A glacier that had held a mountainside steady for millennia retreated just enough to expose unstable rock, and on August 10, 2025, that rock fell into Alaska’s Tracy Arm Fjord, creating a tsunami 481 meters tall. According to reporting on the incident, it was the second-largest tsunami ever recorded, and the largest one not triggered by an earthquake.
Researchers studying the Tracy Arm disaster have uncovered something that challenges how we usually think about climate risks. The slow retreat of glaciers isn’t just an aesthetic loss or a sign of global warming. In places like Alaska, it can be the direct precursor to geological catastrophe.
A Wave Taller Than the Burj Khalifa
The collapse itself was sudden and violent. According to a paper published in Science and research presented at the European Geosciences Union 2026 General Assembly, the mountainside gave way in the early morning hours, sending a vast amount of rock into the narrow fjord. The tsunami that resulted, 481 meters at its highest point, exceeded the height of all but 14 buildings on Earth.
For days afterward, the fjord didn’t settle. The water continued to churn in what scientists call a seiche, a standing wave that persisted long after the initial tsunami had crashed against the fjord’s walls. Drone footage captured the aftermath: icebergs floating in turbulent water, exposed rock faces where the mountainside had sheared away.
The narrow shape of the fjord made the disaster even worse. Unlike tsunamis that spread out over the open ocean, this wave got funneled through a tight channel. All the energy from the rockfall got squeezed into the fjord’s walls, making the wave way more powerful and destructive. Despite its immense power, the tsunami claimed no lives, something that Daniel Shugar, the geomorphologist from the University of Calgary who led the study, partly credits 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.”
The Glacier That Held Everything in Place
Understanding why the mountain collapsed requires looking back decades, to a glacier that has been steadily vanishing. South Sawyer Glacier had retreated by roughly 500 meters in just the spring of 2025 alone. The glacier had been acting like a support system, holding the mountainside in place. As the ice thinned and pulled back, it no longer provided this support, leaving the rock unstable and vulnerable.
Satellite images now show that this issue extends beyond South Sawyer Glacier, with many slopes in Alaska moving above thinning glaciers. Scientists call this process “debuttressing,” where the glacier’s retreat removes its stabilizing effect. While heavy rainfall might have triggered the collapse, Shugar’s team believes the glacier’s retreat was the primary cause, exposing the rock to failure.
Climate Change as a Trigger, Not Just a Trend
The Tracy Arm tsunami represents a new type of climate-related disaster: a sudden, violent consequence of warming with little warning. Similar landslide-triggered tsunamis have occurred in places like Taan Fiord in Alaska and Dixon Fjord in Greenland, all linked to climate change rather than seismic activity.
This type of hazard is hard for traditional risk assessments to handle. Earthquakes give some seismic warning, and hurricanes can be tracked for days. But a glacier slowly retreating over months or years doesn’t seem like an immediate threat until it suddenly becomes one.
Glaciologist Leigh Stearns from the University of Pennsylvania, who was not involved in the Tracy Arm study, emphasized how deceptive the gradualness can be.
“Often, we think of glacier retreat as a long and continuous thing, but [it] can trigger sudden catastrophic events,” she said.
A bigger concern is the expansion of human infrastructure into these vulnerable areas. Shugar pointed out that while the actual risk to any individual ship remains low, the continued development of new settlements, mining camps, and oil and gas operations in Alaska could increase the risk.
“The risk could definitely grow as we build more infrastructure,” he said.
Both Shugar and Stearns see Tracy Arm as a warning signal that demands attention before the next disaster.
“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.”
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