Alaska Landslide Triggered 481-Metre Tsunami Last Year, Study Finds — A Warning for B.C.

A landslide that sent more than 64 million cubic metres of rock plunging approximately 1,000 vertical metres into Tracy Arm Fjord in southeast Alaska last August generated a tsunami with a run-up height of about 481 metres — the second-highest ever recorded — and researchers warn similar events pose a growing threat to British Columbia coastal towns and cruise traffic.

The Details

The landslide occurred on August 10, 2025, at approximately 5:26 a.m. AKDT (13:26 UTC) in Tracy Arm, south of Juneau, Alaska. The Alaska Earthquake Center detected the seismic signals. No injuries or fatalities were reported from the event.

On August 13, 2025, a U.S. Geological Survey aerial survey captured images of the landslide scar, glacier terminus, and vegetation trimline. Kayakers on Harbor Island reported gear swept away by the tsunami, and boaters in nearby Endicott Arm reported surging waters.

A study published in the journal Science on May 6, 2026, led by Dan Shugar of the University of Calgary, found that rapid retreat of the South Sawyer Glacier — approximately 500 metres in the months before the event — removed support from the mountainside and enabled the landslide. The study included 18 co-authors.

Ezgi Karasözen, a research seismologist at the Alaska Earthquake Center and co-author on the study, developed nascent landslide detection tools that pinpointed the location. Karasözen said, 'The scale of what we are dealing with in Alaska is unprecedented. We have a spectacular landscape, but the hazards that come with that are also very real.'

The resulting tsunami reached a run-up height of about 481 metres, comparable to the tallest viewing platform of the CN Tower in Toronto and approximately as tall as One World Trade Center in New York. Researchers warned the event would have been 'unsurvivable' for any cruise ship in the upper fjord at the time.

The 1958 Lituya Bay landslide in Alaska still holds the record for the highest tsunami run-up, at approximately 524 metres above sea level.

Shugar said, 'On the West Coast, we do have Prince Rupert and Port Alberni, we do have towns at the heads of some of these fiords. There's also a pretty big ecological impact, you know, there's a lot of trees that got completely obliterated and habitat and probably animals, etc., that got obliterated by this tsunami.'

Context

Tracy and Endicott arms are popular cruise ship routes, with more than 20 vessels typically transiting daily during summer months. The South Sawyer Glacier had retreated substantially in the months before the landslide. Had the glacier not retreated, the landslide might have collapsed onto the glacier ice or not occurred at all.

Researchers warn that continued warming, glacier retreat, permafrost degradation, and increasing cruise tourism mean the hazard from landslide-triggered fjord tsunamis is growing. They are concerned about similar hazard cascades in B.C. coastal towns at the heads of fjords, including Prince Rupert and Port Alberni.

What's Next

The study authors emphasized the need for better monitoring of glacier-retreat zones and fjord traffic. The landslide volume estimate of more than 64 million cubic metres came from the U.S. Geological Survey and the Alaska Earthquake Center. The glacier retreat finding of approximately 500 metres and the tsunami run-up estimate of about 481 metres came from the published Science study. No specific timeline for new monitoring systems was announced.