At half past five on the morning of 10 August 2025, more than 60 million cubic metres of rock collapsed into Tracy Arm fjord in southeast Alaska, generating a wave that ran 481 metres up the fjord wall, the second-highest tsunami ever recorded. Remarkably, no vessels were caught in a waterway heavily visited by summer cruise traffic, though kayakers tens of kilometres away were woken by surging water that swept away their equipment.
Because nobody observed the wave directly, an international team led by the University of Calgary reconstructed the event from satellite imagery, seismic recordings and numerical modelling, publishing their findings in Science. An Oxford researcher from the Department of Engineering Science analysed the seismic data and uncovered something unexpected: rather than dissipating, the tsunami's energy became trapped in the steep-sided fjord, sloshing back and forth as a standing wave, or seiche, for more than a day.
This is only the second landslide-induced seiche ever recorded, after the Dickson Fjord event in East Greenland a year earlier, and unlike that single steady pulse, Tracy Arm oscillated in several overlapping rhythms at once, like a struck bell sounding multiple tones. Because such resonances travel as subtle seismic signals detectable around the globe, each fjord's unique signature could become a tool for remotely identifying these hazards, which are expected to grow more frequent as glaciers retreat.