A catastrophic landslide in an Alaskan fjord last summer generated what scientists now confirm was the second-tallest tsunami in recorded history, with waves soaring to an astounding 1,578 feet – exceeding the height of New York’s Empire State Building.
The massive wave struck Tracy Arm Fjord in southeastern Alaska on August 10, 2025, at 5:30 a.m., according to new research published Wednesday in the journal Science. The remote waterway, located within the Tongass National Forest about 50 miles south of Juneau, is known for its dramatic landscape of granite cliffs, cascading waterfalls, and glaciers.
Fortunately, the early morning timing meant no cruise ships or recreational vessels were present in the popular tourist destination, preventing any injuries or fatalities.
University of Calgary geomorphologist Dan Shugar, who led the research team, emphasized the fortunate timing of the disaster. “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,” Shugar stated.
The research team attributes the landslide directly to climate change impacts. Rising temperatures caused a glacier that had been supporting the mountainside to retreat, ultimately leaving the rock formation without adequate support.
Without any photographic or video evidence of the event, scientists pieced together what happened using post-disaster aerial photography, satellite imagery, seismic readings, on-site investigations, and witness accounts from people in the vicinity.
The fjord measures approximately 25 miles in length and just over half a mile in width, flanked by towering cliffs that rise more than 3,280 feet. Researchers calculated the wave’s extraordinary height by examining where vegetation had been completely stripped away, creating stark scars on the rocky walls.
“The clearcut vegetation, like a bathtub ring around the fjord, is probably the most striking difference in how the fjord looks now versus last year, unless you were scuba diving and could see the massive deposit (of rock) on the ocean floor,” Shugar explained.
He described the aftermath as resembling “two different worlds,” with “a very sharp line, below which there is only rock and sediment and some tree stumps, and above which is virgin forest, standing as it did on August 9 before the tsunami.”
The scale of the collapse was enormous – approximately 83 million cubic yards of rock tumbled down in roughly one minute. University College London geophysicist Stephen Hicks, a study co-author, noted this volume equals 24 times that of the Great Pyramid of Giza.
“This collapse triggered a seismic wave observed around the globe,” Hicks reported.
The confined space of the fjord trapped some waves, creating a phenomenon called a seiche – essentially water sloshing back and forth that continued for several days and produced distinctive seismic signatures. A comparable landslide tsunami at Greenland’s Dickson Fjord in 2023 generated a 650-foot wave and similar sloshing effects.
Giant waves known as tsunamis typically result from underwater earthquakes, volcanic activity, or landslides. The record-holding tsunami – reaching about 1,700 feet – also occurred in Alaska at Lituya Bay in 1958 following a landslide.
While localized tsunamis like these can reach extreme heights, open-ocean tsunamis pose greater threats to human life despite being shorter. The devastating 2004 Indian Ocean tsunami, which claimed approximately 230,000 lives, reached 167 feet in Sumatra. Japan’s 2011 tsunami, responsible for over 15,000 deaths, peaked at about 131 feet.
“Tsunamis due to large earthquakes occur because a fault in the crust ruptures the seafloor, causing the vertical displacement of water above it. In the case of landslide events, it is the collapse of material from above the water and into the water that creates the wave,” Hicks explained.
The research revealed promising developments for future disaster prevention. Seismic data showed approximately one week of minor earthquakes preceded the Tracy Arm landslide, indicating fracturing within the eventual slide zone.
“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, in tandem with other observations,” Hicks said.
