We're not going to be so lucky in the future.
In the quiet darkness of an Alaskan summer morning, a mountain gave way — not randomly, but as a consequence of centuries of glacial support suddenly withdrawn by a warming world. The resulting wave, nearly 500 meters tall and the second largest of its kind ever recorded, rewrote a fjord's landscape in under a minute and passed within hours of claiming hundreds of lives. Scientists now see this not as an isolated catastrophe but as a harbinger: as glaciers retreat across Alaska, they are unshouldering the cliffs they once held steady, and the frequency of such events may already be ten times what it was a generation ago. The wilderness that draws travelers seeking to witness climate change is quietly becoming more dangerous because of it.
- 64 million cubic meters of rock collapsed into Tracy Arm Fjord in under a minute, sending a wall of water nearly 500 meters high through a remote but tourist-frequented waterway.
- Cruise ships regularly pass through these fjords during daylight hours — the wave struck in darkness, and that accident of timing alone prevented mass casualties.
- Retreating glaciers are stripping away the natural buttresses that have held Alaskan cliff faces in place for millennia, turning scenic fjords into increasingly unstable terrain.
- Scientists estimate megatsunami frequency in the region may have already increased tenfold in just a few decades, with no slowdown in the glacier melt driving the risk.
- Some cruise operators have pulled routes from Tracy Arm, but researchers are pressing for systemic early-warning infrastructure and a fundamental reassessment of how tourism operates in these hazard zones.
In the early hours of a summer morning last year, 64 million cubic meters of rock tore loose from a mountainside in southeast Alaska and plunged into Tracy Arm Fjord. The water had nowhere to go but up — nearly 500 meters into the air, making it the second-largest megatsunami ever recorded. Trees snapped, cliffs were stripped bare, and the remote fjord was rewritten by violence. Almost no one was awake to see it. That darkness, scientists say, may have saved lives.
Geologist Dr. Bretwood Higman arrived weeks later to find a landscape of broken timber and scarred rock. Tourist cruise ships regularly navigate these waters, and had the collapse occurred during daylight hours, the outcome could have been catastrophic. "I'm quite terrified that we're not going to be so lucky in the future," he said.
Unlike ocean tsunamis that travel thousands of miles, megatsunamis are localized — born when a landslide crashes into confined water. Alaska's steep fjords and narrow channels make it uniquely vulnerable. What distinguished this event for researchers was its cause: a retreating glacier had spent centuries holding up the rock face below it. When the ice withdrew, the cliff lost its support and collapsed. "When the ice retreated, it exposed the bottom of the cliff face, allowing that rock material to suddenly collapse," explained Dr. Stephen Hicks of University College London.
This is the mechanism that most alarms scientists. Glaciers across Alaska are melting at an accelerating pace, removing support from mountainsides that have leaned on them for millennia. Higman estimates these events may now be occurring roughly ten times more frequently than just a few decades ago. The irony is sharp: the very tourism industry marketing these fjords as places to witness climate change is sending more people into a landscape made increasingly dangerous by it. Some cruise operators have already abandoned Tracy Arm routes, but researchers are calling for expanded monitoring, early-warning systems, and a broader reckoning with a coastline that is quietly, irreversibly changing.
In the early hours of a summer morning last year, 64 million cubic meters of rock—enough stone to equal 24 Great Pyramids stacked together—tore loose from a mountainside in southeast Alaska and plunged into Tracy Arm Fjord. The impact happened in less than a minute. The water below had nowhere to go but up, and up it went: nearly 500 meters into the air, making it the second-largest megatsunami ever recorded. The wave swept through the remote fjord with devastating force, snapping trees like kindling and stripping entire mountainsides down to bare rock. Almost no one noticed at the time. The event occurred in darkness, in a place few people were awake to witness. That timing, scientists now say, may have saved lives.
Dr. Bretwood Higman, a geologist based in Alaska, arrived at Tracy Arm a few weeks after the wave hit. What he found was a landscape rewritten by violence—broken timber scattered across the water, cliffs scarred and naked where soil and vegetation had been torn away. He walked the damage and understood immediately how close the margin had been. Tourist cruise ships regularly navigate these waters, drawn by Alaska's raw beauty and the chance to witness glaciers and untouched wilderness. Had the landslide occurred during daylight hours, when vessels were moving through the fjord, the outcome would have been catastrophic. "We know that there were people that were very nearly in the wrong place," Higman said later. "I'm quite terrified that we're not going to be so lucky in the future."
The wave itself was not a typical tsunami. Ocean-going tsunamis, triggered by earthquakes or underwater volcanoes, can travel thousands of miles and devastate distant coastlines—like the 2011 wave that struck Japan. Megatsunamis are different. They form when a landslide, caused either by seismic activity or by unstable rock, crashes into confined water. The wave is enormous but localized, dissipating quickly. Alaska is uniquely vulnerable to them: steep mountains, narrow fjords, frequent earthquakes, and now, increasingly, destabilized terrain. The biggest megatsunami on record occurred in the 1950s and exceeded 500 meters. This one came in second.
What made this particular event significant to researchers was not just its size but what caused it. Using field observations, seismic data, and satellite imagery, Dr. Stephen Hicks of University College London and his team reconstructed the sequence of events. The glacier that had clung to the mountainside for centuries was retreating. As the ice withdrew, it stopped doing what it had always done: holding up the rock face below it. The cliff, suddenly unsupported, gave way. "The glacier was previously helping to hold up this piece of rock," Hicks explained. "When the ice retreated, it exposed the bottom of the cliff face, allowing that rock material to suddenly collapse into the fjord."
This is the mechanism that worries scientists most. Climate change is melting glaciers across Alaska at an accelerating pace. Each retreating glacier is a support system removed from mountainsides that have leaned on them for millennia. The exposed rock becomes unstable. The risk of collapse increases. And with each collapse, the potential for another megatsunami grows. Higman is blunt about what the data suggests. "At this point, I'm pretty confident that these are increasing not just a little bit, but increasing a lot," he said. "Maybe in the order of 10 times as frequent as they were just a few decades ago."
The timing of this hazard increase is grimly ironic. Tourism to remote Alaskan areas is growing. Cruise companies market these fjords as destinations for travelers who want to see glaciers and pristine wilderness—and to witness, firsthand, the effects of climate change. The very phenomenon driving the megatsunami risk is drawing more people into the danger zone. Some cruise operators have already responded. Following the Tracy Arm event, several companies announced they would no longer send ships into that fjord. But the underlying problem remains unsolved. Scientists are calling for expanded monitoring systems across Alaska's vulnerable coastlines, better early-warning infrastructure, and a broader recognition that the landscape itself is becoming more hazardous as the climate shifts. The wave that nearly struck a cruise ship in the darkness last summer was a warning. The question now is whether the industry and the public will heed it before the next one comes.
Notable Quotes
We know that there were people that were very nearly in the wrong place. I'm quite terrified that we're not going to be so lucky in the future.— Dr. Bretwood Higman, Alaskan geologist
At this point, I'm pretty confident that these are increasing not just a little bit, but increasing a lot—maybe in the order of 10 times as frequent as they were just a few decades ago.— Dr. Bretwood Higman
The Hearth Conversation Another angle on the story
Why does a glacier melting matter for a rockslide? They seem unrelated.
The glacier acts like a cork in a bottle. It's been pressing against the base of the cliff for centuries, holding loose rock in place through its weight and cold. When it melts and retreats, that support vanishes. The rock above suddenly has nothing holding it up.
So the megatsunami wasn't caused by the earthquake or the water itself?
No. The water didn't cause it—the water just received it. A massive piece of mountain came loose and fell. The impact of that much rock hitting water in seconds is what created the wave. It's almost like dropping a boulder into a bathtub.
And this is happening more often now?
The researchers think it could be ten times more frequent than it was decades ago. Every glacier that retreats is another cliff face losing its natural brace. Alaska has thousands of them.
Why weren't people killed?
Luck, mostly. It happened at 3 or 4 in the morning. The cruise ships that normally travel through that fjord were anchored elsewhere. A few hours later, and the story would have been very different.
What happens now? Do they just stop going to these places?
Some cruise companies have already pulled out of Tracy Arm. But that's a temporary fix. The real answer is monitoring—knowing which cliffs are unstable, which glaciers are retreating fastest, where the next collapse is most likely. And accepting that some places are becoming more dangerous, not less.