Massive Tsunami Triggered by Landslide in Alaska

Last year, a significant landslide in Alaska resulted in a tsunami that researchers are now studying. It’s being recognized as the second-largest tsunami ever recorded.

In the early hours of August 10, 2025, a landslide descended from a mountainside over a glacier in Tracy Arm Fjord. This event sent debris crashing into the water and produced waves that soared over 1,500 feet high.

The tsunami reached a staggering height of 1,578 feet, sweeping through the picturesque Alaskan waterways, approximately 72 kilometers south of Juneau.

Recent analyses have provided insights into how this catastrophic landslide and subsequent tsunami came to be.

A study published in the journal Science detailed the conditions that triggered the landslide and a tsunami of such magnitude it surpassed the height of New York’s Empire State Building.

“The wave was absolutely immense. I can hardly fathom how terrifying it would have been to witness,” remarked Dan Sugar, the lead author of the study and an associate professor at the University of Calgary.

Unlike many tsunamis that are caused by earthquakes, this one was the result of a massive landslide that unleashed 64 million cubic meters of debris into the fjord—enough material to bury the Great Pyramid of Giza about 24 times. It also generated a seismic signal that could be detected globally for several days.

Putting it into perspective, Sugar compared the movement of water to jumping into a pool, explaining that the water surged approximately 1,600 feet up the steep walls of the fjord.

This remarkable event represents the second-largest tsunami in recorded history, following behind the 1958 Lituya Bay tsunami, which peaked at 524 meters (1,720 feet).

The extraordinary scale of this tsunami was facilitated by the narrow fjord, which amplified the waves and forced the water upward along the mountain walls. A similar phenomenon was observed during the Lituya Bay incident.

Interestingly, there were no clear indicators of the impending tsunami before it struck. Yet, in the days prior, scientists noted an increase in microseismic activity in Tracy Arm, occurring just before the slope gave way.

One key factor leading to the landslide was the glacier retreating below the valley wall. Sugar noted that the previous year, the wall had lost its support and retreated 1,800 feet before collapsing into the water.

The study highlighted the remarkable speed of a tsunami that could rival a skyscraper. Computer simulations suggested that the waves may have traveled at speeds exceeding 150 miles per hour—similar to a high-speed train—manifesting as a deadly 100-meter-high wall of water rushing through the fjord.

To comprehend the risks of landslides and tsunamis, understanding the landscape of Tracy Arm Fjord is crucial.

“The valley walls are so steep and narrow that there’s really only one way for the water to go, and that’s up,” Sugar explained.

Tracy Arm is a fjord that spans about 50 miles, is 0.8 miles wide, and 1,000 feet deep, framed by mountains towering up to 2,000 meters high.

As the landslide triggered the tsunami, it dramatically reshaped the landscape of this beautiful fjord, known for its stunning turquoise glacial waters. During the summer months, the region sees over 20 boats daily, including large cruise ships catering to thousands of tourists.

Fortunately, there were no reported fatalities from the tsunami, but many people witnessed the event from various locations.

The landslide occurred around 5:30 a.m. local time, well before the peak tourist hours. Had it struck later, the outcome could have been disastrous.

This study underscores a significant risk for this popular tourist area: the potential for tsunami-related landslides.

“It’s crucial to consider that if this event had happened five or six hours later, we could have faced a very different scenario. The fjord is a busy route for cruise ships and could have resulted in numerous casualties,” Sugar cautioned. “If tourist ships were present to see glacier caves, they would have been directly in harm’s way. I can’t imagine any vessel surviving waves of that size.”