Alaska Landslide Caused 481m Tsunami Runup, Study Says

A massive landslide in southeast Alaska triggered one of the largest tsunamis ever recorded last year, generating a wave with a 481-meter runup, according to a new study published in the journal Science.

The event occurred at 5:26 a.m. on August 10, 2025, when more than 64 million cubic meters of rock plunged 1,000 vertical meters into the narrow, 48-kilometer-long Tracy Arm Fjord, near the northwest British Columbia border. The resulting tsunami marked the second-highest onshore wave height on record, surpassed only by the 530-meter wave in Lituya Bay, Alaska, in 1958. No fatalities were reported, as the landslide struck in the early morning hours.

Researchers, led by Dan Shugar, an associate professor of earth and environmental sciences at the University of Calgary, determined that the South Sawyer Glacier's rapid retreat of about 500 meters in the preceding months destabilized the slope, allowing the debris to cascade directly into the water. Without this retreat, driven largely by human-caused warming over the past two centuries, the landslide likely would have landed on glacier ice or not occurred at all, the study concluded. Shugar compared the process to a child stuffing...