On the evening of Aug. 9, 2025, passengers on the Hanse Explorer finished taking selfies and videos of the South Sawyer Glacier, and the ship headed back down the fjord. Twelve hours later, a landslide from the adjacent mountain unexpectedly collapsed into the fjord, initiating the second-highest tsunami in recorded history.

We conduct research on earthquakes and tsunamis at the Alaska Earthquake Center, and one of us serves as Alaska state seismologist. In a new study with colleagues, we detail how that landslide sent water and debris 1,580 feet (481 meters) up the other side of the fjord – higher than the top floor of the Taipei 101 skyscraper – and then continued down Tracy Arm. The force of the water stripped the fjord’s walls down to bare rock.

It was just after 5 o’clock in the morning on a dreary day, and fortunately, no ships were nearby. In the months after, some cruise lines started avoiding Tracy Arm. However, the conditions that led to this event are not at all unique to this fjord.

Landslides are common in the coastal mountains of Alaska where rapid uplift, caused by tectonic forces and long-term ice loss, converges with the erosive forces of precipitation and moving glaciers. But a curious pattern has emerged in recent years: Multiple major landslides have occurred precisely at the terminus of a retreating glacier.

Though the mechanics are still poorly understood, these mountains appear to become unstable when the ice disappears. When the landslide hits the water, the momentum of millions of tons of rock is transferred into tsunami waves.

This same phenomenon is playing out........

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