The consequences of a 17-metre-high tsunami triggered by a landslide in August 2024
An atmospheric river brought heavy rains to southern Alaska in early August 2024, triggering a large landslide and tsunami at Pedersen Lagoon.
The series of events which eventually led to the landslide event began to unfold early on the 7th of August, 2024, on a slope on the northwest side of the upper Pedersen Lagoon, 20 miles (equivalent to 32 km) southwest of Seward, Alaska. Debris from the landslide traveled along the Pedersen Glacier before crashing into the water.
Preliminary estimates from the U.S. Geological Survey (USGS) indicate that the landslide moved about 2 million cubic metres of rock and debris - which are huge amounts!
A 17 m high tsunami
According to the National Park Service, when the debris slid into the lagoon, a tsunami of about 17 metres (57 feet) high occurred. Some of the displaced water crashed into the hillsides on the eastern side of the lagoon and some moved along the land between the upper and lower lagoons before dissipating on the eastern shore of the lower lagoon.
The sequence above compares two images, one acquired on August 20, 2024 by the OLI-2 (Operational Land Imager-2) on the Landsat 9 satellite, showing the aftermath of the landslide and tsunami with another earlier image of the same area.
The wave damaged trees and flattened vegetation between the upper and lower parts of Pedersen Lagoon. According to local reports, it also damaged the boardwalk of a lodge on the east side of the lower lagoon. The photograph below, provided by the United States Geological Survey, shows part of the landslide source area near the Pedersen Glacier.
Glaciers can affect the stability of steep terrain, such as the cliffs that line southern Alaska’s glacier-carved fjords. As glaciers retreat, they leave behind slopes vulnerable to landslides. Pedersen Glacier is one of three lake-terminating glaciers in Kenai Fjords National Park that have experienced significant retreat over the past 40 years.
By analysing Landsat images from 1984 to 2021, the researchers found that Pedersen Glacier retreated as much as 2 miles (3.2 kilometres) during that period.
The NASA Earth Observatory images are by Wanmei Liang, using Landsat data from the U.S. Geological Survey. Story by Emily Cassidy.