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Old 11-15-2020, 09:23 AM
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Post The Alaska Tsunami That Can't Be Stopped

The Alaska Tsunami That Can't Be StoppedBy
By: Victoria Peterson & High Country News & The Atlantic - 11-15-20
Re: https://www.theatlantic.com/science/...e-bomb/617082/

Photo link: https://cdn.theatlantic.com/thumbor/...t/original.jpg
Photo by: The landslide in Barry Arm has been lurching toward the ocean since the 1950s. by: GABRIEL WOLKEN

Note: The melting ice has left one small town on the brink of disaster.

Tucked against glacier-capped mountains, the Begich Towers loom over the former secret military port of Whittier, Alaska; more than 80 percent of the small town’s residents live in these Cold War–era barracks. In a typical summer, Whittier’s harbor teems with traffic: barnacle-encrusted fishing boats, sightseeing ships, sailboats, super-yachts, and cruise-liner monstrosities. This summer, however, 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 three colossal waves, each more than 25 feet tall, that crushed waterfront infrastructure, lifting and twisting rail lines and dragging them back to sea. That earthquake—which killed 13 people in the town 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 shaped by both its past and its preparations for an uncertain future. This destabilization is being driven by climate change. While many tsunamis are caused by earthquakes, some can be triggered by landslides. And in Alaska, landslide-generated tsunamis are becoming more likely as many 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 five people. But near Whittier, 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 that of previous events, the state’s top geologist said in the May press release.

The landslide in Barry Arm has been lurching toward 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, a geologist and executive director of Ground Truth Alaska, is working with other scientists to research climate change’s impact on landslide-triggered tsunamis. Such events are “worth worrying about regardless of climate change,” Higman says. “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 also increases the landslide risk. When there’s more water in the atmosphere, precipitation becomes more intense. Higman notes that rain, even more than earthquakes, is prone to triggering landslides. Climate change will make landslides more likely and more frequent, says 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 says.

Detecting and tracking unstable slopes can give local governments time to install warning systems, so scientists are working to identify unstable land; they’re focusing on monitoring landslides near communities in southeast and south-central Alaska.

In mid-October, Gabriel Wolken—the manager of the Climate and Cryosphere Hazards Program 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 are still being processed. However, there are new rockfalls in the area every time he visits, indicating the area’s instability. “The rock itself isn’t very competent,” Wolken says. “It’s basically falling apart.”

Whittier residents are aware of the risk, says Peter Denmark, who runs a commercial kayaking business in the community. 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.

“With the people around town, there’s a laissez-faire attitude about it,” Denmark says. Alaskans have “thick skins” when it comes to disasters, he adds. “If it’s not tsunamis, earthquakes, volcanoes, forest fires—it’s one thing or another.” Still, Denmark says, he’s 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. Bender says that before news of the potential landslide broke, their fleet went into Barry Arm daily. With its scenic location—close to glaciers and a popular beach—the state estimates that during peak tourism season, up to 500 people could be in the area at any given time. Bender has changed tour routes, canceled water-taxi trips, and even canceled a planned wedding. “The danger part of it—people are feeling like, ‘We know what to do in a tsunami,’” Bender says. “It’s the business part of it that we’re all really, you know, hanging by a thread.”

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 landmass off the side of a mountain and into the ocean. “It’s pretty much science fiction,” Higman says.

Smaller landslides might be able to be stabilized from the bottom up. But large landslides, like the one in Barry Arm? “Forget about it,” Liljedahl says. 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 says.

Some locals—like Denmark, the kayak outfitter—might prefer a quicker approach. “My idea was to just blast it down and duck,” he says. “But nobody thought that was a good idea.”

About the writers:

VICTORIA PETERSEN is an editorial intern for High Country News.
HIGH COUNTRY NEWS is a nonprofit media organization that focuses on the American West.
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