On August 9, 2025, a landslide in Alaska's Tracy Arm collapsed into a fjord, generating a tsunami that pushed water and debris 1,580 feet up the opposite mountainside. That makes it the second-highest tsunami runup in recorded history, according to a study from the Alaska Earthquake Center.
The study identifies several early warning signs: the glacier below the slide area had retreated more than a third of a mile in the two months prior, heavy rain had fallen, and thousands of small seismic tremors emanated from the area in the days before. The researchers say these signs would have supported issuing progressive alerts to ships and coastal communities at least a day in advance, even though the exact mechanics of ice loss and slope failure remain poorly understood.
They suggest a yellow-orange-red alert system similar to those used for avalanches and volcanic unrest. Yellow would indicate elevated hazard based on weather and glacier retreat; orange would signal imminent concern as tremors accelerate; red would mean a landslide has begun, detectable by seismic networks within minutes, potentially providing around ten minutes of warning to boats farther away. No such monitoring system currently operates in the U.S., and the researchers note that it would reduce risk, not remove it.