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Physical Geography
by Alan Arbogast
Chapter 13
Tectonic Processes
and Landforms
Lawrence McGlinn
Department of Geography
State University of New York - New Paltz
© 2007, John Wiley and Sons, Inc.
Tectonic Processes and
Landforms
• Plate Tectonics
• Types of Plate Movement
• Plate Convergence
• Earthquakes
• Volcanoes
© 2007, John Wiley and Sons, Inc.
Plate Tectonics
• Theory that Earth’s crust consists of plates that
move individually & collectively
• Helps explain location of mtn ranges, earthquakes, volcanoes & other landforms
• First theorized by Wegener in early 1900s
• Pangaea – supercontinent that existed 300 my
ago – continents spread by Continental Drift
• Theory ignored through 1950s – validated in
more recent research
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Fossil Evidence for Pangaea
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Continental Drift Since Pangaea
Continental Drift
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Mechanisms of Continental Drift
Convection within Earth
Magma Plume pushes plates
apart
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Seafloor Age
Red youngest through green & yellow to blue, oldest
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Current Locations &
Movement of Plates
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Types of Plate Movements
• Passive Plate Margins
• Transform Plate Margins
• Plate Divergence
• Plate Convergence
• Collision
• Subduction
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Passive Plate Margins
Where continental crust and bordering oceanic crust are on
the same tectonic plate – tectonically stable
Example of East Coast
of US on North
American Plate
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Transform Plate Margins
Boundaries where plates slide past each other horizontally
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Plate Divergence
• Lithospheric plates moving away from each other
• Magma plumes move up & out through plate
fractures, plates spread in process called Rifting
• As plates spread, Mid-Oceanic Ridge forms from
rifting
Active and Passive Margins
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Rifting in East Africa
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Plate Convergence
• Collision – two plates of continental crust meet
• Crust crumples causing folding of horizontal
bedrock layers
• Monocline – 1-sided slope rock beds inclined in
one direction over large area
• Anticline – upward arc of folded rock
• Syncline – downward dip in folded rock
• Overthrust fault – intense compression shoves
one part of rock mass over the other
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Collision and Folding
Folding
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Ridge and Valley Evolution
The Folded
Appalachians
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Subduction
Process in which one converging plate is forced beneath another,
usu. oceanic plate under continental
Plate Boundary Relationships
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Earthquakes
• Sudden release of tectonic stress creates
movement in Earth’s crust & shockwaves
through lithosphere
• Fault – fracture between adjoining plates along
which plates can move
• Focus – point in lithosphere where fault breaks
• Epicenter – point on surface directly above focus
© 2007, John Wiley and Sons, Inc.
Earthquake Processes
© 2007, John Wiley and Sons, Inc.
Earthquake Energy
• Waves released by an earthquake:
• P-waves – primary, compressional waves
that travel 1.5-8 km/sec
• S-waves – secondary, vertical waves that
travel 60-70% slower than P waves
• Difference in arrival time of p-waves and swaves, helps estimate distance to epicenter
• Known distance to 3 stations yields location
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Triangulation to Locate ‘Quake
Known distance to stations A, B and C shows location of epicenter
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Seismograph
• Records vertical & horizontal motion of Earth,
& magnitude of motion
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Measuring Earthquakes
• Richter Scale – logarithmic measure where
each whole number represents 10X the
shaking of the next smaller number
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Faulting
• Earthquakes occur along faults – cracks in
Earth’s crust where rocks or plates are displaced
• Fault Types:
• Normal – vertical fault, diverging force
• Reverse – vertical fault, compressional force
• Strike-Slip – horizontal fault, blocks slide past
one another – larger scale called Transform
• Overthrust – upthrown block slides over
downthrown block
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Fault Types
Earthquake
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San Andreas Fault
(Transform Fault)
Movement
Movement
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Basin and Range Province
From Satellite
Horst & Graben Formation
In Landscape
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Volcanoes
• Mts or hills w/ a conduit down into upper mantle
through which magma, ash & gases are ejected
• 3 basic types:
• Cinder-cone Volcanoes
• Composite Volcanoes
• Shield Volcanoes
Volcanoes
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Cinder-Cone Volcanoes
• Small, steep-sided volcano made of magma
fragments & rock debris from central vent
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Composite Volcanoes
• Large, steep-sided volcano built up by layers of
lava & rock debris – over subduction zones –
viscous (low flow), silicate (high gas-explosive
think of shaking coca-cola can) magma explosive eruptions
Cross
Section
Mt. Fuji
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Pacific “Ring of Fire”
• Concentration of composite volcanoes around the
Pacific Basin over subduction zones
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Shield Volcanoes
• Broad, gentle-sided volcanoes formed from lowsilica, low-viscosity (high flow) magma – lava
flows cool & harden to become basalt
Cross Section
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Mauna Loa, Hawaii
Hot Spots
• Stationary points in aesthenosphere from which
a magma plume intermittently pushes through
the crust above
• Plates move over hot spots, carrying deposits of
basalt with them
• Hawaii (& the Emperor Seamount Chain) &
Yellowstone have been shaped by hotspots
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Formation of Hawaii
Emperor Seamount Chain
70 M yrs old – Pac. Plate
1st moved North, then NW
Hawaii
Kauai Oldest – Big Island
(Hawaii) still over hot spot
70 mya
Present
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Yellowstone Hot Spot
North American Plate has moved west,
then northwest over past 16.5 M yrs
Calderas from eruptions
in past 2 M yrs
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Geyser Cross Section
Old Faithful
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