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Southampton engineers to help assess tsunami threat to the UK

Published: 
1 August 2012

Engineers from the University of Southampton are to help assess the threat posed to the United Kingdom by tsunamis that are triggered by colossal – but extremely rare – underwater landslides.

Underwater landslides can be far larger than any landslide seen on land. For example, the Storegga Slide that occurred 8,200 years ago offshore Norway is larger than Scotland. It contained over 3,000 cubic kilometres of material (300 times the amount of sediment carried each year by all of the world’s rivers combined) and ran out for 800 kilometres into the deep ocean. This truly prodigious mega-landslide generated a tsunami that ran up to heights of three to six metres along northern parts of the UK coastline. A modern day event of a similar scale to the Storegga Slide would be likely to lead to significant loss of life and devastating damage to key infrastructure, and there are few other natural events that would have such a disastrous impact on the UK.

A team of scientists, including engineers from the University of Southampton, is embarking on a four–year investigation to assess the hazard that landslide-tsunamis in the Arctic could pose to the UK over the next 100 to 200 years. This team is led by the National Oceanography Centre, Southampton and involves academics from six other UK institutions, together with international project partners.

The team will look at the likely impact on human society and infrastructure, the degree to which existing sea defences are effective, and how the threat of tsunamis can be incorporated into the UK’s multi-hazard flood risk management.

The specific aims of the research project are four-fold: to clarify the frequency and timing of major Arctic submarine slides, to better understand trigger factors and assess whether the frequency of the slides is likely to increase as climate changes and oceans warm, and to assess the magnitude necessary for landslide-tsunamis to flood parts of the UK coast.

The fourth strand of the consortium’s research will be an attempt to quantify the likely cost to the UK of different types of inundation triggered by different types of landslide occurring in different locations.
Southampton engineers will be responsible for delivering specific research to understand the conditions under which Arctic sediments may become unstable and lead to the development of landslides even on low gradients, such as those found on Arctic continental slopes.

Dr Antonis Zervos, from the University of Southampton’s Infrastructure Research Group, said: “To decide whether rapid Arctic climate change will lead to increased risk of Arctic submarine slope failures we must first fully understand the different mechanisms that may cause Arctic sediments to fail. We also need to understand the possible contribution that the dissociation of methane hydrate, which is an ice-like solid made of water and methane found in some sediments, may make to sediment instability.

“We will develop a slope model that will incorporate the properties of sediments that form weak layers on which slides fail, the effects of hydrate dissociation as determined from laboratory tests of hydrate-bearing clays, of seismicity due to ice unloading, as well as the effect of asymmetric loading due to continuous sediment deposition. Systematic use of this model will aid understanding of whether these factors, individually or in combination, are likely to influence the future slide frequency.”

Worldwide, most tsunamis - such as the 2004 Indian Ocean tsunami, and 2011 tsunami offshore Japan - are triggered by large earthquakes near plate boundaries. Tsunamis triggered by mega-landslides are far less frequent than those caused by earthquakes. However, landslide-tsunamis may represent a greater threat to the UK, which is located away from the plate boundaries that create large earthquakes.

In the past, submarine mega-landslides near to the UK have been very rare, and considerable uncertainty still surrounds the frequency of mega-landslides. The available sea floor mapping suggests that at least six mega-slides have occurred beneath the Norwegian and Greenland Seas during the last 20,000 years. It is not yet clear whether all of these mega-landslides generated large tsunamis, or whether they produced two recent tsunami deposits found in the Shetland Islands.

Importantly, it has been proposed that mega-landslides will become more frequent due to future ocean warming that causes melting of gas hydrate which weakens sea floor sediment. It has also been proposed that melting ice sheets will cause an increase in the frequency of large earthquakes, as the Earth’s crust adjusts to the removal of the ice sheet’s weight. Such earthquakes could potentially generate more frequent mega-slides and tsunamis. The project will test these hypotheses rigorously, to determine whether there is credible evidence that the frequency of mega-landslides and tsunamis will increase significantly in the near future.

Scientists have so far been unable to monitor a mega-landslide in action. This is important because the way in which the landslide moves determines the size of the tsunami it produces. Landslides that occur in a series of stages produce much smaller tsunamis. The project will analyse sediment flow deposits generated by mega-landslides to help understand how the landslides moved.

Project leader, Dr Peter Talling of the National Oceanography Centre, Southampton said: “This is the first extensive study to assess the probability and likely impact of a landslide-tsunami on the United Kingdom. It is timely as it has been proposed that climate change may be a factor that increases tsunami frequency significantly. This hypothesis is in need of careful testing. We have assembled a broad range of expertise to look at this issue and to produce findings which will have a significant influence on future decision-making on flood protection and resilience. We hope that the project will produce a step-change in scientific understanding about some of the most remarkable and largest natural events that occur on our planet.”

 

Notes for editors

The £2.3 million project, funded by the Natural Environment Research Council (NERC) will use a range of techniques, including shipboard expeditions that will map the Arctic seafloor and extract sediment cores from the seabed, fieldwork on land to identify and date coastal tsunami deposits, slope stability modelling, laboratory experiments showing how hydrate dissociation affects sediment strength, and modelling of future trends in seismicity.

It will also include modelling of landslide motion, tsunami wave generation and propagation, and how tsunami waves would interact with existing UK coastal defence structures. A sensitivity analysis will aim to capture uncertainties, and the key factors that determine societal cost.

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