Massive underwater landslides that occurred during the Great Alaska Earthquake of 1964 likely caused the formation of tsunami waves that destroyed a small coastal village near Prince William Sound, according to a study by the U.S. Geological Survey (USGS).
The discovery highlights the dangers posed by such submarine landslides to ports and residential areas located near fjords.
The 1964 Great Alaska Earthquake
On March 27, 1964, a magnitude 9.2 earthquake shook Alaskan region of Prince William Sound. The tremor began around 25 kilometers (15.5 miles) below ground, with its epicenter located around 120 kilometers (75 miles) east of the city of Anchorage.
The seismic event produced a tectonic tsunami, as well as about 20 other smaller and local tsunamis, resulting in damages to coastal communities near the quake's location.
One of the communities hit hardest by the tsunamis was the village of Chenega found on Chenega Island. A giant wave destroyed all but two buildings in the village and killed 23 of the 75 residents.
Shortly after the earthquake, scientists tried to investigate the likely cause of the massive tsunami. While they suspected that underwater landslides could have played a major role in the formation of the waves, the investigators were not able to find evidence of such an occurrence near Dangerous Passage or any other waterway surrounding Chenega.
Discovery of a Submarine Landslide Complex
Through the use of modern scientific equipment, such as multibeam sonar technology, geophysicist Daniel Brothers and his colleagues from the USGS discovered a large complex of underwater landslides in Dangerous Passage. This complex can be found in an area of the ocean deeper than what scientists could reach in 1964.
"What makes this slide unusual is that much of the material that slid was at a water depth of 250 to 350 meters (820 to 1150 feet)," USGS geologist and study co-author Peter Haeussler said. "The deeper initiation depth made it particularly good at generating a tsunami."
Evidence found in the landslide complex matched the reports given by eyewitness during the Great Alaska Earthquake. The USGS team calculated that a tsunami produced in the area of the landslide would reach Chenega within three to four minutes. This was consistent with the estimated arrival time of the most damaging tsunami waves.
The findings of the U.S. Geological Survey study are featured in the journal Earth and Planetary Science Letters.