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

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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.