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Mount St. Helens is a mountain inSkamania county, Washington state.On May 18th, 1980, Helens had ahuge eruption that was knownworldwide. At 8:32 am, PDT, themost economically devastatingeruption in history resulted from thisvolcano spewing metric tons ofashes. The largest landslide know toman, ranging 600 kilometers,stormed down the north side of themountain.
This volcano damaged Washingtonin a very interesting way. Instead oferupting in lava, this volcanoreleased huge clouds of ash. Theash acted like sand, falling andburying cars, houses, and people. Intotal, an estimated 57 people werekilled and 250 homes, 47 bridges,24 km of railways, and 298 km ofhighway were destroyed.
Mt. St. Helens is located on the Juan deFuca tectonic plate. Lava built up fromalmost 100 km down. As the lava built up,it became rich with silica and gases; thekey fact to a huge explosion. Thepressure inside of Mt. St. Helens keptgrowing. A 5.1magnitude earthquakehappened right below Mt. St. Helens,causing a landslide, that took all theweight that had been holding the magmain the volcano, off. This caused thevolcano to explode. It erupted with theforce of a hydrogen bomb. People miles
Mount Helens was formed by aconvergent tectonic boundary plate.The Juan de Fuca plate was (andstill is) being pushed under the NorthAmerican plate. This caused magmato be forced up through earth’scrust, forming Mt. St. Helens.Note: That Juan de Fuca is beingpushed under the North Americanplate at an average of 4 cm everyyear.
Earth’s size has not changedsignificantly. Old crust must berecycled or destroyed. This “recycling”happens at boundaries where platesmove towards each other. Theseboundaries are called convergentboundaries. When the plates collide, itmay take millions of years to have oneplate fully go below the other. This oneplate is melted into magma, andsometimes spit out (an eruption).
MagmaGenerationthe Juan de FucaplateNorthAmericanPlateMt. St. HelensSubductionZoneOceanMagmaMagma Ascension MantleMantle(asthenosphere)(Lithosphere)
During 1980, scientists did not havea huge technical understanding ofvolcanic eruptions. Weeks beforethe huge eruption, there were smallearthquakes around Mt. St. Helensbecause of all the pressure.Because of this seismic activityaround the volcano, scientistspredicted it would erupt.
Mt Helens looked like a perfect cinder cone before iterupted. After it erupted, it looked like a cone with thetop cut clean off. There is now a small dome thatformed in the center of the volcano.Before the eruption, Mt. St. Helens was astratovalcano. After the eruption, Mt. St. Helensbecame lava dome volcano. When talking about thetype of volcano, ignore the outer part of Mt. St.Helens, because it is not part of the actual volcanoanymore. lava domes are formed by lava piling uparound the vent. Think of a lava dome as the smalldome of the volcano that is still active, of a oncebigger one. Mt. St. Helens dome grew until 1986.These domes never erupt explosively, and the Mt. St.Helens dome won’t erupt at all again, for a very long
As you can see, the whole north side of the mountain blew up.
Mt. St. Helens eruption created multiplekinds of rocks. Extrusive igneous rockwas formed underground from themagma, and intrusive igneous rock wasformed above ground, because of thedried lava.Some igneous rock turned intometamorphic rock, with the heat from thelava and pressure of the ash.Sedimentary rock was formed from all thesmall rock bits that flew out of the volcano
Earth’s crust is constantly moving,colliding, and changing. The Juande Fuca moves about 4centimeters under the NorthAmerican plate every year. Themovement and slow collision ofthese two plates formed Mt. St.Helens!
When Mt. St. Helens erupted, itmoved rocks hundreds of miles fromthe volcano. That is a form oferosion. Erratic boulders were foundin unnatural places all around Mt. St.Helens, because of the blast.
The ash that roared out of Mt. St.Helens made many fossils out ofplants, animals, and humans.Humans that did not get to evacuatewere covered and suffocated in ash.Nearby plants and animals werealso compressed in ash.
For more on the Mt. St. Helenseruption, please watch a Specialnews Report that was aired in 1980;News Report:http://www.youtube.com/watch?v=BAX6N0SLCoI
The part you have been waiting for!"Mount St. Helens." Wikipedia. Wikimedia Foundation, 27 May2013. Web. 28 May 2013.<http://en.wikipedia.org/wiki/Mount_St._Helens>.Our Science Text book- “Science Probe.” Nelson. Toronto, Ontario,2005.Nelson Education - Home Page." Nelson Education - Home Page.N.p., n.d. Web. 28 May 2013. <http://www.nelson.com/>."Day 24: Mt. St. Helens." Home. N.p., n.d. Web. 30 May 2013.http://brianabbott.net/travels/my-american-tour/pacific-coast-states/day-24-mt-st-helens."Hudson Valley Geologist." Mount St Helens ~. N.p., n.d. Web. 30May 2013.<http://hudsonvalleygeologist.blogspot.ca/2011/05/mount-st-helens.html>.