An unstable slope above Prince William Sound is dropping faster. A complete failure could cause a tsunami.

Last month, scientists noticed new movement on an unstable slope in Prince William Sound, but they’re uncertain where that new movement may lead.

It’s possible the speed-up means rapid failure of the slope may be ahead, which could send the mass of land crashing into the water below. That could, in turn, create a tsunami in nearby fjords and bays as well as inundation, dangerous waves and currents in the community of Whittier — a risk scientists first warned about in 2020.

But it’s also possible the movement could stall, and nothing dramatic or devastating would occur.

The steep slope is located in the Barry Arm fjord, in a narrow stretch of water in Prince William Sound. It’s located 30 miles northeast of Whittier.

Dennis Staley, a research physical scientist at the U.S. Geological Survey who leads the Prince William Sound Landslide Hazards Project, said in late August, scientists noticed a portion of the unstable area began to move.

The movement caused concern because of how swiftly the slope went from not moving to sliding some 50 millimeters per day over a few days, Staley said.

“We don’t like to see landslides accelerate; that makes us a little bit nervous,” Staley said. “And then we also don’t like to see the area that’s expanding.”

It’s challenging, if not impossible, to say how likely the slope is to fail on a given day or during a specific period, Staley said. They can’t say whether the slope will keep on moving and stop at some point, or if a fast-moving landslide — what’s known as a catastrophic failure — is possible.

[Over 24 hours, Harry Potter Lake pulls a disappearing act on Alaska’s North Slope]

“We don’t want to be overly alarmist and say this is something that is inevitably going to end in a catastrophic failure because there’s a strong chance that it won’t, but we do want to keep an eye on the landslide,” he said.

Staley said that scientists have suspended non-essential boat-based activities in Barry Arm out of caution.

“We don’t want our crews in harm’s way should there be any kind of failure,” Staley said.

There are a few potential scenarios for what might happen if the slope fails, said Seldovia-based geologist Bretwood Higman, who has researched Barry Arm. Higman’s sister, an artist and naturalist, was the person who initially pointed out the slope as potentially unstable while she was in the area.

The impacts of the slope’s possible failure depend on the size of the area that crashes into the water and how much water it would displace, Higman said. He noted the level of uncertainty is high — they don’t know how harmful the impacts would be in the town of Whittier. However, he said they’d likely be at least problematic in terms of strong currents potentially damaging the harbor. Different models have shown different-sized waves washing into the community, Higman said.

Higman said there’s no correct answer for people trying to decide whether or not they should spend time in the vicinity of Barry Arm.

“We don’t know enough about it to even pretend like we can tell anyone what they should do,” Higman said.

For his part, Higman said he wouldn’t camp on the beach in the Barry and Harriman fjord areas, given the dangers that even a small tsunami would pose to the site. He’d also be cautious taking a vessel right up below the area of instability.

“That’s not dice I’m comfortable rolling, but that’s just me,” Higman said. “I really, absolutely would not judge someone else making a different decision.”

[Correction: An earlier version of this story included an incorrect spelling of Harriman.]