Steep terrain in regions of Alaska can set the stage for landslides. A landslide may release spontaneously or be triggered by an earthquake, heavy rains, rapid snowmelt, construction activities, or other shifting. Landslides can occur in a variety of settings, from high inland mountains to coastal areas. For example, the thawing of permafrost in high mountains can release loosened rock and soil. Another example is a retreating glacier may cause valley slopes to become more unstable, increasing the risk of landslides. In a different example, many places along Alaska’s rugged coast are poised for landslides above or below the ocean’s surface. If the rocks, earth, and debris released in these locations displace water, they create a tsunami. Some of the largest tsunamis in history originated from landslides.
Researchers have documented massive landslides in Alaska, some of which caused megatsunamis. Some of the most notable events include:
2016: In June, pilot Paul Swanstrom followed a strange dust plume and found the aftermath of a more than 100-million-ton slide onto the Lamplugh Glacier.
2015: On October 17, the collapse of a mountainside near Tyndall Glacier into Taan Fjord after a period of heavy rains caused the giant wave of Icy Bay, with a run-up of 500 feet. (Run-up is the elevation above sea level that a tsunami wave reaches.) This was the largest non-volcanic landslide ever documented in North America.
2014: A 68-million-ton landslide—at least half again as large as the 1958 Lituya Bay rockslide—rumbled down the side of Mount La Perouse and spread out across the glacier below.
2005: A major ice-and-rockslide from the south face of Mt. Steller, possibly caused by a failure of both the hanging glacier at the mountain peak and permafrost instability downslope, spread about 1.5 square miles (4 square kilometers) over the Bering Glacier, covering it about 33-50 feet (10-15 m) deep. This event was large enough to register on seismometers around the world.
1958: Landslides in Lituya Bay following a M7.8 earthquake on the Fairweather Fault produced a megatsunami with 1,720 feet of run-up. The tsunami caused two fatalities, a married couple on a fishing boat that was never found. Four people on two other fishing boats managed to ride out the wave, including a father and his seven-year-old son.
Barry Arm fjord in the Prince William Sound region holds the potential for a dangerous, tsunami-generating landslide. In the summer of 2020, the Earthquake Center installed seismic stations along the fjord as part of a partnership with several state and federal agencies to monitor for landslides. On one of the Earthquake Center stations, a webcam provides visual information to supplement the seismograms.
Tidal Inlet in Glacier Bay has also been identified as a potential tsunami-generating landslide. There are many other potential landslides that have yet to be identified.