Submarine landslides have significant implications for marine ecology and infrastructure, yet these unpredictable events have remained challenging to study. New research co-led by Newcastle University’s Dr Sanem Acikalin and involving an international team of collaborators from 10 institutions, has provided the first direct observations of these elusive events.  

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 organic carbon to the Homathko Delta. Monitoring the submarine channel system suggests that this material eventually gets remobilized and transported offshore.  

Led by Monterey Bay Aquarium Research Institute (MBARI) and Durham University, the team published their findings in the journal Science today (12 November). 

Observing submarine landslides and other processes that contribute to the removal and transport of this material from the delta required an innovative new approach. Over an intensive 18-day field campaign at the Homathko Delta in British Columbia, Canada, where a glacier-fed river flows into a deep fjord, researchers used sonar equipment and sensors to monitor the delta every second. The team mapped the seafloor daily and collected sediment samples to characterise the delta front, with much of the sediment analysis carried out by the Newcastle University team. The samples are now stored at Newcastle University, providing a valuable resource for further research. 

New insights into seafloor processes

Dr Sanem Acikalin, Senior Lecturer in Geology, Newcastle University School of Natural and Environmental Sciences, said: “Underwater landslides are common on deltas, where rivers deposit sediment into the sea. They can damage vital infrastructure, including seabed cables, pipelines and offshore wind turbine foundations, while also transporting sediment, organic carbon and pollutants into the deep ocean. 

“Until now, no one had directly observed a landslide occurring entirely underwater in its natural environment. Before this new study, our understanding of how these landslides develop and behave has largely been based on computer models, laboratory experiments and observations of landslides triggered by human activities such as dredging.” 

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. 

Dr Acikalin said: “The findings have important implications for the design and protection of offshore infrastructure, including seabed cables, pipelines and offshore wind turbines. Engineers need to consider the prolonged forces generated by underwater landslides, rather than focusing solely on sudden impacts. Understanding the different types of landslide is also crucial for choosing the right protection measures, whether that means preventing erosion and reinforcing slopes with rock, or compacting and draining sediment to reduce the risk of sudden collapse.  

“Our findings also highlight how smaller, more frequent landslides can efficiently transport river sediment, carbon and pollutants into the deep ocean. This is particularly significant for global carbon budgets, as fjords alone account for around 11% of the organic carbon buried in the oceans.” 

Submarine landslides are also important for transporting carbon, pollutants, and other materials 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. 

Reference: 

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 

Adapted with thanks from MBARI.