1980 Events - Mt. St. Helen's Erupts
On May 18, 1980, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mount St. Helens in south western Washington state. The volcano had awakened from it's slumber months early and had been in the dome-building stage for several weeks. During the quake, the bulge and surrounding area slid away in a gigantic rockslide and debris avalanche. This released the pressure that had been building up under the dome and triggered a major eruption of the volcano, spewing pumice and ash high int the morning air. Thirteen-hundred feet (400 meters) of the peak collapsed or blew outwards. As a result, 24 square miles of valley was filled by debris from the avalanche. In addition, over 250 square miles of recreation, timber, and private lands were destroyed or damaged by a lateral blast, and an estimated 200 million cubic yards of material was deposited directly by volcanic mudflows into the river channels. Fifty-seven people were presumed killed. Some bodies were never recovered.
For more than nine hours a vigorous plume of ash erupted, eventually reaching 12 to 15 miles above sea level.
The eruption of Mt. St. Helens on May 18, 1980 sent volcanic ash, steam, water, and debris to a height of 60,000 feet. The mountain lost 1,300 feet off it's peak. About 2/3 of a cubic mile of material stream downward from the center of the plume and the formation and movement of pyroclastic flows down the left flank of the volcano.
photos courtesy of the USGS
