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Mt St Helens - 1 Mt St Helens a 50000 year history b...

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1. Mt St Helens a. 50000 year history b. Youngest Cascades volcano c. Most active cascades volcano d. Current cone formed in past ~2200 years e. Last major eruption in 1980-86 f. Current eruption began Oct1, 2004 continues today g. Typical behavior: frequent explosions 2. 1980s Eruption of Mt. St. Helens a. General tectonic setting b. Early eruptive history c. Pre-climactic eruption behavior d. Sequence of events leading to the eruption on May 18, 1980 e. Early Activity- March 15-21, 1980 i. From Jan 1975 –early 1980 only 44 earthquakes ii. From March 15-21, over 100 earthquakes iii. Magnitude 4.1 on march 20 indicated possible magma movement f. Early Activity, March 22-28 i. Phreatic (steam-driven) explosions begin ii. Earthquake activity increases g. Early Activity, March 29-April 11 i. Explosions and earthquakes increase in number and intensity ii. Cone starts to bulge iii. USGS positioned survey stations to measure if a set target was moving h. Early Activity, April 12-May2 i. Bulge on north-side continues to grow ii.
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  • Spring '09
  • Bergantz
  • eruption, Mount St. Helens, 1980 eruption of Mount St. Helens, Early Activity, Pre-climactic eruption behavior

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