Saint Helens, Mount, 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 Cascade Range, mountain chain, c.700 mi (1,130 km) long, extending S from British Columbia to N Calif., where it becomes the Sierra Nevada ; it parallels the Coast Ranges , 100–150 mi (161–241 km) inland from the Pacific Ocean.
..... Click the link for more information. . 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).

Saint Helens, Mount

Volcanic peak in the Cascade Range, southwestern Washington, U.S. Dormant since 1857, it erupted in May 1980 in one of the greatest volcanic explosions ever recorded in North America. Sixty people and thousands of animals were killed in the May 18 event, and 10 million trees were blown down by the lateral air blast. At the event's end Mount St. Helens's volcanic cone had been completely blasted away; in place of its 9,680-ft (2,950-m) peak was a horseshoe-shaped crater with a rim reaching elevations of about 8,000 ft (2,400 m). Further eruptions have occurred since 1980, and a dome of lava has grown in the crater. Mount St. Helens National Volcanic Monument was established in 1982.