Underwater landslides are an enormous and fast-moving collapse of the continental slope, 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 that lies above them, generating tsunamis that travel across the ocean, flooding coastal communities and destroying infrastructure on land.
Underwater landslides can be far larger than their terrestrial counterparts. One of the largest occurred offshore from Norway around 8,200 years ago. This landslide moved an area bigger than Scotland, downslope and triggered a tsunami tens of metres high that impacted UK coastlines.
Smaller underwater landslides can also occur, which pose a threat to seafloor energy pipelines and telecommunications cables. In certain regions, the magnitude and likelihood of such events appears to be increasing as a result of climate change, particularly where more sediment is transferred offshore by river floods and tropical cyclones.
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, pyroclastic density currents (fast moving flows of hot gas and volcanic matter) and poisonous gases.
Very deep water can exert enough pressure on submerged volcanoes to suppress their explosivity, but in shallower waters, the interaction between hot volcanic rocks and water is explosive and can generate ocean impacts such as tsunamis, steam-driven explosions, eruption of rafts of floating volcanic rock and vast, powerful underwater flows of volcanic material.
Many of the volcanoes in our oceans are not mapped and almost none are monitored, making it hard to understand where and when the next big eruption could occur. The partial collapse of Anak Krakatau (Indonesia) generated a tsunami that killed hundreds in 2018. Hunga Volcano (Kingdom of Tonga) disconnected an entire nation from the internet in 2022 by wiping out subsea cables.
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.
As these flows can reach speeds of up to 20 metres per second and travel over hundreds of kilometres, 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, including 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. There, multiple telecommunications cables were broken by a turbidity current that travelled more than 1000km into the deep sea, causing 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.
A tsunami is a series of waves created by the rapid displacement of a large volume of water, triggered by events such as earthquakes, underwater landslides, volcanic eruptions, and in some specific cases, changes in air pressure (known as ‘meteotsunamis’).
They are more likely in regions where earthquake and volcanic activity is greatest, like the Pacific Ring of Fire. However, other less geologically dynamic regions like the UK can still experience tsunamis, particularly as they can cross entire oceans.
Studies have suggested that an earthquake emanating from the Azores-Gibraltar fault zone is the most likely source of a tsunami that would affect the UK coastline. In fact, an earthquake like this destroyed Lisbon in 1755 and generated a tsunami that reached Cornwall and southern Ireland in around four hours. Seismic events like these are monitored by tsunami warning centres, which send tsunami warnings to member countries like the UK.
How does our research protect people?
Sensors: Advances in technology have enabled us to make the first direct measurements of seafloor geohazards such as turbidity currents, to identify their triggers, speed and impacts that they may pose to seafloor infrastructure. This now includes the development of novel passive sensors to detect geohazards without having to place sensors in their pathway.
Surveys: Scientists conduct repeat surveys of active regions of the seafloor to understand and document the dynamic nature of evolving marine geohazards. We have been part of the team interpreting repeat surveys at Hunga and Anak Krakatau volcanoes to understand the impacts of these eruptions and others like them beneath the oceans.
Community data collection: Scientists collect and analyse data to understand the impacts of marine geohazards to Small Island Developing States at all scales. We have analysed a range of community data to understand vulnerability to volcanic events in the South Pacific.
Sediment cores: We analyse sediment cores that provide long term records of past geohazards from the deposits they leave behind on the seafloor. More than 13km of sediment cores are stored and curated by NOC’s British Ocean Sediment Core Research Facility (BOSCORF), providing a valuable archive of past geohazards from around the global ocean.
Simulations: We collaborate on experimental and numerical simulations of marine geohazards, to determine how and why different geohazards are triggered and what their impacts are.
Monitoring systems: We have installed and maintain tsunami-capable monitoring systems, both in the UK and overseas, as well as identifying tsunami and meteo-tsunami events from tide gauge records and core logs. Alongside collaborators our scientists use numerical models to determine the impacts of tsunamis of various origins.
Seafloor mapping: Scientists map seafloor features and capture what they look underwater using cutting edge ocean robots and technology to understand the distribution of marine hazards. These include volcanoes, landslides, faults, hydrothermal systems, and gas escape structures.
“Our research has allowed us to explain the size and failure mechanism of the 2018 landslide at Anak Krakatau.”, says Dr James Hunt. “This is the first time that a volcanic island landslide-tsunami has been studied using satellite images and seafloor mapping in such detail. This knowledge means that we can better model the tsunami that was generated from it, providing a benchmark for such activities. This information may in-turn allow us to better design hazard mitigation strategies.”
Industry collaboration: We work with offshore industries, such as with the International Cable Protection Committee, to share information about past instances of damage from marine geohazards and work out how to design more resilient seafloor infrastructure.
“Subsea cables are crucial to our daily lives, enabling remote working, education, financial trading, and access to telemedicine. As we are increasingly reliant on this global network, it is essential that we assess any potential future disruptions that may emerge as a result of climate change.”
“Our reliance on cables that are no wider than a garden hose is a surprise to many, who regard satellites as the main means of communication. But satellites simply don’t have the bandwidth to support modern digital systems. The ‘Cloud’ is not in the sky – it is under the sea. Ongoing marine geohazard research will help mitigate any social and economic impacts that could arise if industry is not well-informed and prepared.”
Advising authorities: As one of the 17 organisations forming the UK’s Natural Hazards Partnership, part of the Cabinet Office Civil Contingencies Secretariat, we contribute scientific advice for the preparation, response and review of natural hazards. This is just one example of the ways we contribute advice for the benefit of the public.
Advancing future research
There is still a huge amount of work to be done to understand how marine geohazards develop, how they operate and who will be impacted. We’re focussed on understanding:
- How do different marine geohazards initiate, why do they occur where they do, and can we predict where this might occur in the future?
- How do we map, monitor and forecast marine geohazards most effectively to provide warnings to communities, governments and offshore industries?
- What are the credible worst case scenarios for the largest geohazards that remain poorly or completely un-observed from instrumental records?
- How can we best develop response and contingency plans, and enhance future resilience for the regions and infrastructure that are most at risk?
This new understanding will be used to improve the planning and design of future seafloor and coastal infrastructure, to understand and map vulnerabilities and to provide hazard planning and contingency for a more resilient future.
Our research goes deeper
Inside the most EXPLOSIVE volcanic eruption of the 21st Century – Izzy Yeo.
This video is part of the ‘Into the Blue Podcast’ series.
Key NOC projects
Hunt, J.E., Tappin, D.R., Watt, S.F.L., Susilohadi, S., Novellino, A., Ebmeier, S.K., Cassidy, M., Engwell, S.L., Grilli, S.T., Hanif, M. and Priyanto, W.S., 2021. Submarine landslide megablocks show half of Anak Krakatau island failed on December 22nd, 2018. Nature communications, 12 (1), p.2827. https://doi.org/10.1038/s41467-021-22610-5
Talling, P.J., Baker, M.L., Pope, E.L., Ruffell, S.C., Jacinto, R.S., Heijnen, M.S., Hage, S., Simmons, S.M., Hasenhündl, M., Heerema, C.J. and McGhee, C., 2022. Longest sediment flows yet measured show how major rivers connect efficiently to deep sea. Nature communications, 13 (1), p.4193. http://doi.org/10.1038/s41467-022-31689-3
Clare, M.A., Yeo, I.A., Bricheno, L., Aksenov, Y., Brown, J., Haigh, I.D., Wahl, T., Hunt, J., Sams, C., Chaytor, J. and Bett, B.J., 2022. Climate change hotspots and implications for the global subsea telecommunications network. Earth-Science Reviews, p.104296. http://doi.org/10.1016/j.earscirev.2022.104296
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