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

海底滑坡是深海中常见的地质特征。它们出现在各种环境中，从陡峭的火山岛侧翼到缓慢倾斜的沉积物覆盖的露天斜坡。一些海底滑坡在下坡过程中解体，转化为沉积物重力流，可以在相对平坦的海底上运输大量沉积物数百公里（< 10）。海底滑坡和沉积物重力流是全球沉积物从大陆架向深海运输的主要过程，是对日益增长的全球海底基础设施网络（如石油/天然气管道和电信电缆）的主要威胁。海底滑坡也会引发灾难性的海啸。例如，大约8200年前，挪威近海巨大的斯托尔加滑坡（Storegga Slide）引发了海啸，摧毁了从挪威到苏格兰的沿海社区。此外，富砂流的沉积形成了许多世界上最大的石油和天然气储层，而富泥流可能在深海中封存了全球大量的有机碳。提高我们对滑坡和沉积物重力流危害的认识需要来自过去事件的现场数据；这些数据提供了对诸如体积和循环间隔等重要参数的见解。这些数据还有助于我们模拟由山体滑坡引起的海啸，并评估相关风险。在这项研究中，我们建议生成有史以来第一个从源头到汇追踪大规模海底滑坡及其相关沉积物重力流的现场数据集。我们将把重点放在西北非洲近海的摩洛哥浊积岩系统上，在那里，世界上最大的沉积物重力流能够在长达2000公里的距离上输送100立方公里的沉积物。利用过去30年来从整个沉积区收集的200个浅层沉积物岩心数据集，确定了几次地质上最近（过去20万年）流动的体积、源区和时间。先前的研究表明，这些水流大多源于（尚未绘制的）阿加迪尔峡谷上游及其周围的山体滑坡。阿加迪尔峡谷是世界上最大的峡谷之一，长450公里，宽30公里，深1250米。阿加迪尔峡谷上游水深4000米以上的大部分地区尚未开发，因此我们计划利用地球物理工具和沉积物覆盖层对该地区的滑坡进行测绘和采样。新的结果将使我们能够进行一种新的“质量平衡”分析，在这种分析中，我们可以量化1)在最初的滑坡期间撤离的物质体积，2)失败物质的崩解速度和程度，3)由此产生的水流带走的物质体积，以及4)水流中被侵蚀的海底沉积物的体积。这个独特的定量现场数据集将使我们能够解决三个重要的科学问题：1)大型海底滑坡分解成长时间的沉积物流的速度有多快，这个过程如何受到斜坡形状的影响？2)滑坡清除破坏物质的效率如何，即有多少比例的滑坡碎片沉积在斜坡上，有多少转变成流并向远处输送？3)有多少泥沙通过海底侵蚀进入水流，大部分侵蚀发生在哪里？这些结果对于NOC和其他NERC社区正在进行的滑坡-海啸和沉积物重力流模型至关重要，并将改进相关全球地质灾害的评估。

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.