Passengers aboard the Hanse Explorer visited the South Sawyer Glacier on the evening of Aug. 9, 2025, before leaving the fjord. About 12 hours later, shortly after 5am, part of an adjacent mountain collapsed into the water. No ships were nearby at the time.
The impact transferred the momentum of millions of tons of rock into tsunami waves. Water and debris reached 481 metres up the opposite side of the fjord, stripping sections of its walls to bare rock before continuing down Tracy Arm. Some cruise lines began avoiding the fjord in the following months.
Researchers from the Alaska Earthquake Center and their colleagues said the disaster followed several observable changes. The glacier below the landslide area had retreated by more than a third of a mile during the previous two months, with rapid calving as large sections of ice broke away. Heavy rain was also entering fractures in the mountain, increasing water pressure inside the cracks.
Thousands of small seismic tremors emerged from the area during the days before the collapse. The researchers argued that the combination of rapid glacier retreat, weather conditions and seismic activity could have supported escalating alerts if a monitoring programme had been operating.
Under their proposed yellow, orange and red system, rapid retreat and adverse weather could prompt a general yellow alert. An accelerating series of seismic events and a transition to continuous seismic tremor could justify an orange warning for a specific area, potentially including advice to keep vessels away. Detection of a landslide already in progress could trigger a red alert.
Regional seismic monitoring can estimate a large landslide’s approximate size and proximity to open water within minutes, the researchers said. That would offer little protection to vessels next to the collapse, but could provide about 10 minutes of warning farther away.
No US landslide monitoring system currently operates at the scale envisaged. Establishing one would require cooperation among state and federal agencies, stronger monitoring and improved communication networks. The researchers acknowledged that such a system would not eliminate the danger.
Similar risks exist where retreating glaciers meet steep, unstable slopes, including other parts of Alaska, Greenland and Norway. Researchers said the mechanics remain poorly understood, but recent major landslides have repeatedly occurred near the ends of retreating glaciers.