Large Submarine Landslides on Continental Slopes: Geohazards, Methane Release, and Climate Change

Submarine landslides on open continental slopes can be prodigious in scale. They are an important process for global sediment fluxes, and can generate very damaging tsunamis. Submarine landslides are far harder to monitor directly than terrestrial landslides, and much greater uncertainty surrounds their preconditioning factors and triggers. Submarine slope failure often occurs on remarkably low (< 2°) gradients that are almost always stable on land, indicating that particularly high excess pore pressures must be involved. Earthquakes trigger some large submarine landslides, but not all major earthquakes cause widespread slope failure. The headwalls of many large submarine landslides appear to be located in water depths that are too deep for triggering by gas hydrate dissociation. The available evidence indicates that landslide occurrence is either weakly (or not) linked to changes in sea level or atmospheric methane abundance, or the available dates for open continental slope landslides are too imprecise to tell. Similarly, available evidence does not strongly support a view that landslides play an important role in methane emissions that cause climatic change. However, the largest and best-dated open continental slope landslide (the Storegga Slide) coincides with a major cooling event 8,200 years ago. This association suggests that caution may be needed when stating that there is no link between large open slope landslides and climate change.