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Its eruption on May 18,was one of the greatest volcanic explosions ever recorded in North America. Mount St. Helens, named by the English navigator George Vancouver for a British ambassador, had been dormant since An explosive steam eruption on March 27,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. 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 SpokaneWashington, about miles 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 square miles square km were blown down by the lateral air blast.
Further eruptions occurred untiland a dome of lava grew intermittently in the crater.
Seismic activity occurred again between and including some small explosions as well as in and Insquare miles square km of land surrounding the volcano was deated Mount St. Helens National Volcanic Monumentadministered by the U. 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. 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. Mount Rainier National Park is to the northeast.
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Helens on May 18, The lava dome of Mount St. Helens in May Britannica Quiz. All About Mountains Quiz. What is the highest mountain range in South America? In which country are the Southern Alps located? Lace your climbing boots tight, because this quiz will test whether you can conquer the highest peaks of knowledge.
Witness the volcanic eruption of Mount Saint Helens and subsequent flooding wrought by melted glaciers. On May 18,as geologists watched in awe, Mount Saint Helens erupted in a gigantic explosion. Statue of a man planting trees, dedicated to those who replanted the area around Mount Saint Helens, Wash. Get a Britannica Premium subscription and gain access to exclusive content.
Subscribe Now. Learn More in these related Britannica articles:. Helens in the state of Washington in Most of the other high Cascade volcanoes exhibit some of seismic activity. The Mount St. For example, the eruptions of Mount St. Helens from to followed a sequence of small Vulcanian-type explosions, large Pelean and Plinian explosions, and finally extrusions of viscous lava into a lava dome that capped the vent.
The different types of volcanic activity can best be understood by making…. History at your fingertips. up here to see what happened On This Dayevery day in your inbox! address. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox.Bored looking for fun 22 St Helens 22
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Mount Saint Helens