Large landslide triggers localized tsunami in Tracy Arm, Alaska
A large landslide hit Tracy Arm, Southeast Alaska at approximately 05:30 LT (13:30 UTC) on August 10, 2025, generating a localized tsunami, according to the Alaska Earthquake Center.
Tracy Arm-Fords Terror Wilderness - October 2024. Credit: Chris Gabriel
Seismic records indicate that a large landslide involving several tens of millions of cubic meters of material slid into the water in Tracy Arm fjord in Southeast Alaska at 05:30 LT on August 10.
The Alaska Earthquake Center (AEC) reported that the seismic signal was typical of major landslide events and was detected across southern Alaska.
“Seismic signals large enough to be seen widely across southern Alaska confirm a significant landslide in the region at about same time,” AEC said.
Preliminary analysis by the AEC estimated the resulting displacement wave at approximately 0.3 m (1 feet) in height at broader scales. However, eyewitness accounts from Harbour Island in Tracy Arm Inlet suggest that wave heights in certain locations were substantially larger due to local amplification effects within the fjord.
Kayaker Sasha Calvey, camping with two others on Harbour Island, about 72 km (45 miles) south of Juneau, reported that the surge reached a campsite located roughly 7.6 m (25 feet) above the high tide line.
The wave swept away half of their gear, including one boat, personal items, and cooking equipment, and came within about 2.5 cm (1 inch) of entering their tent.
Dr. Dave Petley, landslide specialist, noted that satellite imagery captured by Planet Labs on August 7, 2025, three days before the event, showed no clear fresh landslide scar in the steep terrain surrounding Tracy Arm. The exact source location of the failure has yet to be identified, pending new high-resolution imagery or direct field surveys by boat or air.
Tracy Arm is a steep-sided fjord where glacial retreat, intense rainfall events, and pre-existing slope instability create favorable conditions for large mass movement events capable of generating displacement waves.
It lies within the Tongass National Forest and extends inland from Stephens Passage, branching into two glacier-fed arms — the South Sawyer Glacier and North Sawyer Glacier. The fjord is roughly 48 km (30 miles) long, with steep, glaciated walls rising over 900 m (3 000 feet) above the water.
I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.
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