A 481-meter-high landslide-tsunami in a cruise ship–frequented Alaska fjord

Abstract

early in the morning of 10 August 2025, a >64 × 106–cubic meter landslide struck Tracy Arm fjord in Alaska. The landslide was preconditioned by glacial retreat caused by climate change. The resulting 481- meter runup megatsunami followed an initial 100- meter- high breaking wave traveling at >70 meters per second. The landslide was preceded by several days of microseismicity, which increased in rate and magnitude until ~1 hourbefore failure. The landslide produced globally observed long- period seismic waves equivalent in size to a moment magnitude 5.4 earthquake. A long- period (~66 second) global seismic signal, produced by a landslide- induced seiche trapped within the fjord, persisted for up to 36 hours, the second time a days- long seiche had thus been observed. With fjord regions increasingly visited by cruise ships, and climate change making similar events more likely, this unanticipated, near- miss event highlights the growing risk from landslides and tsunamis in coastal environments