Alaska's 481-Meter Tsunami: Glacier Retreat Triggers Second-Largest Wave Ever Recorded

On August 10, 2025, a glacier that had held a mountainside steady for millennia retreated just enough to expose unstable rock in Alaska’s Tracy Arm Fjord. The rock collapsed, generating a tsunami 481 meters tall,the second-largest ever recorded and the largest not triggered by an earthquake.

Researchers studying the Tracy Arm disaster have uncovered how the slow retreat of glaciers can directly precede geological catastrophe, challenging conventional views of climate risks. Details come from a paper published in Science (doi:10.1126/science.aec3187) and presentations at the European Geosciences Union 2026 General Assembly.

A Wave Taller Than the Burj Khalifa

The mountainside collapse occurred in the early morning hours, sending a vast amount of rock into the narrow fjord. The resulting tsunami reached 481 meters at its highest point, exceeding the height of all but 14 buildings on Earth.

For days afterward, the fjord experienced a persistent seiche, a standing wave. Drone footage captured icebergs in turbulent water and exposed rock faces from the shear.

The fjord's narrow shape amplified the disaster, funneling the rockfall's energy into powerful waves against the walls. Despite its scale, no lives were lost,something Daniel Shugar, geomorphologist from the University of Calgary who led the study, attributes partly to lucky timing.

“The risk to any particular cruise ship [from a tsunami] on any particular day is very low,” he said. “We were unbelievably lucky that the [tsunami] occurred with the timing that it did, and not 5 hours later. The risk certainly still could be increasing as we build new settlements, new mining camps, or new oil and gas infrastructure.”

Daniel Shugar, University of Calgary

The Glacier That Held Everything in Place

South Sawyer Glacier had retreated by roughly 500 meters in the spring of 2025 alone, acting previously as a stabilizing support for the mountainside. As the ice thinned and retreated,a process called debuttressing,the rock became unstable. While heavy rainfall may have triggered the final collapse, the glacier retreat was the primary cause.

Satellite images reveal similar slopes moving above thinning glaciers across Alaska.

Climate Change as a Trigger for Sudden Disasters

The Tracy Arm tsunami exemplifies a new class of climate-related hazard: sudden events from gradual glacier retreat, with little warning. Similar landslide-triggered tsunamis have occurred in Taan Fiord, Alaska, and Dixon Fjord, Greenland,all linked to climate change rather than earthquakes.

Glaciologist Leigh Stearns from the University of Pennsylvania, not involved in the study, noted:

“Often, we think of glacier retreat as a long and continuous thing, but [it] can trigger sudden catastrophic events.”

Leigh Stearns, University of Pennsylvania

Shugar highlighted rising risks from expanding infrastructure:

“The risk could definitely grow as we build more infrastructure.”

Daniel Shugar

Both Shugar and Stearns view Tracy Arm as a critical warning.

“Climate is a threat multiplier, and this research is pushing us to consider cascading hazards,” Stearns said. “Tracy Arm is one example: Small, gradual changes can trigger major events. Hopefully, we won’t need more disasters to prompt action.”

Leigh Stearns