Study of 2025 Alaska landslide and tsunami contains warnings

Rod Boyce
907-474-7185
May 6, 2026

Scientists studying the massive August 2025 landslide and tsunami in Southeast Alaska warn that the likelihood of similar large-scale events has increased substantially across the North as glaciers retreat and permafrost degrades.

The study of the Tracy Arm event revealed the rapid retreat of a supporting glacier and localized seismic signals that began days before the slide. It also provided details about the tsunami that was as tall as the new World Trade Center tower.

A wide aerial view of Tracy Arm in Southeast Alaska shows the scar from the Aug. 10, 2025, landslide descending from a steep mountainside into the fjord near a glacier terminus. Gray rock and debris cut through the center of the mountain, reaching the water below, where floating ice and sediment spread across the fjord. The glacier terminus is visible at lower right, with snow-covered peaks rising above the surrounding mountains. Along the far side of the fjord, a pale trimline marks where the tsunami stripped vegetation from the slopes. The photograph was taken from across the fjord during a U.S. Geological Survey flight on Aug. 13, 2025.
Photo by Cyrus Read/U.S. Geological Survey
The photograph shows the Aug. 10, 2025, landslide, glacier terminus and Tracy Arm as viewed from across the fjord during a U.S. Geological Survey flight on Aug. 13. Note the trimline along the far side of the fjord, caused by the tsunami stripping the walls of vegetation.

鈥淭he scale of what we are dealing with in Alaska is unprecedented,鈥 Alaska Earthquake Center research seismologist Ezgi Karas枚zen said. 鈥淲e have a spectacular landscape, but the hazards that come with that are also very real.鈥

鈥淎laska has large slopes that could fail suddenly and trigger tsunamis,鈥 she said.

The work was led by Dan Shugar of the University of Calgary and published today in . It is the first comprehensive analysis of the Tracy Arm landslide.

Karas枚zen and Michael West, director of the Alaska Earthquake Center, are among the research paper鈥檚 18 co-authors. The is part of the 糖心Vlog Geophysical Institute.

The landslide occurred at 5:26 a.m. Aug. 10 at the head of Tracy Arm, where South Sawyer Glacier meets the water. The fjord lies about 50 miles southeast of Juneau. 

Reports from boaters of surging waters in nearby Endicott Arm prompted the Alaska Earthquake Center to search for a landslide. The earthquake center鈥檚 team used their to quickly pinpoint the landslide location to help guide the response of state and federal authorities.

Researchers later estimated the landslide moved about 64 million cubic meters of material, an amount equal to a cube of material a quarter mile on each side.

More than 20 vessels, including large cruise ships carrying thousands of passengers, typically travel through Tracy and Endicott arms daily during the summer. None was in Tracy Arm at the time, but the authors note the tsunami could have caused fatalities if a ship had been in the upper fjord. 

A black-background infographic compares the run-up heights of several of the world鈥檚 largest tsunamis with famous tall buildings. The graphic includes silhouettes of the CN Tower in Toronto, One World Trade Center in New York, the Petronas Towers in Kuala Lumpur, the Eiffel Tower in Paris and the Elizabeth Tower, also known as Big Ben, in London. Curved colored shapes show tsunami heights rising beside the buildings. The tallest event shown is the 1958 Lituya Bay, Alaska, tsunami, followed closely by the 2025 Tracy Arm, Alaska, landslide-generated tsunami, which reached a run-up height of 481 meters, or nearly 1,600 feet. Smaller curves represent the 2024 Dickson Fjord, Greenland, tsunami, the 2022 Hunga Tonga eruption tsunami and the 2011 Tohoku, Japan, earthquake tsunami. The graphic shows the run-up heights of several of the largest tsunamis compared to some of the world鈥檚 tallest buildings.
Graphic by Steve Hicks/University College London and provided by Shugar et al.
This graphic shows the run-up heights of several of the largest tsunamis compared to some of the world鈥檚 tallest buildings.

Several cruise lines have since adjusted their 2026 itineraries to avoid the area.

Findings from an October field survey provided a clear picture of the tsunami. It had the second-highest slope run-up on record at about 1,580 feet above sea level 2 miles from the landslide. Only the 1958 landslide-generated tsunami in Lituya Bay, Alaska, had a higher run-up, at 1,730 feet.

Computer simulations using the field data show the tsunami had a breaking wave about 330 feet high racing at more than 150 mph when it hit the opposite shore. 

The information can help scientists improve their simulations of potential tsunamis elsewhere. 

鈥淭here are not many events like this with this kind of data for tsunami modelers to work with,鈥 Karas枚zen said.

The research also highlights a four-day period of rapid retreat of South Sawyer Glacier, which had been buttressing the hillside.

The glacier had retreated somewhat in July 2025, but the pace accelerated through Aug. 2-5. and proved to be critical. The retreating glacier left behind a steepened slope without a retaining wall.

An aerial photograph looks down into the steep-walled Tracy Arm fjord in Southeast Alaska. In the foreground, a broad landslide scar cuts down a rocky mountainside toward the water, leaving exposed gray and tan rock and scattered debris. Across the water, the opposite slope shows the area of highest tsunami run-up from the landslide-triggered wave, where vegetation was stripped away along the fjord wall. A glacier terminus with blue ice and dark sediment sits at the head of the inlet beyond the water. The photograph was taken Aug. 13, 2025, during a U.S. Geological Survey field reconnaissance overflight following the Aug. 10, 2025, landslide and tsunami.
Photo by John Lyons/U.S. Geological Survey.
This photograph shows the landslide area in the foreground and, across the water, the area with the highest run-up resulting from the landslide-triggered tsunami in Tracy Arm. The photograph was made during an Aug. 13 U.S. Geological Survey field reconnaissance overflight.

The scientists also noted extensive preslide seismic activity in the hillside that was not from an earthquake. Such seismicity is relatively rare for landslides, Karas枚zen said.

Retrospective analysis of data from distant seismic stations indicates activity began several days prior to the collapse. Signals equivalent to a magnitude 1 to 2 earthquake were occurring about an hour apart.

The rate increased dramatically in the six hours before failure, with signals every 30 to 60 seconds. About two hours before the slide, signals became a continuous vibration that scientists interpret as steady movement along the eventual failure surface. These are distinct from the signal generated during the landslide itself.

鈥淭hese seismic signals were like the hillside saying, 鈥楬ey, I鈥檓 going to fail,'鈥 Karas枚zen said.

The scientists see their work as a wake-up call.

鈥淎laska has sophisticated processes for monitoring and tracking earthquakes,鈥 West said. 鈥淎nd we have procedures and observatories for monitoring volcanoes. But this tremendous and dangerous landslide went undetected, and that is a hazard Alaska needs to come to terms with.鈥

Shugar,  the research paper鈥檚 lead author, said it is important to pay attention, particularly on the West Coast and in polar regions where glaciers are thinning.

鈥淯ltimately what we hope is that coastal municipalities, the cruise ship industry and other stakeholders take these threats seriously,鈥 he said.

ADDITIONAL CONTACTS: Ezgi Karasozen, ekarasozen@alaska.edu; Elisabeth Nadin, enadin@alaska.edu; Dan Shugar, daniel.shugar@ucalgary.ca

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