Alaska's Tracy Arm Fjord Escapes Catastrophe: The Second-Highest Tsunami Ever Recorded
A 2025 Alaska landslide created a 481-m high tsunami in Tracy Arm fjord, the second-largest ever recorded. No injuries occurred due to early timing, but experts warn of future risks in tourist areas.
On the morning of August 10, 2025, a colossal landslide in southeastern Alaska triggered a megatsunami that sent a wall of water surging nearly 500 meters up the steep walls of Tracy Arm fjord. Remarkably, no one was injured—but researchers warn that this near miss is a stark reminder of the growing threat in glacier-fed tourist destinations.
A Gigantic Rockfall Unleashes Chaos
At 5:26 AM local time, a wedge of rock with a volume of at least 63.5 million cubic meters broke free from a mountain above Tracy Arm, a popular fjord known for its dramatic scenery and cruise ship traffic. The mass plummeted into the deep water at the terminus of the South Sawyer Glacier, instantly displacing water and creating an initial breaking wave 100 meters high. This wave tore across the fjord at speeds exceeding 70 meters per second (about 157 mph). When it slammed into the opposite shoreline, it surged up the rocky slope to an elevation of 481 meters above sea level—taller than the Empire State Building.
What Scientists Discovered
The event was meticulously reconstructed by a team led by Aram Fathian, a researcher at the University of Calgary, in a study published in Science. According to Fathian, “It was the second highest tsunami ever recorded on Earth.” Only the 1958 Lituya Bay megatsunami, which reached 530 meters, was larger. Yet this latest disaster went virtually unnoticed outside of scientific circles. “Until now, almost nobody heard about it because it was a near-miss event,” Fathian explains.
Why No One Died: The Crucial Timing
The landslide struck at dawn, a time when virtually no tourists or boaters were on the water. Tracy Arm is a major attraction for cruise ships and kayakers, but at 5:26 AM, the fjord was empty of vessels. Had the event occurred just a few hours later, the outcome could have been catastrophic. This fortunate timing spared lives, but scientists stress that future events may not be so forgiving.
Understanding Landslide Megatsunamis
Tsunamis triggered by underwater earthquakes—like the 2004 Indian Ocean event—usually produce runup heights of only a few tens of meters when they strike land. Landslide tsunamis, by contrast, are far more localized but dramatically more violent. When millions of tons of rock plunge into a narrow, confined body of water such as a fjord, the sudden displacement generates extreme waves. The variation in water depth and the confined geometry amplify the wave's height. Since 1925, scientists have documented 27 landslide tsunamis with runups exceeding 50 meters, but the Tracy Arm event stands out for its sheer size and the fact that it occurred in a heavily touristed area.
Historical Context: The Lituya Bay Standard
The benchmark for landslide megatsunamis remains the 1958 Lituya Bay event in Alaska, which followed a magnitude 7.8 earthquake that dislodged about 30 million cubic meters of rock. The resulting wave stripped vegetation from slopes up to 530 meters above sea level. That event, however, took place in a remote, uninhabited area. Tracy Arm, by contrast, is a well-known tourist destination located about 80 kilometers south of Juneau. Cruise ships regularly navigate its waters during the summer season.
Growing Risks in a Warming World
Climate change is increasing the frequency of landslides in glacial regions. As glaciers retreat, they leave behind unstable valley walls that are prone to collapse. The South Sawyer Glacier, like many in Alaska, has been thinning and receding for decades. Similar landslide-tsunami threats exist in places such as Greenland, Norway, and British Columbia. Researchers are now calling for enhanced monitoring of unstable slopes in tourist-heavy fjords, along with early warning systems that could give people precious minutes to move to higher ground.
The Tracy Arm event is a clear warning: the next megatsunami might not happen at dawn, and it could strike a crowded fjord. With cruise season drawing thousands of visitors each day, the time to prepare is now.