Record-Breaking 481-Meter Tsunami Triggered by Massive Landslide in Alaska

A significant landslide in August 2025 triggered the second-largest tsunami recorded, elevating water levels by over 480 meters in an Alaskan fjord.

The tsunami surged through the fjord at a remarkable speed of at least 70 meters per second, generating a seiche, or reflected wave, that persisted for 36 hours.

Historically, the only larger event was the 1958 Lituya Bay tsunami in Alaska, which surpassed a 530-meter surge.

The Juneau area in Alaska features breathtaking landscapes, where glaciers descend into seas flanked by steep fjords, attracting thousands of cruise ships annually.

However, the tsunami struck at 5:26 a.m. deep within the Tracy Arm Fjord in southeastern Alaska, keeping tourist boats clear of the disaster zone. Dan Sugar from the University of Calgary commented on the event.

“This was an incredibly large and fearsome wave,” Sugar remarked. “If any ship had been in the upper fjord, its survival would have been uncertain.”

Using satellite imagery, seismic data, eyewitness accounts, and computational models, researchers reconstructed the tsunami event. They concluded that retreating glaciers destabilized the surrounding terrain, leading to the massive landslides responsible for the waves.

Throughout the 20th century and recent years, the South Sawyer Glacier has retreated more than 10 kilometers and significantly thinned out.

Despite this retreat, researchers did not anticipate a catastrophic collapse, as 64 million cubic meters of rock plummeted into the fjord. In retrospect, they noted small tremors leading up to the landslide.

At 5:45 a.m., a group of kayakers camped 50 kilometers away awoke to find their site flooded and equipment swept away.

Researchers learned about the disaster within hours due to the landslide triggering a magnitude 5.4 earthquake. However, it took until mid-October for a team to access the area for investigation.

Sugar warns that this event could signal a future with increased tsunami risks due to climate change, stating, “We hope this serves as a wake-up call for policymakers in regions like North America, Greenland, New Zealand, and Chile, where steep terrains border oceans and lakes. These tsunamis are likely an underestimated threat.”

“Generally, tsunamis aren’t directly linked to climate factors, making this a clear example of how climate change can indirectly cause natural disasters previously unassociated with it,” said Martin Koehler from the University of Queensland.

“We were lucky there were no ships in the vicinity during the incident, especially given the regular cruise traffic and the suddenness of the event.”