On March 20, 1980, after 123 years of quiet inactivity, earthquakes began under Mount St. Helens with small steam explosions beginning a week later. The elevation of the mountain was 9,677 feet.
On May 18, 1980, at 8:32 a.m., a magnitude 5.1 earthquake shook Mount St. Helens. The bulge which had started building the previous month 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 of the peak collapsed or blew outwards. As a result, 24 square miles of valley was filled by a debris avalanche, 250 square miles of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards of material was deposited directly by volcanic mudflows into the river channels. The mountain now stands at 8,364 feet. Fifty-seven people were killed or are still missing.This slideshow contains before, during, and after photos.
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