Towering Alaska megatsunami reached 481 metres high, experts say
A landslide caused the immense tsunami in a fjord southeast of Juneau in August 2025
A major Alaskan landslide in August 2025 unleashed a tsunami that climbed nearly 500 metres up the side of the fjord, according to the results of a recent study.
The landslide let loose at the face of the South Sawyer Glacier deep within Tracy Arm, a fjord in southeastern Alaska that’s heavily visited by cruise ships.
The incident highlights the dangers posed to tourists in the region.
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A destructive tsunami fills an Alaskan fjord
Spearheaded by an international group of researchers, the study highlights the harrowing events that unfolded in the Alaskan fjord during the pre-dawn hours on Aug. 10, 2025.
Landslides are common around fast-retreating glaciers. South Sawyer Glacier within Tracy Arm has retreated significantly since the early 1900s, largely as a result of rising temperatures due to climate change.
A large patch of land on the northern face of Tracy Arm let loose at 5:26 a.m. that day, sending more than 64 million cubic metres of hillside crashing down into the waters below.
The event directly displaced much of the water in its path, generating an immense tsunami that climbed 481 metres up the hillside immediately across the fjord. The force of the water stripped away vegetation, leaving behind barren scars easily visible on satellite imagery.
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Tsunami waves continued rushing down the fog-filled fjord, running nearly 200 metres up the hillside several kilometres away from where the landslide occurred. Water sloshed around within the fjord for 36 hours before settling down, the report found.
For context, the highest observation deck on Toronto’s CN Tower is 447 metres above ground level. The Statue of Liberty is 93 metres tall from the ground to the tip of her torch. This tsunami’s maximum height measured the equivalent of roughly 1,900 corgis standing on top of one another.
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Despite occurring far from populated areas, this event could have easily turned tragic. A cruise ship was anchored at the mouth of the fjord on the morning of the landslide and tsunami.
Alaskan fjords, including Tracy Arm, are popular destinations for cruise ships passing through the region. These natural wonders can see more than a million visitors pass through every year, mostly during the warmer months.
The study noted that as many as 20 ships per day enter Tracy Arm during the height of the summer season, including several ships that each carry thousands of passengers.
Similar incidents have occurred around the world
The landslide and tsunami that occurred in Tracy Arm was far from the first of this type of disaster, and it certainly won’t be the last.
A magnitude 7.8 earthquake caused a similar incident in Lituya Bay, Alaska, in July 1958, which generated a tremendous tsunami that overtopped a nearby ridge that rose more than 500 metres in elevation.
One infamous example is northern Italy’s Vajont Dam. An October 1963 landslide behind the dam sent a towering tsunami over the structure and into the valley below, creating a flash flood responsible for killing thousands of people.