Details

On 18 May 18 1980, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mount St. Helens in Washington state. The bulge and surrounding area slid away in a gigantic rockslide and debris avalanche, releasing pressure, and triggering a major pumice and ash eruption of the volcano. Four hundred meters (1,300 ft) of the peak collapsed or blew outwards. As a result, 62 sq km (24 sq mi) of valley was filled by a debris avalanche, 650 sq km (250 sq mi) of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 150 million cu m (200 million cu yd) of material was deposited directly by lahars (volcanic mudflows) into the river channels. Sixty-one people were killed or are still missing. Photo courtesy of USGS/Austin Post.