A Melting Glacier Triggers a 500-Meter Tsunami in Alaska

On August 10, 2025, at 5:26 am local time, a massive landslide in Alaska’s Tracy Arm fjord sent shockwaves through the region. A wedge of rock with a volume of at least 63.5 million cubic meters broke loose from a mountain and plunged into the deep waters near the South Sawyer Glacier. The result was a tsunami that reached an initial height of 100 meters, tearing across the fjord at speeds exceeding 70 meters per second. When it hit the opposite shore, the wave surged up to 481 meters above sea level.

“It was the second highest tsunami ever recorded on Earth,” says Aram Fathian, a researcher at the University of Calgary and co-author of a recent study published in Science that meticulously reconstructed this event. “But until now, almost nobody heard about it because it was a near-miss event.” Fortunately, there were no injuries or fatalities reported following the Tracy Arm fjord tsunami, largely due to its early morning timing. However, Fathian warns, "We might not be so lucky next time."

The Science Behind the Slide

Landslide tsunamis, like the one that occurred in Tracy Arm, are often more localized but also far more violent than earthquake-generated tsunamis, which typically reach runup heights of just a few tens of meters. When millions of tons of rock suddenly fall into a confined body of water, such as a narrow fjord, the displacement of the water column and the variation in water depth produce extremely high waves.

Since 1925, scientists have documented 27 such events with runups exceeding 50 meters. The highest on record is the 1958 Lituya Bay tsunami, which reached an astounding 530 meters. The source of the 2025 Tracy Arm tsunami was a steep rock wedge on the northern side of the fjord. Its headscarp, the upper boundary of the landslide or rockfall, sat roughly 1,025 meters above sea level.

For centuries, the structural integrity of this slope was maintained by the massive South Sawyer Glacier. However, like many other glaciers in the Stikine Icefield, South Sawyer has been retreating due to climate change. "We studied the event from several angles," Fathian explains. The team used high-resolution satellite images taken before and after the event to reconstruct the shape, geometry, axis, and direction of the slide. They also evaluated glacial thinning in the area, concluding that it was the primary cause of the Tracy Arm event.

The collapse was made more likely by industrial-era warming. Researchers calculated a 1.1°C increase in summertime temperatures since around 1875, which has driven up snowline elevations by approximately 169 meters. This warming trend has weakened the structural support provided by the glacier, making such landslides and tsunamis more probable.

What Comes Next

The Tracy Arm tsunami serves as a stark reminder of the increasing risks posed by climate change in regions with glacial activity. While this particular event was a near miss, the potential for future disasters is significant. The study's findings highlight the need for enhanced monitoring and early warning systems to protect communities and tourists who visit these areas.

Fathian emphasizes that understanding the mechanisms behind such events is crucial for developing effective mitigation strategies. "We need to continue studying these phenomena to better predict and prepare for them," he says. As glaciers continue to retreat, the likelihood of similar landslides and tsunamis will only increase, making it imperative for scientists, policymakers, and local communities to work together to safeguard lives and livelihoods.

The Tracy Arm tsunami is a wake-up call that underscores the urgent need for action on climate change. By addressing the root causes and improving our preparedness, we can help ensure that such near-misses remain just that-near misses-and not catastrophic events.