PowerPoint Slideshow about ' Mt. St. Helens' - lelia
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The first sign of activity at Mount St. Helens in the spring of 1980 was a series of small earthquakes that began on March 16. After hundreds of additional earthquakes, steam explosions on March 27 blasted a crater through the volcano's summit ice cap. Within a week the crater had grown to about 1,300 feet in diameter and two giant crack systems crossed the entire summit area. By May 17, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward at least 450 feet to form a noticeable bulge. Such dramatic deformation of the volcano was strong evidence that molten rock (magma) had risen high into the volcano
The Cascade mountains lie along the western coast of the United States. This area is one subjected to frequent earth movements and has a long history of volcanic activity. The mountains have formed as a result of seismic activity. The American coast is part of the North American Plate; the Pacific Ocean to the west overlies the Juan de Fuca plate. The Juan de Fuca plate is being subducted below the North American plate by processes explained by the theory of Plate Tectonics. As the descending Juan de Fuca plate is subjected to increasing pressure it becomes hotter and begins to partially melt. The molten rock, called magma begins to rise towards the surface. When it reaches the surface it erupts and a volcano is formed. Mt St. Helens is the youngest of the volcanoes in the region, being a mere 2,500 years old, but the area has been volcanically active for almost 40,000 years, hence the large number of volcanic mountains forming the Cascade Range.
Even though scientists gathered large amount of data in the months that led up to the eruption and were able to record the events as they happened, the eruption caught the researchers by surprise.
MSH is expected to continue erupting but no one knows for how long. Pyroclastic flows, lahars, ejection of ash and pumice, and even the possibility of lava flows may all lie somewhere in MSH's future.
MSH can't even twitch without scientist knowing about it. Seismic disturbances, gas emissions, temperature, elevation changes (deformation), water levels, sediment flow rates, and even magma movement are all carefully monitored.
$1.1 billion for timber, civil works and agricultural losses. This does not include money for personal property losses, the cost of ash clean-up, or the loss of tourism in the area immediately after the eruption.
Mount St. Helens, Washington, is the most active volcano in the Cascade Range. Its most recent series of eruptions began in 1980 when a large landslide and powerful explosive eruption created a large crater, and ended 6 years later after more than a dozen extrusions of lava built a dome in the crater. Larger, longer lasting eruptions have occurred in the volcano's past and are likely to occur in the future. Although the volcano seems to have returned to a period of quiet, scientists with the U.S. Geological Survey and University of Washington Geophysics Program continue to closely monitor Mount St. Helens for signs of renewed activity.