A massive landslide in a popular Alaska cruise destination triggered a tsunami taller than 1.5 Eiffel Towers — and almost no one saw it coming. New research published in Science explains how it happened and why it could happen again.
Just before dawn on Aug. 10, 2025, a section of mountainside in southeast Alaska gave way and plunged into the sea. The resulting tsunami — measuring a staggering 481 meters in runup height — raced up the walls of Tracy Arm fjord, stripping vegetation as it went. It generated seismic waves equivalent to a magnitude 5.4 earthquake, and it happened just hours before up to 20 cruise ships, recreational boaters and kayakers typically arrive in the area each day.
An international team of researchers has now published a detailed account of the event in the journal Science, calling it one of the most significant glacier-related hazard events ever documented — and a warning that similar disasters may be on the horizon as the planet continues to warm.
What the Data Revealed
Tracy Arm is a narrow, glacier-carved fjord in the Tongass National Forest, roughly 80 kilometers south of Juneau. It draws visitors eager to see the South Sawyer Glacier up close.
On the morning of the landslide, a group of kayakers camped nearby woke around 5:45 a.m. to find water flowing through their tent, carrying away a kayak and much of their gear. A cruise ship anchored near the mouth of the fjord observed strong currents and white water but no obvious wave. Another onlooker described a two-meter wave sweeping along the beach.
Researchers reconstructed the event by combining those eyewitness accounts with satellite imagery, seismic data and numerical modeling. One of the most significant methodological breakthroughs involved the Surface Water and Ocean Topography (SWOT) satellite, a newer instrument capable of detecting the sea-surface structure of large waves even in remote, unmonitored locations.
“Until now, we simply didn’t have a way to observe these waves directly, but our study has demonstrated that using data from the new Surface Water Ocean Topography satellite can reveal the full sea-surface structure of these events, even if no one witnesses them directly,” co-author Thomas Monahan, a senior research associate and Schmidt AI in Science fellow in the Department of Engineering Science at the University of Oxford, said in a news release.
That capability matters enormously. Many of the world’s most hazardous fjords are in remote Arctic and sub-Arctic regions where permanent monitoring infrastructure is scarce or nonexistent. The ability to reconstruct an event of this scale from satellite data alone could transform how scientists identify and track future risks.
No Warning Signs This Time
What makes the Tracy Arm event particularly alarming is the absence of the precursor signals that scientists normally use to anticipate catastrophic landslides. Typically, researchers can detect gradual slope movement — a slow sagging of the terrain — in the weeks, months or even years before a major failure. That early movement gives communities and industries time to respond.
“In this case, that didn’t happen,” lead author Dan Shugar, an associate professor with the Department of Earth, Energy and Environment in the Faculty of Science at the University of Calgary, said in the news release.
Sugar noted that only minor seismic noise preceded the event — too faint to draw anyone’s attention.
“This one was truly a surprise,” Shugar added.
That unpredictability is what makes the findings so significant for risk management. If a slope can collapse catastrophically without warning, the safety protocols that currently govern vessel traffic in fjord environments may be insufficient.
Glacier Retreat Is the Underlying Cause
The research identifies glacial retreat as the primary driver of the near disaster. As glaciers thin and pull back, they remove lateral support from the rock walls and valley flanks they once buttressed. Exposed slopes become more susceptible to destabilization, particularly as freeze-thaw cycles and permafrost degradation also accelerate due to rising temperatures.
The U.S. Geological Survey has already flagged the Tracy Arm area on its website, noting that steep, mountainous landslide areas are “inherently unstable and will continue to change for years following an initial landslide.”
That warning is consistent with the study’s broader conclusion: the hazard is not a one-time event. The landscape remains dangerous, and the dynamics that produced the 2025 tsunami are not unique to Tracy Arm. Scientists say similar conditions exist across glaciated coastlines in Alaska, Canada, Greenland, Norway and other high-latitude regions.
Why It Matters for Students and Young Travelers
Alaska cruises have long been a bucket-list item for college graduates, gap-year travelers and adventure-seekers — and for good reason. The scenery is spectacular. But this event is a reminder that spectacular landscapes can carry hidden risks, and that climate change is actively reshaping those risks in ways that weren’t true a generation ago.
At least six cruise lines have already revised their Alaska itineraries in 2026 in response to ongoing hazards in the Tracy Arm area. For students studying earth sciences, environmental policy, oceanography or climate, the Tracy Arm event is a real-world case study in how glaciological change cascades into physical danger for human populations.
Shugar frames the research as a call to action for the industries and governments that manage coastal access in high-risk zones.
“Ultimately what we hope is that coastal municipalities, the cruise ship industry and other stakeholders take these threats seriously,” Shugar said.
Source: University of Calgary