GEO 101: PHYSICAL GEOGRAPHY
Chapter 12: Tectonics, Earthquakes,
and Volcanism
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Earth’s Topographic Regions
Crustal Formation Processes
Crustal Deformation Processes
Orogenesis (Mountain Building)
Earthquakes
Volcanism
Earth’s Topographic Regions
Figure 12.3
Earth’s Hypsometry
Figure 12.2
Crustal Formation Processes
All continents have a nucleus of ancient crystalline
rock on which the continents “grows” with the addition
of crustal fragments and sediments
Such nucleus is called Cratons
Cratons are commonly stable, and are formed
more than 2 billion years ago
Crustal Formation Processes
Continental Shields: are regions where cratons
are exposed at the surface
Continental Crust and Terranes: are added to
the Cratons through tectonic cycles
Terrane Formation
Crustal Deformation
Processes
When the lithospheric plates or crustal blocks
move relative to each other, they form
different types of structures such as:
• Folding and Broad Warping (bending of the
crusts)
• Faulting (Breaking, causes offset)
Crustal Deformation
Processes
Stress: forces/ unit area (caused by tectonic forces,
gravities, and the weight of the overlying rocks)
(Three type of stress: tension, compression, and shear)
Strain: The response of rocks to stress
(faulting and folding)
Stress and Strain
Figure 12.7
Folding
Figure 12.8
Three types of faults
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•
•
Normal fault (tension): Hanging wall move downwards relative to footwall
Reverse fault (compression): Hanging wall move upwards relative to
footwall
Strike-slip fault (lateral shearing): Blocks move along the fault plane
horizontally
Normal Fault
Figure 12.11
Reverse Fault
Figure 12.11
Strike-slip Fault
Figure 12.11
San Andreas
Fault
Figure 12.12
Faulted Landscapes
Figure 12.14
Orogenesis (Mountain Building)
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Three Types of Orogenies:
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Oceanic-continental plate collision
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Andes, Rocky mountains
Oceanic-continental
Collision
Figure 12.16
Orogenesis (Mountain Building)
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Three Types of Orogenies:
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Oceanic-oceanic plate collision
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Western pacific such as Japan and Indonesia, the
Philippines
Oceanic-oceanic
Collision
Figure 12.16
Orogenesis (Mountain Building)
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Three Types of Orogenies:
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Continental- continental collision
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Himalayas
The Appalachian Mountains
Continental-continental
Collision
Figure 12.16
Convergent Margins: India-Asia Collision
Orogenesis (Mountain Building)
The other type of mountain building:
uplifting of Fault-blocks by magmas or by isostatic
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rebound: Grand Tetons and the Sierra Nevada
Teton Range in Wyoming
Figure 12.17
Earthquakes
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Expected Quakes and Those of Deadly
Surprise:
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plate boundaries
Focus, Epicenter, Foreshock, and
Aftershock
z Focus: The place where the motion of
seismic waves is initiated (the point where
the slip occurs) Æ normally in subsurface
Anatomy of an Earthquake
Figure 12.20
Earthquakes
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Epicenter: The area at the surface directly
above the focus
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Smaller shocks: before the main earthquake
Earthquake Forecast?
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Aftershock: Smaller shocks after the main
earthquake
Æ Important for the rescuing arrangement
Buildup and Release of Stress
Earthquake is recorded
by an instrument called:
seismograph, and
Measurement is charted
on: Richter scale
Earthquake magnitude:
Figure 12.21
>8
7-7.9
6-6.9
Seismographs
Volcanism
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Location and Types of Volcanic Activity
Effusive Eruptions: Gentle eruptions. Magma contains less gases and is rich in iron
and magnesium, thus has low viscosity. Example-- Hawai’i
Explosive Eruptions: Violent eruptions. Magma contain more gases and silica and
has a high viscosity Æ block the conduitsÆ causing high pressure buildup.
Examples: along subduction zones.
Explosive eruptions
Effusive eruptions
Figure 12.25
Chapter 12: Review
Tectonics, Earthquakes,and Volcanism
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Earth’s Topographic Regions
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Plains
High tablelands (Colorado plateau)
Hill and low tablelands
Mountains
Widely spaced mountains
Depressions
See figure 12.3
Chapter 12: Review
Tectonics, Earthquakes,and Volcanism
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Crustal Formation Processes
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All continents have a nucleus (Cratons ) of ancient
crystalline rock
Continental Crust and Terranes are added to the
Cratons through tectonic cycles
Continental Shields: are regions where cratons are
exposed at the surface
Chapter 12: Review
Tectonics, Earthquakes,and Volcanism
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Crustal Deformation Processes
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Crustal blocks are stressed by tectonic forces,
gravity, and overlying rocks
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Stress ( Tension, Compression, Shear)
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Bending (folding)
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Breaking of the curst (Faults)
Chapter 12: Review
Tectonics, Earthquakes,and Volcanism
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Results
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Bending (Folding)
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Breaking of the curst (Faults)
Three types of faults
•
Normal fault (tension): Hanging wall move downwards
relative to footwall
Figure 12.11
Reverse Fault
• Reverse fault (compression): Hanging wall move upwards
relative to footwall
Figure 12.11
Strike-slip Fault
• Strike-slip fault (lateral shearing): Blocks move along the fault
plane horizontally
Figure 12.11
Anatomy of an Earthquake
Figure 12.20
Volcanism
Figure 12.25