Published in the journal *Science Advances*-where it also features on the front cover-the study offers unparalleled insights into underwater avalanches, a natural phenomenon that remains largely mysterious. The research team, co-led by Dr. Chris Stevenson, a sedimentologist from the University of Liverpool's School of Environmental Sciences, successfully mapped this ancient underwater event, which took place around 60,000 years ago in the Agadir Canyon.
Initially triggered by a relatively small seafloor landslide with an estimated volume of 1.5 cubic kilometers, the avalanche rapidly grew, accumulating massive amounts of boulders, gravel, sand, and mud as it traversed through one of the world's largest submarine canyons. It continued its path for an additional 1600 kilometers across the ocean floor.
"The avalanche's force was so immense that it eroded the entire 400-kilometer length of the canyon, extending hundreds of meters up its sides, covering an area of approximately 4500 square kilometers," Dr. Stevenson explained. "It was strong enough to carry cobbles over 130 meters up the side of the canyon."
Unlike terrestrial landslides or snow avalanches, underwater avalanches are invisible and challenging to measure. However, they play a crucial role in redistributing sediments, nutrients, and pollutants across the Earth's surface and pose significant geohazard risks to seafloor infrastructure, including critical internet cables.
The research team's conclusions were drawn from an analysis of over 300 core samples taken from the area during research cruises over the last four decades, alongside seismic and bathymetry data.
Dr. Stevenson added, "This is the first time anyone has managed to map out an entire individual underwater avalanche of this size and calculate its growth factor." He further remarked, "What is so interesting is how the event grew from a relatively small start into a huge and devastating submarine avalanche reaching heights of 200 meters as it moved at a speed of about 15 m/s ripping out the sea floor and tearing everything out in its way."
Dr. Christoph Bottner, a Marie-Curie research fellow at Aarhus University in Denmark, who co-led the research, emphasized the extraordinary nature of the avalanche's expansion: "We calculate the growth factor to be at least 100, which is much larger compared to snow avalanches or debris flows which only grow by about 4-8 times. We have also seen this extreme growth in smaller submarine avalanches measured elsewhere, so we think this might be a specific behaviour associated with underwater avalanches and is something we plan to investigate further."
Professor Sebastian Krastel, head of Marine Geophysics at Kiel University and the chief scientist aboard the cruises that mapped the canyon, highlighted the broader implications of these findings: "Our new insight fundamentally challenges how we view these events. Before this study, we thought that big avalanches only came from big slope failures. But now, we know that they can start small and grow into extremely powerful and extensive giant events." He added, "These findings are of enormous importance for how we try and assess their potential geohazard risk to seafloor infrastructure like internet cables that carry almost all global internet traffic, which are critical to all aspects of our modern societies."
The most recent mapping efforts of the Agadir Canyon were conducted by the Institute of Geosciences, Kiel University, Leibniz Institute for Baltic Sea Research, and GEOMAR Helmholtz Centre for Ocean Research in Germany. Additionally, archived core data from the British Ocean Sediment Core Repository at NOCS Southampton-collected over the past 40 years aboard NERC ships-was analyzed as part of this study.
Research Report:Extreme erosion and bulking in a giant submarine gravity low
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