Alaska’s 481-Meter Tsunami: How a Glacier’s Retreat Triggered a Record-Setting Landslide

In the early hours of 10 August 2025, a mountainside in southeastern Alaska’s Tracy Arm Fjord collapsed into the water below, generating a tsunami that reached 481 meters on the fjord’s opposite shore—taller than all but 14 of the world’s skyscrapers. The event registered on seismic detectors worldwide and triggered days of churning waters in the fjord, known as a seiche.

This drone footage, captured in the aftermath, shows a man paddling through the iceberg-littered fjord. Credit: Bill Billmeier

The landslide produced the second-largest tsunami ever recorded and the largest not linked to an earthquake. A new study published in Science provides compelling evidence that the disaster was triggered by the rapid retreat of South Sawyer Glacier, a consequence of global climate change.

“It’s like if you have a kid and they said they cleaned their room but really all they did was throw everything in the closet. As soon as you open that door, everything falls out.”

No injuries were reported from the rockslide or tsunami, but cruise ships were scheduled to visit the fjord later that morning. Had the collapse occurred just hours later, the outcome could have been catastrophic.

Glacier Retreat: The Hidden Culprit

“While the [South Sawyer] Glacier is in the fjord, it’s supporting those valley walls, like the buttresses on a cathedral,” said Daniel Shugar, a geomorphologist at the University of Calgary who led the study. “As that glacier retreated over the last few decades, it retreated just past the spot that did fail.”

“We know that steep slopes are very sensitive to the things that climate [change] is exacerbating, whether it’s losing permafrost, glacier retreating, or more water in the soil. Often, we think of glacier retreat as a long and continuous thing, but [it] can trigger sudden catastrophic events.”

The glacier, which carved the fjord, had been stabilizing the surrounding slopes. Its retreat under warming temperatures exposed rock that became increasingly vulnerable to collapse. While rainfall may have further weakened the fjord’s walls, the removal of the glacial “buttress” was the decisive factor.

“We know that steep slopes are very sensitive to the things that climate [change] is exacerbating,” said Leigh Stearns, a glaciologist at the University of Pennsylvania, who was not involved in the study. “Often, we think of glacier retreat as a long and continuous thing, but [it] can trigger sudden catastrophic events.”

Visualizing the Disaster

An animation by Patrick Lynett of the University of Southern California provides an overhead view of the landslide’s progression on 10 August 2025.