Major Landslide Triggers 500-Meter Tsunami in Tourist Hub
▼ Summary
– On August 10, 2025, a 63.5 million cubic meter rock wedge fell into Alaska’s Tracy Arm fjord, generating a 100-meter-high wave that surged 481 meters up the opposite shore.
– The event was the second highest tsunami ever recorded, but caused no injuries or fatalities due to its early morning timing.
– Landslide tsunamis, unlike earthquake-generated ones, are more localized but far more violent, with 27 events since 1925 exceeding 50-meter runups.
– The highest recorded tsunami was the 1958 Lituya Bay event, which reached 530 meters.
– The rock slope’s stability had been maintained by the South Sawyer Glacier, which is retreating due to climate change.
At 5:26 a.m. local time on August 10, 2025, a colossal slab of rock,no less than 63.5 million cubic meters in volume,broke free from a mountainside above Alaska’s Tracy Arm fjord. The debris plunged into the deep waters at the foot of the South Sawyer Glacier, generating an initial 100-meter-high breaking wave that raced across the fjord at over 70 meters per second. When that wall of water slammed into the opposite shoreline, it climbed the steep rock face to a staggering 481 meters above sea level.
“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 meticulously reconstructed the event. “But until now, almost nobody heard about it because it was a near-miss event,” he adds. No injuries or fatalities were reported following the Tracy Arm fjord tsunami, largely because it struck early in the morning. Yet, as Fathian warns, we might not be so fortunate next time.
Landslide megatsunamis behave very differently from their earthquake-driven counterparts. Quake-generated tsunamis typically produce runup heights of just a few tens of meters when they hit land. Landslide tsunamis, however, are far more localized but also far more violent. When millions of tons of rock suddenly collapse into a confined body of water,like a narrow fjord,the abrupt displacement of the water column and dramatic variations in depth generate extremely high waves. Since 1925, scientists have recorded 27 such events with runups exceeding 50 meters. The tallest remains the 1958 Lituya Bay tsunami, which reached 530 meters.
The source of the 2025 Tracy Arm tsunami was a steep rock wedge on the northern flank of the fjord. Its headscarp,the uppermost boundary of a landslide or rockfall,sat roughly 1,025 meters above sea level. For centuries, the structural integrity of this slope was held in place by a massive wall of ice: the South Sawyer Glacier. But South Sawyer, like many glaciers in the Stikine Icefield, has been in a state of retreat due to the warming climate, leaving such unstable slopes increasingly exposed.
(Source: Ars Technica)
