Download Geology of Washington

Geology of Washington
A very interesting state, indeed!
Earth Basics
Planetary Structure
•Lithosphere (Crust)
•Mantle (Liquid)
•Outer Core (Liquid)
•Core (Solid)
Lava Lamp
Convection style
currents within mantle
Tectonics
Geology’s Unifying Theory
Continental Arc
Subduction zone is close to continental crust (21 to 30 miles
thick)
Island Arc
Subduction zone is beneath ocean crust (4 to 5 miles thick)
Building Blocks of Washington
Timeline approximately 200 million years
Terrane Belts: Small crustal plates
that combine with larger crust
• These belts are exotics—
they have come from far
away.
• Some are ocean belts of
plate raised up, and others
are volcanic island chains
that were added to N.
America
• Each addition created
subduction and continental
arcs
Intermontane
Volcanic Island Chain
• A series of volcanic islands,
like Hawaii or Japan were
forced onto the North
American plate around
Spokane
• These islands are welded
on, and end about where
Twisp and the Methow
valley is today
Insular Belt
Insular Island Chain
• This island chain was too big
to subduct, so it just welded
on to Washington
• This chain makes up
western BC, Vancouver
Island, and Washington
north of the Skagit River
• Coast Range Arc built many
of the North Cascade
volcanoes
Melange Belt
French word for a mixture or medley of vegetables
Broken Plate
• The plate responsible for
the Insular islands broke up
• Plate from N. California
broke and moved north
• Melange belt is jumble of
rock scraped north by the
moving plate
• Jumble of rocks were
scraped on top of Insular
Belt by passing plate
Crescent Basalt
50 million years ago
Massive ocean lava flow off
coast of WA and OR
Tectonics jam it into area as Olympic
peninsula and Western OR
Almost Modern Times
5 to 7 million years ago
Cascade/Olympic Mountains
• The Cascades and Olympics
are fold mountains
• They are created by the
tremendous pressure
caused by subducting the
Juan de Fuca plate off the
coast
• Eastern OR and WA will be
flooded with lava flows as
well
Today
• Juan de Fuca plate is
being over-ridden by N
American plate
• Subduction zone is off
the NW coast
• Responsible for
volcanoes and
earthquakes
• Major danger of
tsunamis
Mt Rainier
North America’s most dangerous volcano
• Active hydrothermal system
vents sulfer—with water
forms H2SO4
• 25 glaciers on Rainier
• Lahars—60 large in 10,000
years (500 years since last
major)
• Osceola took off top, went
100 miles to Sound (5,600
years ago)
• 150,000 people live on
mudflows
http://www.youtube.com/w
atch?v=N_cyG2dJPpc
The Ice Age Cometh
Puget Lobe
Puget Lakes
Light Blue (Fresh Water)
Dark Blue (Salt Water)
• The Sound was not open to
the ocean
• Whidbey Island was much
larger and blocked ocean
water from entering the
area
• Fresh water lakes filled the
area of the Sound today
• You could walk from Tacoma
to the coast
Extent
• The Puget Lobe
was about 3000
feet thick
• Extended from
Cascades to
Olympics
• Went as far south
as Centralia
Aftermath
• The enormous ice sheet became a very
effective bulldozer, scoring out the Sound
• The ocean connected with the Sound after
chunks of Whidbey were ground away
• Glacial lakes spread a layer of clay throughout
the Sound
• Retreating glaciers left a layer of till, many feet
thick
Soil Composition
Till on Clay
• Clay (superfine soil with low
permeability) above bedrock
• Glacial till (loosely packed,
highly permeable) over the
top
• Water soaks through till,
collects and runs down clay
• Creates slip zones (wet clay
acts like a lubricant)
• Washington leads the nation in
mudflows or slides
• Till is very unsteady in
earthquakes (turns to jelly)
Glacial Till
Glacial Floods
Lake Missoula
Polson Lobe
• This lobe covered the
mountain valleys of
western Montana
• Clark Fork river drains
western Montana—
with the block, a lake
the size of two Great
Lakes formed
• Ice dam breaks and
greatest recorded flood
flows across ID, WA, OR
Missoula Floods
• Harlen Bretz wrote
in the early 20’s, but
unproven until the
50’s
• The water was 400’
tall, moving at least
45 to 80 mph
• Floods west to
Wenatchee and
south to central OR
Results
• E WA scoured like a
beach
• Dry Falls largest we
can find
• Erratic's all over
water’s path
• Provides perfect
template for study
of Mars