A landslide in a popular Alaskan fjord last year triggered the second-tallest tsunami ever recorded, with a wave reaching 481 metres — higher than New York’s Empire State Building — researchers have found, warning that climate change makes a repeat event inevitable.
The tsunami struck Tracy Arm Fjord in southeastern Alaska at 5:30 a.m. on 10 August 2025, surging through the narrow waterway and stripping vegetation from sheer rock walls. Because of the early hour, no cruise ships or other vessels were present and no one was hurt.
“The fact that the landslide occurred this early in the morning was unbelievably lucky. Next time — and there will be a next time — we may not be so lucky,” said Dan Shugar, a geomorphologist at the University of Calgary and lead author of the study, published on Wednesday in the journal Science.
Researchers determined the wave height by measuring where the vegetation had been stripped from the fjord walls, leaving a stark line between bare rock and untouched forest above. “Like two different worlds,” Shugar said.
The landslide was driven by glacier retreat caused by rising temperatures. The glacier that had buttressed the mountain had pulled back, leaving the rock face unsupported until it gave way. About 64 million cubic metres of rock — 24 times the volume of the Great Pyramid of Giza — collapsed in approximately one minute.
“This collapse triggered a seismic wave observed around the globe,” said Stephen Hicks, a geophysicist at University College London and co-author of the study. Some waves became trapped inside the fjord, causing a seiche — a sloshing effect — that lasted several days and produced a distinct seismic signal.
The wave rose to such heights because the enormous volume of water displaced by the collapsing rock was forced through a confined space. Tracy Arm, located about 80 kilometres south of Juneau, is roughly 40 kilometres long and just one kilometre wide, with surrounding cliffs exceeding 1,000 metres.
The tallest tsunami on record — approximately 520 metres — also occurred in Alaska, at Lituya Bay in 1958, also triggered by a landslide. By comparison, the 2004 Indian Ocean tsunami, which killed around 230,000 people, reached 51 metres in Sumatra; the 2011 Japan tsunami, which killed more than 15,000, peaked at about 40 metres.
Hicks said seismic data revealed warning signs in the days before the Tracy Arm event. “With the benefit of hindsight, we have found that the landslide was preceded by about a week of tiny earthquakes indicating fracturing in the eventual landslide mass. This gives us possible hope of developing warning and forecasting systems,” he said.
There were no photographs or video of the tsunami. Scientists reconstructed the event using aerial imagery, satellite and seismic data, fieldwork and accounts from people in the area at the time.
(Reuters)
