Lesson 27 What are volcanoes?. On May 18, 1980, Mount St. Helens, in Washington state blew its top.
Volcanoes Welcome to Washington - the 42 nd State.
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Transcript of Volcanoes Welcome to Washington - the 42 nd State.
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
• 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 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
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