1. Mt. St Helens- 1980 Eruption and present day activity
Austin Thornton and Bobby Lorenz

2. 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,

3. 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.

4. 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

5. 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

6. 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

7. 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.

9. References http://www.olywa.net/radu/valerie/StHelens.html