Saint Helens, Mount


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.

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   volcanic peak in the Cascade Range, southwestern Washington, U.S. Its eruption on May 18, 1980, was one of the greatest volcanic explosions ever recorded in North America.

      Mount St. Helens, named by the English navigator George Vancouver (Vancouver, George) for a British ambassador, had been dormant since 1857. An explosive steam eruption on March 27, 1980, was followed by alternating periods of quiescence and minor eruption. Pressure from rising magma within the volcano caused extensive fissures and the growth of a bulge on the north flank of the peak. On the morning of May 18, an earthquake with a magnitude of 5.1 on the Richter scale triggered a gigantic landslide on the mountain's north face. The north slope fell away in an avalanche that was followed and overtaken by a lateral air blast, which carried a high-velocity cloud of superheated ash and stone outward some 15 miles (25 km) from the volcano's summit; the blast reached temperatures of 660 °F (350 °C) and speeds of at least 300 miles (500 km) per hour. The avalanche and lateral blast were followed by mudflows, pyroclastic flows, and floods that buried the river valleys around Mount St. Helens in deep layers of mud and debris as far as 17 miles (27 km) away. Meanwhile, simultaneously with the blast, a vertical eruption of gas and ash formed a column some 16 miles (26 km) high that produced ash falls as far east as central Montana. Complete darkness occurred in Spokane, Washington, about 250 miles (400 km) northeast of the volcano.

 A total of 57 people and thousands of animals were killed in the May 18 event, and trees over an area of some 200 square miles (500 square km) 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 9,677-foot (2,950-metre) peak was a horseshoe-shaped crater with a rim reaching an elevation of 8,363 feet (2,549 metres). Further eruptions occurred until 1986, and a dome of lava grew intermittently in the crater. Seismic activity occurred again between 1989 and 1991 (including some small explosions) as well as in 1995 and 1998.

 In 1982, 172 square miles (445 square km) of land surrounding the volcano was designated Mount St. Helens National Volcanic Monument, administered by the U.S. Forest Service as part of Gifford Pinchot National Forest. The monument provides a unique opportunity for scientific study of the dynamics of an active composite volcano and for research on how ecosystems respond to cataclysmic disturbances. The monument also presents many recreational and educational opportunities. Visitors can view the crater, lava dome, pumice plain, and effects of the landslide from Johnston Ridge Observatory on the monument's west side, less than 5 miles (8 km) from the volcano. The west side also provides opportunities to observe animals and plants that have recolonized the blast zone and lakes that have formed as a result of the eruption. The edge of the blast zone, marked by standing dead trees, lies in the eastern part of the monument where old-growth forests, undamaged by the blast, still stand. On the south side are lava formations of various ages, including the longest continuous lava tube in the 48 conterminous U.S. states, which formed during an eruption about 2,000 years ago. Mount Rainier National Park is to the northeast.
 

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Universalium. 2010.

Look at other dictionaries:

  • Saint Helens,Mount — Saint Helens, Mount A volcanic peak, 2,549 m (8,363 ft) high, of the Cascade Range in southwest Washington. Before its violent eruption on May 18, 1980, it was 2,949.7 m (9,671 ft) high. The eruption produced a smoke plume visible over much of… …   Universalium

  • Saint Helens, Mount — geographical name volcanic peak 8366 feet (2550 meters) SW Washington in Cascades; in Mount Saint Helens National Volcanic Monument …   New Collegiate Dictionary

  • Mount Saint Helens National Volcanic Monument — geographical name see Saint Helens (Mount) …   New Collegiate Dictionary

  • Mount Saint Helens — Mount St. Helens Mount St. Helens, Juli 2007 Höhe 2.549 m Lage …   Deutsch Wikipedia

  • Saint Helens —   [snt helɪnz], Name von geographischen Objekten:    1) Saint Helens, Stadt in der Metropolitan County Merseyside, England, östlich von Liverpool, 106 400 Einwohner; Glas , ferner Eisen , Messing , keramische, Textil und pharmazeutische Industrie …   Universal-Lexikon

  • Mount Saint Helens — →↑St helens, Mount …   Dictionary of contemporary English

  • Mount Saint Helens — Mont Saint Helens  Ne doit pas être confondu avec mont Saint Helena. Mont Saint Helens Le mont Saint Helens depuis Johnston Ridge, 31 ju …   Wikipédia en Français

  • Saint Helens — St. Helens steht als geographische Bezeichnung für: St Helens (Merseyside), Vereinigtes Königreich St Helens (Borough), Vereinigtes Königreich St Helens (Isles of Scilly), Vereinigtes Königreich St. Helens (Oregon), USA St. Helens (Tasmanien),… …   Deutsch Wikipedia

  • Mount Saint Helens — noun an active volcano in the Cascade Range in southwestern Washington; erupted violently in 1980 after 123 years of inactivity • Syn: ↑Mount St. Helens, ↑Mt. St. Helens • Instance Hypernyms: ↑volcano • Part Holonyms: ↑Cascades, ↑Cascade …   Useful english dictionary

  • Mt. Saint Helens — Mount St. Helens Mount St. Helens, Juli 2007 Höhe 2.549 m Lage …   Deutsch Wikipedia


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