Alaska’s 1,578-Foot Megatsunami Confirmed as Second Tallest on Record

The height places the event just behind the legendary 1958 Lituya Bay tsunami, which was driven by another giant landslide in a similar southeast Alaska area.

Rudy Blalock

Published: 5/6/2026, 11:02:28 PM EDT

Alaska’s 1,578-Foot Megatsunami Confirmed as Second Tallest on Record — Cars leave Homer Spit in Homer, Alaska, on July 16, 2025. (Tim Hatfield via AP)

Alaska’s 1,578-foot tsunami in 2025 ranked as the second-tallest ever documented, driven by a massive landslide that crashed into a remote fjord and sent a wall of water surging up the surrounding slopes, according to a recent scientific study.

In the early hours of Aug. 10, 2025, a huge slope failure struck Tracy Arm, a glacier-carved fjord in southeast Alaska, unleashing what researchers describe as a “megatsunami” that ran up 1,578 feet above the waterline, according to the study. A fjord is defined as a long, deep, and narrow body of water that extends far inland, according to National Geographic.

Scientists say the landslide released about 64 million cubic meters of rock and debris into the fjord, generating a breaking wave more than 100 meters high that raced across the water at more than 70 meters per second, according to the paper published in the journal Science. The height places the event just behind the legendary 1958 Lituya Bay tsunami, which was driven by another giant landslide in a similar southeast Alaska area.

Before the failure, the slope showed days of increased microseismic activity, with the rate and size of tiny earthquakes rising until roughly an hour before the mass finally let go.

Researchers also detected a long-period global seismic signal equivalent to a magnitude 5.4 earthquake when the landslide hit, a fingerprint of the enormous energy suddenly released into the fjord. A separate long-period signal, lasting around 66 seconds, revealed that the tsunami’s energy became trapped within the fjord and reverberated for up to 36 hours after the initial impact.

27 Landslide Tsunamis Recorded Worldwide

Since 1925, researchers have tallied 27 landslide tsunamis worldwide with runups of at least 250 meters, including the 1958 Lituya Bay disaster. That earlier event was triggered by a roughly 30 million cubic meter landslide set off by a magnitude 7.8 earthquake, and its waves climbed across a ridge that stood 530 meters above sea level.

These tsunamis can rise far higher than those produced by earthquakes because they are driven by sudden, localized displacements of water when huge masses of rock plunge into confined basins, most dramatically in places like fjords. The events unfold in minutes, leaving little time to react, which makes early detection and warning of such a major scientific and public safety challenge.

Authors of the paper note that fjords with retreating tidewater glaciers have become increasingly popular with cruise lines and smaller tour boats throughout the Arctic and sub-Arctic, including southeast Alaska. Cruise passenger numbers in Alaska rose from about 1 million in 2016 to an expected 1.6 million in 2025.

At the same time, land-based activities across Arctic and sub-Arctic coasts are also on the rise, bringing more hikers, campers, and boaters into zones where the hazards may not be obvious.