Study details 1,600-foot tsunami from 2025 Alaska landslide
A new study has documented how a landslide in Tracy Arm, a fjord in southeast Alaska, generated a tsunami in 2025 that climbed nearly 1,600 feet, making it the second-highest tsunami ever recorded.
The study, published Wednesday in Science, examined the August 10, 2025, landslide in Tracy Arm, a narrow fjord southeast of Juneau that is frequently visited by cruise ships, tour boats and kayakers.
Researchers found that more than 64 million cubic meters of rock collapsed near South Sawyer Glacier, producing a near-miss event in a heavily trafficked coastal area.
The maximum runup, the highest point reached by the water, was measured at 1,578 feet (481 meters) on the south side of the fjord, about 2 miles (3.3 kilometers) across from the landslide.
The finding places the Tracy Arm tsunami behind only the 1958 Lituya Bay tsunami in southeast Alaska, which reached about 1,740 feet (530 meters) after a landslide triggered by a magnitude 7.8 earthquake.
Researchers said the initial breaking wave was about 330 feet (100 meters) high and moved at more than 156 mph. The wave stripped vegetation from the walls of the fjord and left traces of runup and erosion as far as 31 to 34 miles (50 to 55 kilometers) from the landslide.
No deaths were reported, but scientists said the event showed a growing risk in fjords where retreating glaciers are leaving steep slopes unstable while tourism is increasing.
Tracy Arm and nearby Endicott Arm receive more than 20 boats per day in summer, including up to six large cruise ships a day, some carrying as many as 6,000 passengers and crew.
Several people were in the area when the tsunami moved through the fjord. Kayakers camped on Harbor Island, about 34 miles (55 kilometers) from the landslide, woke to water flowing past their tent, carrying away one of their kayaks and much of their gear. A person aboard the M/V Blackwood described a 6- to 8-foot (2- to 2.5-meter) cresting wave, followed by a smaller wave.
The landslide also produced seismic waves detected around the world, equivalent in size to a magnitude 5.4 earthquake.
Scientists said water sloshing inside the fjord created a long-period seismic signal that lasted up to 36 hours, only the second known case of a days-long landslide-induced seiche detected globally.
The study said the landslide was preconditioned by the retreat of South Sawyer Glacier, which had pulled back enough in the weeks before the collapse to expose part of the base of the slope that later failed. Researchers linked the retreat to regional warming driven by human-caused climate change.
Researchers found small seismic events began several days before the collapse and became more frequent in the hours before the landslide. They said those signals could help future warning systems, but events like this can unfold within minutes, leaving little time for alerts after a slope fails.
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Ella Rae Greene, Editor In Chief
