Alaska’s monster tsunami sent water 1,580 feet up a mountain
A massive landslide in Alaska triggered the second-highest tsunami ever recorded, sending water and debris 1,580 feet up a mountainside just hours after tourists visited the area. Scientists discovered that the disaster was preceded by several warning signs, including rapid glacier retreat, heavy rainfall, and thousands of tiny seismic tremors. As glaciers retreat, similar disasters could become…
On August 9, 2025, the Hanse Explorer was cruising near the South Sawyer Glacier when a landslide unexpectedly occurred. This incident marked the second-highest tsunami ever recorded, with water and debris reaching a height of 1,580 feet (481 meters) up the mountain. The Alaska Earthquake Center, where one of the authors works, conducted a study detailing how the landslide sent water and debris soaring upwards and continuing down the fjord.
The force of the water had stripped the fjord's walls down to bare rock before the waves flowed down Tracy Arm. The event occurred just after 5 o’clock in the morning on a gloomy day, with no ships in the vicinity, allowing for an unexpected safety margin. Since then, some cruise lines have started avoiding Tracy Arm. However, the conditions that led to this event are not unique to this fjord; landslides are common in Alaska's coastal mountains where tectonic forces, ice loss, and erosive forces converge.
Recent years have seen a curious pattern of major landslides occurring precisely at the terminus of retreating glaciers. When the landslide hits the water, the momentum of millions of tons of rock is transferred into tsunami waves. This phenomenon is occurring across the Arctic, including in Greenland and Norway, with potentially deadly consequences.
Countries in the region are trying to come to terms with this growing hazard, recognizing the need for alert systems to warn people about the risk. The Tracy Arm landslide serves as a powerful example, demonstrating how a combination of warm ocean waters, heavy precipitation, rapid glacier retreat, and seismic activity could have been used to issue progressive alerts to ships and nearby areas.
The combination of weather and glacier retreat in early August 2025 was sufficient to warrant a yellow alert, indicating a temporary elevation of the hazard. Within hours of the landslide, thousands of small seismic tremors were recorded, indicating a seismic tremor that warranted an orange alert, signaling immediate concern. These observations, recorded as byproducts of regional earthquake monitoring, provided sufficient evidence to recommend keeping boats and ships out of the fjord.
A monitoring program that can quickly communicate landslide events within minutes could issue a red alert, signaling an event in progress. While such a system may not be fail-proof, it offers a better alternative to no warning at all. The combination of weather, glacier retreat, and steep terrain makes Arctic fjords attractive for visitors, but also poses significant hazards.
The question is not whether these places should be avoided, but how to help people make more informed decisions about visiting these breathtaking landscapes.
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