Bathymetry-based submarine landslide volume assessments

Abstract

Submarine landslides can cause devastating tsunamis. The size of such tsunamis depends on water depth, acceleration, maximum velocity, and initial volume of the landslide. In the past, submarine landslide volume as the most important of these parameters has often been estimated by seismic data. It is well-established that this can lead to a significant over-estimation of the tsunamigenic landslide volume because the seismic data do not allow to distinguish the initially moving volume from material that has been deformed in-situ or incorporated at great water depth. Here, the volume of evacuated material from the source area derived from seafloor morphology is a good measure for the total tsunamigenic landslide volume. The analysis of high-resolution 3D reflection seismic data that cover the same submarine landslide also shows that a much greater volume of the seismically imaged landslide deposit has remained largely in-situ and could thus not have contributed to an associated tsunami. This distinction could not have been made with lower resolution 3D reflection seismic data or with high-resolution 2D reflection seismic data. These findings imply that under circumstances that tend to be fulfilled for small landslides, the bathymetrically derived volume of the source area can be a much better measure for the tsunamigenic volume of submarine landslides than individual seismic profiles.