Last month, scientists noticed new movement on an unstable slope in Prince William Sound, but are unsure where this new movement might lead.
Acceleration would likely mean rapid failure of the slope, which could result in the mass of land bumping into the water below. This, in turn, can trigger tsunamis in nearby fjords and bays as well as dangerous flooding, waves and currents in the Whittier community – risk scientists first I warned him in 2020.
But it’s also possible for the movement to stop, and nothing too dramatic or disruptive will happen.
The steep slope is in Barry Arm Fjord, in a narrow stretch of water at Prince William Sound. It is located 30 miles northeast of Whittier.
In late August, scientists noticed that part of the unstable region was starting to move, said Dennis Staley, a research physicist with the US Geological Survey who leads the Prince William project on landslide hazards.
Staley said the movement caused concern because of the speed with which the ramp went from immobile to slipping by about 50mm a day over the course of a few days.
“We don’t like to see landslides accelerate; it makes us a little nervous,” Staley said. “And then we also don’t want to see the area expand.”
It’s difficult, if not impossible, Staley said, to determine how likely the ramp is to fail on a given day or over a specific period. They cannot say whether the slope will continue to move and stop at some point, or if a fast-moving landslide – what is known as a catastrophic failure – is possible.
“We don’t want to be more alarming and say this is something that will inevitably end in catastrophic failure because there is a strong chance that it won’t, but we do want to keep an eye on the landslide,” he said.
Staley said that scientists Stop non-essential boat-based activities at Barry Arm out of caution.
“We don’t want our crews in harm’s way if there is any kind of failure,” Staley said.
Geologist Bretwood Heigman, who has done research on the Barry Arm, said there are a few possible scenarios for what might happen if the slope fails. Heigmann’s sister, an artist and naturalist, was the one who initially referred to the slope as unstable while in the area.
Hegemann said the effects of a potential slope collapse depend on the size of the area hitting the water and how much water it will displace. He noted that the level of uncertainty is high – they don’t know how damaging the impacts will be in Whittier. However, he said they are likely to be at least problematic in terms of strong currents potentially damaging the port. Hegman said different models showed waves of different sizes washing away in society.
Hegeman said there is no right answer for people trying to decide whether or not they should spend time near Barry Arm.
“We don’t know enough about it to pretend we can tell anyone what to do,” Hegman said.
For his part, Hegman said he would not camp ashore in the Barry and Harriman Strait areas, given the risks that even small tsunamis could pose to the site. He would also be careful to take a ship below the zone of instability.
“This is not a dice I’m comfortable with rolling, but that’s just me,” Hegman said. “I really, definitely wouldn’t judge someone else making a different decision.”
[Correction: An earlier version of this story included an incorrect spelling of Harriman.]
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