Scientists are warning that the sudden collapse of an Alaskan slope currently being propped up by a retreating glacier could trigger a catastrophic tsunami hundreds of feet high. "It could happen anytime, but the risk just goes way up as this glacier recedes," researcher Anna Liljedahl tells the New York Times. The study found the slope above Barry Glacier in a fjord in Prince William Sound is likely to collapse within two decades, but could do so within the year. Though the findings haven't been peer reviewed, "we realized we needed to let people know," says Liljedahl. Briefed on the study, Alaska's Department of Natural Resources warned Thursday that "an increasingly likely landslide could generate a wave with devastating effects on fishermen and recreationalists," per the Anchorage Daily News. "As many as 500 people may be in the area at one time."
The highest tsunami ever documented—it rose to a height of 1,720 feet—was triggered by a landslide that deposited 30 million cubic meters of dirt into Alaska's Lituya Bay in 1958. Yet the collapse of this mile-long slope—which slid 600 feet in six years, from 2009 to 2015—would send 500 million cubic meters of rock and dirt into Barry Arm fjord. "It's in a whole different class than we've ever even studied after the fact, much less before it happens," says researcher Hig Higman. Scientists expect the tsunami to fall to 30 feet high in the 20 minutes it would take to reach the town of Whittier, 30 miles away. The Times notes the town "is typically a disembarkation point for thousands of cruise ship passengers." Liljedahl hopes funding can be found to establish monitoring at the site as a collapse could be triggered by an earthquake, a heat wave, or even heavy rain. (Read more tsunami stories.)