Mount St. Helens - May 18, 1980
… at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mount St. Helens. 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. Thirteen-hundred feet (400 m) of the peak collapsed or blew outwards.
As a result, 24 square miles (62 sq km) of valley was filled by a debris avalanche, 250 square miles (650 sq km) of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards (150 million cu m) of material was deposited directly by lahars (volcanic mudflows) into the river channels.
Sixty-one people were killed or are still missing. USGS Photograph taken on May 18, 1980, by Austin Post.
(via: US Geological Survey)