Download mt.st.helens 4-02-09

Volcanoes
Welcome to Washington - the 42nd
State
Why are we in Washington?
How are volcanoes different in
Washington than Hawaii?
The evergreen state
Space needle – built for the 1962
World’s Fair
Pike’s place market – you can get
anything from fish to tulips
Honey – I’m home
Cascade Range
• We’re in Washington because of the
volcanoes in the Cascade Range
Historic 1847 painting
• The tiny Juan de Fuca plate is subducting
under the North American Plate – this
created the chain of volcanoes
What mountains make up the
Cascade Range
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Mount Thielsen
Mount Stuart
Mount Lassen
Mount Shasta
Mount Rainier
Mount St. Helens
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.
Mount Stuart is a massive rocky
pyramid that utterly dominates the
view from Longs Pass.
Lassen Peak: The volcanic
moonscape of the summit crater.
Mt. Shasta and the prominent "heart", surrounded
by narrow snowfields, from the town of Mt. Shasta.
The massive, icy form of Mount Rainier in the
classic view from the Paradise Inn area on the
south side of the mountain.
Mt. St. Helens before the blast
And after – what happened
• 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.
May 18, 1980
• Graphic shows the amount of material
displaced by the 1980 blast
May 18, 1980 activity
• 1300 ft of the summit • 57 people dead or
vanished
missing
• Debris avalanche was • Miles of road and
more than half a cubic
bridges destroyed
mile
• Crater left was 1.2
• 235 square miles
miles wide, 2.4 miles
were devastated by
long, 2000 ft deep
blast cloud and
volcanic debris
Mudflow-damaged house along the Toutle River.
Downed trees from blast – note
people in lower right
Another view of lahar
January 2007
25 years after the eruption
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.
Next eruption?
Just in case