JULY 1958: LITUYA BAY MEGATSUNAMI

July 30, 2017

Lituya Bay is a T-shaped fjord on the coast of the Alaskan Panhandle, west of Glacier Bay and about 120 miles west-northwest of Juneau. It measures 7 miles long by 2 miles at its widest point and has a narrow mouth that makes navigation difficult during high tides. Water from three glaciers empties into Lituya Bay, which is over 700 feet deep in places.
At 22:15 hours on July 9, 1958, an earthquake with a magnitude of 7.9 struck the Lituya Bay area, the strongest in over 50 years for this region. The earthquake triggered a rockslide of 30 million cubic metres to fall from several hundred metres into the narrow inlet of Lituya Bay. The rockfall generated a wave with a maximum height of 1,720 feet (524 meters) – the world’s largest recorded tsunami. The large mass of rock struck with great force the sediments at bottom of Gilbert Inlet at the head of the bay. The wave then continued down the entire length of Lituya Bay, over La Chaussee Spit and into the Gulf of Alaska. The force of the wave removed all trees and vegetation from elevations as high as 1720 feet (524 meters) above sea level. The impact created a large crater and displaced and folded recent and Tertiary deposits and sedimentary layers to an unknown depth. After the earthquake it was observed that a subglacial lake, located northwest of the bend in the Lituya Glacier at the head of Lituya Bay, had dropped 100 ft (30 m). Scientists were puzzled for some time by the sheer size of the wave, because they could not identify a mechanism that could have created such a massive reaction. Ultimately, it was discovered that a piece of rock, 2,400 feet by 3,000 feet, and 300 feet thick, had dislodged from the face of the northern wall of the inlet, and fallen 2,000 feet into the bay. Incredibly, several eyewitnesses on the bay at the time the tsunami struck, lived to tell the tale. Only two people from a fishing boat died as a result of having been caught by a wave in the bay.
The 1958 wave was by far the largest to devastate Lituya Bay, but it was only the latest to be documented there by the U.S. Geological Survey. Previous monster waves struck the fjord in 1853, 1874, 1899 and 1936. (Source: Various – Image: Lituya Bay in 1958 / USGS)