Post on 30-Dec-2015
Mt. St Helens- 1980 Eruption and present day activity
Austin Thornton and Bobby Lorenz
Background-Mt. St. Helens is an active Stratovolcano
-Located in the Cascade Mountains, in the Pacific Northwest
-Named for British diplomat Lord St. Helens
-Age of rock is 40,000 years old
-Part of “Ring of Fire” which includes 160 active volcanoes
-Most active volcano in Cascades
-Made up of basalt, andesite and domes of dacite,
Before - After sleeping for 123 years, on March 20, 1980 an earthquake with a magnitude of 4.1 was centered under Mt. St. Helens
-March 27th first puff of ash which created 250 foot wide crater
- March 30th 79 Earthquakes occurred on the mountain.
- First harmonic tremors recorded, signaling movement of magma, explosions of rock ash and ice were daily occurrence.
Causes-Type of boundary is an ocean-continent subduction
-Juan de Fuca plate is subducting under North American Plate
-Between early eruptions and big eruption so much pressure built up, the north face of the mountain couldn’t handle it.
-The magma was able to flow out of the open face.
-No one can predict when the volcano will erupt again or how strong it will be
During-8:32 a.m. a 5.1 magnitude earthquake with its epicenter 1 mile below the mountain occurred.
-Caused largest landslide in history occurred, removing 1,300 from mountain and swept away most of the north side of the mountain
-Went from 9th highest peak in Washington to the 30th
-Landslide occurred at over 175 mph
-Eruption melted 70% of snow and ice on mountain, causing massive flooding
-Rock and ash was pushed at 650 mph across the land up-rooting trees as far as 6 miles away
-Nearby lake temperature went from 42 degrees to 100 degrees during landslide
After -57 people were killed
-250 homes destroyed
-47 bridges destroyed
-15 miles of railway destroyed
-185 miles of highway destroyed
-Summit reduced from 9,677 feet to 8,364 feet
-Mile wide horseshoe-shaped crater
-Glacier forming in crater, only glacier growing in 48 continental states
Present Day-1980 was most devastating economic eruption in history
-Weyerhaeuser company had recovered enough blown down trees to build 85,000 three-bedroom homes by 1982
-Gasses and steam still vent from crater
-Still active volcano
-Magma reached surface October 11, 1984 creating lava dome
-New lava dome is growing everyday
-March 8, 2005 a 36,000 plume of steam and ash emerged, which was visible from Seattle and rained ash on Yakima, Washington.
References
• http://www.olywa.net/radu/valerie/StHelens.html• http://www.fs.fed.us/gpnf/mshnvm/• http://en.wikipedia.org/wiki/Mount_St._Helens• http://en.wikipedia.org/wiki/
1980_eruption_of_Mount_St._Helens• http://www.cotf.edu/ete/modules/volcanoes/
vnarrative1.html• http://volcano.und.edu/vwdocs/
frequent_questions/top_101/Helen/Helen5.html