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

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.