100-feet high tsunami hits Alaska fjord after glacier collapse, experts warn similar mega landslides could hit populated towns

A massive landslide near South Sawyer Glacier in Southeast Alaska unleashed a powerful local tsunami early Sunday morning(August 10), sending waves towering up to 100 feet near the source and slamming nearby islands with enough force to strip entire slopes of trees.

The event, which occurred around 5:30 am local time in the remote Endicott Arm area, about 60 miles southeast of Juneau, is being called the largest landslide-triggered tsunami in Alaska since 2015. Scientists say tens or even hundreds of millions of cubic meters of bedrock collapsed into the fjord, displacing vast amounts of water and generating a surge felt more than 75 miles away.

Survivors’ harrowing escape

Three kayakers, Sasha Calvey, Billy White, and Nick Heilgeist, were camping on Harbor Island when they awoke to the roar of rushing water just feet from their tent. Although they had pitched camp well above the high tide line, the wave tore through their site, sweeping away most of their gear and scattering their kayaks, one lodged in a tree, another stranded on a cliff.

“It was just pure chaos out of nowhere,” Heilgeist told reporters. The trio, professional guides on a summer-long Inside Passage expedition, were eventually rescued by the charter yacht Blackwood, whose crew fought strong currents to reach them.

A colossal wave and far-reaching impact

Near Harbor Island, waves were estimated at 10–15 feet high. But closer to the source, at Sawyer Island, the National Park Service recorded a run-up of at least 100 feet, with vegetation completely stripped from rocky slopes save for a lone tree.

The surge reverberated for hours, like water sloshing in a giant bathtub, and was recorded on a tide gauge in Juneau with fluctuations of about one foot.

Although the tsunami was destructive along the fjord, the National Weather Service reported no injuries or damage to infrastructure, a stroke of luck, scientists say, given the early hour and absence of cruise ships or tour boats in the narrow waterway.

The science behind the slide

Unlike more common landslides caused by surface soil failure, this event involved vast slabs of bedrock crashing into tidewater. The Alaska Earthquake Center’s Ezgi Karasözen said preliminary estimates suggest a volume exceeding 100 million cubic meters, though precise measurements will take weeks.

The slide was preceded by an unusual sequence of small earthquakes, hundreds of magnitude 1–2 tremors over roughly 18 hours, offering a rare “precursory signal” that scientists hope could improve future hazard detection.

Seismometers more than 600 miles away picked up the signal, confirming the sheer magnitude of the collapse.

A warning for the future

Experts caution that while this landslide struck in a remote location, similar events could happen near populated coastal towns.