that was, of course, extremely difficult to access safely). The ground is simply too complex to allow simple characterisation. Such a slope could resume movement in a few hours, a few days or even a few years.</p>
<p>Scientists and civil defence officers monitoring such situations have to assess the conditions continuously, making judgements as to the future behaviour. A few years ago in Norway, <a href="https://blogs.agu.org/landslideblog/2014/10/29/mount-mannen-1/">Mount Mannen</a> underwent repeated episodes of increased movement. The community at the foot of the slope was evacuated 18 times before the slope finally collapsed. The scientists were under immense pressure both to keep people safe and to avoid unnecessary disruption, all in the full glare of the national news.</p>
<p>The slope above Brienz/Brinzauls seems to have <a href="https://www.suedostschweiz.ch/ereignisse/zurueck-zu-phase-gruen-in-brienz-brinzauls">settled down</a> since the big landslide in June. Yet as climate change continues to cause environmental change in high mountain areas, the situation there is likely to play out in many more locations. As a consequence, the challenges faced by the authorities in Switzerland are likely to become more common.</p><img src="https://counter.theconversation.com/content/207090/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dave Petley 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>
Satellites can detect land moving by just a few millimetres, but we can never be sure exactly how or when a slope will slide.
Dave Petley, Vice Chancellor and Professor of Geography, University of Hull
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/215202
2023-10-24T15:12:04Z
2023-10-24T15:12:04Z
Himalayan communities are under siege from landslides – and climate change is worsening the crisis
<p>Three-quarters of annual rain in the Himalayas arrives in <a href="https://link.springer.com/chapter/10.1007/978-981-15-4327-2_11">the monsoon season</a> from June to September. Within this rainy period are sudden and extremely intense cloudbursts, which often “pop” over a relatively small area (akin to a cloud bursting open like a balloon). </p>
<p>As climate change is making these cloudbursts and other forms of heavy rainfall <a href="https://link.springer.com/chapter/10.1007/978-981-15-4327-2_8">more intense and more frequent</a> in the Himalayan foothills, the hilly slopes are becoming saturated more frequently, and thus unstable. Rainfall-triggered landslides are already happening extensively across the Himalayas, and things are likely to get worse. </p>
<p>From July to August 2023, the Indian Himalayas, particularly the state of Himachal Pradesh in the northern part of the country, experienced an unprecedented number of cloudbursts which triggered thousands of <a href="https://www.aljazeera.com/news/2023/8/14/dozens-dead-as-floods-landslides-hit-indias-himalayan-region">devastating landslides</a>. The state’s disaster management authority reported that by the end of August, heavy rain and rainfall-triggered landslides had caused <a href="https://www.thehindu.com/news/national/other-states/himachal-limps-back-to-normalcy-as-monsoon-withdraws-state-records-21-excess-rainfall/article67392435.ece">509 fatalities</a>, destroyed at least 2,200 homes and <a href="https://www.bbc.co.uk/news/world-asia-india-66615002">damaged a further 10,000</a>. It is estimated that Himachal Pradesh’s losses from this period amount to US$1.2 billion. Much of the destruction took place during two short periods, one in <a href="https://www.thestatesman.com/india/himachal-rains-death-toll-reaches-223-cm-monitoring-restoration-work-road-connectivity-1503210099.html">mid-July</a> and one in <a href="https://eos.org/thelandslideblog/the-14-august-2023-landslides-in-himachal-pradesh-india">mid-August</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Collapsed road in valley, lots of boulders" src="https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/555591/original/file-20231024-27-flkps9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A section of national highway (NH-03) is swept away by flash floods from cloudbursts in the Kullu district of Himachal Pradesh, July 2023.</span>
<span class="attribution"><span class="source">Ashutosh Kumar</span></span>
</figcaption>
</figure>
<p>The level of damage to buildings, roads and bridges is extremely difficult to comprehend. Several sections of national and state roads have been washed away, a temple in Shimla collapsed and <a href="https://www.bbc.com/news/world-asia-india-66615002">killed 20 people</a>, rural dwellings largely constructed on sloped ground were washed away by rain, and houses are still sliding downhill. </p>
<p>Schools and hospitals have been damaged, posing an ongoing threat to lives. A school in Kullu district was closed for 52 days because the bridge which connected it to a town had been washed away. Local people have had no option but to live in tents with minimal facilities. They are hugely concerned about their safety ahead of a cold and snowy winter.</p>
<p>Four days of heavy rainfall in July 2023 triggered landslides that <a href="https://indianexpress.com/article/cities/shimla/himachal-counts-losses-31-dead-40-bridges-damaged-1300-roads-closed-8827396/">blocked around 1,300 roads</a> including five national highways, leaving the state almost cut off from the rest of India. This had huge knock-on effects as <a href="https://www.indiatoday.in/india/story/heavy-rain-north-india-weather-forecast-himachal-uttarakhand-jammu-landslides-punjab-delhi-haryana-flooded-2404715-2023-07-11">1,255 bus routes were suspended, 576 buses were stranded</a>, more than <a href="https://www.thestatesman.com/india/himachal-successfully-evacuated-70000-tourists-to-safety-cm-1503200900.html">70,000 tourists had to be evacuated</a>, and people could not access key facilities and services. This impeded emergency responders, causing critical delays in search and rescue operations as well as delivery of aid.</p>
<p>Across the whole of India, the summer monsoon and its related cloudbursts are <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2014GL061573">decreasing</a>. But in the Himalayan foothills, they are <a href="https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/joc.5560">increasing significantly</a> – partly because when warm moist air encounters the Himalayan barrier it rapidly lifts and cools, forming large clouds that then dump their rain. With intense rain happening more and more often in the Himalayan foothills, it is likely that 2023’s summer of disasters will occur again.</p>
<h2>Unnecessarily vulnerable</h2>
<p>Although climate change may be to blame for the rise in cloudbursts, in an ideal world rainfall alone needn’t lead to disastrous landslides. But the Himalayas have been made <a href="https://economictimes.indiatimes.com/news/how-to/what-are-cloudbursts-and-is-climate-change-making-them-more-frequent-in-india/articleshow/102229046.cms">more vulnerable</a> by human actions.</p>
<p>The region has largely been <a href="https://www.sciencedirect.com/science/article/pii/S0341816222006130?via%3Dihub">deforested</a>, removing tree roots which reinforce the ground and form a crucial barrier that stops soils washing away. And unplanned developments and haphazard construction have destabilised already fragile slopes.</p>
<p>Initial reports on this year’s landslides suggest the worst damages occurred along artificially cut slopes (for roads or buildings), where there has been a lack of proper provisioning for drainage and slope safety. In both India and Nepal, many of the hill roads have been <a href="https://www.lyellcollection.org/doi/10.1144/qjegh2016-109">haphazardly constructed</a>, which makes landslides during rainfall <a href="https://www.sciencedirect.com/science/article/pii/S0013795222002721">more likely</a>. Construction guidelines and building codes are <a href="https://www.sciencedirect.com/science/article/pii/S0013795222002563">outdated</a> and have been ignored anyway, and there is little assessment of the link between urbanisation and landslide risk. </p>
<p>One obvious solution is to prevent rain from penetrating the ground, so the slopes avoid losing any strength. However, if the soil is entirely prevented from absorbing any rain, the water will instead run off the surface and cause greater flooding problems further downhill.</p>
<p>One engineering solution is to place an artificial soil layer above the natural soil to temporarily hold water in the surface when it is raining extremely hard, preventing it penetrating deeper within the slope. This “<a href="https://ascelibrary.org/doi/10.1061/9780784484968.013">climate adaptive barrier layer</a>” will then release water back to the atmosphere during a later drying period. </p>
<p>As the heavy rain intensifies, it will be hugely important for the Himalayas to implement new user-friendly and reliable construction guidelines that factor in how the climate is changing. Landslides can’t be avoided entirely, and India certainly won’t be able to reverse global warming and the increase in cloudbursts any time soon. But these preventive actions should at least make communities more resilient to the changing climate.</p>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.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">
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<p class="fine-print"><em><span>The authors 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>
Haphazard construction has made the region more vulnerable to increasingly intense rainfall.
Ashutosh Kumar, Assistant Professor, School of Civil & Environmental Engineering, Indian Institute of Technology Mandi
Eedy Sana, PhD Candidate, Geotechnical Engineering, Indian Institute of Technology Mandi
Ellen Beatrice Robson, Postdoctoral research associate, Durham University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/201885
2023-05-04T14:02:22Z
2023-05-04T14:02:22Z
Landslides are a global injustice – they’re rarely caused by the people worst affected
<figure><img src="https://images.theconversation.com/files/523703/original/file-20230502-2182-61xeda.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6000%2C3375&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Joshimath is slowly sliding.</span> <span class="attribution"><span class="source">Amol_M / shutterstock</span></span></figcaption></figure><p>In northern India, a tragedy is playing out in slow-motion. Located at about 2,000 metres elevation in Chamoli District in the Himalayas, Joshimath is an ancient, sacred town of about 17,000 people. Popular with pilgrims and visitors wanting to ski or climb the nearby mountains, the town is a beautiful refuge from the bustle of the plains.</p>
<p>Late in 2022, a new chapter started in the long history of Joshimath as cracks started to develop in buildings across the town. These quickly spread over a large area, ripping apart roads, houses and hotels. These events were widely reported by the Indian media, which generally ascribed them to <a href="https://www.hindustantimes.com/cities/dehradun-news/joshimath-land-subsidence-nearly-700-houses-developed-cracks-in-last-6-weeks-101673962770500.html">“subsidence”</a>. The reality is something else: the town is built upon debris from an ancient landslide. </p>
<p>And that landslide has started to move.</p>
<p>The age of the landslide is unclear, but it is likely to be hundreds or even thousands of years old. The debris has been covered with soil and plants, hiding it from sight and giving local people the impression they were living on solid ground. </p>
<p>The existence of the landslide, and the hazard that it poses, was identified <a href="https://www.tribuneindia.com/news/nation/government-joshimath-subsidence-was-flagged-in-1976-475986">about 50 years ago</a>, but little action has been taken to mitigate the risk. To date at least 860 houses have been rendered uninhabitable, and the landslide continues to move. Hundreds of people are living in temporary camps, with no real clarity as to their future prospects, and thousands more worry that the landslide movement will spread to their part of the town.</p>
<p>Why the landslide started moving again in late 2022 is unclear. In the past few months many fingers have been pointed. Over the past decade, a large hydroelectric “run of the river” scheme has been built in the valleys near the town, which meant building tunnels beneath Joshimath. Shaking caused by blasting has been reported throughout the area. It is unsurprising that people <a href="https://thewire.in/government/joshimath-updates-ntpc-land-subsidence-cracks">believe that there is a link</a>.</p>
<p>In early 2021, a large debris flow swept down the valley below Joshimath, triggered by the <a href="https://www.science.org/doi/10.1126/science.abh4455">collapse of a mountainside</a> high in the mountains, severely damaging the dam from the hydroelectric power scheme and killing over 200 people, mostly dam workers. Some people link the reactivation of the Joshimath landslide to this flow. </p>
<p>A third theory is that climate change, which has caused <a href="https://www.nasa.gov/feature/goddard/2020/climate-change-could-trigger-more-landslides-in-high-mountain-asia">more intense rainfall</a> in the area, has <a href="https://www.hindustantimes.com/india-news/joshimath-sinking-uttarakhand-joshimath-land-subsidence-messing-with-our-environment-experts-on-why-joshimath-is-sinking-101673187029829.html">triggered the landslide</a>. All of these mechanisms are possible. In the absence of detailed scientific investigations, rumours dominate.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1623911423192756224"}"></div></p>
<h2>Many other Joshimaths go unreported</h2>
<p>Sadly, Joshimath is not an isolated case. Landslides are destroying communities right across the high mountains of South Asia, most frequently small, isolated settlements that do not command the attention that has been heaped on Joshimath. Over and again, people lose their major economic assets – their house and land – and are rendered destitute. Women and girls often fare particularly poorly in these circumstances.</p>
<p>In the vast majority of cases, the landslides result from things outside of the control of the people affected, making these events a travesty of social justice. At the macro-level, the increases in rainfall intensity that are occurring in many mountain areas result principally from greenhouse gas emissions that occurred thousands of kilometres away in far richer economies. </p>
<p>In other cases, the landslides are the result of large energy projects that will bring security of supply to distant cities, while isolated communities may still have no reliable supply, and that will generate profits that will bring little benefit to the mountain regions. More locally, landslides often result from roads that serve to bypass their communities, and are sometimes associated with local corruption as, for example, the owners of construction machinery bribe officials to allow road building in unsuitable areas.</p>
<h2>A safety net for landslide victims</h2>
<p>There is a paucity of social justice, or even of discussion about social justice, when it comes to these landslides. The victims at every stage are the local people, who lose their home, their land, their possessions and their livelihood, and sometimes their lives. Even in richer countries landslides are often not an insurable risk, in contrast to floods or windstorms. For most people it is not possible to assess the likelihood of a property being affected by a landslide, so home owners are in effect having to gamble.</p>
<p>It is time to make changes. In the mountains of South Asia, the current rampant, poorly-coordinated development needs to be controlled for the sake of the environment and the local population. There is no case for an embargo on construction across the region, but there is a strong rationale for ensuring that there are proper technical assessments of large schemes; for environmental impact assessments that are scientifically rigorous; for land use planning controls on the basis of hazard and for the careful management of water. When things go wrong, and they will, there is a need for a safety net, either through insurance or through government schemes.</p>
<p>Sadly, failure to act will further drive inequality, causing a further breakdown in the fragile social balance of high mountain areas.</p><img src="https://counter.theconversation.com/content/201885/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dave Petley 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>
When we talk about landslides we need to talk about social justice.
Dave Petley, Vice Chancellor and Professor of Geography, University of Hull
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/201283
2023-03-07T00:15:46Z
2023-03-07T00:15:46Z
The red and yellow sticker dilemma – how do we balance safety with the desire to return home after a disaster?
<figure><img src="https://images.theconversation.com/files/513825/original/file-20230306-30-emvs6.jpg?ixlib=rb-1.1.0&rect=12%2C0%2C4316%2C2882&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Getty Images</span></span></figcaption></figure><p>Just over a month after the Auckland flood, and three weeks on from Cyclone Gabrielle hitting the North Island, the scale of the disasters and the rebuild is clear – as is a sense of being in limbo for those worst affected.</p>
<p>At Muriwai on Auckland’s west coast, locals were reportedly left <a href="https://www.newshub.co.nz/home/new-zealand/2023/03/muriwai-residents-frustrated-with-the-uncertainty-around-when-they-can-go-home.html">frustrated by a lack of information</a> after a community meeting called by Auckland Council last week. So far, 113 homes have been “red-stickered” in the small settlement, with another 75 along Domain Crescent yet to be assessed due to the street’s ongoing instability.</p>
<p>At the centre of it all sits <a href="https://www.legislation.govt.nz/act/public/2004/0072/latest/DLM307300.html">section 124</a> of the New Zealand Building Act. This is the piece of law governing the red or yellow notices (“stickers”) pasted onto houses or buildings deemed “dangerous, affected, or insanitary”. </p>
<p>The situation now playing out at Muriwai provides a case study of the kinds of “pinch points” the use of section 124 can create for territorial authorities and their communities. The lessons learned should inform future disaster responses.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1630840879920422918"}"></div></p>
<h2>Listen to the science</h2>
<p>Ultimately, councils want to keep people safe. But there can be tension when communities feel the risk from a hazard has diminished enough for them to return home and pick up their lives. Not least are concerns that a red sticker on the front of their house is an invitation to thieves. </p>
<p>Talk of “shutting the stable door once the horse has bolted” or “throwing the baby out with the bathwater” is often heard in the aftermath of a natural disaster. The storm has passed, the sun is shining and people want to return to what might seem a more benign environment.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/landslides-and-law-cyclone-gabrielle-raises-serious-questions-about-where-weve-been-allowed-to-build-200250">Landslides and law: Cyclone Gabrielle raises serious questions about where we've been allowed to build</a>
</strong>
</em>
</p>
<hr>
<p>But what is “safe” is vague, and everyone has their own interpretation of risk – including engineers. Some parts of Aotearoa recover faster than others, and councils have different ways of operating. So it’s important local authorities make balanced decisions by prioritising the science.</p>
<p>In Gisborne in November 2021, for example, widespread <a href="https://www.rnz.co.nz/news/national/455378/gisborne-cleans-up-after-floods-and-landslides">landslides occurred</a>, including a substantial slip involving several residential streets. This transitioned into an earthflow, with the most mobile material probably characterised as mudflow.</p>
<p>Contractors quickly installed concrete blocks at the toe of the slope to stop any more debris sliding onto the road (see picture below). Disruption to the community was kept to a minimum.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/513824/original/file-20230306-22-720uau.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">Aftermath of the Hill Road landslide in Gisborne, November 2021: concrete blocks were quickly placed at the toe of the slope to stop remobilisation of landslide debris.</span>
<span class="attribution"><span class="source">Martin Brook</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Avoiding extremes</h2>
<p>There are other examples, however, of government agencies and councils failing to keep people safe – or being over-zealous in their approach to hazard management and community safety.</p>
<p>Most infamously perhaps, in 1966 at <a href="https://en.wikipedia.org/wiki/Aberfan_disaster">Aberfan</a> in South Wales a saturated pile of coal “spoil” slumped and flowed down the valley side. The result of no effective monitoring at all, the slide engulfed a primary school and killed 144, including 116 children. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/massive-outages-caused-by-cyclone-gabrielle-strengthen-the-case-for-burying-power-lines-199949">Massive outages caused by Cyclone Gabrielle strengthen the case for burying power lines</a>
</strong>
</em>
</p>
<hr>
<p>Still in the UK but the other end of the scale, the Cumbria County Council acted very quickly in 2021 when <a href="https://www.bbc.com/news/uk-england-cumbria-58080261">cracks appeared</a> in the soil at the end of a hot summer at Parton on the Cumbria coast. The council <a href="https://cumbriacrack.com/2021/08/06/parton-landslip-villagers-returning-home-and-road-now-open/">evacuated the village</a> for more than a week, and the local school was only reopened 14 months later. </p>
<p>A klaxon warning alarm was installed as a precaution, but the geotechnical investigation showed there had actually been no recent movement of the slope at all. The “tension cracks” were more likely shrinkage cracks due to the soils drying out, not from tensional stresses within an unstable slope.</p>
<p>Both examples demonstrate the importance of understanding the true stability of a slope. Monitoring can be done by remote sensing from helicopter-borne <a href="https://www.neonscience.org/resources/learning-hub/tutorials/lidar-basics">LiDAR</a> (as at Muriwai at present), or space-borne <a href="https://www.usgs.gov/programs/VHP/insar-satellite-based-technique-captures-overall-deformation-picture">InSAR</a>. But knowing what is happening to a slope means being able to see, in high resolution, its physical behaviour over time.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1631554148478115845"}"></div></p>
<h2>The technology exists</h2>
<p>A good example of <a href="https://www.bgs.ac.uk/case-studies/hollin-hill-landslide-observatory-yorkshire-landslide-case-study/">state-of-the-art monitoring</a> is the ALERT system pioneered by the British Geological Survey at the Hollin Hill landslide test site in North Yorkshire. This uses ground surface markers, with a variety of motion and listening sensors installed below in geotechnical boreholes at different depths within the slope.</p>
<p>Monitoring moisture is often the key, as rising soil moisture is often the precursor to any measurable slope movement. The installed sensors stream data directly to a geologist’s office computer, providing the basis for science-based decision-making. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-a-temporary-flood-levy-on-higher-earners-would-be-the-fairest-way-to-help-pay-for-cyclone-gabrielle-200705">Why a temporary flood levy on higher earners would be the fairest way to help pay for Cyclone Gabrielle</a>
</strong>
</em>
</p>
<hr>
<p>The international mining industry has also pioneered the monitoring of unstable slopes within open-pit mines. A land-based radar unit is pointed at a slope and provides measurements in real time to a control room. Trigger levels are set so that movement beyond certain allowable thresholds raises an alarm and the pit floor is evacuated. </p>
<p>A classic example of its effectiveness is a <a href="https://www.geosociety.org/gsatoday/archive/24/1/article/i1052-5173-24-1-4.htm">landslide at Bingham Canyon Mine</a> in Utah in 2013. When radar detected slope movement above the acceptable thresholds, more than 100 workers were evacuated. A 60 million cubic metre rock avalanche occurred the next day. It was the largest non-volcanic landslide recorded in the US, and no one was harmed.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/513823/original/file-20230306-24-j5xd67.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">A large landslide threatens houses in the coastal suburb of Muriwai following Cyclone Gabrielle on February 14 2023.</span>
<span class="attribution"><span class="source">Getty Images</span></span>
</figcaption>
</figure>
<h2>Finding the balance</h2>
<p>Getting the balance right isn’t easy. Councils struggle to keep communities safe (recognising there is no such thing as zero risk) while also involving those communities in key decisions. It’s a dilemma local authorities and government agencies wrestle with across most OECD countries.</p>
<p>An approach to planning and mitigation of hazards based on <a href="https://ourlandandwater.nz/about-us/te-ao-maori/">te ao Māori</a> (the Māori world view) has been advocated, but it’s yet to be determined how this would play out across the Aotearoa’s varied communities and cultures.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/build-back-better-sounds-great-in-theory-but-does-the-government-really-know-what-it-means-in-practice-200514">'Build back better' sounds great in theory, but does the government really know what it means in practice?</a>
</strong>
</em>
</p>
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<p>But based on Muriwai’s experience, an agile and empathetic approach seems important. This would involve community participation in local hazard planning, coupled with rapid installation and application of state-of-the-art monitoring technology.</p>
<p>Anxious communities recovering from tragic events need to feel they are being listened to. Engaging them in the decision-making process – as well as demonstrating the science behind those decisions – is vital. This is especially so when people’s homes and lives depend on the application of section 124 of the Building Act.</p><img src="https://counter.theconversation.com/content/201283/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Brook receives funding from MBIE, Toka Tū Ake EQC, and the Royal Society Te Apārangi. </span></em></p>
The ‘stickering’ of houses under section 124 of the Building Act, and decisions about when it’s safe to return, need to be informed by science. Affected communities should be involved at every stage.
Martin Brook, Associate Professor of Applied Geology, University of Auckland, Waipapa Taumata Rau
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/198984
2023-02-02T00:50:01Z
2023-02-02T00:50:01Z
Slippery slopes: why the Auckland storm caused so many landslides – and what can be done about it
<figure><img src="https://images.theconversation.com/files/507722/original/file-20230201-17339-p2m9rm.jpg?ixlib=rb-1.1.0&rect=20%2C13%2C4529%2C2874&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Getty Images</span></span></figcaption></figure><p>The January 27 storm that hit Auckland <a href="https://www.stuff.co.nz/national/weather-news/131116461/some-parts-of-auckland-city-had-more-than-400mm-of-rain-in-a-week-nearly-everywhere-had-at-least-150mm">broke all previous rainfall records</a> and has caused <a href="https://www.theguardian.com/world/2023/feb/01/auckland-floods-biggest-climate-event-new-zealand-history-flooding">widespread damage</a>, mostly from flooding and landslides. But while climate change helps explain the intensity of the rainfall, the way land has been used and built on in the city is a major factor in what happened.</p>
<p>Such rainfall events generate significant landslides, probably in the thousands. What geologists refer to as “multiple-occurrence regional landslide events” (<a href="https://link.springer.com/article/10.1007/s10346-005-0019-7">MORLEs</a>) are sometimes also triggered by earthquakes (such as happened in <a href="https://www.geonet.org.nz/earthquake/story/2016p858000">Kaikoura in 2016</a>). </p>
<p>But predicting where and when land might slide is not easy. Influencing factors include local geology, the properties of the slope material (soil and/or rock), slope geometry and angle, surface vegetation cover, drainage, and any buildings which can add weight and “load” to a slope. </p>
<p>Combinations of these factors were involved in Auckland, and understanding what happened and why will be important for ensuring the city is protected from similar events in future.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/EhVonqF7DOI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<h2>Weak saturated soil</h2>
<p>Auckland has weak, clay-rich soils formed by the weathering of underlying (often) weak rocks. It also has a lot of steep slopes. Even in their natural state, these slopes can be prone to sliding if the soils become saturated enough.</p>
<p>A further issue is the seasonal drying and wetting of soils. Auckland’s clay-rich soils show high “shrink and swell” properties, meaning there is a natural annual cycle of wetting (swelling) and drying (shrinking). </p>
<p>This can cause a progressive weakening of the soils over years and decades, called “strain-softening” (a bit like taking a steel fork and bending it back and forth). The soil is then more prone to failure when a large rainfall event occurs. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-auckland-floods-are-a-sign-of-things-to-come-the-city-needs-stormwater-systems-fit-for-climate-change-198723">The Auckland floods are a sign of things to come – the city needs stormwater systems fit for climate change</a>
</strong>
</em>
</p>
<hr>
<p>In theory, then, more extreme climate effects could lead to an increased rate of soil deterioration, causing the properties of the soil to change more rapidly.</p>
<p>Rainfall “thresholds” are also important to consider. These are the rainfall totals – measured across either 24, 48 or 72 hour intervals – that can initiate landslides on a given slope. But using rainfall forecasts to predict landslides oversimplifies the issue because the prevailing (“antecedent”) soil moisture conditions are also important. </p>
<p>Soils are made of solids (the grains), water, and air which creates “pore” spaces. If it’s been a very wet few weeks preceding a storm event, water increases within the pores (“porewater”), creating an increase in pressure. This lowers the strength of the soil, meaning less rainfall may be required to trigger landslides.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1620330542221647875"}"></div></p>
<h2>Too close to cliffs</h2>
<p>While climate change and the warming of oceans that pump-prime extreme weather events are certainly pressing issues, changing land use is also of growing importance. Indeed, <a href="https://www.nature.com/articles/s41561-022-01073-3">some studies</a> now suggest it is as important as, or possibly exceeds, the effects of climate change on landslides. </p>
<p>These changes include the removal of vegetation, which allows more water to directly enter the soil; the creation of impermeable surfaces; and the cutting and filling of undulating slopes to enable roads and buildings to be constructed. All of these affect the near-surface drainage and hydrology.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/auckland-floods-even-stormwater-reform-wont-be-enough-we-need-a-sponge-city-to-avoid-future-disasters-198736">Auckland floods: even stormwater reform won’t be enough – we need a ‘sponge city’ to avoid future disasters</a>
</strong>
</em>
</p>
<hr>
<p>A further problem in Auckland is often the lack of adequate building “set-back” distances. This is the distance between a dwelling and a slope or cliff edge. In some countries and jurisdictions this is specified within regional plans and taken very seriously. </p>
<p>One way used to <a href="https://www.columbiaco.com/DocumentCenter/View/3437/PB-01-Slopes-and-Setbacks?bidId=">calculate these distances</a> is to project an imaginary 45 degree plane from the bottom of a slope. One third of the cliff height is then added to this. For example, a 30-metre high slope would have a set-back distance of 40 metres.</p>
<p>But local geology and climate is also important. With weak soils in a humid climate, a conservative rule of thumb could be a set-back distance of three times the height of the slope or cliff. So, a house on a 30-metre high North Shore cliff, with superb views across to Rangitoto Island, should be set-back around 100 metres from the cliff edge. </p>
<p>Yet there are many houses within just a few meters of cliff edges in parts of the North Shore and eastern Auckland. Swimming pools constructed on slopes can add to the loading and stress, making the slope more prone to failure during a significant rainfall event. </p>
<p>Set-back from the bottom of slopes is also important, because inundation (“runout”) from landslides on slopes above houses can occur, as witnessed in various parts of Auckland.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1620617844802347008"}"></div></p>
<h2>Three ways forward</h2>
<p>Looking ahead, there are three broad approaches to mitigating rainfall-induced landslides in Auckland. First, it will be interesting to see how set-back distances are applied and whether changes to the <a href="https://www.aucklandcouncil.govt.nz/plans-projects-policies-reports-bylaws/our-plans-strategies/unitary-plan/Pages/default.aspx">Auckland Unitary Plan</a> are made in light of recent events. </p>
<p>The Earthquake Commission (EQC) <a href="https://www.eqc.govt.nz/news/unique-insurance-scheme-supports-kiwis-as-risk-of-landslides-increases/">covers land within eight metres</a> of homes and outbuildings. But many houses will now be much closer to the edge of properties. For houses still more than eight metres away from a failing slope, gradual slope creep may suggest future failure is only a matter of time.</p>
<p>Second, landowners should limit vegetation removal and make sure stormwater drains properly into reticulated systems, rather than informal soak-aways. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-change-is-already-putting-the-heat-on-insurance-companies-aucklands-floods-could-be-a-turning-point-198764">Climate change is already putting the heat on insurance companies – Auckland's floods could be a turning point</a>
</strong>
</em>
</p>
<hr>
<p>Any surface cracking or bulging, cracked masonry, or difficult-to-open doors or windows should be checked by a chartered engineer. This can be useful in determining what is generally benign (but annoying) seasonal cracking due to soil shrinkage, and what is more serious.</p>
<p>Third, for scientists, engineers and local authorities, a more sophisticated region-wide approach to identifying unstable land is needed. The Interferometric Synthetic Aperture Radar (<a href="https://www.usgs.gov/centers/land-subsidence-in-california/science/interferometric-synthetic-aperture-radar-insar">InSAR</a>) uses space-borne radar to measure ground surface movement at a scale of millimetres-per-year. </p>
<p>I led an EQC-funded team that successfully applied this technique to Gisborne from 2016 to 2021 using the European Space Agency’s <a href="https://sentinels.copernicus.eu/web/sentinel/home">Sentinel satellite constellation</a>. This provides measurements every 12 days, with the raw data being free. It has proved very useful to Gisborne District Council in their planning and decision making. </p>
<p>In Europe, the EU-sponsored <a href="https://land.copernicus.eu/pan-european/european-ground-motion-service">European Ground Motion Service</a> displays almost real-time measurements of slope movements across the continent that anyone can access. Such a service would be useful across New Zealand – and the events in Auckland suggest this should be a priority.</p><img src="https://counter.theconversation.com/content/198984/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Brook receives funding from the Earthquake Commission (EQC).</span></em></p>
Building too close to cliffs and slopes, weak soils, lack of vegetation and increased rainfall all played a part in the massive storm damage to Auckland. The city needs to change the way it uses land.
Martin Brook, Associate Professor of Applied Geology, University of Auckland, Waipapa Taumata Rau
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/184839
2023-01-23T19:18:01Z
2023-01-23T19:18:01Z
Photos from the field: our voyage investigating Australia’s submarine landslides and deep-marine canyons
<figure><img src="https://images.theconversation.com/files/504596/original/file-20230116-20-l0myq9.jpg?ixlib=rb-1.1.0&rect=57%2C11%2C7550%2C5064&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Ali Jam Productions Photography</span>, <span class="license">Author provided</span></span></figcaption></figure><p><em>Environmental scientists see flora, fauna and phenomena the rest of us rarely do. In this series, we’ve invited them to share their unique <a href="https://theconversation.com/au/topics/photos-from-the-field-92499">photos from the field</a>.</em></p>
<hr>
<p>We gathered at the edge of the ship deck, awaiting the return of our sediment corer that had been lowered 4.5 kilometres – half the height of Mount Everest – to the seafloor. Our team of 53 people nervously shuffled together like penguins as we speculated about what we’d find.</p>
<p>It was July 2022. We’d been at sea for 36 days on CSIRO’s <a href="https://mnf.csiro.au/">Research Vessel Investigator</a> to explore the edges of our continent and learn how it evolved through time. While we’re all familiar with the shape of modern Australia, our continental mass actually extends well beyond our shorelines. </p>
<p>Over the 36 days of our voyage, we mapped more than 40,000 square kilometres of the seafloor from as shallow as 22 metres to depths of over 4.8km. And we’ve created 3D visualisations of features never seen before. </p>
<p>The steel corer emerged from the deep glistening like pirate treasure. It marks just one of many samples we collected at sea. Analysing them all will probably take years, but we can still share exciting new maps of the seafloor and what they may reveal – from the threat of tsunami in Australia to evidence of ancient beaches and dunes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A coloured image of the Australian continental land mass" src="https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=258&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=258&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=258&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=324&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=324&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505709/original/file-20230121-18-u06oai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=324&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An exaggerated 3D view of the Australian continental land mass and surrounding oceans. Beyond the shallow continental shelf seas (orange), the continental slope drops abruptly to the deep ocean floor (blue).</span>
<span class="attribution"><a class="source" href="https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search#/metadata/67703">Geoscience Australia/© Commonwealth of Australia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>The threat of tsunami</h2>
<p>Our research voyage aimed to investigate how mud and sand flows from our continent into the deep oceans. Along the way, these different sediments can travel down submarine canyons and form large landslides. </p>
<p>Sometimes, these submarine landslides are large enough to <a href="https://theconversation.com/scars-left-by-australias-undersea-landslides-reveal-future-tsunami-potential-85982">trigger a tsunami</a> – so we’re also working to understand what the local <a href="https://theconversation.com/making-waves-the-tsunami-risk-in-australia-60623">tsunami risk</a> is for Australia’s eastern seaboard communities.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="The front of a ship" src="https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504597/original/file-20230116-18-nz2wpv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The weather at sea isn’t always clear and calm. Early on in the trip we experienced winds of up to 50 knots.</span>
<span class="attribution"><span class="source">Mike Kinsela</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="People on a ship in high-vis jackets watch a cable lower a scientific instrument into the sea" src="https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504598/original/file-20230116-16-yajc4p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Two Argo floats will be part of an international program consisting of a fleet of robotic instruments that drift with the ocean currents to collect information from inside the ocean. Here you can see an Argo float being deployed at dawn while the night shift scientists watch on.</span>
<span class="attribution"><span class="source">Mike Kinsela</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>A big part of understanding the potential threat of tsunami is learning how the material from the submarine landslides along the eastern seaboard has moved down into the deep ocean. For example, does it go as a single, large slab of sediment, failing all at once? Or does it slowly break apart, with smaller pieces heading down slope one at a time as a slurry of sediment and water? </p>
<p>While Australia has a relatively low tsunami risk compared to other places around the world, we are still exposed and so should heed warnings from emergency services.</p>
<p>A recent tsunami to hit Australia was caused by the <a href="https://theconversation.com/waves-from-the-tonga-tsunami-are-still-being-felt-in-australia-and-even-a-50cm-surge-could-knock-you-off-your-feet-175056">underwater volcanic explosion in Tonga</a> in January last year. This brought waves of more than 80 centimetres to the Gold Coast, which could knock you off your feet.</p>
<h2>Mapping the seafloor surface</h2>
<p>We mapped areas of the seafloor with a level of precision not available to previous generations of hydrographers and map-makers in Australia. Some areas were nearly 5km deep and over 100 nautical miles from the coast.</p>
<p>To do this, we use a multibeam system. This involves sending out sound waves from the bottom of the ship in a wide cone-shape. These sound waves bounce off the seafloor back to the ship, giving us information about the depth of the seafloor and allowing us to map any features on its surface. </p>
<p>One feature we remapped was an area of the continental slope offshore of Yamba, New South Wales. Here we see cliffs up to a few hundred metres high – evidence of slope failure and sliding.</p>
<figure>
<style>
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<iframe frameborder="0" class="juxtapose2" width="100%" height="290px" src="https://cdn.knightlab.com/libs/juxtapose/latest/embed/index.html?uid=d05c1564-9ab6-11ed-b5bd-6595d9b17862"></iframe>
<figcaption>A section of seafloor off the coast of Yamba, NSW. The images show the mapped area before and after the voyage, clearly showing newly mapped areas and the large submarine landslide in the middle of the new mapping. Red indicates shallower areas on the continental shelf and purple indicates deeper areas, including the edge of the abyssal plain. The image is looking west towards the Australian continent. Data from CSIRO Marine National Facility. Maps by Elise Buller, Author provided</figcaption>
</figure>
<p>We also remapped the scar from the Bulli submarine landslide, which is the biggest submarine landslide identified on the Australian continental margin to date. At over 25km long and over 10km wide, the Bulli landslide off Wollongong in NSW removed 40 cubic kilometres of sediment from the edge of our continent. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A green, orange and yellow map" src="https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=299&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=299&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=299&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=376&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=376&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505768/original/file-20230123-7722-xurvux.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=376&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Drowned coastal dunes on the continental shelf, 60-100m below present sea level. These dunes were formed above water when sea levels were lower and were preserved as the coastline migrated over them thousands of years later. In mapping these drowned dunes and similar features, we uncovered new evidence of ancient coastlines. Orange and red colours indicate shallower areas, while green colours indicate deeper areas.</span>
<span class="attribution"><span class="source">Data from CSIRO Marine National Facility. Map by Mike Kinsela</span></span>
</figcaption>
</figure>
<p>But to get a true feel for the multibeam system’s capabilities, we also mapped the <a href="https://www.environment.nsw.gov.au/maritimeheritageapp/ViewSiteDetail.aspx?siteid=990">wreck of the Limerick</a>, a ship sunk by Japanese submarines off Australia’s east coast near Cape Byron in 1943. This also supported efforts to understand the current state of the famous shipwreck. </p>
<p>The wreck sits upside down in about 80m of water. To get a better view, we also lowered a camera to the torpedo hole in the side that sunk the ship.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An image of a wrecked ship on the seafloor" src="https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505732/original/file-20230122-52981-vj6l2t.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">A downward looking image of the stern of the MV Limerick wreck collected using the towed drop camera. The MV Limerick sits upside down on the seafloor.</span>
<span class="attribution"><span class="source">CSIRO MNF</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505733/original/file-20230122-49851-2iwitc.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">A sideways looking image of the stern of the MV Limerick wreck clearly showing the ships propellers.</span>
<span class="attribution"><span class="source">CSIRO MNF</span></span>
</figcaption>
</figure>
<h2>Beneath the seafloor</h2>
<p>Understanding what’s on the surface of the seafloor tells us a lot about what has happened over the last few hundreds of thousands of years. </p>
<p>But looking below the surface at the sediment layers beneath can tell us how the seafloor has evolved over millions of years. </p>
<p>To do this, we use techniques that send out pulses of sound that can penetrate the seafloor. These pulses then listen for return signals that bounce off interfaces of different types of sediments and rocks. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two men on a ship at night holding sediment" src="https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504605/original/file-20230116-14-nz2wpv.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">Samples being brought up from the seafloor is always a very exciting moment. Here, Chief Scientist A/ Prof Tom Hubble (right), inspects a freshly retrieved dredge sample late in the night at the end of his shift.</span>
<span class="attribution"><span class="source">Ali Jam Productions Photography</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Through these sub-surface imaging techniques, we have identified a range of interesting features. These include extinct river channels that were previously above the sea surface when sea levels were much lower in the past. </p>
<p>But to really tie things down we need physical samples of the seafloor and the sediment beneath it. Doing this is a challenge when you’re floating kilometres above the seafloor you want to sample.</p>
<p>So we use deep sea sediment corers and dredges, lowered down on winches with kilometres of cable. Corers punch into the seafloor and bring us back a column of sediment, while dredges drag along the bottom pulling up bits of mud and rocks, bringing them on board in big chain baskets. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three scientists peering into a sediment core" src="https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504604/original/file-20230116-20-nz2wpv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">One of the goals of our voyage was to help train the next generation of marine geoscientists. Here, one of the 12 student volunteers, Ruby (left), discusses a freshly retrieved and opened core with principal scientists A/ Prof Hannah Power and Dr Mike Kinsela.</span>
<span class="attribution"><span class="source">Murray Kendall</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Once on board, these samples are carefully analysed to look for key features that will help us piece together the puzzle of the continental margin’s evolution. Further work, such as radiocarbon dating and isotope analysis, is conducted in the months to years after the voyage to complete the analysis. </p>
<p>We’ve collected some fascinating new data that will keep us busy for years to come, but we also had time for table tennis competitions, a few movie nights, and a daily debate on which of the many delicious meals onboard was the favourite. </p>
<p>And we can’t forget the many spectacular sunrises and sunsets!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Person watching the sunset from a ship" src="https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504610/original/file-20230116-12-q15z73.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">Sunrises at sea are unforgettable.</span>
<span class="attribution"><span class="source">Hannah Power</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/184839/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hannah Power receives funding from the Australian Research Council, the NSW State Government State Emergency Management Program, the Queensland Resilience and Risk Reduction Fund, the New Zealand Ministry for Business, Innovation and Employment Endeavour Fund, and ship time from Australia's Marine National Facility. She is a member of the NSW Coastal Council.</span></em></p><p class="fine-print"><em><span>Kendall Mollison receives funding from the Queensland Resilience and Risk Reduction Fund, the New Zealand Ministry for Business, Innovation and Employment Endeavour Fund, and ship time from Australia's Marine National Facility administered by CSIRO. </span></em></p><p class="fine-print"><em><span>Michael Kinsela receives funding from the NSW Department of Planning and Environment and research vessel time from the Marine National Facility (MNF) administered by CSIRO. </span></em></p><p class="fine-print"><em><span>The voyage on RV Investigator described in this article was funded by the Australian Government as part of the CSIRO’s Marine National Facility (MNF) program.</span></em></p>
From a shipwreck to ancient dunes, these researchers created 3D visualisations of seafloor features around Australia – from as shallow as 22 metres to depths of over 4.8 kilometres.
Hannah Power, Associate Professor in Coastal and Marine Science, University of Newcastle
Kendall Mollison, Postdoctoral researcher, University of Newcastle
Michael Kinsela, Lecturer in Coastal and Ocean Geoscience, University of Newcastle
Tom Hubble, Associate Professor, University of Sydney
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/194642
2022-11-17T11:51:29Z
2022-11-17T11:51:29Z
African mountains are feeling the heat of climate change
<figure><img src="https://images.theconversation.com/files/495306/original/file-20221115-23-c6fqra.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mount Kenya</span> <span class="attribution"><span class="source">WanderingNomad / Getty IMages</span></span></figcaption></figure><p>Mountains are special places. They have distinctive climates that are generally cooler and wetter than surrounding lowlands, and they host plants, animals and landscapes that are uniquely found in these environments. However, mountains are under threat because of climate change, and this has an impact on every single property of mountains, including their climate, weathering and erosion processes, soils, ecosystems, water resources, geological hazards, regional economies, and cultural practices. </p>
<p>My <a href="https://peerj.com/articles/14253/">work</a> on the impacts of ongoing climate change in mountains highlights the sensitivity of mountain properties and processes to changes in temperature and precipitation – mainly expressed in mountains as snowfall. However, there is less understanding of mountain systems in Africa compared to other mountains globally. This article therefore focuses on mountain properties in Africa, why these are particularly sensitive to climate change, and why this is important.</p>
<h2>Ice and snow</h2>
<p>One key property of mountains worldwide is that they are often covered by snow and ice (glaciers). This reflects moist air and cold temperatures over mountain summits. Not only do snow and ice present unique habitats for plant and animal species, they also have a vital role in the regional climate systems of mountains. Snow and ice tend to be light in colour, so they reflect sunlight back out to space, keeping the land surface cold. This is called the <a href="https://scied.ucar.edu/learning-zone/how-climate-works/albedo-and-climate">albedo effect</a>. </p>
<p>However, if snowfall does not take place or the snow melts away, the mountain land surface remains dark. This means it absorbs rather than reflects the sun’s energy, making the surface warmer. This can cause more snowmelt, exposing more dark rocks, with more heating and melting. </p>
<p>The outcome of this process is that changing patterns of snowfall have big implications for mountain heat budgets. Mountains worldwide are already <a href="https://iccinet.org/statecryo22/">warming twice as fast</a> as the global average. This makes them particularly sensitive to climate change. </p>
<p>African mountains are not immune to climate change. Small glaciers still exist in three mountain massifs – Mount Kenya (Kenya), Kilimanjaro (Tanzania) and the Rwenzori mountains (Uganda) – but these are in <a href="https://wgms.ch/">rapid retreat</a>. They are also predicted to <a href="https://unesdoc.unesco.org/ark:/48223/pf0000383551">disappear entirely</a> by the middle of the century. Snowfall is also highly variable, such as over the <a href="https://earthobservatory.nasa.gov/images/88509/lesotho-sees-its-heaviest-snowfall-in-two-decades">Maloti-Drakensberg mountains</a> of southern Africa.</p>
<p>The full implications of this loss of ice and snow, and of climate change in African mountains more generally, have not been fully considered. Ice retreat in other deglacierising mountains worldwide leads to a substantial increase in hazards of different types, including rockfalls, landslides and debris flows. These hazards can also take place thousands of years after initial ice retreat. </p>
<p>This may mean that, even though the glaciers that exist in Africa today are very small, any resulting hazards could potentially be large and unpredictable in their timing and location. These are potentially future issues in African mountains. </p>
<p>Another important factor is how snow and ice melt across African mountains will affect their wider landscapes. Snow and ice often serve as water sources to surrounding communities, especially in locations that are water scarce, which includes East Africa. Water availability in the environment influences soils, ecosystems, river processes and the potential for flood and landslide hazards. </p>
<p>The presence of snow and ice therefore has wider environmental significance across mountain landscapes, and in ways that are not fully understood. </p>
<h2>Other important roles</h2>
<p>African mountains are also important for other reasons. For example, they host the Afromontane biogeographical region, a global <a href="https://www.cepf.net/our-work/biodiversity-hotspots/hotspots-defined">biodiversity hotspot</a> of endemic podocarp (conifer) forest species that extends as a corridor through upland areas of southern and eastern Africa. </p>
<p>Above the treeline, alpine pastures provide grazing land for herders, a key socioeconomic and cultural activity in remote mountains in Africa. </p>
<p>Summer and winter tourism – whether in South Africa or Morocco – is also linked closely to mountain landscapes, snow, water and the presence of endemic species. </p>
<p>All of these activities are under threat because of climate change. Mountain ecosystems are critically linked to temperature and precipitation conditions. Climate change may therefore pose problems for both the survival of keystone species and for overall biome integrity, especially where they are encroached by invasive species, agriculture and forestry. These changes also have secondary effects on ecosystem services, food, fuel and carbon storage. </p>
<p>Thus, mountains have a wide range of properties that are linked to climate, and a key question is how mountain systems as a whole will respond to climate change over future decades.</p>
<h2>Mountain communities</h2>
<p>Sustainable development of <a href="https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_CCP5.pdf">mountain communities</a>, where human activity responds to the changing nature of mountain systems, is a key strategy for minimising the impacts of climate change, both in mountains and in surrounding areas. </p>
<p>This can be done by monitoring and treating sources of hazard risk as a result of melting snow and ice, building resilient infrastructure and community resilience, and protecting mountains as sites of geological, ecological and cultural heritage. These actions can help limit climate change impacts on sensitive mountains in Africa and elsewhere.</p><img src="https://counter.theconversation.com/content/194642/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>
Mountain systems are sensitive to climate change. Loss of snow and ice sets off effects which have wide ranging consequences.
Jasper Knight, Professor of Physical Geography, University of the Witwatersrand
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/181627
2022-04-21T13:54:34Z
2022-04-21T13:54:34Z
How geology put a South African city at risk of landslides
<figure><img src="https://images.theconversation.com/files/459089/original/file-20220421-18-ts22r7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This aerial view shows the destruction at Umdloti beach north of Durban. Landslides and floods wreaked havoc.</span> <span class="attribution"><span class="source">Marco Longari/AFP via Getty Images</span></span></figcaption></figure><p>There had been suggestions that the catastrophic landslides in Durban and the greater eThekwini region of South Africa following floods in 2022 were due to <a href="https://www.dailymaverick.co.za/article/2022-04-14-explainer-why-kzn-was-flooded-and-why-its-likely-to-happen-again/?utm_source=top_reads_block&utm_campaign=south_africa">climate change</a> and <a href="https://www.dailymaverick.co.za/article/2022-04-18-kzn-flood-tragedy-exposes-dysfunctional-province-in-midst-of-governance-crisis/">maladministration</a>. While these factors played a role, the fact that landslides occurred comes as no surprise, considering the geology of the area.</p>
<p>eThekwini is a coastal metropolis characterised by hilly terrain dissected by several major rivers such as the Umgeni, Mlazi and Mbokodweni. The region is subtropical, but rains in recent years have been unprecedented and resulted in multiple landslides. </p>
<p>Some of the earliest studies of landslides in the region date to the <a href="https://doi.org/10.1016/0013-7952(75)90034-4">1930s</a>. Mitigation measures including zoning <a href="http://www.durban.gov.za/Documents/City_Government/development_planning_management/Bluff%20Slopes%20-%20Special%20Bylaws.pdf">regulations</a> are in place for some parts of the region. But knowledge of the geotechnical risks of the area didn’t prevent tragic disaster. </p>
<p>As a geotechnical engineer I study the effects of water on the stability of sloping ground. Many natural slopes are in a delicate state of equilibrium: the downward movement of the inclined soil is just balanced by the resisting strength between the soil grains.</p>
<p>When water is introduced, the water pressure pushes soil particles apart, reducing this strength. Also some soils, such as clays, are more slippery and present an even greater landslide risk. </p>
<p>In eThekwini, sloping ground, water and clay combined to leave devastation in their wake.</p>
<h2>Greater eThekwini geology</h2>
<p>Ground adjacent to the sea from Durban to Mtunzini (a coastal town 140km north of Durban) is almost exclusively made up of ancient red sand dunes termed the Berea formation. South of the Durban harbour these sands form a ridge called the Bluff and north of the harbour they form the Berea Ridge. In some places these sand dunes are extremely steep.</p>
<p>The sands of the Berea formation were subject to intense investigation in the late 1950s following landslides <a href="https://www.osti.gov/etdeweb/biblio/5230023">along the Bluff</a>. The strength of the Berea sands was not uncharacteristic for sandy material. But the Bluff slopes were steeper than would be expected based on the soil’s strength. The only reason the slopes hadn’t collapsed was that plant growth was reinforcing the soil.</p>
<p>The investigation showed the slopes’ stability was not significantly affected by rainfall. That makes sense as these slopes have been battered by storms over geological time. But concentrated flows from poorly controlled flood water or broken water pipes were found to be catastrophic.</p>
<p>The reason is that as the Berea sands have little to no clayey stickiness, or plasticity, they are extremely prone to erosion. When large torrents of water flow over the sands they simply erode to form <a href="https://www.timeslive.co.za/news/south-africa/2022-04-13-watch-aerial-footage-shows-severe-devastation-from-kzn-floods/">gulleys</a>. The video below clearly demonstrates the power of water over these loose sands.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/S_j9W31ScRQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Umdloti has been devastated by heavy rainfall, mudslides and landslides.</span></figcaption>
</figure>
<h2>Inland shales</h2>
<p>Inland from Durban are shales of the Pietermaritzburg formation. They dip down from their main exposure in the inland city of Pietermaritzburg towards the sea at Durban.</p>
<p>These shales were formed from thin layers of clay and silt deposited in slow-moving water bodies during the geological past. When exposed at the surface, the shales break down or weather. Depending on their mineral content, some layers weather to very slippery clay.</p>
<p>It only takes a small increase in water pressures along these layers to trigger a landslide. The shales are not very permeable, so it can take a long time for the water pressure to become high enough to cause instability. It could eventually happen as a result of seepage from leaking pipes or long rainy seasons.</p>
<p>The residential area of Clare Estate, which witnessed landslides during the <a href="https://www.nytimes.com/2022/04/12/world/africa/floods-mudslides-south-africa.html">flooding</a> in 2022, is built on these shales. Tragically this is not the first time landslides have occurred <a href="http://doi.org/10.13140/2.1.1871.3601">here</a>. Slides in these shales have been investigated since the <a href="https://doi.org/10.1016/0013-7952(75)90034-4">1930s</a>. </p>
<h2>Natal group sandstones</h2>
<p>Another part of the geology of eThekwini are the sandstones of the Natal group. These sandstones weather into a sandy material but there are also layers containing clay. While water can easily flow into the sandy layers it can become trapped by the clayey layers.</p>
<p>During heavy rainfall events this can cause excess water pressure, liquefying the sand so it runs like water. A review of landslides in the eThekwini region between 1971 and 1991 showed that when short rainfall events exceeded 20% of mean annual rainfall, landslides <a href="http://doi.org/10.1007/s002549900077">could be expected</a>.</p>
<p>During the 2022 floods, over 300mm fell over four days (9-11 April 2022), equating to <a href="https://www.weathersa.co.za/Documents/Corporate/Medrel12April2022_12042022142120.pdf">30% of mean annual rainfall</a>. This clearly exceeded the landslide threshold. The situation was made worse by the storms coming at the end of the rainy season when the ground was already saturated.</p>
<p>Sadly, the houses of the KwaNdengezi settlement near Durban were no match for the forces of nature unleashed by the deluge of water over those <a href="https://www.reuters.com/news/picture/heavy-rains-claim-45-lives-in-south-afri-idUSKCN2M41BT">three days</a>. Some houses were swept away as the ground gave way and others were simply too close to flood lines to withstand the surging water.</p>
<h2>Mitigation measures</h2>
<p>Landslides in the eThekwini region should come as no surprise. We know which areas are at risk and why. Zoning and early warning systems would seem to be logical measures to take. </p>
<p>The eThekwini municipality does have <a href="http://www.durban.gov.za/Documents/City_Government/development_planning_management/Bluff%20Slopes%20-%20Special%20Bylaws.pdf">by-laws in place for some risky areas like the Bluff</a> and it does publish maps <a href="http://gis.durban.gov.za/cmv-cgis/viewer/?config=cgisPublicViewer">highlighting areas of risk</a>. The 2022 landslides suggest more work is required to fully zone the region and to enforce by-laws.</p>
<p>Landslide mitigation is always difficult, though. Landslide zoning has met with fierce political resistance in Japan and the US as land devalues if marked as <a href="https://hdl.handle.net/10520/EJC189270">risky</a>. Landslide prediction systems are also costly to implement and can warn residents too late.</p>
<p>Anywhere in the world, the technical problems surrounding landslide mitigation are often the least challenging to solve. The real problems typically lie with social and political issues which require considerable finesse and thought to resolve.</p><img src="https://counter.theconversation.com/content/181627/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Charles MacRobert 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>
Sloping ground, water and clay combined to leave devastation in its wake in Durban.
Charles MacRobert, Senior lecturer, Stellenbosch University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/181360
2022-04-14T15:04:09Z
2022-04-14T15:04:09Z
Floods in South Africa: protecting people must include a focus on women and girls
<figure><img src="https://images.theconversation.com/files/458179/original/file-20220414-18-c45s0k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A general view of the damage in an informal settlement heavy rains, mudslides and winds in Durban, on April 13, 2022.</span> <span class="attribution"><span class="source">Rajesh Jantilal/AFP via Getty Images)</span></span></figcaption></figure><p>Climate change is one of the main factors contributing to recurring floods experienced in many parts of the world over the <a href="https://archive.ipcc.ch/publications_and_data/ar4/wg2/en/ch3s3-4-3.html#:%7E:text=Floods%20depend%20on%20precipitation%20intensity,%2C%20dams%2C%20or%20reservoirs">past years</a>. In 2021, the <a href="https://www.ipcc.ch/about/">Intergovernmental Panel on Climate Change</a> reported that emissions of greenhouse gases from human activities contributed approximately <a href="https://www.ipcc.ch/2021/08/09/ar6-wg1-20210809-pr/">1.1°C</a> of global warming between 1850 and 1900. Unless drastic measures are taken to <a href="https://www.ipcc.ch/2021/08/09/ar6-wg1-20210809-pr/">curb emissions</a> over the next 20 years, the global temperature is expected to warm by more than 1.5°C. This implies that if extreme measures are not taken, floods will continue to wreak havoc on many regions around the world.</p>
<p>The Durban (eThekwini) area of South Africa has experienced many floods over the recent years. They have wreaked havoc. For instance, in April 2019, <a href="https://floodlist.com/africa/south-africa-floods-kzn-eastern-cape-april-2019">a deadly flood and landslides hit the area</a>. The region is currently reeling from what is seen as the worst flood in the history of South Africa. More than 300 people have <a href="https://ewn.co.za/2022/04/13/death-toll-due-to-kwazulu-natal-s-devastating-floods-hits-253">lost their lives</a>. There is also excessive damage to infrastructure and homes.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/0AfLMNLlvsM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The worst flood in the history of South Africa.</span></figcaption>
</figure>
<p>When disastrous events like floods are combined with social inequities, their effects are much greater. Impoverished communities, which in South Africa are predominantly black communities, are more likely to face even worse effects. Owing to historical spatial and housing arrangements which were based on “race”, many black communities still occupy flood-prone informal settlements, exposing them to a higher risk of disaster. </p>
<p>After the floods in 2019 we undertook <a href="https://journals.sagepub.com/doi/abs/10.1177/00219096211069646">research</a> to explore the vulnerability and adaptation experiences of black women in eThekwini. We selected four local areas that had been severely affected by the flood, including Umlazi, Ntuzuma, Inanda and Kwamashu, for the case study. </p>
<p>The study explored the factors that shaped the vulnerability and adaptation experiences of women. We conducted face-to-face interviews and focused group discussions with a sample community of black African women who had experienced flood effects in the selected localities.</p>
<p>Our <a href="https://journals.sagepub.com/doi/abs/10.1177/00219096211069646">research</a> showed that gender interacts with other social factors to expose black women in particular to the effects of floods.</p>
<p>The recent downpours in eThekwini are a stark reminder that the South African government must invest significantly in flood resilience and adaptation mechanisms. Extra attention must be given to vulnerable communities and individuals to ensure equity and justice in the steps to mitigate the impact of climate change.</p>
<h2>Poverty and vulnerability</h2>
<p>Our research showed, in empirical terms, that women and girls living in poverty face many forms of discrimination and pressure during flood disasters. Severe flood wipes away people’s sources of livelihood, plunging them into more extreme poverty conditions. The interviews showed that the burden of providing food and other essentials to the family fell to the women in these localities. We also found that the vulnerability of women was shaped by intersectional gendered power relations. This, in turn, entrenched abusive behaviour from some of the men in the family. </p>
<p>Our study also showed that some interventions exposed women and girls to possible abuse. For example, one response to flooding from the eThekwini municipality has been to open up community halls for victims. This forces men, women and girls to cohabit in the refuge halls, exposing women to potential abuse while in these supposedly “safe” spaces.</p>
<p>This is not to say that the women were always victims. Many said they were aware that they had to shoulder much of the responsibility for the family’s welfare. This gave them agency and strength, which in turn made them more adaptive. </p>
<p>For many women, especially single parents, the fear that any impending flood events would affect their children gave them the ability to find proactive ways of adapting.</p>
<p>We also found that the women had knowledge arising from their experience that could be useful in complementing municipal <a href="https://theconversation.com/local-knowledge-adds-value-to-mapping-flood-risk-in-south-africas-informal-settlements-181304">management interventions</a>. Women were open to being trained in simple flood management skills, such as how to divert running water away from the house. Training of this kind could be organised in small groups across different wards.</p>
<h2>The implications</h2>
<p>To address gender equity in climate adaptation, we recommend a shift in addressing black women’s vulnerability. Adaptation planners need to take the different dimensions of vulnerability into consideration when putting together plans. Experience shows that adaptation planners focus on improving infrastructures. But this isn’t enough. A wider perspective is needed that addresses both the vulnerability of the built environment (physical vulnerability) as well as social aspects, such as the vulnerability of women and girls. Even here, a nuanced approach needs to be taken given that women face different challenges based on where they live and their social, racial and economic identities.</p><img src="https://counter.theconversation.com/content/181360/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors 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>
Women and girls living in poverty face many forms of discrimination and pressure during events like flood disasters.
Fidelis Udo, Researcher, University of KwaZulu-Natal
Maheshvari Naidu, Full Professor in Anthropology, University of KwaZulu-Natal
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/175247
2022-01-23T19:09:15Z
2022-01-23T19:09:15Z
5 ways climate change increases the threat of tsunamis, from collapsing ice shelves to sea level rise
<figure><img src="https://images.theconversation.com/files/441876/original/file-20220121-9541-as4ejs.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C2983%2C1986&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 enormous eruption of the underwater volcano in Tonga, Hunga Tonga-Hunga Ha'apai, triggered a <a href="https://www.reuters.com/business/environment/tonga-volcano-generates-tsunami-us-tsunami-monitor-said-2022-01-15/">tsunami</a> that reached countries all around the Pacific rim, even causing a <a href="https://apnews.com/article/oil-spills-business-tonga-peru-trending-news-3a92a17e2101945afcb22f5eb5bfb2ad?utm_campaign=SocialFlow&utm_source=Twitter&utm_medium=AP">disastrous oil spill</a> along 21 beaches in Peru. </p>
<p>In Tonga, waves about 2 metres high were recorded before the sea level gauge failed, <a href="https://twitter.com/ConsulateKoT/status/1483384039826464768/photo/1">and waves of up to 15m</a> hit the west coasts of Tongatapu Islands, ‘Eua, and Ha’apai Islands. Volcanic activity could continue for weeks or months, but it’s hard to predict if or when there’ll be another such powerful eruption.</p>
<p>Most tsunamis are caused by earthquakes, but a <a href="http://tsunami.org/what-causes-a-tsunami/">significant percentage</a> (about 15%) are caused by landslides or volcanoes. Some of these may be interlinked – for example, landslide tsunamis are often triggered by earthquakes or volcanic eruptions. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1482437044785889286"}"></div></p>
<p>But does <a href="https://www.un.org/en/climatechange/what-is-climate-change">climate change</a> also play a role? As the planet warms, we’re seeing more <a href="https://www.usgs.gov/faqs/how-can-climate-change-affect-natural-disasters">frequent and intense</a> storms and cyclones, the melting of glaciers and ice caps, and sea levels rising.
Climate change, however, doesn’t just affect the atmosphere and oceans, it affects the Earth’s crust as well. </p>
<p><a href="https://www.reuters.com/article/us-climate-geology-idUSTRE58F62I20090916">Climate-linked</a> geological changes can increase the incidence of earthquakes and volcanic eruptions which, in turn, can exacerbate the threat of tsunamis. Here are five ways this can happen.</p>
<h2>1. Sea level rise</h2>
<p>If greenhouse gas emissions remain at high rates, the average global sea level is <a href="https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities">projected to rise</a> between 60 centimetres and 1.1m. <a href="https://www.un.org/sustainabledevelopment/wp-content/uploads/2017/05/Ocean-fact-sheet-package.pdf">Almost two thirds</a> of the world’s cities with populations over five million are at risk.</p>
<p>Rising sea levels not only make coastal communities more vulnerable to flooding from storms, but also tsunamis. Even modest rises in sea level will dramatically increase the frequency and intensity of flooding when a tsunami occurs, as the tsunami can travel further inland. </p>
<p>For example, <a href="https://www.science.org/doi/10.1126/sciadv.aat1180">a 2018 study</a> showed only a 50 centimetre rise would double the frequency of tsunami-induced flooding in Macau, China. This means in future, smaller tsunamis could have the same impact as larger tsunamis would today.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1483741932970983428"}"></div></p>
<h2>2. Landslides</h2>
<p>A warming climate can increase the risk of both submarine (underwater) and aerial (above ground) landslides, thereby increasing the risk of local tsunamis. </p>
<p>The <a href="https://www.nrdc.org/stories/permafrost-everything-you-need-know">melting of permafrost</a> (frozen soil) at high latitudes decreases soil stability, making it more susceptible to erosion and landslides. More <a href="https://climate.nasa.gov/news/2951/climate-change-could-trigger-more-landslides-in-high-mountain-asia/">intense rainfall</a> can trigger landslides, too, as storms become more frequent under climate change. </p>
<p><a href="https://www.usgs.gov/faqs/how-do-landslides-cause-tsunamis#:%7E:text=Tsunamis%20are%20large%2C%20potentially%20deadly,a%20result%20of%20submarine%20earthquakes.&text=Tsunamis%20can%20be%20generated%20on,a%20rapidly%20moving%20underwater%20landslide.">Tsunamis can be generated</a> on impact as a landslide enters the water, or as water is moved by a rapid underwater landslide. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/waves-from-the-tonga-tsunami-are-still-being-felt-in-australia-and-even-a-50cm-surge-could-knock-you-off-your-feet-175056">Waves from the Tonga tsunami are still being felt in Australia – and even a 50cm surge could knock you off your feet</a>
</strong>
</em>
</p>
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<p>In general, tsunami waves generated from landslides or rock falls dissipate quickly and don’t travel as far as tsunamis generated from earthquakes, but they can still lead to huge waves locally.</p>
<p>In Alaska, US, glacial retreat and melting permafrost has exposed unstable slopes. In 2015, this melting caused a landslide that sent 180 million tonnes of rock into a narrow fjord, <a href="https://www.nature.com/articles/s41598-018-30475-w">generating a tsunami reaching 193m high</a> – one of the highest ever recorded worldwide. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441884/original/file-20220121-8856-1regaso.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Scientists survey damage from a megatsunami in Taan Fiord that had occurred in October, 2015 after a massive landslide.</span>
<span class="attribution"><span class="source">Peter Haeussler, United States Geological Survey Alaska Science Center/Wikimedia</span></span>
</figcaption>
</figure>
<p>Other areas at risk include <a href="https://www.sciencedirect.com/science/article/pii/S0921818121000849">northwest British Columbia</a> in Canada, and the Barry Arm in Alaska, where an <a href="https://dggs.alaska.gov/hazards/barry-arm-landslide.html">unstable mountain slope</a> at the toe of the Barry Glacier has the potential to fail and <a href="https://www.woodwellclimate.org/wp-content/uploads/2020/05/Letter-to-Stakeholders_-Barry-Arm-Landslide-Final.pdf">generate a severe tsunami</a> in the next 20 years.</p>
<h2>3. Iceberg calving and collapsing ice shelves</h2>
<p>Global warming is accelerating the <a href="https://www.businessinsider.com.au/chasing-ice-glacier-calving-climate-change-2014-10?r=US&IR=T">rate of iceberg calving</a> – when chunks of ice fall into the ocean.</p>
<p>Studies predict large ice shelves, such as the Thwaites Glacier in Antarctica, will <a href="https://news.climate.columbia.edu/2021/12/17/crucial-antarctic-glacier-likely-to-collapse-much-earlier-than-expected/">likely collapse</a> in the next five to ten years. Likewise, the Greenland ice sheet is <a href="https://climate.nasa.gov/news/3062/warming-seas-are-accelerating-greenlands-glacier-retreat/">thinning and retreating</a> at an alarming rate.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Iceberg near ship" src="https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/441878/original/file-20220121-8497-jjkh3d.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">Icebergs colliding with the seafloor can trigger underwater landslides.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>While much of the current research focus is on the sea level risk associated with melting and collapse of glaciers and ice sheets, there’s also a <a href="https://nhess.copernicus.org/articles/12/415/2012/">tsunami risk</a> from the calving and breakup process. </p>
<p>Wandering icebergs can trigger <a href="https://www.nature.com/articles/s41561-021-00767-4">submarine landslides and tsunamis</a> thousands of kilometres from the iceberg’s original source, as they hit unstable sediments on the seafloor.</p>
<h2>4. Volcanic activity from ice melting</h2>
<p>About 12,000 years ago, the last glacial period (“ice age”) ended and the melting ice triggered a dramatic <a href="https://eprints.lancs.ac.uk/id/eprint/32995/2/Tuffen_PTRSL.pdf">increase in volcanic activity</a>.</p>
<p>The correlation between climate warming and more volcanic eruptions isn’t yet well constrained or understood. But it may be related to <a href="https://pubs.er.usgs.gov/publication/70182772">changes in</a> stress to the Earth’s crust as the weight of ice is removed, and a phenomenon called “<a href="http://people.rses.anu.edu.au/lambeck_k/pdf/152.pdf">isostatic rebound</a>” – the long-term uplift of land in response to the removal of ice sheets. </p>
<p>If this correlation holds for the current period of climate warming and melting of ice in high latitudes, there’ll be an increased risk of volcanic eruptions and associated hazards, including tsunamis.</p>
<h2>5. Increased earthquakes</h2>
<p>There are a number ways climate change can increase the frequency of earthquakes, and so increase tsunami risk. </p>
<p>First, the weight of ice sheets may be <a href="https://royalsocietypublishing.org/doi/10.1098/rsta.2010.0031">suppressing fault movement and earthquakes</a>. When the ice melts, the isostatic rebound (land uplift) is accompanied by an increase in earthquakes and fault movement as the crust adjusts to the loss of weight. </p>
<p>We may have seen this already in <a href="http://www.geotimes.org/oct04/NN_glacier.html">Alaska</a>, where melting glaciers reduced the stability of faults, inducing many small earthquakes and <a href="https://www.sciencedirect.com/science/article/pii/S0921818104000487?casa_token=BGo_KzIOuJkAAAAA:UHyQvV-tvVulwAfvOFPJILcG2206iyZhOM9TCVS_VAh0UdLimWrfu_NJRTHJVtwlKBL0cfA">possibly the magnitude 7.2 St Elias earthquake</a> in 1979.</p>
<p>Another factor is low air pressure associated with storms and typhoons, which studies have also shown can trigger earthquakes in areas where the Earth’s crust is already under stress. Even relatively small changes in air pressure can trigger fault movements, as <a href="https://www.nature.com/articles/nature08042">an analysis</a> of earthquakes between 2002 and 2007 in eastern Taiwan identified. </p>
<h2>So how can we prepare?</h2>
<p>Many mitigation strategies for climate change should also include elements to improve tsunami preparedness. </p>
<p>This could include incorporating projected sea level rise into tsunami prediction models, and in building codes for infrastructure along vulnerable coastlines. </p>
<p>Researchers can also ensure scientific models of climate impacts include the projected increase in earthquakes, landslides and volcanic activity, and the increased tsunami risk this will bring.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-causes-a-tsunami-an-ocean-scientist-explains-the-physics-of-these-destructive-waves-175213">What causes a tsunami? An ocean scientist explains the physics of these destructive waves</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/175247/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jane Cunneen 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>
Climate change doesn’t just affect the atmosphere and the oceans, it affects the Earth’s crust as well.
Jane Cunneen, Adjunct Research Fellow, Curtin University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/129390
2020-01-13T14:42:09Z
2020-01-13T14:42:09Z
How music helps us understand displaced communities in Uganda
<figure><img src="https://images.theconversation.com/files/309089/original/file-20200108-107204-1rjw7i3.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">EPA/STEPHEN MORRISON</span></span></figcaption></figure><p>Studies <a href="https://www.cambridge.org/core/journals/journal-of-american-studies/article/adelaida-reyes-songs-of-the-caged-songs-of-the-free-music-and-the-vietnamese-refugee-experience-philadelphia-temple-university-press-1999-5950-cloth-1995-paper-pp-218-isbn-1-56639-685-9-1-56639-686-7/4AF1FBCCC97A2B0A95709A803C62AED3">dealing with displacement</a> have shown that music is among the vehicles <a href="https://www.unhcr.org/figures-at-a-glance.html">the displaced</a> adopt to communicate their grievances. </p>
<p>For the Ugandan survivors of a landslide who are relocated to a faraway camp, for example, music becomes the most effective mode of communication. That’s because music can play a dual role: it entertains while at the same time passing on specific messages to listeners. And due to its ability to use <a href="https://www.grammarly.com/blog/metaphor/">metaphors</a>, music communicates on different levels to different people. One song can be interpreted differently by more than one person. </p>
<p>Because of these unique qualities, <a href="https://books.google.co.za/books?id=Tc5RCwAAQBAJ&pg=PA285&lpg=PA285&dq=Makwa,+Dominic+D.B.+This+Is+the+Life+We+Have:+Music+and+Displacement&source=bl&ots=2Tp05yRiLb&sig=ACfU3U3yMDaVYzriJtFIoGHTFuoEovckew&hl=en&sa=X&ved=2ahUKEwizl8q1kfbmAhVMdcAKHTcWBAUQ6AEwAHoECAoQAQ#v=onepage&q=Makwa%2C%20Dominic%20D.B.%20This%20Is%20the%20Life%20We%20Have%3A%20Music%20and%20Displacement&f=false">my research found</a>, it is easier to communicate through music to deliver important and sensitive messages that cannot be comfortably conveyed through daily speech. </p>
<h2>The Nametsi landslide</h2>
<p>Bududa is a district in Bugisu, located along the slopes of Mount Elgon in Eastern Uganda. It has had a <a href="https://www.aljazeera.com/news/2019/06/dead-dozens-missing-landslides-uganda-190605115548553.html">history of landslides</a> which have negatively affected the life of its inhabitants. </p>
<p><a href="https://www.researchgate.net/publication/321331197_Landslides_in_Africa_the_Emerging_Trends_of_Slope_Catastrophes_and_the_Factors_Driving_Instability_in_the_Continent">Landslides</a> involve soil mixed with boulders moving down steep slopes and burying people’s farms, animals and houses in the process. Although landslides leave behind survivors, many people are buried under the rubble. </p>
<p><a href="https://www.who.int/hac/crises/uga/sitreps/uganda_sitrrep_5march2010.pdf">The Nametsi landslide</a> put Bududa in the headlines. It occurred on 1 March 2010 and is the <a href="https://www.researchgate.net/publication/273136616_The_Bududa_landslide_of_1_March_2010">most severe landslide</a> recorded in Uganda’s history. It destroyed entire villages – hitting Nametsi, Namasheti and Kubehwo in the Bukalasi sub county. The landslide officially killed about 100 people but left a further 300 people unaccounted for and over 1,000 survivors homeless. Because there was no place to resettle survivors in Bududa, the Ugandan government relocated them to Panyadoli Camp in Southwestern Uganda, adjacent to the Kiryandongo Refugee Camp, the latter created for international refugees. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309091/original/file-20200108-107204-17xnibn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Workers search for bodies at the scene of a landslide in Bududa district in 2012. The eastern Ugandan region is regularly devastated by these natural disasters.</span>
<span class="attribution"><span class="source">EPA-EFE/RONALD KABUUBI</span></span>
</figcaption>
</figure>
<h2>Life in Panyadoli Camp</h2>
<p>Panyadoli is located in Kiryandongo District, far from Bududa, with almost 400km between them. Despite the odd hill, the place is generally flat. The sparse population explains the abundant bushes, which harbour snakes and other animals. In this place, there are almost no streams where people can fetch water. When the landslide survivors arrived, the only source of water was one borehole to serve a community of over 300 people. Other social amenities including schools, health facilities and markets were <a href="https://reliefweb.int/report/uganda/why-bududa-landslide-victims-decline-resettlement">far from adequate</a>. </p>
<p>Apart from cultivating the two-and-a-half acre piece of land the government allocated them, few economic opportunities were available to the landslide survivors. They could not sell coffee or engage in other businesses as they had in Bududa. To compound it all, most landslide survivors could confidently speak only one language – <a href="https://www.researchgate.net/publication/282669972_A_GENEALOGICAL_RECONSTRUCTION_OF_LUBUKUSU_LUMASABA_AND_LUGISU">Lugisu</a>. Lugisu is the language of the Bagisu, who are the majority in Bududa. Communication as they interacted with host communities in healthcare centres, schools and markets was a huge challenge. </p>
<p>As most of the landslide survivors had lived in their villages all of their lives without ever relocating, I wanted to find out how they were coping with life in their new home. What facilities were at their disposal? How different are they from what they had in Bududa? In cases where they were not happy with the government’s intervention, how do they communicate their grievances?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309421/original/file-20200110-97126-1c0gjsq.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">A typical scene at a resettlement camp in Uganda, where jerry cans queue up at the only water source in the camp.</span>
<span class="attribution"><span class="source">Dorah Ntunga/Oxfam/FLICKR</span></span>
</figcaption>
</figure>
<h2>The story of a song</h2>
<p>Different forms of communication were used by Bududa landslide survivors to articulate their experiences in Panyadoli Camp. Having meetings with different stakeholders was one of the means of communication. However, because of the ability to disguise the message through entertainment, music became the main vehicle for communication. </p>
<p>Music was adopted because these survivors did not feel comfortable to complain directly about land, the social amenities provided and how contracts for constructing their houses were awarded. Another tricky issue was theft, where they thought the police knew the people who were stealing things in the camp but were just covering up. The landslide survivors noted that whenever they tried to complain about these issues, authorities looked at them as ungrateful people who could not appreciate anything, though they’d had nothing when they were relocated to this camp. </p>
<p>When women from the Bududa Women Association performed the song Obu Bulamu Bweesi Khuli Nabwo (This Is The Life We Have), their aim was to dramatise these issues that were negatively affecting them. </p>
<p>Through this song, women talked about the nature of the shelters they were staying in. They talked about weak tarpaulins they had received from the Office of the Prime Minister and how these exposed them to rain. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fWHGlpodZoY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The author recorded the women of the camp performing This Is The Life We Have.</span></figcaption>
</figure>
<p>They also used this song to talk about corruption in the camp. A case in point was when they argued that the seeds they had received for planting were not supplied by the Office of the Prime Minister as had been claimed. The seeds had in fact been given by the church. </p>
<p>The song communicated about poor health services, waterlogged fields, the shortage of food and their inability to speak English and Kiswahili, the ‘languages of the camp’. </p>
<p>And it addresses the thefts in the camp. The lyrics point to the police guarding the camp as the root cause of this problem. The song was also a call for transparency around the awarding of contracts for the construction of houses for the landslide survivors.</p>
<h2>The power of metaphor</h2>
<p>This song used metaphors to embed its messages. For example by singing, ‘Water has finished our food’, these women were indirectly saying that the plots of land given to them were waterlogged and therefore could not yield much food. Similarly, by singing, ‘Up there, they (children) were going to school’, they were referring to Bududa as a place with schools where their children used to get education. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/309094/original/file-20200108-107200-4tp4vy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&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 village woman mourns as she sits at the scene of a landslide in Budada, Uganda.</span>
<span class="attribution"><span class="source">EPA/RONALD KABUUBI</span></span>
</figcaption>
</figure>
<p>Songs of this nature could be sung before any audience. However, I also realised that such music was mainly performed before ‘visitors’ from Bududa. As other scholars have <a href="https://searchworks.stanford.edu/view/4767893">argued</a>, displaced people never stop associating with those they left behind. Anybody who visits them is looked at as a possible mediator, someone who can present their grievances to relevant authorities. By singing this song in my presence, the landslide survivors looked at me as someone who could readily pass on their message to government and other authorities that could help them. </p>
<p>This research is significant in the contemporary period especially as relocation of people across the world has become rampant due to political instability and natural disasters. As governments and the United Nations grapple with resettling people, they need to pay attention to alternative means that displaced people use to communicate their concerns. Such communication channels can be harnessed to understand exactly what such people want in order to avoid tension which may cause more unrest.</p><img src="https://counter.theconversation.com/content/129390/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dominic D.B. Makwa 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>
Displaced by a landslide, Ugandan survivors could not speak the language of the region where they were relocated - but music allowed them a voice.
Dominic D.B. Makwa, Lecturer, Makerere University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/127645
2019-12-02T16:13:08Z
2019-12-02T16:13:08Z
Mars: we may have solved the mystery of how its landslides form
<figure><img src="https://images.theconversation.com/files/304533/original/file-20191130-156099-nlzv2v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mars landslide. The blue area represents the landslide debris.</span> </figcaption></figure><p>Some landslides on Mars seem to defy an important law of physics. <a href="https://eos.org/research-spotlights/makes-long-runout-landslides-mobile">“Long, runout landslides”</a> are formed by huge volumes of rock and soil moving downslope, largely due to the force of gravity. But their power is hard to account for. With volumes exceeding that of the Empire State Building, they move at high speeds of up to 360 kilometres per hour over flat surfaces for up to tens of kilometres. </p>
<p>This seems to indicate that there is no or very little friction present. Friction is the fundamental physical force resisting motion of one surface sliding relative to another. The lack of friction in these long landslides – compared to normal, shorter ones – is comparable to suddenly losing traction when driving a car on a wet or icy surface: you pull the breaks, but you stop well beyond where you intended.</p>
<p>To explain this conundrum, scientists <a href="https://www.sciencedirect.com/science/article/abs/pii/S0032063311001589?via%3Dihub">have suggested</a> that these landslides must have taken place at a time when the area was covered in ice. But in our recent paper, <a href="https://www.nature.com/articles/s41467-019-12734-0">published in Nature Communications</a>, we have come up with another answer. The results could help us protect against harmful landslides – both on Mars and on Earth.</p>
<p>Geologists have discussed the odd behaviour of martian landslides since they were first identified nearly half a century ago. These types of landslides <a href="https://en.wikipedia.org/wiki/Sturzstrom">have occurred on Earth</a> in its geological history too, but because our planet is active with erosion, atmospheric weathering (wind, rain and so on), vegetation cover and plate tectonics, their evidence can be masked if not completely erased.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304532/original/file-20191130-156103-1m0o7kn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Cerberus Fossae, with steep slopes having active landslides.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>This is the reason why we study long, runout landslides on other planets in our solar system. There are in fact a number of advantages of doing so. On the red planet, landslides and their morphological features are well preserved for millions of years because of the reduced erosion rate and absence of vegetation and plate tectonics. </p>
<p>We now also have available satellite images of the surface of Mars with a resolution that is better than what we have for some regions here on Earth. As a result, we can conduct observations and measurements that are not so granted on our planet.</p>
<h2>New findings</h2>
<p>Valles Marineris on Mars is a 4,000km <a href="https://theconversation.com/from-silicon-valley-to-valles-marineris-is-humanity-ready-for-elon-musks-mars-vision-66244">long, straight canyon</a>, as deep as 8km. It is situated just south of the martian equator, where extraordinary examples of long, runout landslides are present. In our study, we focused on one of the best-preserved landslides – with a size similar to the entire State of Rhode Island in the US.</p>
<p>The landslide shows long ridges that extend in the direction of the movement for almost the entire length of the deposit. As mentioned, these ridges have previously been interpreted to be a result of underlying ice at the time of the landslide. This hypothesis <a href="https://www.researchgate.net/figure/a-The-Sherman-landslides-fallen-in-Alaska-in-1964-Courtesy-USGS-b-La-Perouse_fig3_320926736">is supported by the fact</a> that similar structures have been observed on terrestrial landslides on glaciers.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/JUbQM47QXwQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Based on this similarity, the presence of the ridges on martian landslides have been used in support of the theory that Mars <a href="https://www.theverge.com/2016/5/26/11772702/mars-ice-age-climate-change">was once covered in ice</a>. But the presence of glaciers and their timing at such martian latitude <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103517308333">is hotly debated</a>. What’s more, it is still unclear which exact mechanisms created these ridges during the ice age.</p>
<p>To investigate whether there may be other explanations, we made computer models of the landslide called <a href="https://en.wikipedia.org/wiki/Digital_elevation_model">“digital elevation” models</a>. These are 3D representations of terrain, obtained from high-resolution satellite images and the terrain’s elevation data. From this data, we could calculate the thickness of the landslides, the length of the ridges, their height and their wavelength – that is the distance from crest to crest between two ridges next to each other. </p>
<p>We showed that the wavelength of the ridges is constantly two to three times the value of the thickness of the landslide. This relationship has previously <a href="https://hal.archives-ouvertes.fr/hal-01432240/file/PRLpeigne01.pdf">only been demonstrated in laboratory experiments</a> – which do not involve ice – and our result is the first field evidence. </p>
<p>This suggests that ice is not a necessary condition for the formation of the long ridges. Instead, we propose that the ridges could have formed at high speeds due to underlying layers of unstable, light rocks. These layers would have been created by vibrations and collisions of rock particles at the bottom of the slide with the rough surface of the valley. This would have initiated a “convection process” – transfer of heat by movement – that caused upper denser and heavier layers of rock to fall and lighter rocks to rise. </p>
<p>Once we had accounted for this mechanical instability – and coupled it with the movement at phenomenal high speed of the slide – we could show that vortices extending in the direction of the landslide’s movement were generated, giving rise to the long ridges that we observe on the surface of the landslide.</p>
<p>The findings are important. On Earth, the incomplete record of such catastrophic events can lead to misinterpretations and overlooking of the hazard of these landslides. But, as they happened in the past, they will happen in the future, posing great risk to infrastructures and people lives. </p>
<p>Turning our look further away to understand what is near us is sometimes a fundamental change of perspective. But, as we know landslides are also still happening on Mars, these studies will set the background knowledge for risk mitigation of human settlements on Mars, no matter how far in the future they are still.</p><img src="https://counter.theconversation.com/content/127645/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Giulia Magnarini receives funding from the UK Science and Technology Facility Council (STFC). </span></em></p><p class="fine-print"><em><span>Tom Mitchell receives funding from the UK Science and Technology Facility Council (STFC)</span></em></p>
New research on landslides on Mars could help protect against devastating landslides on Earth.
Giulia Magnarini, Phd Candidate of Earth Sciences, UCL
Tom Mitchell, Associate Professor of Earthquake Geology and Rock Physics, UCL
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/114702
2019-04-03T12:55:15Z
2019-04-03T12:55:15Z
Thawing permafrost is triggering thousands of landslides across the Arctic
<figure><img src="https://images.theconversation.com/files/267326/original/file-20190403-177171-15anjrd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Mackenzie River carves its way through the permafrost tundra of northern Canada.</span> <span class="attribution"><span class="source">inEthos Design / shutterstock</span></span></figcaption></figure><p>Early spring temperatures in the town of Deadhorse, on the north coast of Alaska, average -17°C. But with global warming affecting the Arctic more than anywhere, things are changing fast. At the end of March 2019, temperatures in Deadhorse hit 3°C, a whole <a href="https://www.accuweather.com/en/us/deadhorse-ak/99734/march-weather/331774?monyr=3/1/2019">20°C warmer</a> than the long-term seasonal average.</p>
<p>Such huge variations are not normal or natural, and it is important we understand their long term environmental impacts. Now, scientists working on an island off the north coast of Canada, relatively near to Deadhorse, have discovered evidence that warming in the Arctic is triggering <a href="https://www.nature.com/articles/s41467-019-09314-7">thousands of landslides</a> that could reshape the landscape for good.</p>
<p>The landslides are found in those high latitude areas where the ground consists of frozen soil and rock, known as “permafrost”. Closer to the poles, and at higher elevations, the surface can be frozen all year. Where temperatures are slightly less cold in the summer, perhaps because of a lower altitude or a greater distance from the pole, the surface of the permafrost melts most years. This melted layer is often saturated with water and thus is very weak, creating boggy conditions when the thaw develops. And where the permafrost is on a slope, melting often rapidly leads to instability, resulting in landslides. </p>
<p>As temperatures rise, those “summer months” above freezing can stretch into spring and autumn, the hottest days become hotter, and <a href="https://insideclimatenews.org/news/16012019/permafrost-thaw-climate-change-temperature-data-arctic-antarctica-mountains-study">large areas of permafrost are melting</a>. One potential impact is an increase in landslides, and recent studies have suggested that there is some evidence that this might be occurring on some <a href="https://journals.sagepub.com/doi/full/10.1177/0959683618798165">high altitude slopes</a>. </p>
<p>But the latest research from Canada, published in the journal <a href="https://www.nature.com/articles/s41467-019-09314-7">Nature Communications</a>, has demonstrated a dramatic increase in landslides in recent years – even at sea level. The researchers focused on Banks Island, an expanse of treeless tundra about the size of Sri Lanka or Ireland, with 68,000 muskoxen and just <a href="https://www12.statcan.gc.ca/census-recensement/2011/dp-pd/prof/details/page.cfm?Lang=E&Geo1=CSD&Code1=6101041&Geo2=PR&Code2=61&Data=Count&SearchText=Sachs%20Harbour&SearchType=Begins&SearchPR=01&B1=All&GeoLevel=PR&GeoCode=6101041&TABID=1">112 humans</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=622&fit=crop&dpr=1 600w, https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=622&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=622&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=781&fit=crop&dpr=1 754w, https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=781&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/267300/original/file-20190403-177163-m5xmpc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=781&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Permafrost in the Arctic. Banks Island is marked in red, Deadhorse in blue.</span>
<span class="attribution"><span class="source">NSIDC / Philippe Rekacewicz, UNEP/GRID-Arendal</span></span>
</figcaption>
</figure>
<p>They looked at a particular type of landslide known as “retrogressive thaw slumps” which can occur on comparatively gentle slopes when permafrost thaws. These landslides generally move slowly downhill, but what makes them particularly problematic is that once they start they tend to grow, and it is very difficult to arrest their development. </p>
<p>The team looked for signs of these landslides in archive imagery of Banks Island between 1984 and 2015. The results were dramatic: in 1984 only 63 active retrogressive thaw slumps could be identified, but by 2013 this number had increased to 4,077 – a 60-fold increase. Mapping the number of new landslides occurring each year over the study period, scientists realised that many more landslides developed in years with particularly warm summers. In the four warmest summers – 1999, 2011, 2012 and 2013 – almost 3,900 landslides developed.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=335&fit=crop&dpr=1 600w, https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=335&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=335&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=421&fit=crop&dpr=1 754w, https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=421&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/267120/original/file-20190402-177193-uthv9q.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=421&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Just 63 active landslides (red dots) in 1984 became 4,077 by 2013.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41467-019-09314-7">Lewkowicz et al</a></span>
</figcaption>
</figure>
<h2>This could be happening right across the Arctic</h2>
<p>The study has significant implications. First, it shows a dramatic increase in the rate of permafrost degradation through landsliding. Most of the new landslides are now causing substantial erosion as the released sediment moves into watercourses and will cause changes in lakes and rivers even away from the landslides. </p>
<p>Second, it is clear that these changes are associated with years with high summer temperatures. While this study only looked at a single – albeit very large – island in Canada, there is nothing exceptional about this region climatically or geologically, which suggests that something similar will be happening in many other permafrost areas.</p>
<p>And finally, rising temperatures in the Arctic mean permafrost is likely to degrade at a dramatically increased rate. Using the IPCC climate projections, in this area alone the researchers expect 10,000 or more new landslides per decade by 2075. If this is extended across other permafrost areas in Canada, Siberia and beyond, high latitude climate change will have a major impact on the landscape. This is likely to alter the ecosystems in these areas, but as yet it is impossible to estimate the ways in which they will change.</p>
<p>Through time we are getting a better sense of how landscapes are responding to changes in climate. It is clear that permafrost is extremely sensitive to change – and the effects are likely to be profound.</p>
<hr>
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<img alt="" src="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=140&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=140&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=140&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263883/original/file-20190314-28475-1mzxjur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=176&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/imagine-newsletter-researchers-think-of-a-world-with-climate-action-113443?utm_source=TCUK&utm_medium=linkback&utm_campaign=TCUKengagement&utm_content=Imagineheader1114702">Click here to subscribe to our climate action newsletter. Climate change is inevitable. Our response to it isn’t.</a></em></p><img src="https://counter.theconversation.com/content/114702/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dave Petley 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>
Climate change has caused a 60-fold increase in active landslides on one Canadian Arctic island.
Dave Petley, Professor of Geography and Vice-President for Research and Innovation, University of Sheffield
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/111345
2019-02-10T19:14:11Z
2019-02-10T19:14:11Z
Melting Himalayan glaciers: a big drop in a bucket that’s already full
<p>A <a href="https://link.springer.com/book/10.1007%2F978-3-319-92288-1">new report</a> has warned that even if global warming is held at 1.5°C, we will still lose a third of the glaciers in the Hindu Kush-Himalaya (HKH) region. What does that mean for rivers that flow down these mountains, and the people who depend on them? </p>
<p>The HKH region is home to the tallest mountains on Earth, and also to the source of rivers that sustain close to 2 billion people. These rivers supply agriculture with water and with sediments that fertilise soils in valleys and the floodplain. </p>
<p>Some of these rivers are hugely culturally significant. The Ganges (or Ganga), for instance, which flows for more than 2,525km from the western Himalayas into the Bay of Bengal, is personified in Hinduism as the goddess Gaṅgā. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257843/original/file-20190207-174857-jk1rf2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Ganga River at Rishikesh, as it exits the Himalayas.</span>
<span class="attribution"><span class="source">Anthony Dosseto</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/warm-ice-in-mount-everests-glaciers-makes-them-more-sensitive-to-climate-change-new-research-107325">Warm ice in Mount Everest's glaciers makes them more sensitive to climate change – new research</a>
</strong>
</em>
</p>
<hr>
<h2>When it rains, it pours… literally</h2>
<p>Before we get to the effect of melting glaciers on Himalayan rivers, we need to understand where they get their water.</p>
<p>For much of Himalayas, rain falls mostly during the monsoon active between June and September. The monsoon brings heavy rain and often causes <a href="https://www.youtube.com/watch?time_continue=99&v=QxoMqrjzM5E">devastating floods</a>, such as in <a href="https://www.theguardian.com/world/2013/jun/24/india-uttarakhand-floods-rescue-death-toll">northern India in 2013</a>, which forced the evacuation of more than 110,000 people.</p>
<figure>
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<figcaption><span class="caption">2013 floods in Uttarakhand, India.</span></figcaption>
</figure>
<p>But the summer monsoon is not the only culprit for devastating floods. Landslides can dam the river, and when this dam bursts it can cause dramatic, unpredictable flooding. Some of those events have been linked to folk stories of floods in <a href="https://theconversation.com/geomythology-can-geologists-relate-ancient-stories-of-great-floods-to-real-events-63434">many cultures around the world</a>. In the Himalayas, a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0277379113002874">study</a> tracking the 1,000-year history of large floods showed that heavy rainfall and landslide-dam burst are the main causes.</p>
<p>When they melt, glaciers can also create natural dams, which can then burst and send floods down the valley. In this way, the newly forecast melting poses an acute threat.</p>
<p>The potential problem is worsened still further by the Intergovernmental Panel on Climate Change’s <a href="https://www.ipcc.ch/report/managing-the-risks-of-extreme-events-and-disasters-to-advance-climate-change-adaptation">prediction</a> that the frequency of extreme rainfall events will also increase.</p>
<h2>Come hell or high water</h2>
<p>What will happen to Himalayan rivers when the taps are turned to high in this way? To answer this, we need to look into the past. </p>
<p>For tens of thousands of years, rivers have polished rocks and laid down sediments in the lower valleys of the mountain range. These sediments and rocks tell us the story of how the river behaves when the tap opens or closes.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257845/original/file-20190207-174894-ksaduy.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">Rock surfaces tell us where the river was carving into its bed.</span>
<span class="attribution"><span class="source">Anthony Dosseto</span></span>
</figcaption>
</figure>
<p>Some experts <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/30/10/911/192283/impulsive-alluviation-during-early-holocene">propose</a> that intense rain tends to trigger landslides, choking the river with sediments which are then dumped in the valleys. Others <a href="https://www.sciencedirect.com/science/article/abs/pii/S027737911000168X">suggest</a> that the supply of sediments to the river generally doesn’t change much even in extreme rainfall events, and that the main effect of the extra flow is that the river erodes further into its bed.</p>
<p>The <a href="https://www.sciencedirect.com/science/article/abs/pii/S0277379118300325">most recent work</a> supports the latter theory. It found that 25,000-35,000 years ago, when the monsoon was much weaker than today, sediments were filling up Himalayan valleys. But more recently (3,000-6,000 years ago), rock surfaces were exposed during a period of strong monsoon, illustrating how the river carved into its bed in response to higher rainfall.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/257846/original/file-20190207-174870-3o7iha.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">Sediments laid down in Himalayan valleys support agriculture, but also tell us the ancient story of rivers that carried them.</span>
<span class="attribution"><span class="source">Anthony Dosseto</span></span>
</figcaption>
</figure>
<p>So what does the past tell us about the future of Himalayan rivers? More frequent extreme rainfall events mean more floods, of course. But a stronger monsoon also means rivers will cut deeper into their beds, instead of fertilising Himalayan valleys and the <a href="https://en.wikipedia.org/wiki/Indo-Gangetic_Plain">Indo-Gangetic plain</a> with sediments.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/devastating-himalayan-floods-are-made-worse-by-an-international-blame-game-83103">Devastating Himalayan floods are made worse by an international blame game</a>
</strong>
</em>
</p>
<hr>
<p>What about glaciers melting? For as long as there are glaciers, this will increase the amount of meltwater in the rivers each spring (until 2060, according the <a href="https://link.springer.com/book/10.1007%2F978-3-319-92288-1">report</a>, after which there won’t be any meltwater to talk about). So this too will contribute to rivers carving into their beds instead of distributing sediments. It will also increase the risk of flooding from outburst of glacial lake dams.</p>
<p>So what is at stake? The melting glaciers? No. Given thousands or millions of years, it seems likely that they will one day return. But on a more meaningful human timescale, what is really at stake is us – our own survival. Global warming is reducing our resources, and making life more perilous along the way. The rivers of the Himalayas are just one more example.</p><img src="https://counter.theconversation.com/content/111345/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anthony Dosseto receives funding from the Australian Research Council.</span></em></p>
A new report predicts that one-third of the ice in the Himalayas will melt, even if we contain global warming to 1.5C. So what does that mean for the flood-prone valleys below?
Anthony Dosseto, Associate Professor, University of Wollongong
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/104720
2018-10-30T14:14:53Z
2018-10-30T14:14:53Z
Africa’s roads are badly built, and there aren’t enough. This can be fixed
<figure><img src="https://images.theconversation.com/files/241602/original/file-20181022-105757-peefhw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rift Valley Road in Ethiopia.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>One of the fastest growing economies in Africa, Ethiopia, has an <a href="http://www.ethcrge.info/crge.php">ambitious plan</a> to cut a green, sustainable path to becoming a middle-income country by 2025. Along the way, the country faces growing urban migration and rising demand for food – challenges that are linked by, and depend on, roads for access, supply and mobility.</p>
<p>In 1997, the total road network in Ethiopia was 26,550 kilometres. By 2014 it reached 99,522 km. For the country to reach its ambitious growth targets it’s aiming to double this to over <a href="http://www.globalconstructionreview.com/news/ethiopia-double-road-network-200000km-2020/">200,000 km by 2020</a>. </p>
<p>But new roads in Ethiopia and across sub-Saharan Africa often change the landscape, bringing dust, flooding and erosion. The impact is felt most by rural communities. Roads can negatively affect water flows to wetlands, block fish movements and cause landslides, as well as impact the livelihoods of millions of people.</p>
<p>There is a solution: an <a href="http://www.globalresiliencepartnership.org/wp-content/uploads/2018/02/Meta-Meta-Solution-Statement.pdf">approach</a> to road building developed by Dutch social enterprise MetaMeta shows that it’s possible to reduce the impact of new roads and support food production by harvesting excess water. </p>
<p>Under a project rolled out in Ethiopia as well as nine other countries including <a href="http://www.globalresiliencepartnership.org/teams/metameta/">Bangladesh</a>, roads are being built using innovative designs and drainage structures to collect water caused by flooding. This has solved an infrastructural issue while conserving water that can be used for crops and to feed livestock. </p>
<h2>Well built roads</h2>
<p>Practitioners at <a href="http://metameta.nl/">MetaMeta</a> found that more than a third of households in Tigray, northern Ethiopia, reported flooding as a result of new roads with negative effects on crop production for around one in ten households.</p>
<p>The study found that poor road construction can lead to soil erosion on farms and plots of land hugging the roadside. In addition, construction can increase the cost of road maintenance and repairs. This in turn limits transport options, including restricting access to markets, schools and hospitals. The net cost is damaged livelihoods.</p>
<p>One solution, developed by MetaMeta, helps both mitigate the impact of new roads and support food production by harvesting excess water with “smart roads”. A project called <a href="http://roadsforwater.org/">Roads for Water</a> is testing the concept. Funded by the <a href="http://www.globalresiliencepartnership.org/">Global Resilience Partnership</a>, an independent partnership of public and private organisations focusing on the most vulnerable people and places, this project uses innovative road concepts, designs and <a href="https://link.springer.com/chapter/10.1007/978-3-319-66239-8_7">drainage structures</a> to collect water caused by flooding. </p>
<p>For example, roads can route water to storage ponds or underground aquifers. Road drifts can help to retain water in dry riverbeds, and ensure systematic spreading of floodwaters.</p>
<p>By harvesting rainwater, communities living near road networks can increase their resilience to shocks such as floods and droughts.</p>
<p>In Ethiopia the project showed that USD$1,800 per km investment is sufficient to implement such measures, and can directly benefit over two million people.</p>
<p>This compares favourably with annual maintenance expenditures <a href="http://roadsforwater.org/wp-content/uploads/2013/10/the-burden-of-maintenance_roads-in-SSA.pdf">per kilometre of USD$1,100 per year</a> on rural roads in sub Saharan Africa and a periodic maintenance of USD$11,200 often incurred from water damage.</p>
<p>These smart roads are increasing resilience to shocks, such as floods because water is being harvested and maintenance costs are reduced. They are also driving down the cost of road construction through, for example, the reuse of borrow pits for permanent water storage rather than requiring them to be backfilled. This is a considerable cost saving measure and additionally creates a local water resource. </p>
<p>In <a href="https://edition.cnn.com/2017/09/01/asia/bangladesh-south-asia-floods/index.html">Bangladesh</a>, for example, smart roads are helping build resilience to floods that submerged a third of the country last year. If countries like Ethiopia and Bangladesh are to become more resilient they will need innovative solutions to an increasingly uncertain climate.</p>
<p>The importance of building resilient roads will only intensify as populations grow and countries develop.</p>
<p>Globally, an estimated 900 million rural people still don’t have access to road and transport infrastructure. The <a href="http://blogs.worldbank.org/ppps/forecasting-infrastructure-investment-needs-50-countries-7-sectors-through-2040">investment gap</a> on global roads is expected to approach USD$1.6 trillion per year for the next 40 years as increasing amounts of roads are built, especially in the developing world.</p>
<p>But solutions for better roads won’t work unless they are driven by local ideas and are compatible with local needs and contexts. Collaboration and buy-in between local partners – from engineers to technicians, farmers, labourers and governments departments – is critical. Solutions as simple as bringing the ministry responsible for roads together with the ministry responsible for water and talking them through the challenges and opportunities can produce remarkable results.</p>
<p>_Frank van Steenbergen, the head of MetaMeta, also contributed to the article. _</p><img src="https://counter.theconversation.com/content/104720/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathanial Matthews is the Program Director of the Global Resilience Partnership. </span></em></p><p class="fine-print"><em><span>Frank van Steenbergen 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>
Smart roads in Africa could help reduce the impact of flooding and other disasters that affect rural communities.
Nathanial Matthews, Senior fellow, King's College London
Frank van Steenbergen, Water management specialist, Utrecht University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/104662
2018-10-10T17:59:20Z
2018-10-10T17:59:20Z
Mount Etna: volcano is sliding towards the sea and now we know why
<figure><img src="https://images.theconversation.com/files/240048/original/file-20181010-72127-hzk23x.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/beautiful-mediterranean-sicilian-coastal-landscape-cruising-405035131?src=V3dRBEkzpU60JGLY5gEP3A-1-5">Arts Illustrated Studios/Shutterstock</a></span></figcaption></figure><p>The southeast flank of Mount Etna in Sicily is <a href="https://www.bbc.co.uk/news/science-environment-43522169">sliding towards the sea</a> at a rate of several centimetres a year. This might not sound like much, but the kind of stress that this movement creates inside volcanoes can cause devastating landslides. If, one day, Etna’s movement significantly increases then it could have serious consequences. </p>
<p>With this in mind, scientists such as myself have been studying Etna to try to better understand what’s going on. Now research <a href="http://advances.sciencemag.org/content/4/10/eaat9700">published in Science Advances</a> presents strong evidence that Etna’s slide isn’t caused by pressure from magma inside the volcano, as previously thought. Instead, it’s likely caused by gravity pulling on Etna’s lower underwater slopes, far from the summit. The researchers emphasise that this means Etna is more susceptible to catastrophic collapse than had previously been realised, and that the same might be true of other coastal and island volcanoes.</p>
<p>My colleagues and I first calculated the speed of Etna’s movement earlier this year, showing that the entire edifice slid downslope at an average of <a href="https://doi.org/10.1007/s00445-018-1209-1">14 millimetres a year</a> between 2001 and 2012. But the whole volcano is also expanding outwards from the summit in all directions, meaning its total annual movement towards the sea is several centimetres.</p>
<p>The new research looks for the first time at what is happening at the underwater foot of the volcano, 1,200 metres below sea level and 12 kilometres from the shoreline. Data from five underwater transponders gathered between April 2016 and July 2017, showed the underwater slope remained stable for a year but then slid four centimetres in one eight-day period before finally stabilising again.</p>
<p>The data shows that the amount of movement is smallest at the summit and biggest at the foot of the volcano. But if movement was caused by the magma inside Etna then the biggest movement would occur near the volcanic centre. The researchers also found that the sea floor movement 12 kilometres from the shore is focused along a single geological fault. But near the coast, the strain is divided between two fault systems.</p>
<p>This all suggests that the movement began offshore and spread towards the summit. There were no associated earthquakes during the eight-day episode, indicating that the movement wasn’t caused by seismic activity. Instead, it’s likely to be the effects of gravity pulling on the volcano.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/240054/original/file-20181010-72127-1wmm65i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Etna is expanding outwards from the summit and sliding towards the sea.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/aerial-picture-mount-etna-volcanic-crater-1087082336?src=5WibQ419WiX2uZEiE8P4OA-1-23">GLF Media/Shutterstock</a></span>
</figcaption>
</figure>
<p>For the past 50 years, the science of volcano movements has been <a href="https://radar.community.uaf.edu/files/2017/04/Mogi1958.pdf">dominated by the idea</a> that most volcanoes have a shallow magma chamber that expands as it fills with magma before an eruption. This causes the walls of the chamber to eventually fracture and allows magma to escape from the side of the volcano. Measuring the volcano’s surface movement would allow you to calculate the depth of the magma chamber. It is this kind of model that is usually used to explain expanding volcanoes.</p>
<p>But many scientists including myself have found that while some well-studied volcanoes in <a href="https://www.ncbi.nlm.nih.gov/pubmed/17809512">Hawaii</a>, <a href="https://www.nature.com/articles/266318a0">Iceland</a> and elsewhere fit this kind of model, other volcanoes <a href="https://www.sciencedirect.com/science/article/pii/S0377027302002366">contradict it</a>. This suggests there are other factors that explain volcano movement and can affect eruptions. </p>
<p>In the 1990s, volcanologist <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/94JB00578">Andrea Borgia suggested</a> that the steadily increasing amount of lava and volcanic rock deposited near the top of tall volcanoes caused their summits to subside and their slopes to spread outwards. This idea has gained ground as volcanoes around the world provide us with <a href="https://pubs.geoscienceworld.org/gsa/geology/article-abstract/32/7/573/29472/volcano-spreading-controlled-by-dipping-substrata?redirectedFrom=fulltext">more and more geological evidence</a>, which the new research paper adds to.</p>
<h2>Etna’s uncertain future</h2>
<p>So what does this mean for Etna? We can say with certainty that catastrophic collapse, in which an entire sector of a volcano slides off in a gigantic landslide, has occurred on the downslope side of other gravitationally sliding volcanoes. The devastation caused by such events, which occur worldwide about four times a century, means that the possibility has to be taken seriously. </p>
<p>Unfortunately, we don’t yet have enough detailed knowledge of the build-up to such events to make meaningful predictions about specific volcanoes. So while the authors of the latest paper argue that because Etna’s slide is caused by gravity it makes a collapse more likely, we still can’t give an indication of when or even if this will actually happen.</p><img src="https://counter.theconversation.com/content/104662/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Murray received funding from NERC until 2009.</span></em></p>
Gravity, not magma, is forcing Etna to move, increasing the chances of collapse.
John Murray, Senior Research Fellow, School of Environment, Earth and Ecosystem Sciences, The Open University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/92933
2018-03-07T02:23:54Z
2018-03-07T02:23:54Z
The science of landslides, and why they’re so devastating in PNG
<figure><img src="https://images.theconversation.com/files/209214/original/file-20180306-146655-nxayso.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A magnitude 7.5 earthquake took place on February 25, 81km southwest of Porgera, Papua New Guinea. </span> <span class="attribution"><a class="source" href="https://earthquake.usgs.gov/earthquakes/eventpage/us2000d7q6#map">US Geological Survey </a></span></figcaption></figure><p>A <a href="https://earthquake.usgs.gov/earthquakes/eventpage/us2000d7q6#executive">magnitude 7.5 earthquake</a> struck the Southern Highlands region of Papua New Guinea on February 25, 2018. This was followed by a series of <a href="http://www.abc.net.au/news/2018-03-05/aftershocks-rattles-quake-hit-papua-new-guinea/9508534">aftershocks</a>, producing widespread landslides that have <a href="https://www.theguardian.com/world/2018/mar/04/papua-new-guinea-hit-by-aftershocks-of-fatal-earthquake">killed dozens and injured hundreds</a>. The same landslides have cut off roads, telecommunications and power to the area. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"968515779175075840"}"></div></p>
<p>The PNG government has declared a <a href="http://www.abc.net.au/news/2018-03-02/png-declares-state-of-emergency-after-earthquake/9501496">state of emergency</a> in the region. There is growing concern over <a href="https://blogs.agu.org/landslideblog/2018/02/28/papua-new-guinea-crisis/">several valleys that have been dammed by landslides</a> and are beginning to fill with water - now ready to collapse and surge downstream, directly towards more villages.</p>
<p>Why is Papua New Guinea so susceptible to landslides? It’s a combination of factors - steep terrain, earthquakes and aftershocks plus recent seasonal rains have created an environment that is prone to collapse.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-active-volcanoes-on-my-asia-pacific-ring-of-fire-watch-list-right-now-90618">Five active volcanoes on my Asia Pacific 'Ring of Fire' watch-list right now</a>
</strong>
</em>
</p>
<hr>
<h2>How land becomes unstable</h2>
<p>The Earth around us is generally pretty stable, but when the ground shakes during an earthquake it can start to move in ways we don’t expect. </p>
<p>Pressure changes during an earthquake create an effect in the soil called <a href="https://www.sciencealert.com/watch-this-awesome-experiment-shows-how-liquefaction-occurs-during-an-earthquake">liquefaction</a>, where the soil itself acts as a fluid.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/b_aIm5oi5eA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">When wet soil is exposed to physical pressure, other physical changes take place.</span></figcaption>
</figure>
<p>When lots of water is present in the soil, as is the case now during the monsoon season in Papua New Guinea, liquefaction can happen even more easily.</p>
<p>When liquefaction occurs, the earthquake creates changes due to friction. Imagine a visit to the greengrocer, where an accidental bumping of a carefully stacked pile of apples can cause cause them all to suddenly collapse. What was holding the pile together was friction between the individual apples – and when this disappears, so does the pile.</p>
<p>In an earthquake, two tectonic plates slip past one another deep underground, rubbing together and cracking the nearby rocks. The effects of this movement up at the surface can vary depending on the nature of the earthquake, but one feature is fairly common: <a href="https://video.nationalgeographic.com/video/earthquake-montage">small objects bounce around</a>. The sand grains just below the surface do the same thing, but a bit less excitedly. A few metres down, grains could be bouncing around just enough to lose contact with each other, removing the friction, and becoming unstable.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/209215/original/file-20180306-146650-19al7kj.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">A 2012 landslide in the southern highlands of Papua New Guinea.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/dfataustralianaid/10707695855/in/photolist-hjcLST-hjcJVM-7XNWEw-nrjyQn/">dfataustralianaid/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Things are normally stable because they’re sitting on top of something else. When that support suddenly disappears, things tend to fall down – this is the classic dodgy folding chair problem experienced by many.</p>
<p>In engineering, we call this “failure” – and in the building industry it usually occurs immediately before the responsible engineer receives a call from a lawyer. Mechanically, this failure happens when the available friction isn’t enough to support the weight of the material above it.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-after-an-earthquake-how-does-a-tsunami-happen-83732">Explainer: after an earthquake, how does a tsunami happen?</a>
</strong>
</em>
</p>
<hr>
<h2>When soil acts like fluid</h2>
<p>Once a slope fails, it starts to fall downhill. If it really slides, then we’re back to the same situation of grains bouncing around. Now, none of the grains are resting against each other, and the whole thing is <a href="https://blogs.agu.org/landslideblog/2018/02/22/river-of-rock-1/">acting like a fluid</a>. </p>
<p>A couple of interesting things happen at this point. First, as the grains are bouncing around, small particles start to fall through all the newly formed holes that have opened up. This occurs for the same reason that you find all the crumbs at the bottom of your cereal box, and all of the unpopped kernels at the bottom of your bowl of popcorn. Once these smaller fragments accumulate at the bottom of the flowing landslide, they can help it slide more easily, accelerating everything and increasing its destructive power. </p>
<p>Second, landslides typically flow faster at the surface than below, so as large particles accumulate at the top they are also the ones moving the fastest, and they start to collect at the front of the landslide. These large particles, often boulders and trees, can be incredibly damaging for any people or structures in their path. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/209232/original/file-20180307-146697-1bsk93y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Simulation of a landslide impacting a structure.</span>
<span class="attribution"><span class="source">Benjy Marks/USyd</span></span>
</figcaption>
</figure>
<p>The image above shows a laboratory simulation of a landslide flowing down a slope and hitting a fixed wall. The spherical particles are coloured by size (small is yellow; large is blue). Data from these sorts of studies can help predict the forces that an object will feel if it gets hit by a landslide.</p>
<h2>Watching and waiting</h2>
<p>These complex dynamics mean that we really need to know a lot about the geography and geology of a particular slope before any kind of reliable prediction could be made about the behaviour of a particular landslide. </p>
<p>In the remote areas of Papua New Guinea, accumulating this data at every point on every slope is a tough challenge. Luckily, huge advancements have recently been made in remote sensing, so that planes and satellites can be used to extract this vital information. </p>
<p>Using <a href="http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/geodetic-techniques/interferometric-synthetic-aperture-radar">sophisticated sensors</a>, they can see past foliage and map the ground surface in high resolution. As satellites orbit quite regularly, small changes in the surface topography can be monitored. Scientists hope that by using this information, unstable regions that haven’t yet failed can be identified and monitored.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/controversial-artist-elizabeth-durack-gave-us-a-sensitive-insight-into-the-lives-of-papuan-women-79423">Controversial artist Elizabeth Durack gave us a sensitive insight into the lives of Papuan women</a>
</strong>
</em>
</p>
<hr>
<p>Papua New Guinea is located on an active fault line and has had <a href="https://earthquaketrack.com/p/papua-new-guinea/recent">nine major earthquakes in the past five years</a>. Combined with the often remote and steep terrain, together with a monsoon season that delivers repeated heavy rainfall events, it is a particularly active area for landslides to develop. </p>
<p>The dry season in Papua New Guinea will not arrive until June. During the current wet season we may see even more slopes fail due to destabilisation by the recent earthquakes.</p><img src="https://counter.theconversation.com/content/92933/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjy Marks receives funding from the Australian Research Council. </span></em></p>
Why is Papua New Guinea so susceptible to landslides? Steep terrain, earthquakes and aftershocks plus recent seasonal rains have created an environment that is prone to collapse.
Benjy Marks, Lecturer in Geomechanics, University of Sydney
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/90086
2018-01-22T11:27:16Z
2018-01-22T11:27:16Z
Global toll from landslides is heaviest in developing countries
<figure><img src="https://images.theconversation.com/files/202601/original/file-20180119-80197-6j0fs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Searching for victims after a rain-triggered mudslide that blanketed a village and killed at least 178 people in north China's Shanxi province, Sept. 13, 2008. </span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/China-Landslide/1a904fba52434f17868cbcf18d20bd56/18/0">AP Photo/Andy Wong</a></span></figcaption></figure><p>This month’s tragic <a href="https://theconversation.com/deadly-california-mudslides-show-the-need-for-maps-and-zoning-that-better-reflect-landslide-risk-90087">mudslides in Montecito, California</a> are a reminder that natural hazards lurk on the doorsteps of many U.S. homes, even in affluent communities. Similar events occur every year around the world, often inflicting much higher casualties yet rarely making front-page headlines. </p>
<p>During my field research as a geologist, I have seen destruction from landslides firsthand in many parts of the world, including Nepal, China, Indonesia and Peru. In my view, these losses could be mitigated by improving our scientific understanding of landslides and debris flows (moving masses of mud, sand, soil, rock, and even sometimes ice), and by helping societies communicate the resulting risks more effectively – particularly in developing countries, where the damage is most severe.</p>
<h2>Thousands killed in single events</h2>
<p>The damage from landslides can be staggering. In the <a href="https://landslides.usgs.gov/learn/majorls.php">most destructive recorded cases of the 20th century</a>, thousands of people died in single events. For example, catastrophic debris flows from Nevado Huascarán – the highest mountain peak in Peru – <a href="http://news.bbc.co.uk/onthisday/hi/dates/stories/january/11/newsid_3306000/3306665.stm">killed as many as 4,000 people in 1962</a> and <a href="https://www.ngdc.noaa.gov/hazardimages/picture/show/785">another estimated 18,000-20,000 in 1970</a>. Globally, the <a href="https://svs.gsfc.nasa.gov/4305">highest numbers of fatalities from landslides</a> occur in the mountains of Asia and Central and South America, as well as on steep islands in the Caribbean and Southeast Asia.</p>
<p>Wherever slopes are steep, there is a chance that they will fail. Most of the time, the odds are low. But heavy rainfall or a large earthquake can destabilize precarious balances and unleash the raw power of tumbling rocks and debris. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jNVwspunNn0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Hikers narrowly avoid a massive debris flow in Aconcagua, Argentina in 2016.</span></figcaption>
</figure>
<p>The <a href="https://ca.water.usgs.gov/flooding/wildfires-debris-flow.html">risks increase after wildfires</a>, as we have seen in Montecito. They also can be <a href="http://www.issw.ch/fe/gebirgshydrologie/wildbaeche/projekte/vegetationswirkungen_rutschungen/rickli_et_al_2001.pdf">exacerbated by deforestation and land use change</a>. Earthquake-triggered landslides, while less frequent than those induced by rainfall, have been responsible for some of the greatest losses of life. During the 2008 Wenchuan earthquake in China’s Sichuan province, <a href="http://dx.doi.org/10.1038/ngeo1806">20,000 deaths</a> were attributed to landslides – roughly one-fourth of the total deaths from the quake.</p>
<p>The effects of smaller landslides also add up. <a href="https://blogs.agu.org/landslideblog/about/">Dave Petley</a>, an earth scientist at the University of Sheffield, has calculated that landslides caused <a href="https://blogs.agu.org/landslideblog/2012/08/16/global-patterns-of-loss-of-life-from-landslides-my-new-paper-in-the-journal-geology/">32,322 fatalities between 2004 and 2010</a> – equivalent to over 4,500 deaths each year. For comparison, <a href="http://www.worldmapper.org/posters/worldmapper_map250_ver5.pdf">floods are estimated to have killed an average of roughly 7,000 people each year</a> between 1975 and 2000.</p>
<h2>Heavy tolls in developing countries</h2>
<p>As with many natural disasters, the effects of landslides are disproportionately severe in developing countries. Between 1950 and 2011, debris flows killed an average of <a href="https://doi.org/10.1007/s11069-013-0907-4">23 people per event in developing countries</a>, compared to 6 fatalities per flow in advanced economies. </p>
<p>This difference may reflect a number of factors, including the resilience of basic infrastructure and emergency services; the availability of health care to treat people who are injured or left homeless; and patterns of development that determine where people live. Improving basic economic conditions and construction standards in high-risk areas could go a long way toward mitigating losses from landslides, as well as from earthquakes, tropical storms and other natural disasters.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202604/original/file-20180119-80203-15db70c.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">In April 2017, a hillside saturated by melting snow and rainfall collapsed near the village of Kurbu-Tash in southern Kyrgyzstan. Over the following weeks, a slow-moving river of fine-grained soil flowed down a valley and engulfed dozens of homes.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/IOTD/view.php?id=90255&eocn=image&eoci=related_image">NASA Earth Observatory</a></span>
</figcaption>
</figure>
<h2>Early warnings save lives, but require data and models</h2>
<p>Another major difference is that, at least in many cases, wealthy countries have early warning systems that can alert people to imminent risks. Casualties in Montecito would likely have been much higher in the absence of warnings from scientists and government agencies in the days and hours leading up to the tragedy. </p>
<p>The evacuation orders in Montecito were based on models for debris flow risk generated by the U.S. Geological Survey. The USGS uses decades of data collected from past events to predict how much rain is needed to start <a href="https://landslides.usgs.gov/hazards/postfire_debrisflow/">debris flows after wildfires</a> in the Western United States. As a storm approached the California coast in early January, authorities used these debris flow hazard maps to issue advance warnings to residents in the Thomas Fire region near Montecito. Initial warnings came days before the mudslides occurred. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"950218973773090817"}"></div></p>
<p>Then, at about 3:00 a.m. on Jan. 9, as a band of particularly intense rainfall approached the most susceptible areas, authorities issued an emergency alert for people to evacuate. The fact that these alerts came too late for some victims suggests that even U.S. emergency communication systems <a href="http://www.latimes.com/local/lanow/la-me-mudslide-factors-20180111-story.html">can be improved</a>. </p>
<p>There has also been <a href="https://www.independent.com/news/2018/jan/17/straight-talk-montecito-evacuation-reaction-and-fl/">controversy</a> over the fact that some evacuation orders in Montecito were mandatory and others were voluntary. And there is scope to <a href="https://theconversation.com/deadly-california-mudslides-show-the-need-for-maps-and-zoning-that-better-reflect-landslide-risk-90087">improve both landslide hazard maps in the U.S.</a>, and to implement a much-needed <a href="https://www.nytimes.com/2017/09/21/us/california-today-mexico-has-a-quake-warning-system-where-is-californias.html">warning system for earthquakes</a>. Nonetheless, public officials had a lot of information about potential hazards – information that was critical to issuing warnings and getting many people out of harm’s way this month in California.</p>
<p>What would it take for developing countries to have similar opportunities? One starting point would be to improve understanding of when and why landslides are most likely to occur. For example, even though earthquake-triggered landslides cause enormous damage, we do not yet have a reliable framework for predicting landslides and debris flows following large earthquakes. Building better predictive models and using these to improve warnings of landslide risks could save hundreds or even thousands of lives in the future. </p>
<p>This scientific knowledge will be most effective if it is coupled with efforts to improve awareness of associated risks, and to build capacity and willingness for people to respond. These important parts of the puzzle are not easy to put in place in the United States, much less elsewhere.</p><img src="https://counter.theconversation.com/content/90086/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>A. Joshua West receives funding from the U.S. National Science Foundation for research on landslides and debris flows. </span></em></p>
While the Montecito, California mudslides took 20 lives, landslides kill far more people in developing countries. Tighter construction standards and early warning systems could help reduce their toll.
A. Joshua West, Associate Professor of Earth Sciences and Zinsmeyer Early Career Chair in Marine Studies, USC Dornsife College of Letters, Arts and Sciences
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/90048
2018-01-17T03:15:57Z
2018-01-17T03:15:57Z
Post-fire mudslide problems aren’t new and likely to get worse
<figure><img src="https://images.theconversation.com/files/202173/original/file-20180116-53289-438vxy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">As many as 20 people are dead and dozens missing following the Southern California mudslides.</span> <span class="attribution"><span class="source">AP Photo/Marcio Jose Sanchez</span></span></figcaption></figure><p>Several weeks after a series of wildfires blackened nearly 500 square miles in Southern California, a large winter storm rolled in from the Pacific. In most places the rainfall was welcomed and did not cause any major flooding from burned or unburned hillslopes. </p>
<p>But in the town of Montecito, a coastal community in Santa Barbara County that lies at the foot of the mountains blackened by the Thomas Fire, a devastating set of sediment-laden flows killed at least 20 people and damaged or destroyed more than 500 homes. In the popular press these flows were termed “mudslides,” but with some rocks as large as cars these are more accurately described as hyperconcentrated flows or debris flows, depending on the amount of sediment mixed with the water.</p>
<p>Why did these deadly flows happen? To what extent were these flows caused by the fire, the extreme burst of rainfall, or a combination? And what can we do to reduce similar risks in the future? </p>
<h2>Causes of post-fire erosion</h2>
<p>Some national newspapers are saying that these post-fire flows are caused by the loss of vegetation, but as a scientist studying the effects of fires on soils, runoff and erosion, I can say this is not completely accurate. While many wildfires do burn trees and shrubs, the loss of this overlying vegetation canopy only slightly increases the amount of rainfall that reaches the soil surface and the kinetic energy delivered by the raindrops to the ground surface.</p>
<p>The far more important effect of high and moderate severity wildfires is that they can burn off all the surface litter and ground vegetation, leaving a layer of easily removed ash on top of otherwise bare soil. </p>
<figure>
<iframe frameborder="0" class="juxtapose" width="100%" height="480" src="https://cdn.knightlab.com/libs/juxtapose/latest/embed/index.html?uid=24aee54e-fb1e-11e7-b263-0edaf8f81e27">
</iframe>
<figcaption><span class="caption">Photo from NASA Earth Observatory of the Montecito area before the Thomas fire and after the Thomas fire and the subsequent flooding and debris flows. The slider in the middle can be moved to display more of either image.</span></figcaption>
</figure>
<p>In certain vegetation types, like chaparral and coniferous forests, fires will vaporize organic compounds found in the leaf litter. Some of these compounds are driven downward by the heat where they condense on cooler soil particles just below the soil surface. In sufficient quantity and especially in coarser-textured soils, the resulting water-repellent layer impedes the normal downward flow of water. Higher-severity fires also can consume some of the shallow soil organic matter that helps bind together larger soil clumps. </p>
<p>When winds and the first rains arrive, they quickly wash the ash away, and the impact of raindrops on the bare soil can detach and <a href="https://www2.nrel.colostate.edu/assets/nrel_files/labs/macdonald-lab/pubs/SSSAJ-sealing-2009.pdf">disperse small soil particles to create a surface seal or crust</a>.</p>
<p>The net result is that after a high or moderate severity fire the ability of the soil to absorb water decreases from around several inches per hour to perhaps just one-third of an inch per hour. Any additional rainfall becomes surface runoff, and a rainstorm of only one inch per hour can generate 1.5 million cubic feet of runoff per square mile. </p>
<p>The raindrops and surface runoff can easily erode and transport the unprotected soil on the hillsides. The resulting accumulation and concentration of flow and sediment in stream channels can rapidly mobilize massive amounts of rocks and soil. </p>
<p>The resulting mixture of water, eroded soil, and rocks can quickly bulk up to a concentrated mix of water with 10 to 40 percent sediment, or an even more concentrated and deadly debris flow moving at up to <a href="https://en.wikipedia.org/wiki/Debris_flow">20 miles per hour</a>. Once these flows reach flatter areas or encounter obstacles, the velocity decreases and the rocks and mud are deposited. The potential for such flows are exacerbated in much of Southern California because the mountains are steeper than normal due to rapid uplift along regional faults.</p>
<p>With population growth there are ever more houses and other developments at the base of the mountains. Of even greater concern is the placement of houses and other structures on the <a href="https://en.wikipedia.org/wiki/Alluvial_fan">alluvial fans</a> where streams have been depositing sediment and rapidly changing their course over many thousands of years. </p>
<h2>No easy fixes</h2>
<p>When hillslopes are denuded of their surface soil cover by fire or other processes, the resulting increase in runoff and erosion is nearly inevitable. Mulch or other surface cover can be applied to help protect the soil from the raindrop impact, but mulching is difficult and expensive to quickly apply over large areas, and is progressively ineffective on steeper slopes or during more intense storms that <a href="http://dx.doi.org/10.1016/j.catena.2012.11.016">produce more surface runoff</a>. </p>
<p><a href="http://www.latimes.com/local/la-101309-me-rain-g-graphic.html">Debris basins</a> can be constructed to capture the runoff and sediment, but there are problems of finding locations and sizing their capacity for extreme events, as well clearing them prior to large storms.</p>
<p>In Montecito an exceptional storm cell developed over a severely burned area, with nearly an inch of rain in just 15 minutes and over half an inch of rain in just five minutes. Montecito is particularly at risk as the hillslopes above town are oversteepened by faulting and rapid uplift, and much of the town is built on deposits laid down by previous floods. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202226/original/file-20180117-53324-4mni3n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Dunsmir Sediment Basin in Los Angeles County, California.</span>
<span class="attribution"><a class="source" href="https://www.fema.gov/media-library/search/45017#{%22keywords%22:%2245017%22}">FEMA</a></span>
</figcaption>
</figure>
<p>Some <a href="https://fopnews.wordpress.com/2011/01/27/shape-shifters-debris-basins-and-the-san-gabriels/">debris basins</a> were in place, but they were quickly overtopped by the hundreds of thousands of cubic yards of water and sediment. While high post-fire runoff and erosion rates could be expected, it was not possible to accurately predict the exact location and extreme magnitude of this particular storm and resulting debris flows.</p>
<p>There is a long history of comparable post-fire debris flows in the Los Angeles area with a <a href="https://pubs.usgs.gov/wsp/0796c/report.pdf">greater loss of life</a>. Comparable events also <a href="http://boisestatepublicradio.org/post/landslide-buried-boise-mud-55-years-ago-scientists-say-it-could-happen-again#stream/0">have occurred</a> <a href="http://www.azgs.az.gov/arizona_geology/winter10/article_feature.html">elsewhere in the western U.S.</a>, but in most cases the consequences have been much less tragic because wildfires more commonly occur in much less populated areas. This means the resultant effects are often limited to degraded <a href="http://www.clrma.org/files/springconference/Strontia%20Springs%20Sediment%20Removal%204-17-14%20Update.pdf">water quality, loss of aquatic habitat and excess reservoir sedimentation</a>.</p>
<h2>What next?</h2>
<p>Looking to the future, it is very clear that the problem is only going to get worse. </p>
<p>First, climate change is increasing the length and severity of the fire season by <a href="http://www.pnas.org/content/107/45/19167">reducing snowpacks and increasing temperatures</a>. Warmer temperatures increase <a href="https://theconversation.com/wildfires-in-west-have-gotten-bigger-more-frequent-and-longer-since-the-1980s-42993">fire risk</a> as well as the capacity of the atmosphere to hold water, which is <a href="http://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-12-00502.1">increasing rainfall intensities</a>. </p>
<p>Second, a policy of <a href="https://dx.doi.org/10.1126/science.1240294">suppressing wildfires</a> has increased the amount and density of vegetation in some areas. This greater fuel load can result in higher severity fires and more denuded hillslopes. Future wildfires are inevitable, and when there are high temperatures, high winds, low humidity and large fuel loads, it is not possible to safely fight or control a large wildfire. </p>
<p>Nor is it possible to stop the subsequent hillslope runoff and erosion. Debris basins or diversion structures can be built to reduce damage, but these are expensive and often do not have sufficient capacity for extreme post-fire storm events. While we are getting much better at predicting the risk of sediment-laden flows after wildfires through <a href="https://landslides.usgs.gov/hazards/">improved modeling and weather forecasting</a>, the starting point has to be <a href="https://theconversation.com/deadly-california-mudslides-show-the-need-for-maps-and-zoning-that-better-reflect-landslide-risk-90087">stricter zoning rules</a> to minimize construction in vulnerable areas. And once an area does burn, residents must heed the calls for evacuation when post-fire rainstorms are predicted.</p>
<p>On the positive side, most burned areas generally revegetate within two to four years. Once there is less than about 30-35 percent bare soil, there is a <a href="https://www2.nrel.colostate.edu/assets/nrel_files/labs/macdonald-lab/pubs/SSSAJ-sealing-2009.pdf">greatly reduced risk</a> of high runoff and erosion rates.</p>
<p>In Montecito the rapid delineation of risk zones led to the evacuations that undoubtedly helped save many hundreds of lives. What is now important is that the lessons from the Thomas Fire are applied in other areas to help minimize future losses of life and property. This is true in both the short term as more rain falls on the recently burned areas, and over the longer term given our increasingly fire-prone future.</p><img src="https://counter.theconversation.com/content/90048/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lee MacDonald receives funding from the National Science Foundation, USDA Forest Service, CAL-FIRE, and U.S. Army Corps of Engineers. </span></em></p>
A watershed scientist explains why post-wildfire landscapes are so susceptible to landslides – and why those risks are poised to rise.
Lee MacDonald, Professor of Ecosystem Science and Sustainability, Colorado State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/90087
2018-01-16T11:16:54Z
2018-01-16T11:16:54Z
Deadly California mudslides show the need for maps and zoning that better reflect landslide risk
<figure><img src="https://images.theconversation.com/files/201971/original/file-20180115-101489-15v2ncx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Search and rescue personnel scan a home in the aftermath of a mudslide, Jan. 13, 2018, in Montecito, California.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/California-Storms/2ae07779626d4c97a911c5d05ffc5d2c/6/0">AP Photo/Marcio Jose Sanchez</a></span></figcaption></figure><p>Scenic hill slopes can be inspiring – or deadly, as we are seeing after the disastrous debris flows that have <a href="http://www.latimes.com/local/california/la-me-montecito-mudslides-20180114-story.html">ravaged the community of Montecito, California</a> in the wake of heavy rains on Tuesday, Jan. 9, 2018. <a href="http://www.latimes.com/local/lanow/la-me-ln-new-montecito-mud-20180114-story.html">At least 20 people are dead</a>, and four remain missing. More than a hundred buildings have been destroyed or damaged by moving walls of mud and boulders that rumbled down creeks and canyons into houses and roads. </p>
<p>As mountains rise, erosion tears them down. And Southern California’s mountains are rising fast, squeezed up by the action of the region’s active faults. This produces steep slopes that erode quickly, though much of that erosion happens in infrequent events, such as big rainstorms right after big wildfires. </p>
<p>We know that risks vary across the terrain and that some places in landslide-prone zones are more dangerous than others. In some regions the riskiest areas are well downslope or downstream of slide-prone slopes, in the places where debris runs out and comes to rest. Unfortunately, few people are aware of these risks when developers build in and around landslide-prone mountains. </p>
<h2>A predictable disaster</h2>
<p>The U.S. Geological Survey <a href="https://www.nbcnews.com/news/investigations/how-politics-buries-science-landslide-mapping-n73256">estimates</a> that landslides kill 25 to 50 people a year in the United States – more than earthquakes or volcanoes. Yet landslides receive far less attention and research funding than other natural hazards. </p>
<p>Part of the problem is that when a large earthquake strikes, the whole region feels it. But landslides tend to impact localized areas, so they rarely attract widespread attention, except in devastating cases like Montecito. Furthermore, different kinds of landslides present very different hazards. Assessing landslide risks requires an understanding of how erosional processes shape Earth’s surface in different regions. </p>
<p>In a general sense, the threat to Montecito was clear. Scientists and planners have known for decades that the mountains of Southern California are shaped by a cycle of fire, rain and debris flows. Back in 1989, when I was a graduate student studying landslides, journalist John McPhee published his acclaimed book <a href="https://us.macmillan.com/thecontrolofnature/johnmcphee/9780374522599/">“The Control of Nature</a>.” In it, McPhee described scenes of devastation resulting from intense rainfall running off of wildfire-charred slopes to roar down canyons around Los Angeles. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/mknStAMia0Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Landslides occur in all 50 U.S. states, but risks are higher in some areas.</span></figcaption>
</figure>
<p>The Montecito disaster did not come as a complete surprise. Indeed, the U.S. Geological Survey <a href="https://landslides.usgs.gov/hazards/postfire_debrisflow/detail.php?objectid=178">warned</a> of high potential for disastrous landslides if intense rain fell on mountainsides around Santa Barbara that had been scorched by the <a href="http://www.fire.ca.gov/current_incidents/incidentdetails/Index/1922">Thomas wildfire</a> in December. When that perfect storm landed, it hit bare, baked soil that could not readily absorb water. So the rain ran off, picking up soil, boulders and debris as it surged down canyons and streams. These debris-charged torrents slowed only where steep channels gave way to gentler slopes. </p>
<p>Most of the damage occurred <a href="https://www.independent.com/news/2018/jan/14/house-house-damage-assessment-montecito-mudslides/">along the run-out pathways</a> of the debris flows – areas where material can flow after it starts sliding downhill. Yet landslide hazard maps generally don’t show predicted run-out zones. Instead, they typically show only the locations of the source areas where landslides are likely to start. </p>
<h2>Better information for residents</h2>
<p>There are reasons why people keep building homes in landslide-prone areas. Some decide it’s worth the risk. In Seattle, where I live, steep slide-prone slopes tend to offer the best, and most expensive, views. Conversely, in low-income regions such as Appalachia and many developing countries, the poor often are pushed up onto potentially unstable hillsides. Generally, however, I suspect that many Americans living in landslide country are simply unaware of potential hazards that the lay of the land presents to their homes, neighborhoods and businesses. </p>
<p>Sometimes politics or greed plays a role. After <a href="http://www4.ncsu.edu/%7Enwsfo/storage/cases/20040908/">Hurricane Frances</a> hammered North Carolina in 2004, the state legislature approved a program to map landslide hazards. But once the first maps were produced, the program was <a href="https://www.nbcnews.com/news/investigations/how-politics-buries-science-landslide-mapping-n73256">canceled</a> over concerns that the maps would affect land values and be used to regulate development. </p>
<p>Without this kind of information, residents are physically and financially exposed. “Earth movement,” such as landslides, <a href="http://www.homeinsurance.org/dont-assume-earth-movement-coverage-is-standard-in-your-home-insurance/">generally is not covered</a> by homeowner’s insurance policies. And by the time a landslide comes, developers are long gone, leaving homeowners holding the bag. </p>
<p>And, of course, different types of landslides pose different risks. In the slow-moving <a href="https://www.dnr.wa.gov/rattlesnake-hills-landslide">Rattlesnake Ridge landslide</a> in central Washington state, a 20-acre parcel of land is sliding downhill about a foot and half per week. Residents have been moved out of the at-risk zone, and engineers and geologists are monitoring the site in real time to evaluate and update hazard assessments. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/201975/original/file-20180115-101489-1a3yhfd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Upper part of the Oso, Washington landslide site, photographed April 8, 2014 (see small house just inside treeline at lower left for scale).</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/8/84/2014_Washington_Landslide.jpg">USGS/Jonathan Godt</a></span>
</figcaption>
</figure>
<p>In contrast, the <a href="http://www.geerassociation.org/administrator/components/com_geer_reports/geerfiles/GEER_Oso_Landslide_Report_low-res.pdf">Oso landslide</a> north of Seattle on March 22, 2014 was so large and fast-moving that even a real-time warning would not have prevented tragedy. This disaster killed 43 people in a couple of minutes when an entire hillside collapsed. In response, Washington state has started <a href="https://www.dnr.wa.gov/lidar">posting detailed topographical maps online</a> for use in identifying areas at risk for generating landslides. But hazard maps still don’t identify potential downhill run-out zones. </p>
<p>It’s time to get serious about landslide zoning, in the way that the federal government maps <a href="https://www.fema.gov/national-flood-insurance-program-flood-hazard-mapping">areas at serious risk of flooding</a>. Landslide hazard maps delineating potential run-out zones should be part of local land use planning. These maps could help guide zoning decisions and better inform homeowners, banks and insurance companies of potential risks. Ultimately, the best way to reduce landslide risk is to avoid building things we value in places where run-out is likely. For when there’s no controlling nature, there’s only living with her.</p><img src="https://counter.theconversation.com/content/90087/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David R. Montgomery does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
In response to mudslides that have killed at least 20 people in Southern California, a geologist calls for more resources to study and map landslide hazards so residents can understand the risks.
David R. Montgomery, Professor of Earth and Space Sciences, University of Washington
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/85982
2017-12-10T19:09:49Z
2017-12-10T19:09:49Z
Scars left by Australia’s undersea landslides reveal future tsunami potential
<figure><img src="https://images.theconversation.com/files/198258/original/file-20171208-11318-s3r0ck.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Byron Scar, left behind by an undersea landslide. Colours indicate depths.</span> <span class="attribution"><span class="source">Samantha Clarke</span>, <span class="license">Author provided</span></span></figcaption></figure><p>It is often said that we know more about the surface of other planets than we do about our own deep ocean. To overcome this problem, we <a href="https://link.springer.com/chapter/10.1007/978-3-319-20979-1_12">embarked on a voyage on CSIRO’s research vessel, the Southern Surveyor</a>, to help map Australia’s <a href="https://www.britannica.com/science/continental-slope">continental slope</a> – the region of seafloor connecting the shallow continental shelf to the deep oceanic abyssal plain. </p>
<p>The majority of our seafloor maps depict most of the ocean as blank and featureless (and the majority still do!). These maps are derived from wide-scale satellite data, which produce images showing only very large features such as sub-oceanic mountain ranges (like those seen on Google Earth). Compare that with the resolution of land-based imagery, which allows you to zoom in on individual trees in your own neighbourhood if you want to.</p>
<p>But using a state-of-the art sonar system attached to the Southern Surveyor, we have now studied sections of the seafloor in more detail. In the process, we found evidence of huge underwater landslides close to shore over the past 25,000 years. </p>
<p>Generally triggered by earthquakes, landslides like these can cause tsumanis. </p>
<h2>Into the void</h2>
<p>For 90% of the ocean, we still struggle to identify any feature the size of, say, Canberra. For this reason, we know more about the surface of <a href="https://www.scientificamerican.com/article/just-how-little-do-we-know-about-the-ocean-floor/">Venus</a> than we do about our own ocean’s depths. </p>
<p>As we sailed the Southern Surveyor in 2013, a <a href="http://oceanexplorer.noaa.gov/explorations/09bermuda/background/multibeam/multibeam.html">multibeam sonar system</a> attached to the vessel revealed images of the ocean floor in unprecedented detail. Only 40-60km offshore from major cities including Sydney, Wollongong, Byron Bay and Brisbane, <a href="https://link.springer.com/chapter/10.1007/978-3-319-20979-1_12">we found huge scars</a> where sediment had collapsed, forming submarine landslides up to several tens of kilometres across.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=256&fit=crop&dpr=1 600w, https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=256&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=256&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=322&fit=crop&dpr=1 754w, https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=322&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/196409/original/file-20171126-21853-engvjy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=322&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 portion of the continental slope looking onshore towards Brisbane, showing the ‘eaten away’ appearance of the slope in the northern two-thirds of the image, the result of previous submarine landslides.</span>
<span class="attribution"><span class="source">Samantha Clarke</span></span>
</figcaption>
</figure>
<h2>What are submarine landslides?</h2>
<p>Submarine landslides, as the name suggests, are underwater landslides where seafloor sediments or rocks move down a slope towards the deep seafloor. They are caused by a variety of different triggers, including earthquakes and volcanic activity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195983/original/file-20171123-6035-1xs59qb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=553&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 typical evolution of a submarine landslide after failure.</span>
<span class="attribution"><span class="source">Geological Digressions</span></span>
</figcaption>
</figure>
<p>As we processed the incoming data to our vessel, images of the seafloor started to become clear. What we discovered was that an extensive region of the seafloor offshore New South Wales and Southern Queensland had experienced <a href="https://link.springer.com/chapter/10.1007/978-94-007-2162-3_4">intense submarine landsliding over the past 15 million years</a>.</p>
<p>From these new, high-resolution images, we were able to identify over 250 individual historic submarine landslide scars, a number of which had the potential to generate a tsunami. The Byron Slide in the image below is a good example of one of the “smaller” submarine landslides we found – at 5.6km long, 3.5km wide, 220m thick and 1.5 cubic km in volume. This is equivalent to almost 1,000 <a href="http://mobile.abc.net.au/news/2015-08-20/surveyors-find-exact-measurements-of-melbourne-cricket-ground/6709520?pfmredir=sm&WT.ac=statenews_vic">Melbourne Cricket Grounds</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=494&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=494&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195987/original/file-20171123-6013-7yfyg3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=494&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This image shows the Byron Slide scar, located offshore Byron Bay.</span>
<span class="attribution"><span class="source">Samantha Clarke</span></span>
</figcaption>
</figure>
<p>The historic slides we found range in size from less than 0.5 cubic km to more than 20 cubic km – the same as roughly 300 to 12,000 Melbourne Cricket Grounds. The slides travelled down slopes that were less than 6° on average (a 10% gradient), which is low in comparison to <a href="https://www.researchgate.net/profile/GD_Dellow/publication/281318072_Recent_studies_of_historical_earthquake-induced_landsliding_ground_damage_and_MM_intensity_in_New_Zealand/links/57268fb708ae262228b2124e.pdf">slides on land, which usually fail on slopes steeper than 11°</a>. </p>
<p>We found several sites with cracks in the seafloor slope, suggesting that these regions may be unstable and ready to slide in the future. However, it is likely that these submarine landslides occur sporadically over <a href="https://australianmuseum.net.au/the-geological-time-scale">geological timescales</a>, which are much longer than a human lifetime. At a given site, landslides might happen once every 10,000 years, or even less frequently than this. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=295&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=295&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=295&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=371&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=371&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195988/original/file-20171123-6072-1g3jegd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=371&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 collection of submarine landslide scars off Moreton Island.</span>
<span class="attribution"><span class="source">Samantha Clarke</span></span>
</figcaption>
</figure>
<p>Since returning home, our investigations have focused on how, when, and why these submarine landslides occur. We found that east Australia’s submarine landslides are unexpectedly recent, at less than 25,000 years old, and relatively frequent in geological terms.</p>
<p>We also found that for a submarine landslide to generate along east Australia today, it is highly likely that an external trigger is needed, such as an earthquake of magnitude 7 or greater. The <a href="http://rsta.royalsocietypublishing.org/content/364/1845/2009?utm_source=TrendMD&utm_medium=cpc&utm_campaign=Philosophical_Transactions_A_TrendMD_1#sec-4">generation of submarine landslides is associated with earthquakes from other places in the world</a>. </p>
<p>Submarine landslides can lead to tsunamis ranging from small to catastrophic. For example, the 2011 Tohoku tsunami resulted in more than 16,000 individuals dead or missing, and <a href="http://www.sciencedirect.com/science/article/pii/S0025322714002898">is suggested to be caused by the combination of an earthquake and a submarine landslide that was triggered by an earthquake</a>. Luckily, Australia experiences few large earthquakes, compared with places such as New Zealand and Peru.</p>
<h2>Why should we care about submarine landslides?</h2>
<p>We are concerned about the hazard we would face if a submarine landslide were to occur in the future, so we model what would happen in likely locations. Modelling is our best prediction method and requires combining seafloor maps and sediment data in computer models to work out how likely and dangerous a landslide threat is. </p>
<p>Our current models of tsunamis generated by submarine landslides suggest that some sites could represent a future tsunami risk for Australia’s east coast. We are currently investigating exactly what this threat might be, but we suspect that such tsunamis pose little to no immediate threat to the coastal communities of eastern Australia. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/dBuRkqKTyz4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This video shows an animation of a tsunami caused by submarine landslide.</span></figcaption>
</figure>
<p>That said, submarine landslides are an ongoing, widespread process on the east Australian continental slope, so the risk cannot be ignored (by scientists, at least).</p>
<p>Of course it is hard to predict exactly when, where and how these submarine landslides will happen in future. Understanding past and potential slides, as well as improving the hazard and risk evaluation posed by any resulting tsunamis, is an important and ongoing task. </p>
<p>In Australia, <a href="https://soe.environment.gov.au/theme/coasts">more than 85% of us live within 50km of the coast</a>. Knowing what is happening far beneath the waves is a logical next step in the journey of scientific discovery.</p><img src="https://counter.theconversation.com/content/85982/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samantha Clarke receives funding from the Australian Nuclear Science and Technology Organisation (ANSTO) under the Australian Institute of Nuclear Science and Engineering (AINSE) program. </span></em></p><p class="fine-print"><em><span>Hannah Power receives funding from the NSW Government under the State Emergency Management Projects program and the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Tom Hubble has received government funding in the form of ship-time aboard the CSIRO's Marine National Facility (RV Southern Surveyor and RV Investigator) to collect the data and samples required to undertake the research discussed in this article. </span></em></p><p class="fine-print"><em><span>Kaya Wilson 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>
The ocean floor off Australia’s east coast bears the scars of numerous subsea landslides, which have potentially triggered tsunamis over the past several millennia.
Samantha Clarke, Associate Lecturer in Education Innovation, University of Sydney
Hannah Power, Senior Lecturer in Coastal Science, University of Newcastle
Kaya Wilson, PhD Candidate, University of Newcastle
Tom Hubble, Associate professor, University of Sydney
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/82594
2017-08-19T00:54:52Z
2017-08-19T00:54:52Z
Resilience has become a way of life in Sierra Leone, now mourning hundreds lost in mudslide
<p>A nation “once again… gripped by grief”. This was how Ernest Bai Koroma, president of Sierra Leone, <a href="http://www.thesierraleonetelegraph.com/?p=16894">described</a> the effects of the mudslide that devastated Regent, on the outskirts of the country’s capital, Freetown in the early hours of August 14 2017. At least 400 people were killed, hundreds more are still missing, and thousands have been rendered homeless. The vice president, Victor Foh, <a href="http://in.reuters.com/article/us-leone-mudslide-idINKCN1AV0SM">said</a> that: “The disaster is so serious that I myself feel broken.”</p>
<p>Few countries can have exceeded Sierra Leone’s share of recent misfortune. In its brutal 11-year civil war, beginning in 1991, tens of thousands of people lost their lives, countless more suffered mutilation or rape and more than a third of the population was displaced. </p>
<p>Then, in 2014, the country was ravaged by the largest ever <a href="https://theconversation.com/as-sierra-leone-waits-for-ebola-all-clear-its-emotional-scars-will-take-longer-to-heal-46421">Ebola epidemic</a>, which killed at least 4,000 people in Sierra Leone. Such peaks of trauma occurred against a backdrop of extreme poverty and high mortality rates, including one of the highest in the world for women during pregnancy or <a href="http://www.nbcnews.com/id/22782340/ns/health-childrens_health/t/un-child-mortality-highest-sierra-leone/#.WZWOVoqQzm0">childbirth</a>. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"898170011109535744"}"></div></p>
<p><a href="https://books.google.co.uk/books/about/Trauma_Survival_and_Resilience_in_War_Zo.html?id=IuW9CgAAQBAJ&source=kp_cover&redir_esc=y">Research</a> I’ve conducted in Sierra Leone over the past few years provides some understanding of how those currently gripped by grief following the mudslide might respond in the longer term, and what help they might need in addition to very practical resources.</p>
<p>One of my recent <a href="http://researchprofiles.herts.ac.uk/portal/en/publications/ebola-done-donebut-what-has-it-left-behind(fd267747-4842-4d1e-8f72-fbbcdf5ec32d).html">studies</a> focused upon people affected by the Ebola epidemic, including a group who had courageously volunteered to be burial workers. They exposed themselves to the risks of infection, but also of violence from people prevented from carrying out their normal burial rituals, and of ostracism following the epidemic. Nevertheless, they were able to see themselves as being prepared to “stand very tall to fight for our country”.</p>
<p>Another <a href="http://www.tandfonline.com/doi/abs/10.1080/10720537.2012.703568">study</a> concerned former child soldiers. Thousands of boys and girls, in some cases with ages not even in double figures, fought in the civil war. Most were forcibly conscripted, with initiations that often involved having to mutilate or murder family members. </p>
<p>They were typically plied with drugs before battle, and many were used as sex slaves. It might be expected that such experiences would have a severe impact on these young people, but surprisingly those who participated in the research viewed themselves more favourably than did young people who had not fought in the war, and as better people now than ever before. Some of them developed a Community Theatre Agency to help the reintegration of former child soldiers into the community.</p>
<p>Another <a href="http://www.tandfonline.com/doi/abs/10.1080/10720537.2015.1134366">of my studies</a> concerned a group of people who had lost limbs in the war, mostly as victims of the rebels’ favourite form of terror: amputation. They lost not only their limbs but also their hopes and dreams. However, one of them had an idea: </p>
<blockquote>
<p>You guys, never mind we lost our legs, some of us lost our hands, we’re not anything in the sight of God … let’s come together and … play football. </p>
</blockquote>
<p>They <a href="http://www.okayafrica.com/culture-2/the-flying-stars-sierra-leone-amputee-soccer-team-documentary-al-jazeera/">formed a football team</a>, which paradoxically provided opportunities, for example for foreign travel, which would not have been available had they not suffered amputation. It was clear that football played a major role in the recovery of their self-esteem.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/C5M72s6vs_s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<h2>Mental health needs</h2>
<p>Following the civil war, a very high prevalence of mental health problems was reported in Sierra Leone, where treatment facilities are very limited. In the country’s one psychiatric hospital, 75% of its patients were kept in chains when I first visited it in 2007 (with a delegation from Barnet, Enfield, and Haringey Mental Health NHS Trust) – and virtually the only treatment consisted of very heavy doses of major tranquillisers. </p>
<p><a href="https://books.google.co.uk/books/about/Trauma_Survival_and_Resilience_in_War_Zo.html?id=IuW9CgAAQBAJ&source=kp_cover&redir_esc=y">Interviews</a> with the in-patients indicated most felt they needed practical help, for example involving finance, housing, or employment. When those on one of the wards were asked what they would like, their virtually unanimous request was for music. When music cassettes were duly played, most of them spontaneously started dancing, in many cases while still chained until the staff were persuaded to unchain – and dance with – them. During subsequent visits by the delegation over six years, the number of patients kept in chains reduced to about 20%.</p>
<h2>Helping those gripped by grief</h2>
<p>These examples demonstrate the considerable resilience of the people of Sierra Leone – and of people in general – when faced with major tragedies. Although such disasters <a href="https://books.google.co.uk/books/about/Chasing_Chaos.html?id=eXOftGZ_wl8C&source=kp_cover&redir_esc=y">tend to attract</a> armies of international “trauma chasers”, such as <a href="https://books.google.co.uk/books/about/Crazy_Like_Us.html?id=6kt5TB8Lb30C&redir_esc=y">experts</a> on post-traumatic stress disorder (PTSD), it should not be forgotten that PTSD <a href="https://www.ncbi.nlm.nih.gov/pubmed/14736317">is a relatively</a> uncommon response to trauma, as compared to resilience, recovery and growth. </p>
<p>The appropriateness of such Western concepts such as PTSD may also be questioned in a country in which, to <a href="https://books.google.co.uk/books/about/The_Memory_of_Love.html?id=1CO8OND2dwgC&redir_esc=y">quote</a> from the Salonean author Aminata Forna: “You call it a disorder my friend, we call it life.” </p>
<p>Approaches based on listening to, and taking seriously, the views of those affected, or which encourage these people’s own creative initiatives, may be more relevant and effective than Western treatment methods. Some of these, which involve rapid psychological intervention after trauma, <a href="http://journals.sagepub.com/doi/abs/10.1111/j.1745-6916.2007.00029.x">have been found</a> to be at best counter-productive, and possibly harmful.</p><img src="https://counter.theconversation.com/content/82594/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Winter has received funding from Enabling Access to Mental Health Sierra Leone (funded by the European Union), and from the Tropical Health and Education Trust and Unison, via Barnet, Enfield and Haringey Mental Health NHS Trust.</span></em></p>
Mass graves are being dug for hundreds of those killed in a nation once more gripped by grief.
David Winter, Professor Emeritus of Clinical Psychology, University of Hertfordshire
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/68742
2016-11-14T08:27:20Z
2016-11-14T08:27:20Z
Be prepared, always: the tsunami message from New Zealand’s latest earthquake
<p>The tsunami warnings from the latest New Zealand earthquake show how important it is for people to be prepared for such an event.</p>
<p>The early messages from New Zealand’s Ministry of Civil Defence and Emergency Management (MCDEM) on its Twitter account <a href="https://twitter.com/NZcivildefence">@NZcivildefence</a> <a href="https://twitter.com/NZcivildefence/status/797762852488548352">said it was</a> “assessing whether there is any tsunami threat”, but just 30 minutes later it changed this advice to say a tsunami was “possible”.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"797770133754130434"}"></div></p>
<p>So why was the message changed, and what can we learn from it?</p>
<h2>Tsunami risk</h2>
<p>New Zealand is in a very active earthquake zone and the risk of tsunami is high along almost every part of the coastline. Tsunamis are usually generated by the largest earthquakes, of about magnitude 7 or above.</p>
<p>If an earthquake of this size is detected, <a href="http://www.civildefence.govt.nz/assets/Uploads/How-Tsunami-warnings-work-LR.pdf">emergency management services</a> will send out an immediate warning to give people in risk areas the maximum amount of time to evacuate.</p>
<p>But it can take several hours to work out the exact location and magnitude of an earthquake, so emergency services will continually update their message when new information becomes available.</p>
<p>In the case of the recent earthquake and tsunami in New Zealand, the first reports suggested the earthquake had a <a href="https://www.geonet.org.nz/quakes/region/newzealand/2016p858000">magnitude of 6.5</a>, below that expected to generate a tsunami.</p>
<p>It also looked like the earthquake occurred onshore, which again lowered the risk of a tsunami. That’s probably why the MCDEM, which is responsible for alerting the New Zealand public of any tsunami risk, initially sent out a tweet saying it was only assessing any tsunami threat.</p>
<p>This would have been based on the best available information at the time.</p>
<h2>Increased magnitude</h2>
<p>But in the minutes following the quake, the estimates of its magnitude were <a href="http://www.geonet.org.nz/quakes/region/newzealand/2016p858000">raised to 7.5</a>, meaning that there was real risk of a tsunami. A tsunami wave was measured at Kaikoura, on the east coast of the South Island, only minutes after the earthquake. </p>
<p>This would have prompted authorities to make a rapid change to the tsunami warning status. Messages were immediately sent out via Twitter and other means to warn of the tsunami risk.</p>
<p>Tsunami waves of 2.5m were <a href="http://www.weatherwatch.co.nz/content/tsunami-warning-issued-new-zealand">measured at Kaikoura</a>, 1m at Christchurch, and 0.5m at Wellington. The tsunami wave reached the Chatham Islands, 800km east of New Zealand, in about 4 hours, and was measured at Easter Island after 12 hours. </p>
<p>A warning was eventually issued for all of New Zealand’s coasts.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"797809307597213696"}"></div></p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"797811630419496960"}"></div></p>
<p>This was then gradually downgraded over the next few hours as the tsunami threat passed. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"797846187197902848"}"></div></p>
<p>Although the threat from tsunami waves has passed, unpredictable currents can affect beaches for many days following a tsunami, so people are usually warned to stay out of the water.</p>
<h2>Land quake, sea tsunami</h2>
<p>So how was a tsunami generated by an earthquake with its epicentre onshore? </p>
<p>Most <a href="http://www.srh.noaa.gov/jetstream/tsunami/generation.html">tsunamis</a> are generated when a fault ruptures on the sea floor, rapidly pushing up a wall of water which then moves outwards as a wave. When an earthquake occurs on land there is far less risk of this happening.</p>
<p>But tsunamis can also be caused by landslides caused by <a href="https://www2.usgs.gov/faq/categories/9752/3101%20">nearby earthquakes</a>. The east coast of New Zealand near Kaikoura is considered to have a high risk of <a href="http://www.newshub.co.nz/environmentsci/kaikoura-landslide-could-spark-tsunami-2013032307">submarine landslides</a>.</p>
<p>The <a href="http://www.teara.govt.nz/en/map/5605/kaikoura-canyon">Kaikoura Canyon</a>
just offshore from Kaikoura has very steep, unstable sides with a lot of loose sediment. During an earthquake this sediment can fall into the canyon, displacing water and generating a tsunami wave. </p>
<p>We already know that large landslides did occur onshore to the north and <a href="http://info.geonet.org.nz/display/quake/2016/11/14/M7.5+Kaikoura+Quake%3A+What+we+know+so+far">south of Kaikoura</a>. It is highly likely that landslides also occurred in the deep water of the Kaikoura Canyon, and that this is what caused the tsunami. </p>
<p>The first lesson to learn from this is that tsunamis can often strike the coast with very little warning, and people in high-risk zones need to act quickly when an earthquake occurs and not wait for <a href="http://itic.ioc-unesco.org/index.php?option=com_content&view=category&layout=blog&id=1195&Itemid=1195">official warnings</a>.</p>
<p>The second lesson is that despite the incredible technology we now have to measure earthquakes and tsunamis, there are still limits on how quickly we can accurately measure and locate an earthquake and assess the likely tsunami risks. Events such as Monday’s, where the earthquake likely triggered a submarine landslide, make it even harder to quickly calculate the tsunami risk. </p>
<p>Earthquakes and tsunamis are unpredictable although our understanding of the science is improving all the time. </p>
<p>But it takes time to get accurate information to the public after an earthquake and tsunami, so those living closest to the hazard zones need to be aware of natural warning signs and not rely only on official warning messages.</p><img src="https://counter.theconversation.com/content/68742/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jane Cunneen 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>
The threat of any tsunami following an earthquake can take time to assess, so it’s important people who live in risk zones are ready for any event.
Jane Cunneen, Research Fellow, Curtin University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/56528
2016-03-21T15:56:39Z
2016-03-21T15:56:39Z
What we’ve learned from the deadly Oso, Washington landslide two years on
<figure><img src="https://images.theconversation.com/files/115803/original/image-20160321-30949-1bjv2i8.png?ixlib=rb-1.1.0&rect=107%2C0%2C1075%2C508&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Before and after the Oso landslide in 2014.</span> <span class="attribution"><span class="source">Joseph Wartman</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>On March 22, 2014, a hillside above Oso, Washington <a href="http://old.seattletimes.com/flatpages/local/oso-mudslide-coverage.html">collapsed</a>, unleashing a torrent of mud and debris that buried the community of Steelhead Haven. Forty-three people lost their lives, making it one of the single deadliest landslide disasters in U.S. history.</p>
<p>Over the past two years, we’ve learned much about the specific geology of the Stillaguamish River Valley where Oso is located, and the weather that preceded this landslide. One study I co-led <a href="http://dx.doi.org/10.1016/j.geomorph.2015.10.022">identified geologic factors</a> such as weak, saturated ground that made the Oso hillside highly susceptible to landslides. Another investigation found that large landslides similar to the one in Oso <a href="http://dx.doi.org/10.1130/G37267.1">occur with surprising frequency in the region</a> – on average, every 140 years, just a flash in recent geologic time. </p>
<p>A study of the rainstorm that triggered the landslide found that precipitation in the weeks leading up to the event was only moderately intense, though <a href="http://dx.doi.org/10.1175/JHM-D-15-0008.1">unusual in its timing</a> during the normally drier early spring season. </p>
<p>But important questions remain about other aspects of the landslide. Answering them will not only advance landslide science, but can also help protect other threatened communities around the globe. So what do we still need to figure out?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=136&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=136&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=136&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=171&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=171&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115708/original/image-20160320-4417-mn77dm.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=171&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">After the March 22, 2014 Oso, Washington landslide.</span>
<span class="attribution"><span class="source">Joseph Wartman</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Landslide basics</h2>
<p>A landslide – the downslope movement of rock or soil – is a natural geologic process that forms and shapes landscapes. Slides occur when downward forces from gravity exceed the strength of soil or rock within a slope – in other words, when the weight of a hill slope becomes too much to bear. Landslides affect slopes across a wide range of settings, but steep terrain is most precarious. Often, it’s precipitation or earthquakes that trigger landslides.</p>
<p>There are several <a href="http://pubs.usgs.gov/circ/1325/">types of landslides</a>, but most dangerous are flows, which occur when saturated ground transforms into a liquid-like state and inundates downslope areas within minutes. Flow landslides, such as the one at Oso, become disasters when they quickly spill into communities, leaving people virtually no time to escape. </p>
<p>Landslides occur worldwide, including in every U.S. state – the U.S. Geological Survey estimates that, on average, landslides kill <a href="http://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html">25 to 50 people across the country each year</a>.</p>
<p>The global toll is much worse. During the seven-year period ending in 2010, <a href="http://dx.doi.org/10.1130/G33217.1">landslides killed over 32,000 people worldwide</a>, mostly in densely populated mountainous areas with intense rainfall, such as in Asia and Latin America. Knowing that some regions are more susceptible than others, can we minimize the potential damage from future landslides?</p>
<h2>Do human actions contribute to landslides?</h2>
<p>We’ve learned a lot about the geologic aspects of the Oso landslide, but aside from nature, could human activities also have played a role? We know that human actions can contribute to landslides, especially when natural topography is altered to create oversteepened, unstable landscapes, as was the case in a <a href="http://www.bbc.com/news/world-asia-china-35148909">recent disaster in China</a>.</p>
<p>For many decades, anecdotal evidence has suggested that logging on or near hill slopes contributes to their collapse by reducing reinforcement from roots and by altering ecosystems to allow more precipitation to enter the ground. As early as 1930, after a slide occurred in the Oso region, Washington state’s game director noted that “Many people feel that this earth movement was <a href="http://projects.seattletimes.com/2014/building-toward-disaster/">triggered by the intense logging</a> of the forest cover of the land and resulting erosion.” A 1988 study of the area found that timber harvesting does <a href="http://www.seattletimes.com/seattle-news/state-tackles-steep-challenges-to-step-up-logging-oversight/">increase surface water infiltration</a> to the ground, which can destabilize hillsides. </p>
<p>Yet it is clear that landslides bearing a striking resemblance to the 2014 event in Oso have occurred in the region <a href="http://dx.doi.org/10.1130/G37267.1">for at least 2,000 years</a> – long before large-scale timber harvesting began. Though indications are that logging can make some slopeside regions more susceptible to landslides, geologic evidence of earlier slides near Oso makes it unclear what role, if any, timber harvesting played in this event.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=438&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=438&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=438&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=550&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=550&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115755/original/image-20160321-30917-4hhemg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=550&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">High-resolution topographic map of the Oso landslide and surrounding terrain. An older large slide similar to the Oso event is seen immediately to the right of the 2014 landslide.</span>
<span class="attribution"><span class="source">Joseph Wartman with data provided by the Puget Sound LIDAR Consortium</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Living in harm’s way</h2>
<p>Regardless of whether human action has a hand in setting off a particular landslide, its effects may be felt by anyone who lives downslope.</p>
<p>And we still don’t have a good grasp on the interconnected human, social and political factors that lead people to put down roots in dangerous places. Is it because of their lack of scientific understanding or access to incomplete information? Or is existing knowledge simply incomprehensible to public officials and ordinary citizens?</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/115709/original/image-20160320-4453-7y3hx5.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"></a>
<figcaption>
<span class="caption">Oso, Washington community memorial.</span>
<span class="attribution"><span class="source">Joseph Wartman</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>At Oso, the Steelhead Haven community, which was established in the early 1960s, continued to expand even as smaller landslides occurred there during the 1990s and 2000s. In the face of continued threats from landslides, how did residents weigh risk against the cost of abandoning property – and the cherished community that bound them together?</p>
<p>The issue is not unique to Oso; in the decade since a landslide killed 10 people in La Conchita, California, that community, too, has continued to grow. As a La Conchita resident recently lamented, “Where else am I going to go? <a href="http://www.latimes.com/local/california/la-me-la-conchita-20150104-story.html">This is my home</a>.”</p>
<p>So even as our understanding of the natural science aspects of the Oso landslide increases, there is still much we don’t know about the interface between landslides and people. Questions of this nature are complex, multidisciplinary, sometimes contentious and not easy to answer. But they’re important and go beyond scientific curiosities. Indeed, they touch upon issues that are central to land-use planning, resource management and public safety. </p>
<p>There is no doubt that some of these questions will soon be raised in the Washington state courts, where these issues – alleged destabilization from logging and siting a community in a hazardous area – are central to some of the <a href="http://www.heraldnet.com/article/20160225/NEWS01/160229480">pending litigation</a>; however, juries are often not ideal arbiters of scientific issues.</p>
<p>Questions about logging and land-use in hazardous terrain lie at the intersection of the natural, social and applied sciences, so multidisciplinary research will be needed to better understand these issues. And understanding alone will not be enough to save lives and reduce losses. We must also have the political will to translate knowledge into practice through effective public policies.</p><img src="https://counter.theconversation.com/content/56528/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph Wartman receives funding from U.S. National Science Foundation under grants 1439773 and 1548552. </span></em></p>
Landslide researchers continue to learn more about how and where these events occur. It’s trickier to figure out how to minimize potential damage to human communities from future landslides.
Joseph Wartman, Associate Professor of Geotechnical Engineering, University of Washington
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/32396
2014-10-01T14:35:30Z
2014-10-01T14:35:30Z
How deadly landslides can now be predicted using fibre optic sensors
<figure><img src="https://images.theconversation.com/files/60508/original/8zch3t55-1412160137.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1200%2C686&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Too much give.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/andedam/293695/sizes/o/in/photolist-2viH-jWQp1E-2gqsjz-jWQr11-38UwgU-brZrjZ-mbgzYV-mbgytv-mbhris-9zcawn-9zbdu4-7qUGqk-93A2n9-aaAq7-9zbdWx-cnnJf-8ora15-9UnAbF-2uRwW-6xsa8U-7D9hSP-5vsJCA-aemzgg-8STXhQ-8STX8s-6KETjj-egXiie-7D9hSF-9AQ7qT-2viD-2viE-ok3eKF-7D9hTc-av1Amt-oBjHHw-jA4cUc-f7HVxp-574UeF-hFT1UY-cqCoMJ-ghBV78-mTBKZ1-7WwP9V-oS6iWn-p9iYsp-p9zuSM-p9xBDJ-f244Q5-f1NQjc-f245gC-93dVLU/">Gunnar Danielsen</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Landslides happen everywhere and in different geological locations. This can be because <a href="http://abcnews.go.com/International/wireStory/73-dead-landslides-floods-northeast-india-25722676">of flooding</a>, which allows sodden soil to move, or rockfalls and slower, continuous movements of land due to gravity. Landslides are particularly dangerous when they happen without warning, as recently happened in India <a href="http://www.theguardian.com/world/2014/aug/22/japan-landslide-situation-worsens">and Japan</a>. Tens of thousands were killed in the Vargus disaster in Venezuela in 1999.</p>
<p>Some places are prone to flooding – even, in the case of India, monsoons – but to know where a landslide will happen or when it might happen we need good tools. Currently equipment to measure landslides includes rain gauges, such as those used <a href="http://www.thefinancialexpress-bd.com/2014/09/27/58429">in the Chittagong region of Bangladesh</a>, which record levels of rainfall that can then be compared to previous data of levels that triggered a landslide. </p>
<p>But many current systems use point-based sensors, in other words systems that rely on ground plugged devices that are able to monitor only from fixed positions.</p>
<p>We’ve been working on a new way of measuring to predict landslides using optical fibres in cables as sensors. When installed, these sensors can permanently monitor changes happening to the land. The system, called <a href="http://cepof.ifi.unicamp.br/index.php/en/research/optical-communications?id=103">Stimulated Brillouin Scattering</a>, uses the interaction of light with acoustic waves. Basically, when the soil undergoes collapse or sliding, the embedded fibre stretches and we detect this.</p>
<p>These sensing optical fibre cables can be embedded in shallow trenches in the ground to monitor both large landslides and slow slope movements through the elongation induced in the sensing fibre. If you imagine the land as a body, a distribution of these optical fibre sensors act as the “nerve system”. They have the ability to detect a change of one centimetre over a distance of a kilometre. Being able to measure and track early pre-failure soil movements, it is then possible to detect the signs of an imminent landslide.</p>
<p>Unlike these conventional tools, optical fibres make measurements along the whole sensing cable which allows for a fully distributed measurement of land deformation. The advantage is the continuous monitoring of large areas with high accuracy. They can also be used in difficult-to-access places, for example underneath bridges, outside the walls of tunnels, near dams and along pipelines and railways in remote rural areas.</p>
<p>These sensors can also be used to cover very large areas (several square kilometres) with a single fibre cable and to pinpoint the location of failure signs. In traditional point-based systems you have to be lucky to place a sensor in the critical position where something happens otherwise you miss the event. </p>
<p>The optical fibres can also be controlled from a remote point, so fibres can be laid and left with no need for regular inspections, while the data is transmitted via wireless or optical fibre networks. They are also cheaper than traditional point sensors because a single fibre does the trick and no in-situ visits are required.</p>
<p>Optical fibres <a href="http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=833416">have been used</a> to measure creep in road boundaries and to monitor bridges and pipelines. So far, only small-scale tests have been used with regard to landslides. But we believe they could change the way we measure and predict these deadly occurrences.</p><img src="https://counter.theconversation.com/content/32396/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luigi Zeni is affiliated with:
Second University of Naples - Italy
Research Consortium on Advanced Remote Sensing Systems - Italy (<a href="http://www.corista.eu">www.corista.eu</a>)
OPTOSENSING S.r.L. - Italy (<a href="http://www.optosensing.it">www.optosensing.it</a>)</span></em></p>
Landslides happen everywhere and in different geological locations. This can be because of flooding, which allows sodden soil to move, or rockfalls and slower, continuous movements of land due to gravity…
Luigi Zeni, Professor of Electronics, Second University of Naples
Licensed as Creative Commons – attribution, no derivatives.