Extreme erosion by submarine slides

Submarine slides (including slides, slumps, and debris flows) pose major geohazards by triggering tsunami and damaging essential submarine infrastructure. Slide volume, a key parameter in hazard assessments, can increase markedly through substrate and/or water entrainment. However, the erosive potential of slides is uncertain. We quantified slide erosivity by determining the ratio of deposited (V-d) to initially evacuated (V-e) sediment volumes; i.e., slides that gain volume through erosion have V-d/V-e ratio >1. We applied this method to the Gorgon slide, a large (500 km(3)), seismically imaged slide offshore northwestern Australia, and reviewed V-d/V-e ratios for 11 other large slides worldwide. Nine of the 11 slides have V-d/V-e > 1 (median value = 2), showing emplaced volumes increased after initial failure. The Gorgon slide is the most erosive slide currently documented (V-d/V-e = 13), possibly reflecting its passage across a highly erodible carbonate ooze substrate. Our new approach to quantifying erosion is important for hazard assessments given substrate-flow interactions control slide speed and runout distance. The variations in slide volume also have important implications for submarine infrastructure impact assessments, including more robust tsunami modeling.