Lecture 3 Notes

Lecture 3 Notes - Mount St. Helens is part of the Cascade...

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The Cascade Mountains are a volcanic arc Mount St. Helens is part of the Cascade Mountains in Washington and Oregon
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Mount St. Helens is part of the Cascade Mountains in Washington and Oregon Ocean-continent convergent boundary (subduction zone) The Juan de Fuca Plate is subducting beneath the North American Plate in this region.
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Mount St. Helens The most active and explosive volcano in the United States 4500 year history of eruptions Before 1980, it had been dormant since the mid 1800’s (2 month warning!) March 1980 – small to moderate earthquakes April 1980 – more earthquakes and swelling of the NE flank May 1980 – Pyroclastic Eruption – blew out the northern flank of the volcano Hot blast, volcanic ash, lahars (mudslides) About 60 people killed
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Before During After Volcanic ash was ejected 25km into the atmosphere
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Mount Rainier is also a volcano in the Cascades 1.5 million years of eruption history Highest volcano is the U.S. Last eruption – 150 years ago Several million people live in the Seattle-Tacoma area!
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Mudslides pose the greatest threat to the Tacoma, Washington region.
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Volcanic eruptions are often preceded by: 1) Earthquakes 2) Swelling 3) Increased Temperature All due to the rising of magma beneath the volcano
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doesn’t only happen at volcanoes Volcanism : The process by which magma rises through the crust and emerges at the surface as lava Volcano : A hill or mountain constructed by an accumulation of lava and pyroclasts. Volcanism is the more inclusive
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This note was uploaded on 03/03/2010 for the course GEOLOGY glg 321 taught by Professor Na during the Spring '10 term at ASU.

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Lecture 3 Notes - Mount St. Helens is part of the Cascade...

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