How erosive are submarine landslides?

Submarine landslides (slides) are ubiquitous on continental margins. They can pose a major hazard by triggering tsunami and damaging essential submarine infrastructure. Slide volume, which is a key parameter in hazard assessment, can change after initiation through substrate and/or water entrainment. However, the erosive capacity of slides is uncertain. Here, we quantify slide erosivity by determining the ratio of deposited (Vd) to initially evacuated (Ve) sediment volumes. Slides that gain volume through erosion = Vd/Ve>1. We apply this method to a large (500 km3), seismically imaged slide offshore NW Australia, and review Vd/Ve ratios for other large slides worldwide. Nine of the 11 slides have Vd/Ve>1 (median value=2), showing that emplaced volumes increased after initial failure. The Gorgon Slide is the most erosive slide currently documented (Vd/Ve=13), possibly reflecting its passage across a highly erodible carbonate ooze substrate. This new approach to quantifying erosion is important for hazard assessments as substrate-flow interactions control slide speed and run-out distance. The variations in slide volume also have important implications for submarine infrastructure impact assessments, including more robust tsunami modelling.