Climate change intensifies tsunami threat in Alaska

As glaciers retreat and permafrost thaws, massive landslides threaten coastal communities.

 

Tucked against glacier-capped mountains, the Begich Towers loom over Whittier, Alaska. More than 80% of the small town’s 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.

A view of Barry Arm in which the receding Barry Glacier and the vulnerable section of land are visible on the right side of the image.
Photo courtesy Dr. Gabriel Wolken

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 earthquake — which killed 13 people here and caused $10 million worth of damage — still occupies Whittier’s memory.

With tons of rock and rubble precariously perched high above a nearby fjord, ready to crash into the sea, the town’s 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 state’s top geologist said in the May press release.

“(These events) are worth worrying about regardless of climate change. But there are a number of reasons to think climate change makes them a lot more likely.”

The landslide in Barry Arm has been lurching towards the ocean since at least 1957, when Barry Glacier — which once gripped the base of the mountainside and held back the slope — first pulled its load-bearing ice wall out from under the rocky slope. As the glacier retreated, so did the slope’s support system — dragging 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 years — and 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 ice — which once held the hillside in place, supporting it against the fjord’s mountains — has 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 change’s 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 there’s 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 Woodwell Climate Research Center. “It’s a new emerging hazard, and that’s why it’s urgent to do an assessment of where we have these unstable slopes and where they are a hazard to people,” Liljedahl said.

Tracking unstable slopes can give local governments time to install warning systems, so scientists are working to identify unstable land, focusing on monitoring landslides near communities in Southeast and south-central Alaska.

Illustration showing potential range for current tsunami risk in Barry Arm.
Dr. Brentwood Higman & Dr. Patrick Lynett

In mid-October, Gabriel Wolken, the Climate and Cryosphere Hazards Program manager for the Alaska Division of Geological and Geophysical Surveys, took a helicopter to Barry Arm. From the air, he conducted a lidar survey, using a laser scanner to measure the topography of the slide area in fine detail, calculating how the landslide has moved and changed since June. The data is still being processed. But, there are new rockfalls in the area every time he visits, indicating the area’s instability. “The rock itself isn’t very competent,” Wolken said. “It’s basically falling apart.”

There’s no easy way to gently coax a colossal land mass off the side of a mountain and into the ocean.

Whittier residents are aware of the risk, said Peter Denmark, who runs a commercial kayaking business in town. “With the people around town, there's a laissez-faire attitude about it,” Denmark said. Alaskans have “thick skins” when it comes to disasters, he said. “If it’s not tsunamis, earthquakes, volcanoes, forest fires — it’s one thing or another.” Still, Denmark is taking precautions; he avoids the Barry Arm area on kayaking tours.

Kelly Bender and her husband Mike rely on summer tourism in Prince William Sound. From their waterfront office, she charters water taxis, fishing boats, kayaking and sightseeing tours. Before news of the potential landslide broke, Bender said their fleet went into Barry Arm daily. With its scenic location, near glaciers and a popular beach, the state estimates that 500 people could be in the area at any given time during peak tourist season. Bender has changed tour routes, cancelled water taxi trips — even cancelled a planned wedding. “The danger part of it — people are feeling like ‘we know what to do in a tsunami,’” Bender said. “It’s the business part of it that we’re all really, you know, hanging by a thread.” When tsunami warning sirens blare in Whittier, residents know to move swiftly away from the coast and head to higher ground. The state encourages coastal residents to keep a “go bag” filled with emergency supplies and to plan evacuation routes.

While it’s still possible to avert or mitigate many of the worst impacts of climate change, there really isn’t an option to eliminate landslide-generated tsunamis. The state uses howitzer cannons to trigger controlled avalanches in railway and highway corridors, but there's no easy way to gently coax a colossal land mass off the side of a mountain and into the ocean. “It’s pretty much science fiction,” Higman said. Smaller landslides might be able to be stabilized from the bottom up, but large landslides, like in Barry Arm, “forget about it,” Liljedahl said.

Increasing preparedness, installing a robust monitoring system on and near landslides and creating an effective localized alert system are the best ways to protect communities, she said. Some locals, like Denmark, the kayak outfitter, prefer a quicker approach, however. “My idea was to just blast it down and duck,” he said. “But nobody thought that was a good idea.”

Editor’s note: This story has been corrected to show that the Woods Hole Research Center is now called the Woodwell Climate Research Center.

Victoria Petersen is an editorial intern for High Country News. Email her at [email protected] or submit a letter to the editor.

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