The landslide occurred in Tracy Arm fjord, a 30-mile-long inlet with sheer walls thousands of feet high that is part of Tongass National Forest and attracts over 500,000 annual visitors. Scientists estimate the landslide volume at up to 100 million cubic meters, though some reports put it at 64 million cubic meters—the equivalent of 24 Great Pyramids. The rock plunged into the water in under a minute near the face of the South Sawyer Glacier, which has retreated more than a kilometer in recent decades.
A swarm of tiny tremors, magnitude 1–2, occurred in the 18 hours before the slide, and new research published in Science suggests glacier melt driven by climate change is making such collapses far worse by removing ice support and thawing permafrost. According to BBC News - Science, Dr Stephen Hicks of University College London described how the glacier was previously helping to hold up the rock, and when the ice retreated, it exposed the cliff face, allowing the material to suddenly collapse. The resulting tsunami run-up height on the opposite slope was 425 meters, according to Dennis Staley of the USGS, though some measurements indicate it may have reached 470–500 meters.
Only the time it happened – in the early hours of the morning – prevented tourist cruise ships being caught up in the devastation, say the researchers.
The wave was up to 100 feet tall as it traveled down the fjord and was still 15 feet high 30 miles away at Harbor Island. Three kayakers camping on Harbor Island narrowly escaped, according to Sasha Calvey. The landslide occurred early in the morning before cruise ships or excursion boats were in the fjord; a sightseeing vessel and a National Geographic tour boat were scheduled to visit later that day.
According to BBC News - Science, researchers described how only the timing prevented tourist cruise ships from being caught in the devastation, and Alaskan geologist Dr Bretwood Higman called it a close call, noting that people were very nearly in the wrong place. The landslide was detected by seismometers across Alaska and up to 1,000 kilometers away. A research team combined fieldwork, seismic and satellite data to reconstruct the chain of events and trace the wave height.
Dr Bretwood Higman, an Alaskan geologist, said it was 'a close call'.
Dr Higman arrived weeks later and found broken trees littering the mountainside and vast swathes of scarred rock stripped of soil and vegetation. Megatsunamis occur when a landslide caused by an earthquake or loose rock hits water; they are usually localized and dissipate quickly, unlike open-ocean tsunamis triggered directly by earthquakes, which can travel thousands of miles and cause widespread devastation, such as the 2011 Japan tsunami. Alaska is especially vulnerable to megatsunamis because of its steep mountains, narrow fjords and frequent earthquakes.
The biggest known megatsunami occurred in the 1950s and was over 500 meters tall. The exact run-up height of this event remains uncertain due to differing reports, and the precise landslide volume is disputed between 64 million and 100 million cubic meters, which could affect assessments of the event's magnitude. Cruise lines including Holland America Line, Princess Cruises, and Norwegian Cruise Line have canceled Tracy Arm visits for 2026 due to ongoing instability and safety concerns.
We know that there were people that were very nearly in the wrong place.
The USGS states that the area remains hazardous because of potential continued rockfalls and local tsunamis. According to BBC News - Science, Dr Higman expressed fear that future events may not be as lucky, and Dr Hicks noted that more people are visiting remote areas to see natural beauty and learn about climate change, but these are also dangerous places. The event went largely unreported at the time, and specific safety measures and long-term monitoring systems for the fjord have not been detailed.
I'm quite terrified that we're not going to be so lucky in the future.
The glacier was previously 'helping to hold up this piece of rock', and so when the ice retreated, it exposed the bottom of the cliff face, 'allowing that rock material to suddenly collapse into the fjord'.
More people are now going to remote areas - often these tourist cruises are going to see the natural beauty of the area to actually learn more about climate change - but they are also dangerous places to be.