Alaska was lucky to avoid disaster after a landslide and tsunami. What about next time?

On 10 August a large portion of a fjord wall in Tracy Arm collapsed near the South Sawyer glacier, producing a powerful tsunami. Seismic analysis estimates up to 100 million cubic meters of rock fell, launching water an estimated 425 meters up the opposite fjord wall and generating a wave as high as 30 meters that stripped forest and brush from shorelines. The channel was largely empty at the time, avoiding major casualties, though kayakers nearly were hit. Retreating glaciers and steep fjord walls increase the risk of similar large landslides in heavily visited Alaskan tourism areas.

The landslide that triggered a powerful tsunami in Alaska's Inside Passage early on 10 August was a close call, say scientists, tour operators and agency officials, with the risk of such events apparently increasing as glaciers retreat because of climate change. It's a historic event, said scientist Dennis Staley from the US Geological Survey of the slide, which occurred in the Tracy Arm fjord 50 miles (80km) south of Juneau. I feel like we dodged a bullet, he continued, of reports that no one had been hurt, at a destination that can see more than 500,000 annual visitors.

Staley studies landslide hazards in Alaska, including in popular tourism areas. Tracy Arm is a narrow 30-mile (48km) fjord, with sheer walls looming thousands of feet above the water. It ends at the face of the South Sawyer glacier. The dramatic scenery, part of the Tongass national forest, attracts kayakers, boaters and a steady stream of packed cruise ships. But the channel was apparently empty at 5.30am on Sunday, 10 August, when without warning a colossal piece of the fjord wall collapsed.

Staley says it's too early to know the precise size of the slide. But by analyzing its seismic signal, he and others estimate up to 100m cubic meters of rock, or more, fell near the face of the South Sawyer glacier. It threw a wave of ocean water an incredible 1,400ft (425 meters) up the opposite side of the fjord, which will likely make it one of the largest such waves ever recorded.

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