The collapse of an unstable mountain slope in Alaska could trigger a catastrophic tsunami in Harriman Fjord. A retreating glacier is producing this precarious situation, highlighting yet another type of hazard caused by climate change. 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,”. “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. Climate change could be what’s making matters worse. The northern part of the world, including Alaska, is heating, up twice as fast as elsewhere and causing glaciers to melt away. The walls of valleys lose their support when glaciers retreat, creating situations in which rockfalls and landslides can generate tsunamis, provided a body of water exists at the zone of accumulation. These types of events could become more common in a warming world. Anna Liljedahl, a scientist at Woods Hole Research Centre in Massachusetts, said in a press release that it’s not just Alaska but “places like British Columbia and Norway” that could face similar issues as ice melts in precarious ways. “This deforming area of rock has been active for several years, but it is in a remote location,” Dave Petley, a geologist at the University of Sheffield, told Gizmodo. “Thus, it has not been identified previously. The change is that it has been identified, and of course using archive satellite imagery we can now go back to see how it has developed over time. The interesting aspect of this landslide is that it is located at the very snout of a glacier that is retreating. We know that retreating glaciers can cause adjacent slopes to destabilize, a process that we call debuttressing. Worldwide glaciers are retreating in response to climate change, so we are seeing more of these large rock slope failures develop.”