Climate Change Is Intensifying the Tsunami Threat in Alaska

 wired.com  11/21/2020 13:00:00   Victoria Petersen

This story originally appeared in High Country News and is part of the Climate Desk collaboration.

Tucked against glacier-capped mountains, the Begich Towers loom over Whittier, Alaska. More than 80 percent of the small towns residents live in the Cold War-era barracks in this former secret military port, whose harbor teems every summer with traffic: barnacle-encrusted fishing boats, sightseeing ships, sailboats, superyachts and cruiseliner monstrosities. This summer, coronavirus travel restrictions put a damper on tourism in the usually buzzing port. Then came warnings of a potentially devastating tsunami.

Whittier residents have been mindful of tsunamis for generations. In 1964, the Good Friday earthquake was followed by a 25-foot wave that crushed waterfront infrastructure, lifting and twisting rail lines and dragging them back to sea. The Good Friday earthquakewhich killed 13 people here and caused $10 million worth of damagestill occupies Whittiers memory.

With tons of rock and rubble precariously perched high above a nearby fjord, ready to crash into the sea, the towns present is being shaped by both its past and preparations for an uncertain future. This destabilization is being driven by climate change: Tsunamis are becoming more likely in Alaska as hillsides, formerly reinforced by glaciers and solidly frozen ground, loosen their hold on once-stable slopes.

On May 14, an Alaska Department of Natural Resources press release and a public letter from 14 scientists warned locals of a possible landslide-generated tsunami. Alaska has identified three similar events in the past: Tsunamis in 2015 and 1967 occurred in remote areas, while one in 1958 killed two people whose boat was capsized. But the unstable slope in Barry Arm, a narrow steep-walled fjord in Prince William Sound, is vastly more dangerous. The potential energy from a catastrophic slide here is approximately 10 times greater than previous events, the states top geologist said in the May press release.

The landslide in Barry Arm has been lurching towards the ocean since at least 1957, when Barry Glacierwhich once gripped the base of the mountainside and held back the slopefirst pulled its load-bearing ice wall out from under the rocky slope. As the glacier retreated, so did the slopes support systemdragging the rock face downward toward the ocean, leaving a distinct, zig-zagging indentation in the hillside. Between 2009 and 2015, Barry Glacier retreated past the bottom edge of the landslide, and the slope fell 600 feet. Since 2006, Barry Glacier has receded by more than two miles. Scientists believe the slope is likely to fail within the next 20 yearsand could even do so within the year.

Climate change makes land more unstable and increases the risk of landslide-caused tsunamis. As the climate warms, glaciers melt and recede, pulling back from the mountainsides they were hugging. Barry Glacier's wall of icewhich once held the hillside in place, supporting it against the fjords mountainshas thinned, edging away from the rock face, releasing its support and revealing an unstable slope that is slipping downward toward the ocean. Brentwood Higman, geologist and executive director of Ground Truth Alaska, is working with other scientists to research climate changes impact on landslide-triggered tsunamis. [These events] are worth worrying about regardless of climate change, Higman said. But there are a number of reasons to think climate change makes them a lot more likely.

As glaciers recede, the land above them also becomes more unstable. The craggy alpine region of south-central Alaska is already thawing dramatically. Once-frozen slabs of rock, dirt and ice are releasing trapped liquids and becoming more prone to sliding down mountains.

Another less-obvious symptom of climate change increases the risk. When theres more water in the atmosphere, precipitation becomes more intense. Rain, even more than earthquakes, is prone to trigger landslides, Higman said. Climate change will make landslides more likely and more frequent, said Anna Liljedahl, an associate scientist with the Woods Hole Research Center. Its a new emerging hazard, and thats why its urgent to do an assessment of where we have these unstable slopes and where they are a hazard to people, Liljedahl said.

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