Download Plate Tectonics of the Pacific Northwest

Beauty and the Beast
Plate Tectonics of the Pacific Northwest
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Mt. Garibaldi
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Glacier Peak
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Plateau
Mt.
Hood
Three
Sisters
Cascade
Volcanoes
Mt.
Mazama
Mt
McLoughlin
Mt.
Mountains Shasta
Basin
Range
Province
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PACIFIC PLATE
JUAN de FUCA
PLATE
NORTH AMERICAN
PLATE
Crustal
Earthquake
Volcanic
Earthquake
Magma
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Earthquake
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Earthquake
Mid-Ocean Locked Zone
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Earthquake Ju Su
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Plate Sweats
Hot Water
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Plate
Boundaries:
Hotspot
Divergent
Convergent
Basin and
Range
Province
Slab
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Gr
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Lassen
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PLATE
Offshore Earthquake
Mt. Jefferson
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Klamath
Juan de Fuca
Ridge
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Will lley
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Willamette
Valley
Coast Range
Mt. St. Helens
Cascade
Volcanoes
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Washington
Oregon
Mt. Adams
Boundary
PACIFIC
Mt.
Rainier
Columbia
Plate
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Mt. Baker
Olympic
Mtns.
JUAN de
FUCA PLATE
Olympic
Mountains
and
Coast Range
Canada
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Cascadia Subduction Zone
Transform
Binder Foldout & CEETEP Poster
Beauty and the Beast
“The same geological processes that threaten our lives with earthquakes,
tsunamis, and volcanic eruptions also nourish our spirits by creating the
spectacular mountains, valleys, and coastlines of the Pacific Northwest.”
Mt. St. Helens National
Olympic National Park
Volcanic Monument
Plate Tectonics
The Earth’s interior is convecting.
Plates are driven by cooling of Earth.
Gravity provides the “ridge push” and
“trench pull” forces to move plates.
About a dozen plates; some plates have continents; some don’t.
Plates move a few centimeters per year (the rate of fingernail growth).
Volcanoes and earthquakes are concentrated at plate boundaries.
Lithosphere in Earth Context
oceanic crust
continental crust
Thickness of lithosphere (= tectonic plates) ~ 100 km.
Lithosphere is crust on top and mantle on bottom.
Oceanic crust is basalt, thickness = 7 km.
Continental crust is granite, average thickness = 40 km.
Granite is less dense than basalt.
Earth
- vs Egg
Earth –vs- Egg
Earth radius = 6370 km
Lithosphere thickness = 100 km
What % of Earth radius is lithosphere? ~1.6%
2%
Egg radius = 0.75 inch
Egg shell thickness = 0.015 inch
2%
What % of egg radius is shell?
How do these compare?
Lithosphere is to Earth as shell is to egg.
Mechanical Behaviors
Rock Tongs
Elastic: bends and recovers.
Brittle: elastic UP TO A LIMIT,
then BREAKS.
COLD rocks are brittle.
Ductile: permanent deformation.
WARM rocks are ductile.
Lithosphere (= Tectonic Plate)
Granite
Basalt
40 km
thick,
variable
7 km
thick
Lithosphere: outer ~100 km.
Contains crust + upper mantle.
Cold, rigid, and brittle; can fracture.
Asthenosphere: deeper, hotter mantle.
Can flow like silly putty.
A VISCOELASTIC SOLID. NOT LIQUID!!
“Oceanic
Crust”
“Continental
Crust”
“Earth’s Mantle”
Parks and Plates
©2005 Robert J. Lillie
Three Kinds of Plate Boundaries
Transform
Divergent
Convergent
Plate Boundaries of the Western US
Transform Plate Boundary
Strike-slip faulting
San Andreas Fault
North
American
Plate
Pacific
Plate
Strike-Slip Fault
Produced by shearing forces.
Transform
Plate
Boundaries
Transform Plate Boundaries
Earthquakes on Transform Boundaries
Strike-slip faulting with horizontal motion parallel to fault.
Shallow depths, almost never deeper than 20 km. Why?
Many small EQs (M<6). Some strong (M6) and major (M7) EQs.
Divergent Plate Boundaries
Spreading ocean ridges
Continental rift zones
Divergent Boundaries in Oceans
are Seafloor Spreading Centers
Example: Mid-Atlantic Ridge.
Divergent
Plate
Boundaries
Divergent Plate Boundaries
Normal Fault
Foam Faults
Produced by extensional forces.
Age of Juan de Fuca
and Gorda Plates
New oceanic plate
formed at the
spreading ridge. Plate
is young at the ridge
and gets older with
distance away from the
ridge.
Juan de Fuca Plate is
“only” 10 million years
old when it subducts.
Earthquakes on Divergent Boundaries
Normal faulting due to extension.
Shallow depths, rarely deeper than 10 km. Why?
Many small EQs (M<6). Some strong (M6) and major (M7) EQs.
World Map of Plates
Explore Spreading Ocean Ridges
and Transform Plate Boundaries
Convergent Plate Boundaries
Ocean - Ocean subduction zone, Marianas
Ocean – Continent subduction zone, Cascadia
Continent – Continent collision zone, Himalayas
Why does an oceanic plate subduct
beneath a continental plate?
Swimming Pool
“Earth’s Mantle”
Parks and Plates
©2005 Robert J. Lillie
“Oceanic
Crust”
“Continental
Crust”
“Earth’s Mantle”
Parks and Plates
©2005 Robert J. Lillie
Easy to
Subduct.
Parks and Plates
©2005 Robert J. Lillie
Hard to
Subduct!
Parks and Plates
©2005 Robert J. Lillie
Continental Crust is THICKER, and therefore
MORE BOUYANT than Oceanic Crust
Parks and Plates
©2005 Robert J. Lillie
Plate capped with thin Oceanic Crust subducts
beneath plate capped with thick Continental Crust
Parks and Plates
©2005 Robert J. Lillie
Convergent
Plate
Boundary
Entire region is the
“Cascadia Subduction Zone”
Cascadia Subduction Zone
Reverse (Thrust) Fault
Foam Faults
Produced by compressional forces.
Earthquakes on Convergent Boundaries
Thrust faulting due to compression.
EQs to 100 km depth on plate boundary megathrust AND
within the converging plates.
EQs to greater depths occur within subducting oceanic plate.
Wide range of magnitudes. Most M8 & M9 great EQs are
shallow megathrust events in subduction zones.
Cascadia Animation
World Map of Plates
Explore Convergent Plate Boundaries
Robert J. Lillie
Bernard Garcia
National
Parks in
two
mountain
ranges.
Parks and Plates
©2005 Robert J. Lillie
Terrane Accretion
A TERRANE consists of crust that is too thick
and buoyant to subduct. The continent grows
outward as terranes are added to the margin.
Olympic National Park
Coastal Ranges
Marine sedimentary
layers deposited on
the seafloor then
scraped off onto the
continental margin.
Olympic National Park
Pillow Basalt
Formation of Pillow Lava
Lava Erupts into Cold Ocean Water
Oceanic Crust
Video of Pillow Lava
Terrane Accretion
Beauty and the Beast
Plate Tectonics of the Pacific Northwest
bd
Su
NORTH
AMERICAN
Va
nc
ou
PLATE
ve
Mt. Garibaldi
Rid
ge
de
Fu
ca
e
dg
Ri
Cascade
Volcanoes
Mt.
Mazama
Basin
Offshore Earthquake
and
Range
a
rr
Province
y
le
da
va
Ne
ge
an
al
tV
ea
Gr
e
Si
R
st
oa
Lassen
Peak
Ca
Ne
lif
PACIFIC PLATE
JUAN de FUCA
PLATE
Crustal
Earthquake
Basin and
Range
Province
Volcanic
Earthquake
Magma
Rifting
Earthquake
Slab
Go
rd
a
tte
ame
Will lley
Va
Three
Sisters
Mt
McLoughlin
Mt.
Mountains Shasta
s
C
ea
dr
An lt
n au
Sa F
PLATE
NORTH AMERICAN
PLATE
Mt. Jefferson
Klamath
GORDA
PLATE
Juan de Fuca
Ridge
Plateau
Mt.
Hood
Cascade
Volcanoes
t
ge d
Pu un
So
Washington
Oregon
Mt. St. Helens
Willamette
Valley
Boundary
PACIFIC
Mt.
Rainier
Mt. Adams
Coast Range
n
Glacier Peak
Columbia
Plate
Jua
Mt. Baker
Olympic
Mtns.
JUAN de
FUCA PLATE
Olympic
Mountains
and
Coast Range
Canada
get
Pu und
So
g
tin
s.
Idaho
uc
rI
Cascadia Subduction Zone
or
va
Earthquake
Mid-Ocean Locked Zone
Ridge
Earthquake Ju Su
an bd
“THE BIG ONE”
de uct
i
n
ca g
Pla
Fu
Plate Sweats
Hot Water
te
ni
da
a
Plate
Boundaries:
Hotspot
Divergent
Convergent
Transform
Geology of Olympic Na0onal Park h"p://geomaps.wr.usgs.gov/parks/olym/index.html Robert J. Lillie
Yachats Forma=on Oceanic Basalt Lava Flows ~ 35 Million Years Old (Late Eocene -­‐ Oligocene) Heceta Head Lighthouse State Scenic Viewpoint, Oregon
Beauty and the Beast
Mt. St. Helens National Volcanic
Monument, Washington
Robert J. Lillie
U. S. Geological Survey
“The same geological processes that threaten our lives with
earthquakes, tsunamis, and volcanic eruptions also nourish our spirits
by creating the spectacular mountains, valleys, and coastlines of the
Pacific Northwest.”
Crater Lake National Park