A 481-metre tsunami struck alaska’s Tracy Arm fjord on 10 August 2025 after a landslide dropped 1km onto South Sawyer glacier and into the water. The wave hit just as cruise traffic was moving through a 48km fjord visited by about three ships a day.
The new research, led by Dan Shugar of the University of Calgary and published on Wednesday in Science, says the event was the world’s second-tallest recorded tsunami. Researchers tied the scale of the wave to rapid glacier retreat, saying the landslide likely would not have produced such a surge without it.
Tracy Arm fjord on 10 August
The sequence began at 5.26am local time, when a large landslide collapsed vertically onto the South Sawyer glacier and into Tracy Arm fjord. The tsunami reached 481 metres, or 1,578ft, and triggered a 36-hour seiche. Researchers said the landslide also generated long-period seismic waves equivalent to those of a 5.4 magnitude earthquake.
Dennis Staley, a US Geological Survey scientist, described the event at the time as “a historic event” and told, “I feel like we dodged a bullet.” Two cruise ships carrying thousands of passengers had visited the area the day before, and a sightseeing vessel from Juneau and a National Geographic tour boat were due to enter the fjord just hours after the landslide.
Dan Shugar’s Science study
Shugar’s team wrote that fjord regions increasingly visited by cruise ships and climate change making similar events more likely create a growing risk from landslides and tsunamis in coastal environments. The study also said such waves can have substantially higher runups than earthquake tsunamis because confined fjords allow localized changes in water depth and direct water-column displacement from slope failure.
The researchers said, “without the rapid glacier retreat, the landslide would likely not have resulted in such a wave because it would have collapsed entirely onto glacier ice or might not even have occurred at all.” The world’s tallest tsunami on record remains the 530-metre wave recorded in Lituya Bay, Alaska, in 1958.
For cruise operators and passengers moving through Tracy Arm, the practical takeaway is plain: the fjord can produce extreme waves with little warning, and the hazard is tied to changing glacier conditions rather than a single isolated slide.
