Novel method to map the morphology of submarine landslide headwall scarps using remotely operated vehicles

Submarine landslides are one of the main marine geohazards worldwide. In order to better estimate their risk and develop mitigation measures, a better understanding of the failure mechanisms is needed. However, observing landslides in real time is near to impossible, hence careful study of both the failed sequence and the deposit is still the main source of information. Until recently, studies of the headwall scarps of submarine landslides were mainly based on shipboard acoustics and the descriptions of analogues on land. The increasing availability of Remotely Operated Vehicles (ROVs) now allows in-situ, close-up investigations in the marine environment. In this paper we present a novel methodology to obtain a detailed map of the headwall morphology of submarine landslides, including detail on vertical cliffs, overhanging strata and biological colonisation. Using a high-resolution multibeam system mounted on the front of a working-class ROV, rather than in a traditional downward looking configuration, we mapped three sections of a scallop-shaped headwall scarp which is part of the Rockall Bank Slide Complex, west of Ireland, as part of the SORBEH cruise funded by the Irish Government and the ERC CODEMAP project. The resulting 3D model provides insights in the build-up of the failed sequence, allowing advances in the understanding of rupture mechanisms. It can be combined with close-up video ground-truthing and carefully collected samples to create a complete picture of the headwall scarp.