Geohazards

Underwater landslides are enormous, fast-moving collapses of the continental slope. This is the area of land between the edge of a continent (that lies under the ocean) and the deep-ocean floor. These landslides displace the seawater sitting above them, generating tsunamis that travel across the ocean, flooding coastal communities, and destroying infrastructure on land.

Underwater landslides can be far larger than those on land. One of the largest occurred offshore from Norway around 8,200 years ago (Medium). This landslide moved an area larger than Scotland downslope and triggered a tsunami tens of metres high that impacted UK coastlines.

Smaller underwater landslides also occur, posing a threat to seafloor energy pipelines and telecommunications cables. In certain regions, the magnitude and likelihood of these events appear to be increasing due to climate change, particularly where river floods and tropical cyclones transfer more sediment offshore.

A huge number of Earth's volcanoes are found in the oceans. These submerged or partially submerged volcanoes can pose a wide range of hazards to communities and the environment, such as explosions, ash, lava, poisonous gases, and pyroclastic density currents (fast-moving flows of hot gas and volcanic matter).

Very deep water can exert enough pressure on submerged volcanoes to suppress their explosivity. However, in shallower waters, the interaction between hot volcanic rocks and water is explosive. This can generate ocean impacts such as tsunamis, steam-driven explosions, eruptions of floating volcanic rock rafts, and vast, powerful underwater flows of volcanic material.

Many of the volcanoes in our oceans are not mapped, and almost none are monitored. This makes it hard to understand where and when the next large eruption could occur. For example, the partial collapse of Anak Krakatau (Indonesia) generated a tsunami that killed hundreds in 2018 (British Geological Survey).

Underwater avalanche-like flows called turbidity currents are mixtures of sand, mud, and water that travel downslope because they are denser than the surrounding seawater. They form the largest sediment accumulations, deepest canyons, and longest channels on Earth.

These flows can reach speeds of up to 20 metres per second and travel over hundreds of kilometres. Because of this, they pose a hazard for seafloor infrastructure. This includes the global network of telecommunications cables that currently carries more than 99% of all digital data traffic worldwide, covering the internet and trillions of dollars of financial trading every day.

Damage to seafloor cables has provided new insights into these flows, including those triggered by large river floods offshore West Africa in 2020 (Geographical). There, multiple telecommunications cables were broken by a turbidity current that travelled more than 1,000 km into the deep sea. This caused the internet from Nigeria to South Africa to slow down during the early stages of the COVID-19 lockdown, just when capacity was most needed.

Scientists map seafloor features and capture what they look like underwater using cutting-edge ocean robots and technology. This helps us understand the distribution of marine hazards, including volcanoes, landslides, faults, hydrothermal systems, and gas escape structures.

We work with offshore industries, such as the International Cable Protection Committee, to share information about past instances of damage from marine geohazards. This helps us work out how to design more resilient seafloor infrastructure.