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A rare and extreme tsunami hit an Alaskan fjord three years ago, after 180 million tonnes of mountain rocks fell into the water, resulting in a devastating wave that devastated the trees and reached more than 600 feet.
The October 2015 cataclysm in Taan Fiord, southeastern Alaska, appears to have been the fourth highest tsunami of the past century, and its origins – related to glacier retreat – suggest global warming.
The new study even calls it a "climate change hazard".
"More and more landslides will occur as the mountain glaciers continue to shrink and the alpine permafrost thaws," the authors write, under the guidance of groundtruth trekking geologist Bretwood Higman.
"Thirty years ago, 40 years ago, the Taan Fiord did not exist at all, it was filled with ice," said Dan Shugar, a geoscientist at the University of Washington in Tacoma and another of 32 authors of institutions. in the United States, Canada and Germany.
But the Tyndall Glacier glacier retreated 10 miles between 1961 and 1991 while clearing more than a thousand feet before stabilizing at its current location. It did not just open the fjord; he also removed a very large mass of ice that had risen and supported its mountain walls, according to the study.
When the massive landslide took place right in front of the glacier, the confined shape of the fjord gave rise to a truly gigantic resulting wave, which traveled as fast as 60 miles to the hour.
"Imagine putting a bowling ball in your bathtub," Shugar said. "The water can go on either side of the tub, but when it hits the side of the tub, it can not go in. So the only way to get there is to go up."
Shugar said the tsunami was not the best known, but that it was in the same kind.
"The largest ever recorded was just down the Alaska Highway in Lituya Bay, and it was a remarkably similar kind of event, a landslide came down, reached the terminus of a glacier he said. "In this case, it was preceded by a great earthquake."
This wave reached 1,719 feet in 1958. It is not known, of course, what types of violent events on Earth may have occurred in the more distant past, but it is likely that tsunamis are even more extreme.
To document the 2015 tsunami, the scientists arrived fairly quickly, scientifically speaking, after detecting the initial seismic signature of the landslide, eight months later. They proceeded to study the wreckage left behind, detecting shorelines stripped of vegetation, large piles of rocks and debris, and even smaller rocks sunk deep into tree trunks. almost as if they had been hit by an explosion.
No one was present or injured, but Shugar is concerned that a cruise ship could end up in an Alaska Fjord during future extreme events. He also notes that a recent tsunami of the same nature in Greenland has killed four people.
In other words, this is not the only event of its kind and we can expect more types of extremes as massive glaciers recede and mountains around them. they react.
"As the slopes of the mountain adapt to new conditions, they can release unique rocks, rock avalanches or fail entirely," said Martin Lüthi, geographer of the University of Zurich. that rock, but has not been involved in the current study. "Several very large landslides have occurred in areas of rapid deglaciation around the world and triggered large waves of tsunami when they reached lakes or fjords."
"The authors are certainly right to propose, map and monitor potential danger zones in order to mitigate the future damage caused by large tsunamis generated by landslides," Lüthi added.
"Their interpretations of the role of glacier retreat in creating the risk configuration are compelling and frightening," said Ronadh Cox, a Williams College geoscientist who studied the power of extreme waves to move rocks and other large rocks. objects. "That seems to me to be a landmark study."
Tsunamis and avalanches are not the only dangers caused by glacier retreat. The melting of mountain glaciers can also leave large lakes at high altitudes; these lakes can then flow suddenly, cascading down the slopes.
For glaciers in or near deep waters, large chunks of ice can also create waves in the fjords.
In the end, the event just documented in Taan Fiord shows the mega-scale at which climate change is changing landscapes – and the corresponding scale of consequences.
"The problem is that as we create more of these steep slopes, we have the potential to generate more of these events," said Shugar.
– The Washington Post
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