How do submarine landslides disintegrate and form long run-out turbidity currents in the deep ocean, and how erosive are these flows?

Submarine landslides are a common geological feature in the deep ocean. They occur in a range of environments, from steep volcanic island flanks to areas of gently sloping sediment-covered open slope. Some submarine landslides disintegrate during their passage downslope and transform into sediment-gravity flows that can transport huge volumes of sediment for hundreds of kilometres over relatively flat ocean floor (<1o). Submarine landslides and sediment-gravity flows are the dominant process for global sediment transport from the continental shelf to the deep ocean, and are a major threat to an increasing worldwide network of seafloor infrastructure, e.g. oil/gas pipelines and telecommunications cables. Submarine landslides can also generate catastrophic tsunamis. For example, the giant Storegga Slide offshore Norway about 8200 years ago produced a tsunami that devastated coastal communities from Norway to Scotland. In addition, the deposits of sand-rich flows form many of the World's largest oil and gas reservoirs, while mud-rich flows may sequester globally significant volumes of organic carbon in the deep ocean. Improving our understanding of landslide and sediment-gravity flow hazards requires field data from past events; these data provide insights into important parameters such as volume and recurrence interval. These data also help us to model landslide-generated tsunamis and assess the associated risks.

In this study we propose to generate the first ever field dataset tracing a large-scale submarine landslide and its associated sediment-gravity flow from source-to-sink. We will focus on the Moroccan Turbidite System offshore NW Africa, where the World's largest sediment-gravity flows were able to transport >100 km3 of sediment across distances up to 2000 km. The volume, source area and timing of several geologically recent (last 200,000 years) flows has been identified, using a dataset of >200 shallow sediment cores collected from across the entire depositional area over the last 30 years. Previous work has shown that most of these flows originated from (as yet unmapped) landslides in and around upper Agadir Canyon, which is one of the largest canyons in the World at 450 km long, up to 30 km wide and 1250 m deep. Most of upper Agadir Canyon above 4000 m water depth is unexplored, so we plan to map and sample landslides in this area using geophysical tools and sediment corers. The new results will allow us to undertake a novel 'mass balance' analysis, where we can quantify 1) the volume of material evacuated during the initial landslide, 2) the rate and extent of disintegration of failed material, 3) the volume of material removed by the resulting flow, and 4) the volume of eroded seafloor sediment incorporated in the flow. This unique quantitative field dataset will allow us to tackle three important science questions:

1) How quickly do large submarine landslides disintegrate into long run-out sediment flows, and how is this process influenced by shape of the slope?

2) How efficiently do landslides remove failed material, i.e. what proportion of landslide debris is deposited on the slope and how much transforms into a flow that is transported distally?

3) How much sediment is incorporated into the flow through seafloor erosion, and where does most of this erosion take place?

The results will be vital for ongoing landslide-tsunami and sediment gravity-flow modeling being undertaken by NOC and others in the NERC community, and will improve assessment of associated global geohazards.

Landslides and sediment gravity flows are a potential hazard to an increasing global network of seafloor infrastructure, including oil/gas pipelines and telecommunications cables. The results of this project will feed directly into a larger programme of work on submarine geohazards being undertaken at NOC. This work has strong end-user involvement, including government, industry and academia. For example, Wynn is a contributor to the newly formed 'Natural Hazards Partnership', which was initiated by the Civil Contingencies Secretariat of the UK Government Cabinet Office in order to ensure effective co-ordination of natural hazards research and rapid dissemination of results to government end-users. NOC is a partner in this initiative, which will help guide the evolution of the UK National Risk Register. On the industry side, Wynn was instrumental in developing a relationship with Willis Re, a global insurance and reinsurance broker that employs about 20,000 people worldwide; this relationship recently resulted in NOC becoming Associate Members of the Willis Research Network. The reinsurance sector is becoming increasingly engaged in submarine hazards research, and joining the WRN has provided NOC scientists with an opportunity to directly interact with this sector at workshops and meetings. Wynn and colleagues have already provided information to the WRN about the general risks posed by submarine landslides and associated tsunamis. Wynn is also collaborating with Prof Lionel Carter (Victoria University, Wellington, New Zealand), who is Marine Environmental Advisor to the International Cable Protection Committee (ICPC). Carter, Wynn and colleagues from ICPC have recently undertaken a joint project documenting three separate cable-break events offshore Taiwan since 2006. This project has resulted in a recent submission to Geophysical Research Letters. The results of this work will be provided to ICPC through regular meetings and workshops.

Wynn and Masson also have significant experience of interaction with the oil and gas sector, advising on submarine geohazards and modern analogues for deep-water clastic reservoirs. The results of this work have specific geographic relevance to this sector, as the study area around upper Agadir Canyon is currently a zone of active hydrocarbon exploration. Significant hydrocarbon reserves are currently being exploited elsewhere on the northwest African margin, including the major Chinguetti gas field that sits within the slide scar of the giant Mauritania Slide. Wynn and Masson have both advised companies involved in production of this gas field, e.g. Woodside Petroleum. An improved knowledge of the timing and processes of landslides and sediment gravity flows will inform geohazard assessment of current and future developments along this margin. More generically, the results of this project will contribute to the deliverables of the UK Turbidite Architecture and Process Studies (UK-TAPS) industry consortium, currently led by Dr Peter Talling at NOC. As Lead Co-ordinators, Wynn and Talling generated >£0.5M of industry funding for UK-TAPS between 2002-07, and Wynn led a joint NERC-TAPS project that collected valuable analogue data through a coring cruise to Agadir Basin in 2004 (CD166). This project attracted >£180k of industry co-funding from a consortium that included Shell, ExxonMobil, BHP Billiton, ConocoPhillips, Norsk Hydro and BP. UK-TAPS continues to be engaged in the delivery of annual workshops and presentations with sponsors in Houston and elsewhere.