Alaska Glacier Retreat Triggers Second Largest Tsunami Ever Recorded

A Near-Miss Catastrophe

At 5:26 AM on August 10, 2025, an entire mountainside collapsed into Tracy Arm fjord in southeastern Alaska, creating a tsunami that reached 481 meters—nearly 1,600 feet—on the opposite shore . The wave, taller than New York's Empire State Building, ranks as the second-highest tsunami ever recorded , surpassed only by Alaska's 1958 Lituya Bay event.

More than 20 vessels, including large cruise ships carrying thousands of passengers, typically travel through Tracy Arm daily during summer, but none was present at the time . Scientists called it "unbelievably lucky" timing—if the collapse had occurred just five hours later, the consequences could have been catastrophic .

Climate Change as the Culprit

The landslide was preconditioned by glacial retreat caused by climate change . South Sawyer Glacier has undergone long-term thinning and retreat over the last century, with acute episodes documented since 2000, and in spring 2025 alone, the ice retreated several hundred feet, exposing the rock that ultimately collapsed .

Lead researcher Daniel Shugar explained the process: "While the glacier is in the fjord, it's supporting those valley walls, like the buttresses on a cathedral" . The glacier that carved the fjord was also holding its slopes in place, and the ice's retreat under warming temperatures exposed rock that became vulnerable to crumbling .

The landslide moved about 64 million cubic meters of material—equivalent to a cube a quarter mile on each side . The event produced globally observed seismic waves equivalent to a magnitude 5.4 earthquake , and a seiche trapped within the fjord persisted for up to 36 hours .

A Growing Threat to Tourism

Tracy Arm fjord sees upwards of 500,000 visitors per year, with cruise passenger numbers in Alaska reaching 1.6 million annually . The tourism industry has responded swiftly to the new risk assessment. At least three major cruise lines—Carnival, Holland America, and Royal Caribbean—have altered their 2026 itineraries to avoid Tracy Arm, citing safety concerns .

Satellite imagery indicates that many slopes in Alaska and beyond are in motion, with "a huge majority of shifting slopes above the lower parts of thinning glaciers" . Researchers emphasize the importance of attention in polar regions where glaciers are thinning: "Ultimately what we hope is that coastal municipalities, the cruise ship industry and other stakeholders take these threats seriously" .

The Challenge Ahead

Scientists detected extensive pre-slide seismic activity that began several days before the collapse, with signals equivalent to magnitude 1-2 earthquakes occurring about an hour apart . The rate increased dramatically in the six hours before failure, with signals every 30-60 seconds, becoming continuous vibration two hours before the slide .

This pattern offers hope for early warning systems, but the challenge remains immense. "The scale of what we are dealing with in Alaska is unprecedented," notes researcher Ezgi Karasözen. "We have a spectacular landscape, but the hazards that come with that are also very real" .

As climate change accelerates glacier retreat across the Arctic, the Tracy Arm event serves as both a scientific breakthrough and an urgent warning. The next landslide-triggered tsunami may not occur at dawn in an empty fjord—and the tourism industry's rapid response suggests they understand the stakes.