On August 10, 2025, South Sawyer Glacier's 500m retreat in Alaska's Tracy Arm Fjord destabilized a mountainside, causing a massive rockfall that generated a 481m tsunami, the second-largest ever recorded and tallest non-earthquake one. The narrow fjord amplified the wave, creating persistent seiches, but no lives were lost due to timing. Experts like Daniel Shugar link it to 'debuttressing' from climate-driven glacier melt, warning of risks to expanding infrastructure amid similar events in Taan Fiord and Greenland.
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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.
Rockfall into fjord creating the 481-meter wave. (Credit: Torie Roman via Pexels)
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.
Persistent seiche with icebergs in the fjord. (Credit: Torie Roman via Pexels)
Map of Tracy Arm, Alaska, showing key locations related to the 2025 glacier collapse and tsunami. Credit: Science
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.”
Glacier debuttressing process in Tracy Arm. (Credit: Beth Fitzpatrick via Pexels)
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.
Images showing the glacier collapse in Tracy Arm, Alaska, on August 7 and 13, 2025. Credit: Science
Climate Change as a Trigger for Sudden Disasters
Example of climate-linked landslide tsunami hazard. (Credit: Pok Rie via Pexels)
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.”
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.”
