The huge tsunami in the Alaskan fjord was the second largest in the world

Tracy Arm Fjord, located in southeastern Alaska within Tongass National Park, offers a magnificent view, with a narrow sea inlet surrounded by high granite cliffs, waterfalls... One morning last year, it was also the site of a powerful landslide that triggered a huge localized tsunami.

Researchers have now determined that the tsunami of August 10, 2025, was the second-highest ever recorded, with a wave reaching a height of 481 meters – taller than the Empire State Building in New York. The tsunami swept through the fjord, violently removing vegetation from the steep rock walls.

The fjord was a popular destination for tourists, but because the tsunami struck at 5:30 a.m., there were no cruise ships or other ships in the area and no one was injured.

Researchers said the landslide was caused by climate change. The glacier that supported the mountain retreated due to rising temperatures, which eventually left the rock unsupported, Reuters reports.

"The fact that the landslide happened so early in the morning was an incredibly lucky circumstance. Next time - and there will be a next time - we may not be so lucky," said Dan Sugar, a geomorphologist at the University of Calgary and lead author of the study published in the journal Science.

Places like these were at the very center of the impacts of climate change.

There were no photographs or videos of the tsunami, so scientists reconstructed the events using aerial photographs taken afterwards, satellite and seismic data, fieldwork at the site itself, and accounts from people who were nearby at the time.

Tracy Arm, about 80 kilometers south of the Alaskan capital, is about 40 kilometers long and one kilometer wide, with cliffs that are more than 1.000 meters high. Researchers determined the height of the wave by measuring areas where vegetation was removed, leaving dramatic scars on the rocks. The wave grew so high because a huge amount of water was displaced by the falling rocks through a narrow space.

"The obvious removal of vegetation, like a bathroom ring around the fjord, is probably the most striking difference in how the fjord looks now compared to last year, unless you've been diving and seen a huge deposit (of rocks) on the seabed," Sugar said.

"The removed vegetation is actually a very sharp line, below which there is only rock and sediment and some stumps, and above that is the intact forest, which stood as it did on August 9th, before the tsunami. Like two different worlds," Sugar added.

About 64 million cubic meters of rock collapsed in about a minute. That's 24 times the volume of the Great Pyramid of Giza, according to Stephen Hicks, a geophysicist at University College London and co-author of the study.

"This collapse caused a seismic wave that was recorded around the world," Hicks said.

Some of the waves got stuck in the fjord, causing what is called a seiche - a churning of water - that lasted for several days and created a separate seismic wave, Hicks said. A similar tsunami-induced landslide in Greenland's Dixon Fjord in 2023 caused a wave about 200 meters high and a seiche.

Tsunamis are huge waves caused by earthquakes, underwater volcanic eruptions, or landslides. The world's highest tsunami, about 520 meters high, was also a localized event, occurring in Lituya Bay, Alaska, in 1958 after a landslide.

Tsunamis in the open ocean can travel vast distances and cause massive damage to coastlines and loss of life. The tsunami caused by the 2004 Indian Ocean earthquake, which killed about 230.000 people, was 51 meters high in Sumatra. The tsunami caused by the 2011 earthquake in Japan, which killed more than 15.000 people, reached a height of about 40 meters, Reuters recalls.

"Tsunamis are caused by large earthquakes because a crack in the crust causes the seafloor to shift, which causes the water above it to move vertically. In the case of a landslide, it's the fall of material from the land into the water that creates the wave," Hicks said.

Seismic data showed that there were actually warning signals before the landslide in Tracy Arm.

"Given that we now have hindsight, we found that the landslide was preceded by about a week of small earthquakes that indicated a rupture in the final mass of the landslide. This gives us potential hope for developing warning and forecasting systems, along with other observations," Hicks said.