Detection and Assessment of a Large and Potentially Tsunamigenic Periglacial Landslide in Barry Arm, Alaska

The retreat of glaciers in response to global warming has the potential to trigger landslides in glaciated regions around the globe. Landslides that enter fjords or lakes can cause tsunamis, which endanger people and infrastructure far from the landslide itself. Here we document the ongoing movement of an unstable slope (total volume of 455 × 106 m3) in Barry Arm, a fjord in Prince William Sound, Alaska. The slope moved rapidly between 2010 and 2017, yielding a horizontal displacement of 120 m, which is highly correlated with the rapid retreat and thinning of Barry Glacier. Should the entire unstable slope collapse at once, preliminary tsunami modeling suggests a maximum runup of 300 m near the landslide, which may have devastating impacts on local communities. Our findings highlight the need for interdisciplinary studies of recently deglaciated fjords to refine our understanding of the impact of climate change on landslides and tsunamis. Plain Language Summary Climate warming and the resulting retreat of glaciers may destabilize mountain slopes, triggering landslides. For those landslides that enter fjords, the induced tsunamis are a significant hazard to coastal communities. Despite this risk, most periglacial landslides have been detected only after the event. Using satellite data, we detect a large, slow‐moving landslide in Barry Arm, Alaska, and assess its hazard potential. The volume of the landslide is estimated to be 8 times larger than the 17 June 2017 Karrat Fjord landslide in Greenland, which generated a tsunami and killed four people. We found that the Barry Arm landslide moved rapidly between 2010 and 2017, while Barry Glacier quickly thinned and retreated from the landslide area. If the entire unstable slope would collapse, it could generate a tsunami with a runup up to 300 m in the vicinity of the landslide with hazardous waves reaching local communities in Prince William Sound, which is frequently visited by fishermen, tourists, and cruise ships. Our study highlights the need to systematically assess the emerging hazards of landslides and tsunamis influenced by climate change. Key Points This study quantifies the motion of a large periglacial landslide It is unique that such a landslide is detected before potential failure This study calls attention to the glacier‐retreat‐landslide‐tsunami hazards cascade