Alaska’s Tracy Arm Fjord Records Second-Highest Tsunami in History After Massive Landslide

The Event: A Catastrophic Landslide and Tsunami

In the early hours of August 10, 2025, a colossal slab of rock—estimated at 63.5 million cubic meters—broke free from a mountain overlooking Alaska’s Tracy Arm fjord. The collapse occurred at 5:26 a.m. local time, sending the debris plummeting into the deep waters at the terminus of the South Sawyer Glacier. The impact generated a breaking wave initially 100 meters high that raced across the fjord at speeds exceeding 70 meters per second. When this wall of water struck the opposite shoreline, it surged up the steep rock face to a height of 481 meters above sea level.

Alaska’s Tracy Arm Fjord Records Second-Highest Tsunami in History After Massive Landslide — Source: arstechnica.com

“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 Science study that reconstructed the event in detail. “But until now, almost nobody heard about it because it was a near-miss event,” he adds. Remarkably, no injuries or fatalities were reported—largely because the tsunami occurred in the early morning, well before the area’s typical tourist activity began.

A Near Miss for a Popular Tourist Destination

Tracy Arm is a narrow, glacier-carved fjord located south of Juneau, Alaska, and is a major draw for cruise ships and kayakers who come to witness its towering ice walls and calving glaciers. On any given summer day, hundreds of visitors might be exploring the fjord’s waters. But on that August morning, the area was nearly deserted. The early timing meant that no cruise ships had yet entered the fjord, and most tour operators had not started their day. This fortunate circumstance turned what could have been a tragedy into a scientific marvel.

The event serves as a stark reminder that landslide tsunamis pose a genuine risk even in remote wilderness regions. Fathian and his colleagues urge authorities to monitor unstable slopes near popular waterways more closely, especially as climate change accelerates glacial retreat and destabilizes mountain faces.

Understanding Landslide Megatsunamis

Most tsunamis are triggered by earthquakes and produce runup heights—the maximum elevation a wave reaches on land—of just a few tens of meters. Landslide tsunamis, however, are far more localized but also far more violent. When millions of tons of rock suddenly plunge into a confined body of water, such as a narrow fjord, the direct displacement of the water column combined with irregular bathymetry can generate extreme waves. Since 1925, scientists have documented 27 events with runups exceeding 50 meters. The record holder remains the 1958 Lituya Bay tsunami in Alaska, which reached a staggering 530 meters.

Why They Are So Dangerous

The danger of landslide tsunamis lies in their unpredictability and immense energy. Unlike earthquake-driven tsunamis that may allow hours of warning, a landslide can occur with no precursor signals. The wave’s speed and height are also amplified in narrow fjords, making them particularly hazardous for boats and coastal infrastructure. In the Tracy Arm case, the wave’s runup of 481 meters is nearly as high as the Empire State Building—yet the event went largely unnoticed by the public.

Scientific Significance

The Science study led by Fathian’s team provides the first detailed reconstruction of the Tracy Arm event. Using satellite imagery, seismic data, and field surveys, they modeled the landslide’s volume, trajectory, and the resulting wave dynamics. Their findings not only shed light on a near-miss disaster but also improve our understanding of how such events unfold in glaciated terrain. As Arctic regions warm, similar landslides are expected to become more frequent, making this research critical for hazard assessment.

Volume of rock: 63.5 million cubic meters (roughly 25,000 Olympic swimming pools)
Initial wave height: 100 meters
Runup on opposite shore: 481 meters above sea level
Time of event: 5:26 a.m. local time (minimal human presence)
Rank: Second-highest tsunami ever recorded (after Lituya Bay, 1958)

What This Means for the Future

The Tracy Arm tsunami is a wake-up call. As glacial retreat continues to destabilize mountain slopes, more landslides are likely—and not all will happen at dawn. As the researchers note, we might not be so lucky next time. Improved monitoring of vulnerable fjords, real-time satellite surveillance, and community warning systems could help mitigate the risk. For now, the event stands as a powerful example of nature’s raw force and the thin margin that sometimes separates a scientific curiosity from a human catastrophe.