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A tsunami swept the trees along the wall of this long fjord in Alaska. (Trekking the ground truth)
Three years ago, a rare and extreme tsunami fell on an Alaskan fjord after 180 million tonnes of mountain rocks fell into the water, resulting in a devastating wave that stripped the tree banks and reaches heights greater than 600 feet. documented Thursday.
The cataclysm of October 2015 in Taan Fiord, in southeastern Alaska, appears to have been the fourth tsunami recorded in the last century and its origins – related to the removal of a glacier – suggest that it is the type of event most often of a warming climate.
The new study even calls it "danger caused by climate change".
"More and more landslides will occur as mountain glaciers continue to decline and the alpine permafrost thaws," the authors write, under the direction of groundtruth trekking geologist Bretwood Higman.
"Thirty or forty years ago, 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 one of 32 authors in the study from institutions in the United States, Canada, and Germany.
But the Tyndall Glacier glacier retreated from about 10 miles between 1961 and 1991, while refining more than 1,000 feet, before stabilizing at its present 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 he hits the side of the tub, he can not go anymore. So the only way to go is to get 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 large earthquake."
This wave reached 1,719 feet in 1958. Of course, it is not known what kind of violent events the Earth could have produced in the more distant past, but it is likely that the 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 began to study the wreckage, detecting stripped shorelines of vegetation, large nicks of rocks and debris, and even the smallest rocks sunk deep into the trunks of trees, almost as if they had been hit by an explosion.
This stretch of coast along the Taan Fjord is relatively flat, with large alluvial deposits. When a tsunami swept them away in 2015, he stripped the surface of the vegetation, leaving "beaches" that stretch up to 150 feet of altitude. (Truth Trekking on the ground, used with permission.)
No one was present or injured, but Shugar worries about the possibility that a cruise ship could end up in an Alaskan fjord during a future event. He also points out that a recent, Similarly, a tsunami in Greenland killed four people.
In other words, this is not the only event of this type, and we can expect more types of extremes as the massive glaciers recede and the mountains around them react.
"As the slopes of the mountain adapt to new conditions, they can release unique rocks, rock avalanches or fail entirely," said Martin Lüthi, a geographer from the University of Zurich who recently documented a smaller tsunami in a Greenland fjord rather than stone, but was not involved in the current study. "Several very large landslides occurred in the fast deglaciation areas around the world and triggered large waves of tsunami when they reached the lakes or fjords."
"The authors are certainly right to identify, map and monitor potential danger zones in order to mitigate the future damage caused by the large tsunamis generated by landslides," Lüthi added.
"Their interpretations of the role of glacier retreat in creating hazard patterns are compelling and frightening," said Ronadh Cox, a geoscientist at Williams College, Mass., Who has studied the power of extreme waves to move rocks and others. big 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.
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