A study from the University of Liverpool has unveiled the colossal scale and devastating impact of a massive underwater avalanche that struck the northwest coast of Africa some 60,000 years ago. This research, published in Science Advances, provides unprecedented insights into the magnitude and destructive force of submarine avalanches, a phenomenon shrouded in mystery until now.

The study was led by Dr. Chris Stevenson, a sedimentologist from the University of Liverpool’s School of Environmental Sciences. He and his team have, for the first time, successfully mapped the entire trajectory of a giant submarine avalanche, revealing that it originated as a relatively small underwater landslide in the Agadir Canyon. This initial event involved about 1.5 cubic kilometers of material but rapidly grew more than 100 times in size as it traveled across the Atlantic Ocean floor. As the avalanche progressed, it picked up rocks, gravel, sand, and mud, carving a destructive path through one of the world’s largest submarine canyons and extending 2,000 kilometers across the seabed.

The avalanche was so powerful that it eroded a 400-kilometer stretch of the canyon, cutting hundreds of meters into its sides and affecting a total area of about 4,500 square kilometers. The force of the flow was so immense that it hurled boulders to heights of over 130 meters up the canyon walls. This immense scale of destruction challenges previous understandings of submarine avalanches, which were thought to be much less extensive.

3D image of giant underwater avalanche which took place nearly 60,000 years ago in the Agadir Canyon
3D image of giant underwater avalanche which took place nearly 60,000 years ago in the Agadir Canyon. Credit: Dr. Christoph Bottner / Aarhus University

Unlike more familiar natural disasters such as landslides or snow avalanches, submarine avalanches are invisible and exceedingly difficult to study. However, they play a critical role in transporting sediments, nutrients, and even pollutants across the ocean floor. These avalanches also pose significant geological risks to undersea infrastructure, such as internet cables that are vital to global communications.

The Liverpool research team analyzed over 300 core samples collected from the region during various research expeditions over the past 40 years. This, combined with seismic and bathymetric data, allowed them to reconstruct the submarine avalanche in detail. Dr. Stevenson highlighted that this is the first time a submarine avalanche of this scale has been fully mapped and its growth factor calculated. He noted that the event, which began modestly, evolved into a massive and destructive avalanche reaching heights of 200 meters and traveling at speeds of approximately 15 meters per second.

To put the size of this event into perspective, Dr. Stevenson compared it to a skyscraper-sized avalanche moving at over 64 kilometers per hour, cutting a trench 30 meters deep and 15 kilometers wide from Liverpool to London. This enormous flow then spread out over an area larger than the United Kingdom, burying it under a meter of sand and mud.

Overview map of North West African Margin showing the pathway of the event and its erosional marks on the seafloor
Overview map of North West African Margin showing the pathway of the event and its erosional marks on the seafloor. Credit: University of Liverpool

The study’s co-leader, Dr. Christoph Bottner from Aarhus University, emphasized the extraordinary growth factor of the avalanche, which exceeded 100 times its initial size—a stark contrast to snow avalanches or debris flows that typically expand by a factor of only 4 to 8. This suggests that such extreme growth may be a characteristic feature of submarine avalanches, warranting further investigation.

Professor Sebastian Krastel, head of Marine Geophysics at Kiel University and chief scientist on the expeditions that mapped the canyon, noted that this research fundamentally challenges previous assumptions. The findings demonstrate that even small underwater landslides can escalate into massive, highly destructive events. This has significant implications for assessing the geological risks these avalanches pose, especially to critical infrastructure like internet cables, which are essential for modern society.

The most recent mapping of the Agadir Canyon was conducted by the University of Kiel’s Geosciences Institute, the Leibniz Institute for Baltic Sea Research, and Germany’s GEOMAR Helmholtz Centre for Ocean Research. Core samples were analyzed from the British Ocean Sediment Core Repository, collected over 40 years on various NERC ships.

SOURCES

University of Liverpool

Christoph Böttner et al., Extreme erosion and bulking in a giant submarine gravity flow. Sci. Adv. 10, eadp2584(2024). DOI:10.1126/sciadv.adp2584

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