World’s first mapping of a gigantic, devastating prehistoric underwater avalanche

In a major hit for the news programme Isn’t it crazy what science can find out?! researchers at the University of Liverpool have revealed the evolution and incredible destruction caused by a gigantic underwater avalanche nearly 60,000 years ago.

The team used more than 300 core samples taken over the past 40 years from the seafloor of the Atlantic Ocean off the northwest coast of Africa. Combined with seismic and bathymetric data from the area, they were able to map the path of the avalanche, which evolved from a small underwater landslide into a devastating climate event.

“This is the first time anyone has managed to fully map a single underwater avalanche of this magnitude and calculate its growth factor,” said Chris Stevenson, a sedimentologist at the University of Liverpool’s School of Environmental Sciences and co-leader of the team, in a statement.

“The interesting thing is how the event developed from a relatively small beginning to a huge and devastating underwater avalanche,” he explained, “reaching heights of 200 meters. [656 feet] because it was moving at a speed of about 15 m/s [49 feet/second] It tears up the sea floor and everything in its path.”

Starting from a volume of only 1.5 cubic kilometers, the avalanche (or rather a ball of gravel, sand and mud) developed into a huge and powerful avalanche, capable of eroding 400 kilometers along one of the largest underwater canyons in the world, the Agadir Canyon, as well as about 4,500 square kilometers of the canyon walls.

“To put it in perspective, that’s an avalanche the size of a skyscraper moving at more than 40 miles per hour. [64 kmph] from Liverpool to London, digging a trench 30 m deep [98 feet] deep and 15 km [9.3 miles] “The storm spreads out, destroying everything in its path,” Stevenson said. “Then it spreads over an area larger than Britain, burying it under about a metre of sand and mud.”

This is a truly impressive result, not least because underwater avalanches are so mysterious even today. You can’t see them and they are extremely difficult to measure; it’s also difficult to predict when they will occur or how destructive they will be. Creating this image of a prehistoric underwater avalanche is therefore not only useful because it tells us something about the past: it also provides important data about how powerful such events can be, how they can occur and how big the threat can be when they do occur.

“Our new findings fundamentally challenge our view of these events,” says Sebastian Krastel, head of the Department of Marine Geophysics at the University of Kiel and lead scientist on board the mapping cruises of the canyon. “Before this study, we thought that large avalanches only occur as a result of large landslides. But now we know that they start small and can develop into extremely powerful and extensive mega-events.”

In fact, this prehistoric avalanche was about 12 to 25 times larger than a normal snow or debris avalanche: “We calculated the growth factor to be at least 100,” explained Christoph Bottner, Marie Curie Research Fellow at Aarhus University in Denmark and co-leader of the team.

“We have also observed this extreme growth in smaller underwater avalanches measured elsewhere,” Bottner added. “So we believe this may be a specific behavior associated with underwater avalanches and we plan to investigate this further.”

And that’s very good news. Invisible and barely measurable avalanches thousands of meters beneath the waves may seem like an esoteric niche topic, but the truth is that such events have the potential to affect all of our lives.

Why? One reason: submarine internet cables.

“These findings have enormous implications for the way we try to assess the potential georisk to seafloor infrastructure,” Stevenson explained, “such as internet cables, which carry almost all global internet traffic and are critical to all aspects of our modern societies.”

The study was published in the journal Science Advances.