Plate Tectonics of the Pacific Northwest · Plate Tectonics The Earth’s interior is convecting....
Transcript of Plate Tectonics of the Pacific Northwest · Plate Tectonics The Earth’s interior is convecting....
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Beauty and the Beast
NORTH AMERICANPLATE
CascadeVolcanoes
OlympicMountains
andCoast Range
Juan de FucaRidge
JUAN de FUCAPLATE
PACIFIC PLATE
Mid-OceanRidge
Plate SweatsHot Water
Magma
Locked ZoneEarthquake
“THE BIG ONE”
Coa
st Ra
nge
Willa
mette
Valley
Range
Basin
Province
and
San A
ndreas
Fault
Mt. Garibaldi
Glacier Peak
Mt.Rainier
Mt. Adams
Mt. St. Helens
Mt.Hood
Mt. Jefferson
ThreeSisters
Mt.Shasta
LassenPeak
Plateau
Columbia
MtMcLoughlin
Pla
teB
oundary
Sierra Nevada
Great Valley
Coast Range
CanadaCanada
Washington
OregonId
ah
oId
ah
o
NevadaCalifornia
PACIFIC
PLATE
NORTHAMERICAN
PLATE
CascadeVolcanoes
JUAN deFUCA PLATE
Mt. Baker
Puget
Sou
nd
Juan de
Fuca
Rid
ge
Subducting
OlympicMtns.
Mt.Mazama
Klamath
MountainsGORDAPLATE
Gor
da R
idge
PlateBoundaries:
Divergent Convergent Transform
Vancouver Is.
SlabEarthquake
CrustalEarthquake Rifting
Earthquake
VolcanicEarthquake
Offshore Earthquake
Plate Tectonics of the Pacific Northwest
Hotspot
Willa
mette
Valley
Puget
Sound
Subducting
Juan de Fuca Plate
Basin andRange
Province
Cascadia Subduction Zone
Binder Foldout & CEETEP Poster
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Mt. St. Helens National Volcanic Monument
“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.”
Beauty and the Beast
Olympic National Park
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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.
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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.
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Lithosphere in Earth Context
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.
oceanic crust continental crust
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Earth - vs - Egg
Earth radius = 6370 km Lithosphere thickness = 100 km What % of Earth radius is lithosphere? Egg radius = 0.75 inch Egg shell thickness = 0.015 inch What % of egg radius is shell? How do these compare?
1.6%
2%
~ 2%
Lithosphere is to Earth as shell is to egg.
Earth –vs- Egg
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Mechanical Behaviors
Elastic: bends and recovers. Brittle: elastic UP TO A LIMIT,
then BREAKS. COLD rocks are brittle.
Ductile: permanent deformation.
WARM rocks are ductile.
Rock Tongs
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Lithosphere (= Tectonic Plate)
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!!
Basalt 7 km thick
Granite 40 km thick, variable
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“Oceanic Crust”
“Continental Crust”
“Earth’s Mantle”
Parks and Plates ©2005 Robert J. Lillie
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Three Kinds of Plate Boundaries Transform Divergent Convergent
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Plate Boundaries of the Western US
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Transform Plate Boundary
Strike-slip faulting
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San Andreas Fault
Pacific Plate
North American Plate
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Strike-Slip Fault
Produced by shearing forces.
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Transform Plate
Boundaries
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Transform Plate Boundaries
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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.
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Divergent Plate Boundaries
Spreading ocean ridges Continental rift zones
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Divergent Boundaries in Oceans are Seafloor Spreading Centers
Example: Mid-Atlantic Ridge.
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Divergent Plate
Boundaries
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Divergent Plate Boundaries
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Normal Fault Foam Faults
Produced by extensional forces.
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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.
Age of Juan de Fuca and Gorda Plates
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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.
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World Map of Plates Explore Spreading Ocean Ridges and Transform Plate Boundaries
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Ocean - Ocean subduction zone, Marianas Ocean – Continent subduction zone, Cascadia Continent – Continent collision zone, Himalayas
Convergent Plate Boundaries
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“Earth’s Mantle”
Why does an oceanic plate subduct beneath a continental plate?
Parks and Plates ©2005 Robert J. Lillie
Swimming Pool
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“Oceanic Crust”
“Continental Crust”
“Earth’s Mantle”
Parks and Plates ©2005 Robert J. Lillie
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Easy to Subduct. Parks and Plates
©2005 Robert J. Lillie
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Hard to Subduct!
Parks and Plates ©2005 Robert J. Lillie
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Continental Crust is THICKER, and therefore MORE BOUYANT than Oceanic Crust
Parks and Plates ©2005 Robert J. Lillie
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Plate capped with thin Oceanic Crust subducts beneath plate capped with thick Continental Crust
Parks and Plates ©2005 Robert J. Lillie
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Entire region is the “Cascadia Subduction Zone”
Convergent Plate
Boundary
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Cascadia Subduction Zone
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Reverse (Thrust) Fault Foam Faults
Produced by compressional forces.
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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.
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Cascadia Animation
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World Map of Plates
Explore Convergent Plate Boundaries
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Robe
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Parks and Plates ©2005 Robert J. Lillie
National Parks in
two mountain ranges.
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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.
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Olympic National Park
Coastal Ranges
Marine sedimentary layers deposited on the seafloor then
scraped off onto the continental margin.
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Pillow Basalt
Olympic National Park
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Oceanic Crust
Lava Erupts into Cold Ocean Water
Formation of Pillow Lava
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Video of Pillow Lava
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Terrane Accretion
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Beauty and the Beast
NORTH AMERICANPLATE
CascadeVolcanoes
OlympicMountains
andCoast Range
Juan de FucaRidge
JUAN de FUCAPLATE
PACIFIC PLATE
Mid-OceanRidge
Plate SweatsHot Water
Magma
Locked ZoneEarthquake
“THE BIG ONE”
Coa
st Ra
nge
Willa
mette
Valley
Range
Basin
Province
and
San A
ndreas
Fault
Mt. Garibaldi
Glacier Peak
Mt.Rainier
Mt. Adams
Mt. St. Helens
Mt.Hood
Mt. Jefferson
ThreeSisters
Mt.Shasta
LassenPeak
Plateau
Columbia
MtMcLoughlin
Pla
teB
oundary
Sierra Nevada
Great Valley
Coast Range
CanadaCanada
Washington
Oregon
Ida
ho
Ida
ho
NevadaCalifornia
PACIFIC
PLATE
NORTHAMERICAN
PLATE
CascadeVolcanoes
JUAN deFUCA PLATE
Mt. Baker
Puget
Sou
nd
Juan de
Fuca
Rid
ge
Subducting
OlympicMtns.
Mt.Mazama
Klamath
MountainsGORDAPLATE
Gor
da R
idge
PlateBoundaries:
Divergent Convergent Transform
Vancouver Is.
SlabEarthquake
CrustalEarthquake Rifting
Earthquake
VolcanicEarthquake
Offshore Earthquake
Plate Tectonics of the Pacific Northwest
Hotspot
Willa
mette
Valley
Puget
Sound
Subducting
Juan de Fuca Plate
Basin andRange
Province
Cascadia Subduction Zone
Geology of Olympic Na0onal Park h"p://geomaps.wr.usgs.gov/parks/olym/index.html
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Robe
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Heceta Head Lighthouse State Scenic Viewpoint, Oregon
Yachats Forma=on Oceanic Basalt Lava Flows
~ 35 Million Years Old (Late Eocene -‐ Oligocene)
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Rob
ert J
. Lill
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U. S
. Geo
logi
cal S
urve
y
Mt. St. Helens National Volcanic Monument, Washington
Crater Lake National Park
“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.”
Beauty and the Beast