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