In 2025, Alaska was hit by the second-highest tsunami in history. Its vibrations travelled around the world for 36 hours

On August 10, 2025, a massive landslide in Alaska triggered a tsunami that sent water and debris 1,580 feet (481 metres) up a mountainside. The tsunami struck Tracy Arm, a narrow fjord in southeastern Alaska, just hours after tourists had visited the area to see its glaciers. The water stripped vegetation from the slopes and exposed bare rock, leaving a visible scar across the landscape. Despite the scale of the disaster, no fatalities or significant damage to infrastructure were reported. The event produced the second-highest tsunami run-up documented in the historical record. The findings also revealed that the landslide generated seismic waves equivalent to a magnitude 5.4 earthquake, while water trapped inside the fjord continued to oscillate for up to 36 hours. The disaster has drawn attention to the risks posed by landslides in Alaska's steep, glacier-covered terrain, where retreating ice can contribute to the destabilisation of mountain slopes.

What happened in Alaska?

Around 5:30 a.m. local time on August 10, 2025, a massive section of a mountainside collapsed into Tracy Arm fjord. According to the US Geological Survey (USGS), the landslide involved more than 64 million cubic metres of material.

The debris, which included rock, ice, trees and other material, plunged into the water and displaced an enormous volume of it, triggering a powerful tsunami. The initial breaking wave was 100 metres high and travelled at more than 70 metres per second. The water then surged up the opposite mountainside, reaching an elevation of 481 metres above sea level. The run-up was high enough to make the event the second-highest documented in the historical record. The tsunami's effects were also detected as far away as Juneau, where a tide gauge recorded a wave of approximately 36 centimetres (1.2 feet) about an hour after the landslide.


The landslide lasted approximately two minutes. Incidentally, the landslide was preceded by several days of small seismic events, known as microseismicity. These events increased in frequency and magnitude until approximately an hour before the mountainside collapsed.

The tsunami sent vibrations around the world for 36 hours

The landslide did more than generate a massive tsunami. It also produced long-period seismic waves that were detected around the world and were equivalent in size to a magnitude 5.4 earthquake.

After the initial wave, water continued moving back and forth inside the fjord in a phenomenon known as a 'seiche'. This occurs when water trapped within a lake, fjord or other basin oscillates between its boundaries. The resulting seismic signal had a period of approximately 66 seconds and persisted for up to 36 hours.

Researchers said the observation was particularly significant because a days-long seiche of this kind had been documented only once before.

The damage was visible on the surrounding mountainsides

The tsunami left clear evidence of its reach across the landscape. Water rushing up the fjord's walls stripped vegetation from the slopes, exposing areas of bare rock.

In some locations, the effects extended roughly 180 feet above the normal water level. At Sawyer Island, the National Park Service reported a run-up of at least 100 feet, with vegetation removed from the slopes.

Researchers examined these marks to reconstruct how far the water travelled and establish the tsunami's maximum run-up height.

Why did nobody die?

The NOAA National Weather Service office in Juneau reported no known injuries, fatalities or significant infrastructure impacts from the event.

The timing may have helped limit the consequences. The landslide occurred in the early morning, when relatively few people were likely to be on the water. The tsunami also occurred near low tide, which may have reduced some of its effects along the shoreline.

However, the absence of casualties does not mean the event posed little danger. Tracy Arm is visited by cruise ships, tour boats and other vessels, and a similar landslide occurring when people were closer to the impact zone could have had far more serious consequences.

The relatively small wave recorded in Juneau also highlights how tsunami effects can vary substantially with distance from the source and the shape of the surrounding waterway.