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With a wave surge of nearly 200 meters, the tsunami that devastated an Alaskan fjord in 2015 was one of the largest ever recorded. But with no one killed, he almost went unnoticed.
It was triggered by a huge rock fall caused by the melting of the Tyndall Glacier, which, according to experts, gave them the clearest image to date of tsunamis generated by landslides.
According to a study published Thursday in Scientific Reports, global warming causing an unprecedented retreat of glaciers leads to an increased risk of tidal waves caused by the collapse of weakened rocky slopes.
"As glaciers are thinning around the world, they are dramatically changing their landscapes, and in the case of Taan Fjord, the result has been a massive tsunami," said Dr. Dan Shugar, assistant professor of geoscience at the University of Hawaii. University of Tacoma. The report.
"The tsunami was triggered by a huge landslide in October 2015, which occurred over a glacier that had shrunk considerably in the late 20th century," he said. at AFP.
The tsunami generated a wave flow, the maximum vertical extension of the swell on a beach, 193 meters (633 feet).
Glacial ice supports and digs steep slopes. Thus, when the ice melts, the underlying bedrock remains exposed and unstable, increasing the probability of falling rocks and landslides.
"We need to better understand the risk of these steep slopes in a changing climate," Shugar said.
The study provides a reference for risk modeling of landslides and tsunamis, the authors said.
"Our results draw attention to an indirect effect of climate change that increases the frequency and magnitude of natural hazards near the glacial mountains."
– Mapping of a giant tsunami –
Most recent research on tsunami risks has focused on earthquake-related research, such as that of the Indian Ocean in 2004.
Little is known about landslide tsunamis, which are relatively rare, with the best documented example dating back 60 years.
"This is the first time scientists are studying a landslide tsunami," said co-author Dr. Bretwood Higman, executive director of Ground Truth Trekking.
"For decades, the most studied landslide tsunami was the Lituya Bay event in 1958, but many of the techniques we use were inaccurate or impossible at the time," he said. he declares.
In addition to being rare, such events tend to occur in remote and dangerous locations and traces of geological evidence left behind tend to hide quickly.
This time, the experts were able to capture high-quality satellite images and other data before the slide showing how the ground creaked and shifted as the glacier retreated.
– Separate sedimentary recording –
Crucially, they were also able to obtain a detailed picture of the distinct sedimentary record left by the tsunami, which could shed light on past incidents and provide clues to predict future risks.
"We were able to map the deposits of this event in detail, which allowed us and other researchers to better reconstruct where and when similar events occurred elsewhere.
Signs indicating that the rock wall of Taan Fjord was unstable were discovered nearly 20 years ago, with collapsing ice slopes providing a warning of where such events might occur.
"Monitoring the progressive movement of descent into mountain ranges around the world, while being a technical challenge, would be a step forward in our ability to mitigate risk," they wrote.
In addition to tsunamis caused by landslides, experts also warn of an increasing risk of tidal waves caused by icebergs that break off from a glacier.
KK
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