Scientists warn that a receding glacier in Alaska has primed a huge slope of rock and dirt for a landslide that could create a tsunami in Prince William Sound, report Morgan Krakow and Alex DeMarban for the Anchorage Daily News.
The warning, which came last week in the form of a public letter signed by 14 scientists from 14 separate institutions, estimates a total collapse of the slope could result in a tsunami some 30 feet high crashing on the shores of Whittier within 20 minutes—a town with several hundred year round residents that also serves as a hub for thousands of fishers, hunters and cruise ship passengers looking to explore the area’s arresting natural beauty.
The researchers write that this landslide-tsunami calamity could occur any time within the next two decades.
“It could happen anytime, but the risk just goes way up as this glacier recedes,” Anna Liljedahl, a hydrologist with the Woods Hole Research Center who is based in Alaska and signatory of the letter, tells Henry Fountain of the New York Times.
The research is preliminary and has not yet been peer-reviewed, Liljedahl tells the Anchorage Daily News. She and the other scientists felt the potential urgency of the findings merited their swift disclosure.
“We wanted to let the public know that there is a chance that this landslide might fail catastrophically," Liljedahl tells the Anchorage Daily News. “There’s also a chance that it might not.”
The precarious escarpment is located in the Barry Arm fjord, 60 miles east of Anchorage and 30 miles from Whittier, where the icy tongue of Barry Glacier touches brine. The Barry Glacier, like many around the world, has receded as human activities have warmed the planet. (Average global temperatures have risen by 2 degrees Fahrenheit since 1880, according to NASA). In the last 20 years, Barry Glacier has receded roughly 2 miles.
As Barry Glacier’s bulk has melted away, a huge quantity of newly unsupported earth has started to slide toward a precipitous drop into the waters below. An analysis from Chunli Dai, a geophysicist at Ohio State University and one of the letter’s signatories, found that the glacier’s two-decade retreat has corresponded with 600 feet of slippage on the part of the estimated 650 million cubic yards of rock and soil contained in the hillside.
The New York Times reports that only a third of this gargantuan landmass remains buttressed by ice, leaving it, in geologic terms, teetering on the brink. A landslide could be caused by an earthquake, days of heavy rain or even a heatwave that triggers excessive snowmelt.
A total collapse of the slope could jack up a tsunami hundreds of feet high, the researchers say. Whittier is the only town in the vicinity, but the tsunami would not have a direct path to its shores. Instead the tsunami would probably ricochet between fjords until being stepped down to a still destructive wave roughly 30 feet high.
“As global warming continues to thaw glaciers and permafrost, landslide-created tsunamis are emerging as a greater threat – not just in Alaska, but in places like British Columbia and Norway,” says Liljedahl in a statement from the Woods Hole Research Center.
A tsunami in Barry Arm could be “at least as large as some of the largest in the state’s recorded history,” according to a statement from the Alaska Division of Geological and Geophysical Surveys (DGGS).
The largest tsunami ever recorded occurred in 1958 in Lituya Bay, Alaska, per the United States Geological Survey. The landslide loosened some 40 million cubic yards of debris spawned a wave that was 1,720 feet high at its maximum, judging from the destruction wrought on the opposing hillside. (At 650 million cubic yards of debris, the unstable hillside identified by researchers at Barry Arm holds over 16 times more than the amount of debris unleashed in the 1958 landslide.)
More recently in 2015, a landslide in Taan Fjord sent roughly 10 million cubic yards of material tumbling into the waters of the remote area west of Yakutat, Alaska and caused a tsunami that was initially more than 600 feet high.
“It’s in a whole different class than we’ve ever even studied after the fact, much less before it happens,” Bretwood Higman, a geological researcher who cosigned the letter and runs an organization called Ground Truth in Seldovia Alaska, tells the New York Times.
Dave Dickason, Whittier’s mayor, tells the Anchorage Daily News the researchers’ warning is “concerning, but it’s not concerning enough to cause us to evacuate the city of Whittier at this time.”
Alaska plans to work with state and federal agencies to further assess the risk posed by a tsunami and to install monitoring equipment at the location of the potential landslide, per a statement.
Potential visitors to Whittier should be apprised of the risk, Ronnie Daanen, a geohydrologist with Alaska’s DGGS, tells the Anchorage Daily News, but, he adds, “this landslide has been moving for a few years, and it hasn’t gone down yet. So we can’t say, ‘Don’t go to Whittier.’ But it could happen.”