Submarine landslides have significant implications for marine ecology and infrastructure, yet these unpredictable events have remained challenging to study. New research led by MBARI Research Specialist Rebecca Englert and Durham University Associate Professor Matthieu Cartigny, with an international team of collaborators from 10 institutions, has provided the first direct observations of these elusive events. The team published their findings in Science today.

The Homathko Delta is located at the head of the Bute Inlet in British Columbia, Canada. Offshore of the delta is a 50-kilometer (31-mile) submarine channel system. Every summer, river discharge from seasonal snowmelt delivers large amounts of sediment and carbon to the Homathko Delta. Monitoring in the submarine channel system suggests that this material eventually gets remobilized and transported offshore. Observing submarine landslides and other processes that contribute to the removal and transport of this material from the delta required an innovative new approach: installing sonar systems in the mouth of a fast-flowing river.

The research team combined sonar, multibeam seafloor mapping, and moorings to enable high-resolution monitoring of seafloor activity. During fieldwork in 2022, they observed about 30 submarine landslides over an 18-day period, and logged detailed, direct observations of three active landslides. The team used these data to differentiate landslide failure mechanisms and understand how landslides evolve downslope, aspects of landslides which have been previously hypothesized from theory and experiments, but have never been directly observed naturally.

Submarine landslides on the Homathko Delta Front evolve from instabilities in water-saturated sediment at the transition from the river to the fjord. Unlike liquefaction where a disturbance, like an earthquake or sediment loading, causes sediment grains to pack more tightly, increasing pressure in the water between the sediment grains and resulting in instantaneous failure, submarine landslides on the Homathko Delta result from breaching. In this failure mechanism, sediment grains move apart during a disturbance, causing a decrease in interstitial water pressure and a suctioning effect that temporarily strengthens the sediment. As the water pressure returns to normal, the sediment slowly and progressively fails over a prolonged period of several minutes to hours. These events evolve into turbidity currents, which are powerful slurries of water and sediment that can travel several kilometers downslope.

The team’s findings in the Homathko Delta are applicable to other sandy deltas and submarine canyon heads around the world where similar conditions exist that could set up breach failures, including Monterey Bay’s submarine canyon.

This work has implications for hazard assessments in nearshore sandy environments. Submarine landslides put offshore infrastructure at risk and cause shoreline retreat. Breach failures require different mitigation strategies compared to other failure types. Their transformation into turbidity currents that can travel farther from the shore means that hazards related to landslides can extend far downslope.

Submarine landslides are also important for transporting carbon, pollutants, and other material to offshore environments. This study demonstrates that breach failures can occur very regularly and quickly transfer material several kilometers offshore, underscoring the close link between coastal environments and the deep seafloor. 

This research was conducted with the support of the Homalco First Nation, and funded by Royal Society grants DHF\R\231008; RF\ERE\210157, Canada Foundation for Innovation grant JELF 40459, Leverhulme Trust Early Career Fellowship grant ECF-2021-566, Natural Environment Research Council (NERC) grants NE/Y005589/1, NE/Z504038/1, NE/M017540/2, NE/R001960/2, and NE/W000601/1, European Research Council Grant GEOSTICK (Grant agreement ID: 725955), and the David and Lucile Packard Foundation.

Research Publication:

Englert, R.G., M.J.B. Cartigny, M.L. Baker, S. Acikalin, D. Mastbergen, N. Tracey, S.C. Ruffell, D.H. Shugar, D.G. Lintern, R. Aggarwal, L. Bailey, D. Bell, M.A. Clare, S.M. Hubbard, G. Lobato, D. Parsons, S. M. Simmons, C. Stacey, P. Talling, and M. Tilston. 2026. Direct monitoring of breaching in deltaic submarine landslides. Science, aef8444. https://doi.org/10.1126/science.aef8444

Story by Senior Science Communication and Media Relations Specialist Raúl Nava

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