Massive Landslide Triggers Near-Miss Tsunami in Popular Fjord Area
8A huge landslide in a remote fjord created a towering tsunami, reaching 500 meters in height. Luckily, the event happened early in the morning, so there were no injuries or deaths. Scientists now warn that similar events could happen again with potentially greater consequences.
The Event and Its Impact
On August 10, 2025, at around 5:26 am local time, a massive chunk of rock broke loose from a mountain above Alaska’s Tracy Arm fjord. This slide involved at least 63.5 million cubic meters of debris plunging into the deep waters at the glacier’s end. The impact generated an initial wave over 100 meters high, racing across the fjord at speeds over 70 meters per second.
When the wave hit the opposite shoreline, it surged up steep cliffs, reaching a stunning 481 meters above sea level. This made it the second-highest tsunami ever recorded on Earth. Despite the scale, the event went largely unnoticed because it occurred when few people were around. No injuries or fatalities resulted, but it was a close call that could have been deadly if it had happened later in the day.
Understanding Landslide-Generated Tsunamis
Landslide tsunamis like this are different from those caused by earthquakes. They tend to be more localized but can be far more violent. When millions of tons of rock fall into a confined body of water, they displace huge amounts of water suddenly, creating enormous waves. Since 1925, scientists have documented 27 such events with runups over 50 meters, with the highest being the 1958 Lituya Bay tsunami at 530 meters.
The 2025 event originated from a steep rock slope on the northern side of the fjord. The top of the landslide source sat about 1,025 meters above sea level. For centuries, this slope was held in place by a thick glacier called South Sawyer Glacier. But climate change has been causing glaciers worldwide to retreat, including this one, which significantly weakened the slope’s stability.
The retreat of the glacier exposed the base of the slope, removing the icy “buffer” that had supported the rock. By July 2025, just weeks before the slide, the glacier had thinned by over 100 meters in some areas, leaving the rocks more vulnerable to collapse. These changes, driven by global warming, increased the likelihood of a landslide in this area.
Signs of an Imminent Disaster
Scientists analyzed satellite images taken weeks before the event and found no obvious signs of tension cracks or deformation on the slope. From the outside, it looked stable. However, underground, the rocks were already grinding and shifting. Seismic sensors recorded small, repeated earthquakes starting as early as August 5. By August 9, these mini-quakes happened every hour, and the intervals between them shrank to less than a minute as the slope destabilized.
About an hour before the landslide, seismic signals merged into a continuous grinding sound, indicating that the rocks were slipping. When the failure finally occurred, the displaced rock hit the water with enough force to be felt globally. Seismic waves from the event were recorded worldwide and matched the energy release of a magnitude 5.4 earthquake. The water in the fjord also oscillated, creating a standing wave that lasted for 36 hours.
Potential Risks and Future Threats
This event highlights how vulnerable areas like Tracy Arm are to natural disasters. The fjord is a popular tourist destination, with over 20 boats and up to six large cruise ships navigating its waters daily during the summer. Had the landslide happened later in the day, more people could have been hurt or trapped by the towering waves.
Scientists warn that climate change is increasing the risk of such landslides. The ongoing retreat of glaciers weakens mountain slopes, making them more prone to collapse. As global temperatures continue to rise, similar events could become more frequent, posing a serious threat to nearby communities and visitors.
While this was a near-miss, it serves as a reminder of the power of natural forces and the importance of monitoring vulnerable landscapes. Better understanding and early warning systems could help prevent future tragedies in these fragile environments.
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