A Sudden Landslide Triggered Alaska’s 2025 ‘Mega-Tsunami.’ Now, Scientists Have Identified Warning Signs to Predict Similar Events

Natural disasters like the one at Tracy Arm fjord, about 45 miles south of Juneau, could become more common as climate change alters frigid landscapes, according to researchers

Sara Hashemi | Daily Correspondent

May 26, 2026 2:23 p.m.

Share

Copy linkEmailSMSFacebookXRedditLinkedInBlueskyPrint

Add as preferred source

In the early morning hours of August 10, 2025, a massive landslide caused at least 2.3 billion cubic feet of rock—roughly 24 times the volume of the Great Pyramid of Giza—to plummet into Tracy Arm fjord. It’s a popular tourist destination around 45 miles south of Juneau, Alaska. The ensuing splash triggered a “mega-tsunami,” with a wave rising around 1,580 feet above sea level on the other side of the body of water.

Despite being the second-largest landslide-induced tsunami on record, the event went largely unreported at the time. Luckily, no one was injured.

Now, a study published in the journal Science on May 6 details what happened and identifies possible warning signs of landslides based on satellite images, eyewitness accounts, earthquake detector data and computer simulations. Understanding the lead-up to this “near-miss” event can help regional stakeholders create better monitoring and alert systems, especially as the risk of landslide-generated tsunamis rises due to glacier melt driven by climate change.

“Normally, with these gigantic rock avalanches, they often give some sort of warning signs in the weeks, months, years prior when the slope is slowly moving down the mountain. It’s sagging, and then it catastrophically gives way in a rock avalanche,” says study co-author Dan Shugar, a geomorphologist at the University of Calgary in Canada, in a statement. “In this case, that didn’t happen.”

Records indicated that prior to the natural disaster, the nearby South Sawyer Glacier had rapidly shrunk, exposing the rockface of a mountain on the northern side of the fjord that ultimately fell. The glacier’s retreat—likely due to climate change—meant ice no longer pressed the rock against the mountainside, making it unstable.

Scientists have noticed that several large landslides have occurred at the lower edge of retreating glaciers, although the mechanisms connecting the two events aren’t fully understood, write study co-authors Michael E. West and Ezgi Karasözen, seismologists at the University of Alaska Fairbanks, in the Conversation.

Animation of the Aug. 10, 2025, landslide and tsunami in Tracy Arm, Alaska.

Watch on

At first glance, the landslide appears to have happened without warning. Satellite imagery showed no evidence of cracks or scarring on the slope before the collapse. But the signs did appear underground, the researchers found. Data from earthquake sensors revealed that small, repeating local earthquakes were happening in the days leading up to the landslide. Similar tremors have occurred before recurrent ice avalanches on Iliamna Volcano in Alaska and landslides not involving ice, the authors note in the study.

The vibrations were “probably tiny bits of slip on the base of the landslide, and it can do that only so much before it’s got to break apart and fall,” explains Jackie Caplan-Auerbach, a study co-author and seismologist at Western Washington University, to Christian Elliott at the New York Times.

The analyses revealed that a day before the landslide, the tremors took place about once every hour. But they kept occurring closer together until they happened once every 30 to 60 seconds, then possibly merged into a unified movement with no discrete events right before the landslide. 

The subsequent rock tumble triggered a massive tsunami that stripped vegetation from the fjord’s walls. Although Tracy Arm is a popular tourist destination, no one reported injuries from the catastrophic event, probably because it happened at 5:26 am.

Still, some people in the surrounding region noticed its impact. Kayakers camping on Harbor Island near the fjord say that their gear was swept away, reported Alaska Public Media’s Eric Stone in 2025. Observers on a small cruise boat around 53 miles from the landslide also witnessed a surge of water, per the study. If the landslide had occurred when people were closer to its source, the consequences would have been vastly different, according to the researchers.

The team says the glacier retreat and seismic signals detected in the hours prior to the landslide would have been enough to issue a time-sensitive warning for the region. “The signs were arguably sufficient to recommend keeping boats and ships out of the fjord,” write West and Karasözen in the Conversation.

“The bar is, can we do better than missing most of these,” says Noah Finnegan, a geomorphologist at the University of California, Santa Cruz, who was not involved in the study to the Times. “So, getting a handle on why these precursors happen and what their relationship is to catastrophic collapse is an area many people are interested in.”

With climate change accelerating glacier retreat, particularly in the Arctic, it’s increasingly important to have monitoring tools in vulnerable regions. The research team plans to further investigate landslide warning signs like the ones they detected at Tracey Arm. “These signals could be promising for developing early warning systems in similar conditions or areas,” says Aram Fathian, a study co-author and Earth scientist at the University of Calgary, to Jacek Krywko at Ars Technica.

“Hopefully this kind of data ends up on desks of policymakers and regulators to come up with practical and appropriate measures,” he says.

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.