The rapid retreat of an Alaska glacier and the precarious condition of a mountain slope that had previously been buttressed by the melting ice so alarmed a team of scientists that they issued a public letter warning of possible catastrophe.
Barry Arm in Alaska’s Prince William Sound, they warned, could be the site of a huge mountainside collapse, bigger than any ever recorded in Alaska, causing a massive and destructive tsunami, they said in their May 14 letter.
“It could happen today. It could happen this summer. It could happen in 20 years,” said one of the team members, Anna Liljedahl, a Homer, Alaska-based glacier and permafrost expert with the Woods Hole Research Center.
The scientists, from a variety of institutions and agencies, had just started work on a NASA- and National Science Foundation-funded project tracing land movement in the North American Arctic when they calculated the risks at Barry Arm. A partial or complete collapse at the mile-wide landslide zone is likely within 20 years, they found. An earthquake, heat wave or a heavy rainfall event could trigger the collapse, they said in their letter.
The scientists are not the only people sounding the alarm. The commissioner of Alaska’s Department of Natural Resources, upon briefing, directed the department to issue a public warning about an “increasingly likely landslide could generate a wave with devastating effects” on those using the area.
The potential of a landslide-triggered tsunami in Barry Arm may be unusually acute, but changing conditions around the Arctic are making such catastrophes more likely. Shrinking glaciers and thawing mountain permafrost have combined to destabilize slopes around the region. Southeast Alaska and nearby areas of Yukon and British Columbia have been a particular hotspot for such landslides.
North America’s biggest non-volcanic landslide on record happened at Taan Fiord in southeast Alaska in 2015, at a site where Tyndall Glacier had retreated rapidly and a mountainside suddenly gave way. The slide dumped 180 million tons of rock, or 80 million cubic yards of material, into the fjord. The result was a localized tsunami that reached elevations of 193 meters. The wave of water was one of the highest recorded tsunamis ever in the world, according to experts.
But a full collapse of the mountain slope that used to be buttressed by Barry Glacier would dwarf that and other recent slides, according to the scientists’ calculations. It would put about 650 million cubic yards of rock rubble into the water, In a worst-case scenario, a huge tsunami would cascade through well-used parts of Alaska’s Prince William Sound, sending a wall of water about 30 feet high to the port town of Whittier, about 30 miles away from Barry Arm.
“It’s just mind-boggling. It’s kind of hard to get your head around how huge this thing is,” Liljedah said.
Sheer size is not the only danger factor. While Taan Fjord was deserted, with slide and tsunami discovered only after the fact, Barry Arm and Prince William Sound is in the most populous part of Alaska and well-used by boaters, fishermen and tourists. On any given summer day, the scientists said in their letter, there could be hundreds of people in the vicinity of Barry Arm, which is only 60 miles from Anchorage.
Already, a similar slide has been fatal elsewhere in the north.
A massive landslide in Greenland in 2017 sent a 100-meter tsunami, devastating the fishing village of Nuugaatsiaq, killing four people and washing away several houses.
In Alaska, the only landslide-generated local tsunami that caused deaths occurred in 1958. A magnitude-7.7 earthquake triggered a slide in Lituya Bay in southeast Alaska. The 40 million cubic yards of rock that fell generated a wave that reached more than 1,700 feet, ripping trees off a mountainside. It was the highest tsunami ever recorded. Two boaters in Lituya Bay died, and three other people outside of Lityua Bay were killed in the earthquake.
Glacial melt and permafrost thaw have made these events more likely, even in the absence of earthquakes.
Along with northern areas like Alaska, British Columbia, Greenland, Norway, some non-Arctic areas are at risk of big landslides that could cause tsunamis, said Marten Geertsema, a geology expert who is one of the scientists on the team.
The combined factors of glacial melt and mountain permafrost thaw can differ in magnitude depending on location, said Geertsema, who works for the British Columbia government and who traveled to Taan Fiord to conduct on-site research after the tsunami there.
In high-altitude areas, such as some of the southeast Alaska and neighboring Canadian sites, thaw of mountain permafrost is more likely the primary cause, with glacial melt more likely the secondary cause, he said.
In the case of Barry Arm, the glacial wasting is likely to be the proximate cause of any future landslide, he said. In places like Prince William Sound, the mountains there do not rise as high as those elsewhere, but the glaciers are receding rapidly.
Alaska and other glaciated areas can learn from Norway, Liljedahl and Geertsema said.
Norway has set up early warning systems to detect movements on vulnerable slopes, Geertsema said. They can detect underwater bulging of slopes, another warning sign, he said. There can be an array of instruments that can be deployed to replicate the Norwegian warning system, he said.
Ultimately, the Barry Arm site needs to be measured and monitored in some way, he said.
“I would say in the meantime, be careful because you just don’t know,” he said. “We know it’s moving. We don’t know when it will fall catastrophically.”
It is possible, he and Liljedahl said, that the slope will continue to slide gradually and gently, avoiding any massive and sudden collapse.
And it is also possible that Barry Arm and Barry Glacier are not the only ticking time bombs in Alaska and elsewhere.
“I wouldn’t be surprised if we found 10 more of those these just sitting in southcentral and southeast (Alaska). There’s so much land and so few people,” Liljedahl said.