Barry Arm landslide threat may cause less severe tsunami than originally thought

Published: Jul. 9, 2021 at 10:02 PM AKDT
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ANCHORAGE, Alaska (KTUU) - The United States Geological Survey released a major update potentially easing concerns about a Prince William Sound threat. More than a year after first bringing attention to a slowly-moving landslide in Barry Arm, about 30 miles from Whittier, scientists now say the landslide likely doesn’t have the power of destruction it was originally thought to hold.

Preliminary studies showed the slide could cause a 30-foot tsunami to hit Whittier if it were to release rapidly, but now, according to a USGS study, a worst-case scenario shows waves may only reach 7 feet high just offshore of the town.

“I think there’s still a concern,” USGS Landslide Hazards Program Coordinator Jonathan Godt said. “But what we have now is a better understanding of what we’re dealing with, and that should help and we hope it will help folks in Whittier and elsewhere in Prince William Sound make decisions about what to do next.”

He said scientists don’t yet have a good understanding of what a worst-case scenario could look like on the streets of Whittier, a community of about 300.

While the predicted size of the potential tsunami is downgraded, Godt said the hazard is still significant. The potential tsunami is still considered to be able to create destruction in Whittier, but that could change with future studies.

“It puts a better understanding of the worst-case, and that’s a very helpful piece of information, particularly as we design and implement further studies,” Godt said.

While the threat of a large tsunami hitting Whittier is likely lowered, recreating in the Barry Arm area is still a major concern. The new study shows waves in the arm could hit more than 150 feet.

“This report doesn’t change the recommendation that the Forest Service and the Coast Guard have to avoid that area,” Godt said. “What I hope that we can do is provide people information so that they can make an informed choice.”

For the past year, the Tsunami Warning Center has been preparing for the possibility of a destructive tsunami. In newly-released footage from this spring, the center installed pressure gauges to help detect a wave leaving Barry Arm.

“They detect a change in that water level and an unusual rate that does not match up with a tidal cycle,” Tsunami Warning Coordinator Dave Snider said. “That information is relayed back from a transmitter through the cell phone network, actually, back to the national Tsunami Warning Center, which tells the watchstanders that unusual changes occurring in the water levels here, which could be the sign of a catastrophic tsunami.”

The new gauges are one of the first monitoring efforts the Tsunami Warning Center has put in place for a landslide-induced-tsunami risk.

The National Tsunami Warning Center is designed to warn for tsunamis triggered by earthquakes, Snider said.

“Landslides tsunamis are a whole different animal,” he said.

Before these gauges, the center didn’t have a way to measure for a tsunami leaving the Barry Arm area of Prince William Sound.

Snider said the gauges don’t lower the risk from landslide-triggering tsunamis in Prince William Sound, but they do give the capability to cope with the risk.

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