Alaska Landslide Pushed Tsunami 1,580 Feet Up a Mountain

In August 2025, a wall of mountain in Alaska slid into a narrow fjord and shoved the water 1,580 feet up the slope on the other side. That makes it the second-highest tsunami ever recorded, and it splashed higher than the top floor of the Taipei 101 skyscraper.

A splash that stripped the rock bare

The landslide fell from the mountain beside the South Sawyer Glacier and hit the water in Tracy Arm, a long, steep inlet. Water and debris raced 1,580 feet (481 meters) up the far side of the fjord, then kept moving down Tracy Arm. The force was strong enough to scrape the fjord's walls down to bare rock.

Just twelve hours earlier, passengers on the Hanse Explorer had been taking selfies and videos of the South Sawyer Glacier. Then the ship headed back down the fjord. The mountainside collapsed just after 5 o'clock in the morning on a dreary day, and no ships were nearby. In the months that followed, some cruise lines began avoiding Tracy Arm altogether.

Signs showed up days in advance

Researchers at the Alaska Earthquake Center study earthquakes and tsunamis, and one of them serves as Alaska's state seismologist. In a new study with colleagues, they describe several warning signs in the days and weeks before the collapse.

• The glacier below the landslide area had retreated more than a third of a mile in the two months beforehand, and large chunks of ice had been breaking off and falling into the water.
• It was August, when warm ocean water and heavier rain help glaciers shrink and slopes weaken. Rain gets into cracks in the mountain and raises the water pressure inside them, pushing the rock closer to breaking.
• Thousands of small tremors came from the area of the slide in the days before it fell.

The researchers argue that those signs together would have been enough to warn ships, homes and businesses at least a day before the mountainside gave way, if a monitoring program had existed. They sketch what such a program might do on a yellow-orange-red scale: a yellow alert when weather and fast glacier retreat raise the hazard across a general area, an orange alert when the small tremors build into a continuous hum of seismic energy, and a red alert when an event is under way. They say a large landslide can be detected and its rough size measured within a couple of minutes of starting.

The same pattern is turning up far beyond Alaska

Landslides are common in Alaska's coastal mountains, where the land is rising and long-term ice loss is under way, and where rain and moving glaciers wear the rock down. But the researchers note a curious pattern: several major landslides have struck right at the end of a retreating glacier, where mountains appear to become unstable once the ice disappears. The mechanics are still poorly understood.

The same phenomenon is playing out from Alaska to Greenland and Norway, sometimes with deadly consequences. Across the Arctic, countries are trying to come to terms with the growing hazard, and the options are not attractive: avoid vast stretches of coastline, or live with a risk that is not well understood. The researchers see an obvious role for alert systems, but only if scientists understand better where and when landslides are likely to happen.

They point to avalanche alerts as a comparison. People are still killed in avalanches, but warning systems have helped make winter backcountry travel safer for more of them. The National Oceanic and Atmospheric Administration's tsunami warning program, they note, has spent decades fine-tuning how to spread messages quickly.