volcanic peak, 8,365 ft (2,551 m; 9,677 ft/2,950 m before its 1980 eruption) high, SW Wash., 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. A series of earth tremors began 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 nearly 20 mi (32 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 60,000 ft (18,300 m) into the air, blanketing a large area in the NW United States with volcanic ash. A smaller eruption occurred a week later, on May 25, and then again on Apr. 11, 1982. The summit of Mt. St. Helens was replaced by a horseshoe-shaped crater 2,460 ft (750 m) deep. The volcano and surrounding area are now a national monument and have provided biologists with a unique opportunity to observe ecological succession and the reestablishment of natural habitats.

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

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