Alaska Mountain Collapse Triggered 1,578-Foot Megatsunami in Tracy Arm Fjord

A megatsunami wave triggered when part of an Alaskan mountain crumbled into the sea struck Tracy Arm Fjord in southeastern Alaska on 10 August 2025, reaching 1,578 feet (481 metres) and becoming the second-highest tsunami ever recorded. Researchers said the landslide was driven by climate change, with the glacier that once buttressed the mountain retreating and leaving the rock face unsupported. Dan Shugar, a geomorphologist at the University of Calgary and lead author of the study published in Science, warned, "The fact that the landslide occurred this early in the morning was unbelievably lucky." Stephen Hicks, a University College London geophysicist and study co-author, said, "This collapse triggered a seismic wave observed around the globe."

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The wave hit the tourist spot at 5.30am, so no cruise ships or other vessels were present in the area when the tsunami happened, and researchers said the early timing was the reason there were no injuries. In the aftermath, scientists reconstructed the event using aerial photos taken afterward, alongside other data, because there were no photographs or video recordings of the tsunami. Shugar said, "Next time - and there will be a next time - we may not be so lucky." Hicks added that the scientists had found warning signs, saying, "we have found that the landslide was preceded by about a week of tiny earthquakes indicating fracturing" in the eventual landslide mass.

The Guardian described the event as a warning for cruise lines and coastal environments, noting that the tsunami reached 481 metres (1,578ft) and that the sequence began at 5.26am local time on 10 August 2025. It said the landslide collapsed 1km vertically onto the South Sawyer glacier and into the narrow, 48km fjord, producing a 36-hour seiche and long-period seismic waves equivalent to those of a 5.4 magnitude earthquake. Researchers said the risk is increasing because fjord regions are visited by cruise ships while climate change drives glacier retreat, and they called for stronger risk mitigation measures including "systematic monitoring of unstable slopes" and "enhanced protection for local communities, tourists and critical infrastructure." The Guardian also reported that Dennis Staley from the US Geological Survey called the tsunami "a historic event" and said, "I feel like we dodged a bullet."

“The world’s second-tallest tsunami wave on record tore through the remote Tracy Arm fjord in Alaska last August, leaving immense destruction in its wake”

CNN