New findings have shown how an underwater avalanche dramatically expanded to over 100 times its original size, resulting in extensive destruction as it traveled 2000 kilometers across the seabed of the Atlantic Ocean near the North West coast of Africa. This research offers a unique perspective on the magnitude, strength, and effects of one of nature’s enigmatic events—underwater avalanches.
Recent studies from the University of Liverpool have disclosed how an underwater avalanche increased in size by more than 100 times, leading to significant devastation as it traversed 2000 km of the Atlantic Ocean seafloor off the North West coast of Africa.
In research published in the journal Science Advances (and featured on the cover), scientists provide a groundbreaking understanding of the scale, force, and consequences of underwater avalanches, one of nature’s puzzling wonders.
Dr. Chris Stevenson, a sedimentologist from the University of Liverpool’s School of Environmental Sciences, co-led a team that, for the first time, has mapped a massive underwater avalanche from start to finish, which occurred almost 60,000 years ago in the Agadir Canyon.
Their investigation shows that this event began as a modest seafloor landslide, with a volume of about 1.5 km3. It then grew over 100 times larger, accumulating boulders, gravel, sand, and mud while moving through one of the planet’s largest submarine canyons, continuing for an additional 1600 km across the Atlantic seafloor.
This avalanche possessed such strength that it eroded the full extent of the canyon, which spanned 400 km, and several hundred meters up its walls—totaling around 4,500 km2. Its force was so intense that it transported cobbles over 130 meters up the canyon’s side.
Unlike traditional landslides or snow avalanches, underwater avalanches remain hidden from sight and are quite challenging to measure. Nevertheless, they play a crucial role in the transportation of materials like sediments, nutrients, and pollutants across Earth’s surface. They also present a significant threat to underwater infrastructure, such as internet cables.
The research team examined over 300 core samples collected from the area during research missions over the last four decades. By combining this data with seismic and bathymetric information, they were able to outline the immense underwater avalanche.
Dr. Stevenson stated: “This marks the first time we have successfully mapped out a complete individual underwater avalanche of such magnitude and calculated its growth factor.”
“It’s intriguing to see how the event escalated from a relatively small initiation into a massive and destructive submarine avalanche, reaching heights of 200 meters as it moved at approximately 15 m/s, ripping through the sea floor and uprooting everything in its path.”
“To give some context: envision an avalanche the size of a skyscraper, traveling at over 40 mph from Liverpool to London, creating a trench that is 30 meters deep and 15 kilometers wide while destroying whatever lies in its path. It then spreads over an area greater than the UK, smothering it with around a meter of sand and mud.”
Dr. Christoph Bottner, a Marie Curie research fellow at Aarhus University in Denmark and co-leader of the team, mentioned, “We estimate the growth factor to be at least 100, which is significantly larger compared to snow avalanches or debris flows, which only expand by about 4-8 times. We have observed similar extreme growth patterns in smaller underwater avalanches measured in different locations, indicating that this might be a distinctive behavior related to underwater avalanches, which we aim to explore further.”
Professor Sebastian Krastel, head of Marine Geophysics at Kiel University and chief scientist aboard the research missions that mapped the canyon, added: “Our new insights significantly alter our understanding of these events. Previously, we believed that large avalanches originated only from substantial slope failures. Now we recognize that they can develop from small beginnings into powerful and extensive giant events.”
“These discoveries are critical for assessing the potential risks these avalanches pose to underwater infrastructure, like internet cables that facilitate almost all global internet traffic, which are vital to various aspects of our contemporary society.”
The latest mapping cruises of the Agadir Canyon were orchestrated by the Institute of Geosciences, Kiel University, Leibniz Institute for Baltic Sea Research, and GEOMAR Helmholtz Centre for Ocean Research, Germany. A collection of archived core data was analyzed from the British Ocean Sediment Core Repository at NOCS Southampton, gathered aboard NERC ships over the past 40 years.
