The Giant of Tracy Arm: Alaska’s Second-Highest Tsunami Ever Recorded
In the remote wilderness of Alaska, a geological event recently occurred that redefined our understanding of localized disasters. On August 10, 2025, a massive landslide triggered a megatsunami in the Tracy Arm fjord, producing a wall of water that surged to a staggering 481 meters above sea level. While the event resulted in no casualties, its scale serves as a stark reminder of the violent power hidden within the world’s glacial landscapes.
The Anatomy of a Near-Miss
The event unfolded at 5:26 am local time. A massive wedge of rock, with a volume of at least 63.5 million cubic meters, detached from a mountain on the northern side of the fjord. The rock’s headscarp—the uppermost boundary of the landslide—was positioned roughly 1,025 meters above sea level.
As this immense mass of rock plummeted into the deep waters at the terminus of the South Sawyer Glacier, it displaced the water column with extreme force. This created an initial breaking wave 100 meters high that tore across the fjord at speeds exceeding 70 meters per second. When the wave slammed into the opposite shoreline, it surged up the steep rocks to reach its peak height of 481 meters.
“It was the second highest tsunami ever recorded on Earth,” says Aram Fathian, a researcher at the University of Calgary and co-author of a recent Science study that reconstructed the event. “But until now, almost nobody heard about it because it was a near-miss event.”
The timing of the landslide was the only reason it didn’t become a tragedy. Because it occurred in the early morning hours, no people were in the immediate vicinity and no injuries or fatalities were reported.
Landslide Megatsunamis vs. Earthquake Tsunamis
Most people associate tsunamis with massive undersea earthquakes. However, the Tracy Arm event was a “landslide tsunami,” which operates on a different physical mechanism. While earthquake-generated tsunamis are widespread and typically reach runup heights of a few tens of meters when they hit land, landslide tsunamis are far more localized and significantly more violent.
The violence of these events is driven by two main factors:
- Direct Displacement: Millions of tons of rock falling suddenly into the water push the water column aside with immense energy.
- Confined Geography: When this happens in a narrow fjord, the variation in water depth and the restricted space amplify the wave’s height and power.
A Historical Perspective on Megatsunamis
The Tracy Arm event is part of a rare but documented pattern of extreme geological events. Since 1925, scientists have identified 27 such events with runups exceeding 50 meters. Even with this record, the 2025 Alaska event stands out for its sheer magnitude.
It is surpassed only by the 1958 Lituya Bay tsunami, which remains the highest ever recorded, reaching a runup height of 530 meters. The proximity of the Tracy Arm wave’s height to the Lituya Bay record underscores the extreme nature of the South Sawyer Glacier collapse.
Key Takeaways: The Tracy Arm Event
- Date and Time: August 10, 2025, at 5:26 am local time.
- Landslide Volume: At least 63.5 million cubic meters of rock.
- Maximum Runup: 481 meters above sea level.
- Wave Speed: Exceeded 70 meters per second.
- Global Ranking: The second highest tsunami ever recorded on Earth.
- Outcome: No injuries or fatalities due to the early hour of the event.
The Tracy Arm fjord tsunami highlights a critical vulnerability in tourist-frequented glacial areas. While we were lucky this time, the reconstruction of this event in the Science study warns that these localized megatsunamis are a recurring threat in steep-walled fjords across the globe.