Direct monitoring of breaching in deltaic submarine landslides

Submarine landslides threaten seabed infrastructure and trigger the transport of globally important amounts of sediment, carbon, and pollutants to deep-sea environments. However, fully submarine landslides have never been directly monitored in nature. Past hypotheses for their failure mechanism and dynamics therefore remain unvalidated for natural settings, including that prolonged upslope-migrating failures (breaching) occur in sandy seafloor environments. In this work, we present direct underwater monitoring of fully submarine landslides at Homathko Delta in western Canada that retrogress slowly upslope, indicating breaching-type failure. Their prolonged rather than instantaneous nature has important implications for the stress that seabed structures must be designed to withstand. Prolonged landslides also initiate sustained sediment flows (turbidity currents) that efficiently transport sediment, carbon, and pollutants further offshore.