A massive rock slope collapsed into the Tracy Arm fjord in southeast Alaska in the summer of 2025, triggering a tsunami that sent water more than 1,500 feet up the fjord's steep walls, according to Columbia University seismologist Goran Ekstrom.
No tourists were present in the fjord at the time, but they could have been: cruise ships regularly conduct sightseeing tours there. Ekstrom, Newberry Professor of Earth and Environmental Sciences and a professor at Lamont-Doherty Earth Observatory, part of the Columbia Climate School, recently published research in the journal Science on the tsunami with colleagues from several institutions.
"It was an outrageous event," Ekstrom said. "Imagine a very steep-walled fjord, carved by a glacier. One whole side of that fjord, this huge rock slope, collapses into the water. When that mass hits, it pushes water up the opposite wall to extraordinary heights."
The wave left a visible scar where it stripped away large trees along the slopes. "It would not have been good to be there with a cruise ship carrying a thousand people," Ekstrom said.
Asked whether such events are becoming more likely as the climate warms, Ekstrom said yes. "The simplest way to think about this is that ice buttresses the mountainsides," he said. As glaciers retreat, they leave behind extremely steep, gravitationally unstable rock slopes that can fail catastrophically. Had the landslide occurred 20 years earlier, the glacier would have extended farther down the fjord and the rock would have hit ice rather than water, producing a landslide but not a tsunami.
Ekstrom's role was the seismology. Landslides of this size produce signals that resemble earthquakes but have a characteristic shape, detectable on seismometers worldwide. He estimated the Tracy Arm landslide's mass at about 200 million tons, with a seismic magnitude of about 5.4 — large for a landslide, though not among the very largest in absolute volume.
The global seismic data comes from a tradition of data sharing, with instruments funded by agencies such as the U.S. National Science Foundation and operated through consortia, plus the U.S. Geological Survey's global network and near-global networks run by France, Germany and other countries.
Colleague Pat Lynett at the University of Southern California produced numerical animations of the event. "The animations give you this almost shocking, visceral perspective on the event," Ekstrom said. In one video, Lynett simulated a jet ski trying to escape the tsunami. "Even going 70 miles an hour, you would not have been able to outrun it."
Ekstrom also described detecting a huge landslide minutes before devastating floods in Nepal, contradicting initial reports of a glacier collapse. "Global warming and glacier melting make the mountainsides more unstable, causing landslides like this one to occur more frequently," he said, adding that with more people and infrastructure in river valleys, effective warning systems are essential.