A 2025 Alaskan tsunami was one of the largest on record, new research finds

A tsunami that struck an Alaskan fjord in 2025 sloshed higher than the height of the top floor of One World Trade Center in New York, new research shows.

The study, published May 6 in the journal Science, found that the tsunami reached 1,578 feet (481 meters) up the slopes of the fjord, making it one of the tallest tsunamis ever recorded. It would have easily washed over the roof of New York's One World Trade Center, which stands 1,368 feet (417 m), not including its spire.

The study also found that the tsunami formed a standing wave, or "seiche," that sloshed back and forth in the narrow fjord for over a day. It's only the second time such a seiche has been recorded.

The tsunami hit Tracy Arm fjord, south of Juneau, on Aug. 10, 2025, when a massive landslide dropped 2.1 billion cubic feet (60 million cubic meters) of rock into the fjord's waters. The fjord is the outlet for the South Sawyer Glacier, which had been on a rapid retreat. It's not clear whether that retreat destabilized the slope or whether recent rains were more to blame, but the resulting tsunami was one of the largest on record. The only one known to be higher is a 1958 earthquake-triggered wave in Lituya Bay, Alaska, which scoured one slope to the height of 1,720 feet (524 m).

Although the fjord is often visited by cruise ships, it was empty on Aug. 10. Kayakers at the fjord's mouth, miles away, reported that their equipment was washed away by strong waves, but no one was hurt or killed by the tsunami.

Because no one saw the wave, discovering exactly what happened took some detective work. Thomas Monahan, a senior research associate in engineering at the University of Oxford, and his colleagues used satellite imagery and seismic data to build computer models of the tsunami. They observed long-lasting reverberations indicating that the wave splashed back and forth as a seiche. This phenomenon was previously observed in Greenland in 2023. The signal was more complex in Alaska than in Greenland, however, the researchers reported.

"This study shows that enclosed basins like fjords can effectively act as giant tuning forks, with the resonance determined by their shape and geometry," Monahan said in a statement. "This gives each fjord a unique 'signature' when they are affected by energetic events such as megatsunamis."

The satellite observations, gleaned from the Surface Water Ocean Topography satellite operated by NASA and France's space agency, also showed that the wave was more energetic than computer models would have predicted, Monahan said.

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Credit: The OLI (Operational Land Imager) on Landsat 8 and Landsat 9.

Cruise lines have canceled their incursions into the fjord this year due to the possible risk of another slide. Study co-author Stephen Hicks, an Earth scientist at University College London, said the research might point to a way to predict such slides.

"With hindsight, there were some warning signs," he said in the statement. "Tiny earthquakes occurred at an increasing rate in the days to hours before the landslide, signaling that this mass of rock was starting to crack. Many seismic monitoring stations provide data in real-time, so this gives us some optimism that we can turn what we have learned into a warning system."