In Alaska in 2015, tsunami waves hit 600 feet, data say

South Florida Sun-Sentinel (Sunday) - - News - By Chris Mooney The Washington Post

A rare and ex­treme tsunami ripped across an Alaskan fjord three years ago af­ter 180 mil­lion tons of moun­tain rock fell into the water, driv­ing a dev­as­tat­ing wave that stripped shore­lines of trees and reached heights over 600 feet, a large team of sci­en­tists has doc­u­mented.

The Oc­to­ber 2015 cat­a­clysm in Taan Fiord in south­east­ern Alaska ap­pears to have been the fourth high­est tsunami recorded in the past cen­tury, and its ori­gins — tied to the re­treat of a glacier — sug­gest it’s the kind of event we may see more of due to a warm­ing cli­mate.

“More such land­slides are likely to oc­cur as moun­tain glaciers con­tinue to shrink and alpine per­mafrost thaws,” the au­thors, led by ge­ol­o­gist Bret­wood Hig­man of Ground Truth Trekking, write last month in Na­ture Sci­en­tific Re­ports. “Thirty-odd, 40 years ago, Taan Fiord didn’t ex­ist at all. It was filled with ice,” added Dan Shugar, a geo­sci­en­tist at the Univer­sity of Washington in Ta­coma and an­other of the study’s 32 au­thors, who hail from in­sti­tu­tions in the United States, Canada and Ger­many.

But the glacier, Tyn­dall Glacier, re­treated back­ward some 10 miles from 1961 to 1991, while thin­ning out by over a thou­sand feet, be­fore sta­bi­liz­ing at its cur­rent lo­ca­tion. That hasn’t merely opened up the fjord; it has also re­moved a very large ice mass that had braced and sup­ported its moun­tain walls, the re­search said.

When the mas­sive rock­slide oc­curred just in front of the glacier, the con­fined shape of the fjord led to the truly gi­gan­tic re­sul­tant wave, which trav­eled as fast as 60 mph.

“Imag­ine drop­ping a bowl­ing ball into your bath­tub,” said Shugar. “The water can go to ev­ery side of the bath­tub. but when it hits the side of the bath­tub it can’t go any more. So the only way it can go is up.”

Shugar said the tsunami was not the big­gest known, but it’s in the same genre. “The big­gest that’s ever been recorded was ac­tu­ally just down the Alaskan road, in Li­tuya Bay, and it was a re­mark­ably sim­i­lar kind of event, a land­slide came down, hit the ter­mi­nus of a glacier, and went into the fjord water it­self,” he said.

That wave reached 1,719 feet in the year 1958. To doc­u­ment the 2015 tsunami, the sci­en­tists ar­rived rel­a­tively quickly on the scene, sci­en­tif­i­cally speak­ing, af­ter de­tect­ing the ini­tial land­slide’s seis­mic sig­na­ture — eight months later. They pro­ceeded to study the wreck­age left be­hind.

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