Direct observation of a submarine landslide reveals seafloor processes

Direct observation of a submarine landslide in Canada's Homathko Delta has revealed previously unknown processes governing these seafloor events. Submarine landslides, which can damage critical infrastructure and transport sediment and pollutants to the deep ocean, have traditionally been difficult to study due to their remote and unpredictable nature.

Researchers from Newcastle University, Durham University, MBARI and Durham University collaborated to directly observe these events for the first time. The Homathko Delta, located at the head of Bute Inlet in British Columbia, Canada, serves as a natural laboratory for studying these phenomena. Every summer, seasonal snowmelt contributes vast amounts of sediment and organic carbon to the delta, which eventually gets mobilized and transported offshore through submarine landslides.

To capture these processes, the research team employed an innovative approach involving sonar equipment and sensors to continuously monitor the delta for 18 days, mapping the seafloor daily and collecting sediment samples. Analysis of these samples, much of which was conducted at Newcastle University, provided crucial insights into the mechanisms behind these landslides.

The findings indicate that submarine landslides on the Homathko Delta develop through a process called "breaching," where sediment grains move apart during a disturbance, decreasing interstitial water pressure and strengthening the sediment. As water pressure returns to normal, the sediment slowly fails over several minutes to hours, forming turbidity currents that can travel several kilometers downslope.

This mechanism differs from liquefaction, where sediment grains pack tightly and fail suddenly, often triggered by human activities like dredging. Understanding these gradual, extended failure processes has significant implications for hazard assessments and infrastructure protection in nearshore sandy environments. By considering the prolonged forces generated by underwater landslides, rather than focusing solely on sudden impacts, engineers can better design and protect offshore facilities such as seabed cables, pipelines, and offshore wind turbines.

Additionally, these insights highlight the importance of recognizing the role of smaller, more frequent landslides in transporting river sediment, carbon, and pollutants into the deep ocean, with implications for global carbon budgets and the distribution of organic carbon in fjords.