Volcanoes

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Volcanoes
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Welcome to Washington - the 42nd State
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Why are we in Washington?

• How are volcanoes different in Washington than
  Hawaii?

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The evergreen state
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Space needle built for the 1962 Worlds Fair
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Pikes place market you can get anything from
fish to tulips
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Honey Im home
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Cascade Range

• Were in Washington because of the volcanoes in
  the Cascade Range

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Historic 1847 painting
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• The tiny Juan de Fuca plate is subducting under
  the North American Plate this created the chain
  of volcanoes

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What mountains make up the Cascade Range

• Mount Thielsen
• Mount Stuart
• Mount Lassen
• Mount Shasta
• Mount Rainier
• Mount St. Helens

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• Mount Thielsen Mount Thielsen is one of the
  "pointiest" mountains in the world, but the firm
  rock of the summit pinnacle makes it an easy
  climb.

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Mount Stuart is a massive rocky pyramid that
utterly dominates the view from Longs Pass.
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Lassen Peak The volcanic moonscape of the summit
crater.
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Mt. Shasta and the prominent "heart",
surrounded by narrow snowfields, from the town of
Mt. Shasta.
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The massive, icy form of Mount Rainier in the
classic view from the Paradise Inn area on the
south side of the mountain.
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Mt. St. Helens before the blast
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And after what happened
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• Mt. St. Helens is on an ocean-continent
  subduction boundary (the Juan de Fuca plate is
  subducting under the N. American plate). Mt. St.
  Helens is an active stratovolcano.

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May 18, 1980
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Realizing their
dangerous situation, the pilot put the plane into
a steep dive to gain speed, and thus was able to
outrun the rapidly mushrooming eruption cloud
that threatened to engulf them. The Stoffels were
fortunate to escape, and other scientists were
fortunate to have their eyewitness account to
help unscramble the sequence and timing of the
quick succession of events that initiated the
May 18 eruption.The
collapse of the north flank produced the largest
landslide-debris avalanche recorded in historic
time. Detailed analysis of photographs and other
data shows that an estimated 7-20 seconds (about
10 seconds seems most reasonable) elapsed
between the triggering earthquake and the onset
of the flank collapse. During the next 15
seconds, first one large block slid away, then
another large block began to move, only to be
followed by still another block. The series of
slide blocks merged downslope into a gigantic
debris avalanche, which moved northward at
speeds of 110 to 155 miles an hour. Part of the
avalanche surged into and across Spirit Lake, but
most of it flowed westward into the upper
reaches of the North Fork of the Toutle River. At
one location, about 4 miles north of the summit,
the advancing front of the avalanche still had
sufficient momentum to flow over a ridge more
than 1,150 feet high. The resulting hummocky
avalanche deposit consisted of intermixed
volcanic debris, glacial ice, and, possibly,
water displaced from Spirit Lake. Covering an
area of about 24 square miles, the debris
avalanche advanced more than 13 miles down the
North Fork of the Toutle River and filled the
valley to an average depth of about 150 feet the
total volume of the deposit was about 0.7 cubic
mile. The dumping of avalanche debris into Spirit
Lake raised its bottom by about 295 feet and its
water level by about 200 feet.- NEXT PAGE -
Schematic cross sections of Mount St. Helens
showing the cryptodome of magma that produced
the bulge and the three major blocks that
collapsed to form the debris avalanche (After
USGS Professional Paper 1250). Compare with
photographs in "The Catastrophic First Minute."
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• Graphic shows the amount of material displaced by
  the 1980 blast

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May 18, 1980 activity

• 1300 ft of the summit vanished
• Debris avalanche was more than half a cubic mile
• 235 square miles were devastated by blast cloud
  and volcanic debris

• 57 people dead or missing
• Miles of road and bridges destroyed
• Crater left was 1.2 miles wide, 2.4 miles long,
  2000 ft deep

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Mudflow-damaged house along the Toutle River.
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• Downed trees from blast note people in lower
  right

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Another view of lahar
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January 2007
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25 years after the eruption
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Current eruption over

• The nearly three and a half years of eruption at
  Mount St. Helens is over for now and on July 10,
  2008, scientists lowered the volcano alert level
  from Advisory to Normal and the aviation color
  code from Yellow to Green.
• Mount St. Helens reawakened in October 2004 when
  four explosions blasted steam and ash up to
  10,000 feet above the crater.
• Growth of this lava dome continued until late
  January 2008.
• Five months have passed with no signs of renewed
  eruptive activity. Earthquakes, volcanic gas
  emissions, and ground deformation are all at
  levels seen before the eruption began.

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Next eruption?
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Just in case