Will climate change in the Arctic increase the landslide-tsunami risk to the UK?

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment


Submarine landslides can be far larger than terrestrial landslides, and many generate destructive tsunamis. The Storegga Slide offshore Norway covers an area larger than Scotland and contains enough sediment to cover all of Scotland to a depth of 80 m. This huge slide occurred 8,200 years ago and extends for 800 km down slope. It produced a tsunami with a run up >20 m around the Norwegian Sea and 3-8 m on the Scottish mainland. The UK faces few other natural hazards that could cause damage on the scale of a repeat of the Storegga Slide tsunami. The Storegga Slide is not the only huge submarine slide in the Norwegian Sea. Published data suggest that there have been at least six such slides in the last 20,000 years. For instance, the Traenadjupet Slide occurred 4,000 years ago and involved ~900 km3 of sediment. Based on a recurrence interval of 4,000 years (2 events in the last 8,000 years, or 6 events in 20,000 years), there is a 5% probability of a major submarine slide, and possible tsunami, occurring in the next 200 years. Sedimentary deposits in Shetland dated at 1500 and 5500 years, in addition to the 8200 year Storegga deposit, are thought to indicate tsunami impacts and provide evidence that the Arctic tsunami hazard is still poorly understood.

Given the potential impact of tsunamis generated by Arctic landslides, we need a rigorous assessment of the hazard they pose to the UK over the next 100-200 years, their potential cost to society, degree to which existing sea defences protect the UK, and how tsunami hazards could be incorporated into multi-hazard flood risk management. This project is timely because rapid climatic change in the Arctic could increase the risk posed by landslide-tsunamis. Crustal rebound associated with future ice melting may produce larger and more frequent earthquakes, such as probably triggered the Storegga Slide 8200 years ago. The Arctic is also predicted to undergo particularly rapid warming in the next few decades that could lead to dissociation of gas hydrates (ice-like compounds of methane and water) in marine sediments, weakening the sediment and potentially increasing the landsliding risk.

Our objectives will be achieved through an integrated series of work blocks that examine the frequency of landslides in the Norwegian Sea preserved in the recent geological record, associated tsunami deposits in Shetland, future trends in frequency and size of earthquakes due to ice melting, slope stability and tsunami generation by landslides, tsunami inundation of the UK and potential societal costs. This forms a work flow that starts with observations of past landslides and evolves through modelling of their consequences to predicting and costing the consequences of potential future landslides and associated tsunamis. Particular attention will be paid to societal impacts and mitigation strategies, including examination of the effectiveness of current sea defences. This will be achieved through engagement of stakeholders from the start of the project, including government agencies that manage UK flood risk, international bodies responsible for tsunami warning systems, and the re-insurance sector.

The main deliverables will be:
(i) better understanding of frequency of past Arctic landslides and resulting tsunami impact on the UK
(ii) improved models for submarine landslides and associated tsunamis that help to understand why certain landslides cause tsunamis, and others don't.
(iii) a single modelling strategy that starts with a coupled landslide-tsunami source, tracks propagation of the tsunami across the Norwegian Sea, and ends with inundation of the UK coast. Tsunami sources of various sizes and origins will be tested
(iv) a detailed evaluation of the consequences and societal cost to the UK of tsunami flooding , including the effectiveness of existing flood defences
(v) an assessment of how climate change may alter landslide frequency and thus tsunami risk to the UK.

Planned Impact

Our project will provide the scientific basis for decisions by three major types of stakeholder.

UK Flood-Risk Management (Environment Agency; Department for Environment Food and Rural Affairs; Scottish Government): Project results will be disseminated to DEFRA and the Environment Agency (EA) who manage the risk of flooding in England and Wales, and Scottish Government that has responsibility for policy on flood management in Scotland. Our results will be used within a multi-risk framework for UK flooding that includes storm surge and rainfall sources. The EA will be involved in Work Block 6, which will utilise their 'National Flood and Coastal Defence Database' of both government and third party assets. Our analysis of potential magnitude of landslide-tsunami generated flood inundation, frequency and societal cost would be incorporated with their previous initiatives such as 'Risk Assessment for Flood and Coastal Defence Strategic Planning (RASP)'. RASP provides a flexible hierarchical method for assessing flood risk from multiple sources, and strategic prioritisation of flood defences and targeting of flood warning and emergency preparedness. We will inform the Department of Business, Innovations and Skills (as they have interest in foresight and analysis of future risks to the UK), Department of Energy and Climate Change (for offshore energy structures), and Department of Transport of project results.
The Intergovernmental Oceanographic Commission of UNESCO (IOC) has a mandate from the international community to co-ordinate tsunami early warning and mitigation in the North Atlantic. They have established a tsunami information centre and have a series working groups, including those for 'hazard assessment, risk and modelling', and 'regional tsunami warning system architecture'. They provide the correct route for project results to inform future warning and mitigation strategies for landslide-tsunami. They also provide a forum for exchange of technical information with European partners (such as those involved with the EU Transfers FP6 project in 2006-2009). We will report to the two IOC working groups on our tsunami modelling and estimates of UK risk and vulnerability. Key project results and final report will be disseminated through the IOC.

Re-Insurance Sector: Willis and their Research Network will be strongly involved as formal project partners, especially in building of geospatial data bases and estimates of societal cost. Willis is the world's 3rd largest insurance and re-insurance broker and the Willis Research Network (WRN) that they created is the world's largest collaboration between academic partners worldwide and the insurance industry. They facilitate access to other WRN members working on related risks, and access to the global insurance sector through WRN meetings. Willis will provide their staff time for project meetings, workshops, and ad-hoc discussions with project members. The consortium project will have access to the global insurance sector through additional meetings hosted and organised by Willis. Willis will host two of the PDRA positions in their offices in London, and during these visits the PDRAs will learn how geospatial tools are used by industry.

Wider Users: The subject of infrequent but potentially high impact landslide needs to be conveyed carefully to a wider (non-scientific) audience, as shown by previous press coverage of landslide-tsunamis in the Canary Islands. Project results will be disseminated by press releases (from both NOC and NERC Arctic Research Programme Office) and by a dedicated website. The cruise will form part of the NOC Classroom-at-Sea project to involve school children. We seek to involve the NERC programme's Knowledge Exchange co-ordinator with this wider dissemination of the project and its results.
Description Findings from the collaborative case study on geotechnical profiling of deep ocean, sensitive sediments at AFEN submarine slide: Following an intensive testing programme on 8.4m length of core made available to us, two hypotheses were formed for the causes of failure. One possibility is progressive failure of the sensitive sediment in Unit #5, which would have required a trigger such as local slope over-steepening, hydrate dissociation or earthquake loading. A different possibility is flow liquefaction of the silt in Unit #5, as the plasticity of the clayey silt (at 11-12 %) is sufficiently low for liquefaction to occur, and particle size distribution and visual description data strongly support this mechanism, which would explain the long runout distances that have been observed at AFEN. Acceptance of a particular mechanism of failure at AFEN will require further testing at other locations, to establish the widespread presence of sensitive or liquefiable materials in the slope area.
A separate study examined the effect of gas hydrate on the strength and stiffness of some sands using our bespoke gas hydrate triaxial apparatus. Cylindrical specimens of given porosity & methane hydrate content were prepared using the 'excess gas method' and sheared undrained at constant effective stress and rate of shearing for sands. These tests were then compared with their corresponding host sediments with no hydrates. We found gas hydrate dissociation not only removes cementing but also releases freshwater and significant amounts of trapped gas that are dependent on multiple factors such as type of sediment, available pore space, hydrate morphology, and hydrate saturation. The presence of pock marks in areas of known seabed instability suggests that hydrate dissociation may have been a factor in triggering failure at these locations. Having reviewed the mechanisms by which the strength and stiffness of seabed sediment may be changed during dissociation, our study focuses on the results of laboratory testing to evaluate the effects of loss of hydrate cement on strength and stiffness, for a range of sand-sized materials with differing particle size, specific surface area, and particle shape, using a laboratory gas hydrate triaxial apparatus. The results suggest that both the strength and the stiffness of hydrate-cemented granular materials are affected significantly by the specific surface available for hydrate cementation and, to a certain extent, by the particle shape. Uniform coarse granular sediments of lower specific surface area can suffer significant loss of stiffness and strength upon hydrate dissociation, changing the sediment from dilative to contractive. Finer-grained sediments appear less affected by dissociation.
Exploitation Route The findings have been published in reputable research journals, so more information on this is available in the public domain. As a direct result due to expertise developed from this grant we were approached by NOC and Marum University, Bremen, Germany for EU H2020 - Submarine LAndslides and Their impact on European continental margins as project partner (PDRA1) to train and transfer knowledge to a PhD student (ESR 9).
As a result of this project findings and expertise developed, we have also been approached by GFZ Potsdam, Gemany to participate as EU project partner for MarTERA project on gas hydrates. Currently we are hosting research fellow from GFZ to enable characterisation of gas hydrate bearing sediments from our expertise (PDRA1).
Sectors Energy,Environment

Description Collaboration with GFZ, Potsdam, Germany 
Organisation Helmholtz Association of German Research Centres
Department German Research Centre for Geosciences
Country Germany 
Sector Private 
PI Contribution We are facilitating the testing of gas hydrate-bearing sandy sediments, by providing training for, and allowing use of, the Gas Hydrate Resonant Column that was developed at Southampton, and which is a unique piece of apparatus. 3. Developed international collaborations for future funding opportunities - GFZ, Potsdam, Germany with collaborative research activities funded by 'COST' - European Cooperation in Science and Technology.
Collaborator Contribution Our partners will provide data on the seismic properties of gas hydrate-bearing sanding sediments that they have developed at GFZ, especially on attenuation. The resulting data will be complementary to tests we have already carried out and is expected to result to joint publications.
Impact N/A as the collaboration was very recently established.
Start Year 2017