First Direct Observation of an Underwater Landslide Rewrites the Hazard Playbook

In breaching, the grains move apart instead. Interstitial water pressure — the pressure of water held between sediment particles — drops, producing a suction effect that temporarily strengthens the sediment. As pressure returns to normal, the slope fails slowly and progressively over several minutes to hours. These failures then evolve into turbidity currents: powerful slurries of water and sediment that can travel several kilometers downslope.

In plain terms: the seafloor does not snap — it leaks, slowly, and then races away as a current.

Why had no one seen this before?

"Until now, no one had directly observed a landslide occurring entirely underwater in its natural environment," Acikalin, senior lecturer in geology at Newcastle University's School of Natural and Environmental Sciences, said. Before this study, understanding of how underwater landslides develop and behave rested largely on computer models, laboratory experiments, and observations of failures triggered by human activity such as dredging.

Underwater landslides are common on deltas, where rivers deposit sediment into the sea. They can damage seabed cables, pipelines and offshore wind turbine foundations, while moving sediment, organic carbon and pollutants into the deep ocean.

What changes for engineers?

The findings apply to other sandy deltas and submarine canyon heads worldwide where similar conditions could set up breach failures — including Monterey Bay's submarine canyon. They carry direct consequences for hazard assessment in nearshore sandy environments, where landslides threaten offshore infrastructure and drive shoreline retreat.

"Engineers need to consider the prolonged forces generated by underwater landslides, rather than focusing solely on sudden impacts," Acikalin said. "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."

Breach failures demand different mitigation strategies than sudden collapses, and their transformation into turbidity currents means hazards can reach far downslope from where the slope first gave way.

What does this mean for the carbon cycle?

The study also shows that smaller, frequent landslides can move river sediment, carbon and pollutants into the deep ocean with remarkable efficiency. That matters for global carbon accounting: as Acikalin noted, fjords alone account for around 11% of the organic carbon buried in the oceans.

The recorded breach failures recur regularly and transfer material several kilometers offshore quickly, underscoring how tightly coastal environments couple to the deep seafloor.

The findings come from one delta over 18 days, so extrapolation to other sites carries uncertainty — but the mechanism itself, observed rather than modeled, gives practitioners a measured template for what to design against.

One landslide, watched second by second, changes how the industry should size its defenses.

Publication details: Rebecca G. Englert et al., "Direct monitoring of breaching in deltaic submarine landslides," Science (2026). DOI: 10.1126/science.aef8444