A wall of rock collapsed into Alaska’s Tracy Arm fjord last August, and according to a FOX Weather report hosted by meteorologist Bob Van Dillen, the landslide triggered a “megatsunami” so large that it is now considered the second-tallest tsunami ever recorded.
Van Dillen introduced the event as one of those natural disasters that is almost difficult to picture, not only because of the height of the wave, but because it was not caused by the kind of major offshore earthquake people usually associate with tsunamis.
To explain what happened, Van Dillen spoke with Dan Shugar, an associate professor in the Department of Earth, Energy and Environment at the University of Calgary, who described the wave as “unfathomably large” and said it would have been terrifying to witness from anywhere nearby.
A Tsunami Without An Earthquake
Shugar told Van Dillen that tsunamis are most often caused by earthquakes, especially when large sections of the seafloor shift suddenly and send waves racing across open ocean. But in Tracy Arm, he said, the cause was different: an enormous mass of rock dropped into the water all at once, displacing the fjord much like a person jumping into a bathtub or swimming pool.
That comparison is simple, but the scale is not. Instead of a person hitting the water, Tracy Arm saw a landslide of roughly 64 million cubic meters of rock collapse into the fjord.
Shugar said that is enough material to fill the Great Pyramid of Giza about 24 times, a number that helps make sense of a volume that otherwise feels almost impossible to imagine.
The physical setup of Tracy Arm made the wave even more extreme. Unlike an earthquake-triggered tsunami in the open Pacific, where water can spread outward over a huge area, Shugar said the steep, narrow walls of the fjord gave the water very little room to go.
In that setting, the displaced water had one main direction available, and that was upward.
A Wave Nearly 1,700 Feet High
Van Dillen asked how high the wave became at its peak, and Shugar said the highest point measured from satellite imagery and helicopter surveys was 481 meters.
That works out to roughly 1,600 to 1,700 feet high, making it the second-highest tsunami ever recorded.
It is the kind of number that can be stated plainly but still resists ordinary understanding. A wave hundreds of feet taller than many skyscrapers did not sweep across a wide beach in the usual image people have of a tsunami; instead, it surged up the walls of a remote Alaskan fjord after a catastrophic landslide dropped into the water below.
This is where the phrase “megatsunami” feels less like exaggeration and more like the only available word. Most tsunamis are measured by their impact at shorelines after long-distance travel, but landslide-generated waves in tight fjords can produce staggering run-up heights because the energy is trapped and forced against steep terrain.
Shugar said the wave’s height was measured using both satellite imagery and helicopter surveys, which allowed researchers to map how far up the fjord walls the water had reached.
Why The Mountainside Failed
According to Shugar, landslides often have a specific trigger, such as an earthquake or a period of heavy rainfall, but they also tend to have deeper causes that prepare a slope to fail long before the final collapse.
In this case, he said one of the main factors was likely the retreat of the glacier at the bottom of the fjord.
Shugar explained that the glacier had retreated by about 1,800 feet in the year leading up to the landslide, with part of that retreat happening in the two weeks before the collapse. As the glacier pulled back, it removed support from the valley wall, leaving the slope more vulnerable.
He was careful not to reduce the whole event to a single moment, noting that the slope was probably being set up by decades of retreat. Still, he said the recent retreat in the weeks before the slide may have been the “straw that broke the camel’s back.”
That detail matters because it places the disaster in a broader geological story. A landslide like this can appear sudden, and in one sense it is, but the conditions that allow it to happen can build slowly for years as ice, rock and gravity interact in a changing mountain landscape.
A Wave No Boat Could Outrun
Van Dillen asked how fast the wave was moving, especially since the fjord’s shape pushed so much of the energy upward.
Shugar said computer simulations suggested the wave moved at about 150 miles per hour, fast enough that “there’s no way you could outrun it,” no matter what kind of boat someone was in.
FOX Weather showed a computer animation from the perspective of someone on the water, as if they were traveling on a jet ski. Shugar said the animation showed the wave overtaking that point of view even at very high speed.
That part of the report is chilling because it shifts the event from scientific scale to human scale. A wave that high and that fast leaves almost no room for reaction once it is already moving.
Shugar said early warning would be a critical issue in a place like Tracy Arm, but he also noted that a warning only hours before the event might not have done much. In hindsight, he said, if scientists had known a couple of days earlier that the slope was beginning to break up, that might have given ships time to get out of the area.
A Disaster That Could Have Been Much Worse
One of the most sobering parts of Shugar’s explanation was his warning about timing.
He told Van Dillen that if the landslide had happened five or six hours later, the situation could have been dramatically different because Tracy Arm is popular with cruise ship traffic.
Some of those ships carry thousands of people, and Shugar said they often travel toward the head of the fjord so passengers can view glacier calving. If a ship had been near the source area when the wave formed, he said he could not see how it would have survived.
That is not alarmist speculation; it is a practical assessment of what a 481-meter wave traveling through a narrow fjord could do to any vessel unlucky enough to be nearby.
The fact that the event appears to have avoided mass casualties should not make it feel smaller. If anything, it shows how thin the line can be between a record-setting geological event and a human catastrophe.
The Fjord Was Scarred Like A Giant Lawn Mower Passed Through
After the collapse, Shugar said most of the 64 million cubic meters of rock ended up deposited on the ocean floor. But the most visible changes above the water were left along the walls of the fjord.
As the tsunami moved outward, he said, it clear-cut forest in many places up to about 100 meters, or roughly 350 to 400 feet, above the ocean surface.
Shugar compared the effect to a “gigantic lawnmower” moving along the edge of the fjord and leveling everything in its path. He emphasized that these were not small trees, but large coastal rainforest trees familiar to people in Alaska, Washington and Oregon.
To knock trees of that size down like matchsticks required a force that is hard to comprehend, and it left behind a landscape that now carries the physical signature of the wave.
The tsunami was recorded at Juneau, about 70 miles away, where Shugar said the water-level change was only about a foot high. At that distance, it would have been noticeable near the water, but not especially damaging.
Inside the fjord, however, the water continued sloshing back and forth with enough force to create seismic energy recorded around the world for about a day and a half.
Shugar compared it to tea sloshing in a cup after someone trips, except on a vastly larger scale.
Second Only To Another Alaska Megatsunami
Van Dillen closed the discussion by asking what tsunami still ranks above the Tracy Arm event.
Shugar said the largest recorded tsunami also happened in Alaska, in 1958, when a landslide-triggered wave in Lituya Bay reached about 530 meters high.
In that case, he explained, an earthquake triggered the landslide, which then triggered the wave. The Tracy Arm event followed a somewhat different chain, but both disasters involved a massive amount of rock suddenly entering a confined body of water.
That comparison underscores something important about Alaska’s fjords and steep coastal landscapes. These places are spectacular because of their dramatic terrain, but that same terrain can generate rare events of extraordinary violence when unstable slopes fail.
Van Dillen called the discussion “amazing,” and that reaction fits. The numbers are almost too large to absorb: 64 million cubic meters of rock, a wave peak of 481 meters, movement at roughly 150 miles per hour, and trees stripped hundreds of feet up the fjord walls.
What happened in Tracy Arm was remote, but it was not small. According to Shugar’s explanation to FOX Weather, it was a record-class landslide tsunami that could have become a far deadlier disaster if the timing had been different.
For now, it stands as a powerful reminder that some of the planet’s most dangerous waves do not begin far offshore with an earthquake. Sometimes they begin when a mountainside, weakened over time, finally lets go.
Mark grew up in the heart of Texas, where tornadoes and extreme weather were a part of life. His early experiences sparked a fascination with emergency preparedness and homesteading. A father of three, Mark is dedicated to teaching families how to be self-sufficient, with a focus on food storage, DIY projects, and energy independence. His writing empowers everyday people to take small steps toward greater self-reliance without feeling overwhelmed.
