Mount Saint Helens volcanic peak, 8,363 ft (2,549 m; 9,677 ft/2,950 m before its 1980 eruption) high, SW Wash., historically the most active volcano in the Cascade Range . Dormant since 1857, Mt. St. Helens erupted on May 18, 1980, in one of the largest volcanic explosions in North American history; prior to that event there were a series of earth tremors and steam explosions beginning on Mar. 20, 1980. During the eruption a great portion of the rock facing on north side of the mountain fell, followed by a lateral blast of stone, ash, and poisonous gas that carried debris 17 mi (27 km) and flattened and buried surrounding forest. The disaster took some 65 lives, wiped out substantial populations of elk, deer, bear, and coyote, and destroyed 230 sq mi (600 sq km) of vegetation. A volcanic plume rose 80,000 ft (24,400 m) into the air, blanketing a large area of the NW United States with volcanic ash. The summit of Mt. St. Helens was replaced by a horseshoe-shaped crater 2,460 ft (750 m) deep. A number of smaller eruptions, beginning on May 25 and continuing into 1986, resulted in lava flows that built up a dome in the crater; a new, dome-building eruption began in 2004. The volcano and surrounding area are now part of Mt. St. Helens National Volcanic Monument and have provided biologists with a unique opportunity to observe ecological succession and the reestablishment of natural habitats.

Bibliography: See S. A. Kellar, ed., Mount St. Helens (1982).

St Helens, Mount Volcanic peak in the Cascade Range, sw Washington state. Dormant since 1857, it erupted on May 18, 1980, killing 60 people. The 2950m (9578ft) summit was reduced to 2560m (8312ft) with a deep horseshoe crater. Two more eruptions occurred in the following two weeks, and it is predicted to erupt again in the early 21st century.

http://www.fs.fed.us/gpnf/mshnvm

MOUNT ST. HELENS

Early Signs of Activity

Located seventy miles from Portland, Oregon, in a sparsely populated region of southwestern Washington State, Mount St. Helens erupted in 1980 in one of the largest volcanic explosions in North American history. The mountain's last eruption had been recorded by the American soldier, explorer, and political leader John C. Fremont in 1857. Signs of significant seismic and volcanic activity began as early as 27 March 1980, when the first venting of smoke and ash began. As many as 250,000 residents in nearby counties, including several hundred loggers, forest rangers, and residents in the immediate vicinity of Mount St. Helens, were either evacuated or warned.

The Volcano Erupts

At 8:32 A.M. on Sunday 18 May 1980 Mount St. Helens erupted. Millions of tons of earth were shot as high as 65,000 feet into the air. Heated rock and ash poured down the mountain's northern side. In a short time, what had been a 9,677-foot mountain measured only 8,364 feet. A crater two and one-half miles long and one mile wide had been created. One scientist compared the force of the explosion to five hundred Hiroshimasized atomic bombs. Sixty-one people lost their lives as a result. Thousands of elk and coyotes; hundreds of deer, bobcats, and black bears; and an estimated fifteen mountain lions were also killed in the blast. Ash from the volcanic eruption fell on half of the state of Washington as the public witnessed the awesome event on television.

Subsequent Activity

A second eruption occurred a week after the initial blast, on 25 May. A dome of molten rock had formed by October 1980, and another, less spectacular, eruption took place on 11 April 1981. Five years later, in May and June 1985, a series of minor earthquakes accompanied by mild volcanic activity worried residents, but no major volcanic activity followed. Scientists predicted, however, that the volcano would erupt again early in the twenty-first century.

Sources:

D. E. Bilderback, ed., Mount St. Helens, 1980: Botanical Consequences of the Explosive Eruption (Berkeley: University of California Press, 1987);

"Eruption of Mount St. Helens," Scientific American, 244 (March 1981): 68-80;

"Mt. St. Helens is Calm," Science News, 127 (29 June 1985);

"Volcano, Dormant for 123 Years, Begins Erupting in Washington State," New York Times, 28 March 1980.