Monday, May 29, 2023

Climate change intensifies tsunami threat in Alaska

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This story at the origin appears in High Country News and is part of the Climate office collaboration.

Nestled against glacier-covered mountains, the Begich Towers dominate Whittier, Alaska. Over 80% of the town’s inhabitants live in Cold War-era barracks in this former secret military port, whose port is teeming with traffic every summer: barnacle-encrusted fishing boats, tourist vessels, sailboats , superyachts and cruiser monstrosities. This summer, coronavirus-related travel restrictions have dampened tourism in the usually bustling port. Then came the warnings of a potentially devastating tsunami.

The people of Whittier have known about tsunamis for generations. In 1964, the Good Friday earthquake was followed by a 25-foot wave that crushed waterfront infrastructure, lifting and twisting the railroad tracks and pulling them back to sea. The Good Friday earthquake – which killed 13 people here and caused $ 10 million in damage – still looms large in Whittier’s memory.

With tons of rock and rubble perched precariously above a nearby fjord, poised to crash into the sea, the city’s present is shaped both by its past and by preparations for an uncertain future. . This destabilization is due to climate change: tsunamis are more and more likely in Alaska as hillsides, once reinforced by glaciers and solidly frozen ground, loosen their grip on once-stable slopes.

On May 14, a Alaska Department of Natural Resources press release and one public letter from 14 scientists warned residents of a possible tsunami caused by a landslide. 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 capsized. But the unstable slope of Barry Arm, a narrow, steep-sided fjord of Prince William Sound, is far more dangerous. The potential energy of a catastrophic slide here is about 10 times greater than previous events, the state’s top geologist said in the May press release.

The landslide at Barry Arm has tipped towards the ocean since at least 1957, when the Barry Glacier – which once gripped the base of the mountain side and held back the slope – first pulled its load-bearing ice wall from under the rocky slope. As the glacier retreated, so did the slope support system – dragging the rock face down toward the ocean, leaving a distinct zigzag indentation in the hill. Between 2009 and 2015, Barry Glacier retreated past the lower edge of the landslide and the slope dropped 600 feet. Since 2006 Barry Glacier has moved back more than two miles. Scientists believe the slope will likely fail within the next 20 years – and could even fail within a year.

Climate change is making land more unstable and increasing the risk of tsunamis caused by landslides. As the climate warms, glaciers melt and retreat, retreating from the mountain sides they hugged. The ice wall of the Barry Glacier – which once held the hill in place, propping it up against the mountains of the fjord – has thinned, moving away from the rock face, releasing its support and revealing an unstable slope that slides towards the ocean. Brentwood Higman, geologist and executive director of Ground Truth Alaska, works with other scientists to study the impact of climate change on landslide-triggered tsunamis. “[These events] are worth worrying about regardless of climate change, ”Higman said. “But there are a number of reasons to believe that climate change makes them much more likely.”

As the glaciers retreat, the land above them also becomes more unstable. The rugged alpine region of south-central Alaska is already thawing dramatically. Patches of once frozen rock, earth and ice release trapped liquids and become more prone to slipping into mountains.

Another less obvious symptom of climate change is increasing the risk. When there is more water in the atmosphere, precipitation becomes more intense. Rain, even more than earthquakes, is likely to trigger landslides, Higman said. Climate change will make landslides more likely and more frequent, said Anna Liljedahl, associate scientist at the Woods Hole Research Center. “This is a new emerging danger, and this is why there is an urgent need to do an assessment of where we have these unstable slopes and where they pose a danger to people,” said Liljedahl.


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