NASA satellite images show how a massive tsunami in Alaska changed the landscape forever
Popular Science...
New satellite images are helping scientists understand a major tsunami that changed the landscape of a popular tourist destination in Alaska forever.
On August 10, 2025, a tsunami larger than the Eiffel Tower ripped through Tracy Arm fjord in southeast Alaska. The rapid retreat of the South Sawyer Glacier triggered a landslide that swept huge rocks down the picturesque waterway visited by millions aboard Alaskan cruises every summer. At least 64 million cubic meters of rock slid down the slope of the glacier. The rocks created an enormous tsunami that stripped trees and other vegetation from the opposing fjord wall up to 1,578 feet above sea level.
The NASA-USGS Landsat satellite images show the dramatic changes to the landscape. In one photo taken on July 26, 2025, the fjord is surrounded by green vegetation.
In the second image, taken nine days after the landslide on August 19, the fjord is dominated by a gray scar made by the cascading rock.
“The bright landslide scar on the north side of the fjord is striking, as is the ‘bathtub’ ring around the fjord showing the areas where the forest was leveled by the tsunami,” said Dan Shugar, a geomorphologist at the University of Calgary.
Sawyer Island, located about 6 miles away from the landslide, also turned from green to brown. Only a few trees still stood at the island’s higher elevations.
Over the past several months, Shugar and his colleagues combined satellite, airborne, and ground-based observations with eyewitness accounts and simulations to build a complete story with how this historic event transformed. Their analysis was published May 6 in the journal Science.
Their analysis found that water continued to slosh around the fjord for more than one day. Geologists call this water-sloshing phenomenon a seiche. Both the landslide and resulting seiche produced seismic signals that were detected around the world and equivalent to a magnitude 5.4 earthquake.
The Landsat images also show that the South Sawyer Glacier retreated significantly in less than a month. Typically, glacial retreat takes much longer.
“Part of that occurred between the date of the first image and the date of the landslide,” Shugar said. “But part of it is from the landslide itself, which broke off a big chunk of the terminus of South Sawyer Glacier, resulting in a slurry of icebergs in the fjord.”
Fortunately, no one was injured in the event, largely because it occurred around 5:30 a.m. local time. The wave did sweep away some gear from a group of kayakers camping on Harbor Island near the fjord’s mouth. Passengers aboard a small cruise ship in neighboring Endicott Arm also reported swings in water levels and a strong current associated with the tsunami.
In response to the event, at least six cruise lines have eliminated the Tracy Arm fjord from their itineraries for 2026 due to the hazards. The United States Geological Survey also warns that steep, mountainous landslide areas are “inherently unstable” and that the Tracy Arm fjord tsunami will likely continue to change the landscape.
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