Photo of the August 10, 2025 landslide source area captured during a field reconnaissance overflight on August 13, 2025.
In the early morning hours of August 10, 2025, a massive landslide occurred along the shoreline of Tracy Arm Fjord, approximately 80 miles southeast of Juneau, Alaska. The landslide, consisting of millions of pounds of ice, trees and other debris, plunged into the fjord and generated a tsunami in an area with heavy shipping and boating activity. The tsunami was detected as far as Juneau.
Map of Tsunami Observations for the 2025 Tracy Arm event. Orange circles and columns are post-tsunami survey or eyewitness measurement locations. Blue circles are tide gauge measurement locations. Credit: NOAA/NCEI, July 2026
Although there were no casualties or extensive damage to human-built structures from the landslide or tsunami, the event was scientifically significant. The tsunami produced a runup height—the highest elevation above sea level on land reached by the water, rather than the height of an individual wave—of over 1,500 feet, making it the second highest tsunami runup height ever documented in the global historical record.
A bar chart showing the top 10 highest runup observations in history.
This information is kept in the tsunami database maintained by NOAA’s National Centers for Environmental Information (NCEI), which is part of the National Environmental Satellite, Data, and Information Service (NESDIS). NCEI scientists compile and curate records of tsunami events and impacts worldwide, including runup measurements. This information is essential for researchers, emergency planners, coastal communities and the tourism and maritime industries to better understand hazardous events like the one in Tracy Arm.
Landslide-generated tsunamis are relatively common in Alaska’s steep and glaciated terrain. When large volumes of rock, soil, ice or other material rapidly move into a body of water from above or below, they can displace enough water to create powerful seismic waves. The size and strength of the resulting tsunami depend on several factors, including the volume of material involved, the speed it is moving and the depth of the water where it enters. In fact, the vast majority of high tsunami runup historical observations (more than 300 feet) involve landslides, not earthquakes.
Data collected from events like the Tracy Arm tsunami help improve scientific understanding of these potentially dangerous events. NCEI’s runup height data provides a critical foundation for research, hazard assessment and future forecasting efforts. While no operational warning system currently exists for tsunamis generated by landslides, information from events such as this one contributes to the development of future monitoring and warning capabilities.
Oblique aerial photo of the August 10, 2025 landslide headscarp. Credit: U.S. Geological Survey, NOAA/NCEI
The landslide occurred at approximately 5:30 a.m. local time and lasted about two minutes. It generated seismic waves that enabled scientists to determine its location, estimate its volume and calculate its duration. Researchers measured the tsunami’s runup height by examining evidence left on the hillslope opposite the landslide. Within weeks, researchers conducted field surveys to collect data on the tsunami effects.
According to NOAA’s National Tsunami Warning Center, the tsunami seiching (standing wave oscillating in a body of water) continued in Tracy Arm for over a day. A group of kayakers camping on the shore of Harbor Island—located more than 30 miles from the landslide near the mouth of the fjord—reported waking up close to 6:00 a.m. to find water flowing past their tent. The surge carried away one of their kayaks and much of their gear.
The tsunami also left visible marks on the surrounding landscape. The water caused damage to inland vegetation, extending roughly 180 feet above the normal water level in some areas. At Sawyer Island, the National Park Service reported a runup of at least 100 feet, with vegetation stripped from the slopes.
Photo of tsunami-inundated shoreline at Williams Cove, near the mouth of Tracy Arm. Credit: U.S. Geological Survey, NOAA/NCEI
NOAA’s National Weather Service office in Juneau reported no known injuries, fatalities or significant infrastructure impacts. The timing of the event likely reduced its consequences, since it occurred during the early morning hours when there were not many people out on the water.
The Tracy Arm landslide consisted of ice, trees and rocks, and scientists believe it was influenced by long-term environmental changes such as glacial retreat. Across Alaska, retreating glaciers and thawing permafrost are increasing the likelihood of similar landslides. In some communities, these hazards have become significant enough to prompt residents to relocate.