Overview map of the North West African Margin showing the course of the event and its erosion traces on the seafloor. Image credit: University of Liverpool
New research from the University of Liverpool has found that an underwater avalanche grew more than 100 times in size, leaving a massive trail of devastation as it traveled 2,000 kilometres across the seabed of the Atlantic Ocean off the north-west coast of Africa.
In a study titled “Extreme erosion and inflation in a giant submarine gravity low” and published in the journal Scientific advancesResearchers are providing unprecedented insights into the scale, power and impact of one of nature’s most mysterious phenomena: underwater avalanches.
Dr Chris Stevenson, a sedimentologist from the School of Environmental Sciences at the University of Liverpool, co-led the team that mapped for the first time from top to bottom a massive underwater avalanche that occurred in the Agadir Canyon nearly 60,000 years ago.
Their analysis shows that the event, which began as a small seafloor landslide with a volume of about 1.5 km², increased in size over 100 times, carrying with it boulders, gravel, sand and mud as it passed through one of the largest undersea canyons in the world before traveling another 1,600 km across the Atlantic Ocean floor.
The avalanche was so powerful that it eroded the entire canyon for 400 kilometers and several hundred meters on the sides – about 4,500 kilometers in total – and it was so strong that it carried debris more than 130 meters up the side of the canyon.
Unlike landslides or snow avalanches, underwater avalanches are invisible and extremely difficult to measure, but they are the primary mechanism for the movement of materials such as sediment, nutrients and pollutants across the Earth’s surface and pose a significant geohazard to seafloor infrastructure such as internet cables.
The research team analyzed over 300 core samples from the area, taken during research cruises over the past 40 years. This, along with seismic and bathymetric data, enabled them to map the massive avalanche.
3D image of a huge underwater avalanche that occurred in the Agadir Canyon almost 60,000 years ago. Photo credit: Dr. Christoph Bottner, Aarhus University
Dr Stevenson said: “This is the first time anyone has been able to fully map a single underwater avalanche of this magnitude and calculate its growth factor.”
“The interesting thing is how the event developed from a relatively small beginning into a huge and devastating underwater avalanche that reached heights of 200 meters while moving at a speed of about 15 m/s, tearing up the seabed and sweeping away everything in its path.
“To put it in perspective, that’s an avalanche the size of a skyscraper moving from Liverpool to London at more than 40mph, digging a trench 100ft deep and 9.3 miles wide, destroying everything in its path. It then spreads over an area larger than the UK, burying it under about a metre of sand and mud.”
Dr Christoph Bottner, Marie Curie Research Fellow at Aarhus University in Denmark and co-leader of the team, said: “We calculated the growth factor to be at least 100, which is much higher than for snow avalanches or debris flows, which only grow about four to eight times as much. We have also observed this extreme growth in smaller underwater avalanches measured elsewhere, so we think it might be a specific behavior of underwater avalanches and we plan to investigate this further.”
Professor Sebastian Krastel, head of the Department of Marine Geophysics at Kiel University and lead scientist on board the mapping cruises to the gorge, added: “Our new findings fundamentally challenge our view of these events. Before this study, we thought that large avalanches only occur as a result of large landslides. But now we know that they can start small and develop into extremely powerful and extensive mega-events.”
“These findings have enormous implications for the way we try to assess the potential georisk to seafloor infrastructure, such as internet cables, which carry almost all global internet traffic and are critical to all aspects of our modern societies.”
The recent cruises to map the Agadir Canyon were led by the Institute of Geosciences, Christian-Albrechts-University of Kiel, the Leibniz Institute for Baltic Sea Research and the GEOMAR Helmholtz Centre for Ocean Research, Germany.
A range of archived core data from the British Ocean Sediment Core Repository at NOCS Southampton were analysed, collected on board NERC vessels over the last 40 years.
Further information:
Christoph Böttner et al, Extreme erosion and inflation in a giant submarine gravity current, Scientific advances (2024). DOI: 10.1126/sciadv.adp2584. www.science.org/doi/10.1126/sciadv.adp2584
Provided by the University of Liverpool
Quote: Study reveals devastating power and colossal extent of giant underwater avalanche off Moroccan coast (21 August 2024), accessed 21 August 2024 from https://phys.org/news/2024-08-reveals-devastating-power-colossal-extent.html
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