The Forensics of a Skyscraper-Sized Tsunami – Image for illustrative purposes only (Image credits: Unsplash)
In the predawn hours of August 10, 2025, a towering mountainside in southeastern Alaska’s Tracy Arm Fjord gave way, sending millions of tons of rock crashing into the frigid waters below. The resulting tsunami climbed 481 meters up the fjord’s opposite wall, dwarfing all but the planet’s 14 tallest skyscrapers and marking the second-highest wave ever measured. Researchers have now pinpointed the retreat of South Sawyer Glacier – accelerated by global warming – as the key factor that destabilized the slope, offering a stark glimpse into climate-driven hazards.
The Landslide That Shook the World
The collapse registered on seismic instruments worldwide, yet produced no significant ground shaking at the surface. For days afterward, the fjord’s waters oscillated in a persistent standing wave called a seiche, churning amid icebergs. No lives were lost, a stroke of fortune overshadowed by the fact that cruise ships had planned visits to the area just hours later.
That narrow timing averted tragedy, but the event’s scale demanded answers. Teams turned to satellite data, drone footage, and field surveys to reconstruct the sequence. The landslide displaced enough material to generate a megatsunami confined within the fjord’s steep confines, amplifying its height dramatically.
Unmasking the Glacier’s Role
A study published in Science laid out the evidence: South Sawyer Glacier, which once buttressed the valley walls like cathedral supports, had pulled back sharply. In spring 2025 alone, it retreated about 500 meters, exposing fractured rock to failure. Daniel Shugar, a geomorphologist at the University of Calgary and lead author, likened the process to a child stuffing a messy room into a closet – stable until the door swings open.
“While the [South Sawyer] Glacier is in the fjord, it’s supporting those valley walls, like the buttresses on a cathedral,” Shugar explained during a press briefing at the European Geosciences Union 2026 General Assembly. Rainfall in the region may have contributed, but the glacier’s withdrawal – part of decades-long thinning – proved pivotal. This “debuttressing” left the slope vulnerable, and subtle triggers likely tipped it over the edge.
A New Breed of Climate-Fueled Mega-Waves
Unlike most tsunamis born from undersea quakes, this one stemmed purely from landslide energy funneled by the fjord’s narrow geometry. It ranked as the largest non-seismic tsunami recorded, trailing only the 1958 Lituya Bay event at 524 meters. Both occurred in Alaska’s glacially carved inlets, where walls concentrate wave power.
Satellite radar images reveal shifting slopes across Alaska and elsewhere, many perched above retreating glaciers. Shugar noted that a “huge majority” show motion tied to ice loss. Glaciologist Leigh Stearns of the University of Pennsylvania, who reviewed the work, emphasized how climate stressors amplify instability: “We know that steep slopes are very sensitive to the things that climate [change] is exacerbating, whether it’s losing permafrost, glacier retreating, or more water in the soil.”
| Event | Wave Height | Trigger |
|---|---|---|
| Lituya Bay, 1958 | 524 meters | Earthquake-induced landslide |
| Tracy Arm, 2025 | 481 meters | Glacier retreat landslide |
| Taan Fiord, 2015 | 193 meters | Landslide (climate-linked) |
Rethinking Risks in a Warming World
The Tracy Arm incident joins a growing tally of glacier-tied landslides, from Alaska’s Taan Fiord to Greenland’s Dixon Fjord. These differ from open-ocean tsunamis, which build power over vast distances before hitting harbors. Fjord-bound waves strike suddenly, often without quake warnings, complicating detection.
“Often, we think of glacier retreat as a long and continuous thing, but [it] can trigger sudden catastrophic events,” Stearns observed. Shugar warned of rising exposure as infrastructure expands into remote areas: mining camps, oil platforms, and tourism routes now encroach on such zones. “The risk to any particular cruise ship on any particular day is very low,” he said, but added, “We were unbelievably lucky that the [tsunami] occurred with the timing that it did, and not 5 hours later.”
Climate acts as a threat multiplier, chaining slow melts to abrupt disasters. As slopes destabilize globally, scientists urge better monitoring – perhaps via expanded radar networks – to map dangers ahead. The Tracy Arm findings, shared on May 6, 2026, signal that such events may intensify, pressing communities to adapt before the next closet door flies open.