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Chapter 12Tectonics, Earthquakes, and
Volcanism
Geosystems 6eAn Introduction to Physical Geography
Robert W. ChristophersonCharles E. Thomsen
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Tectonics, Earthquakes, and Volcanism
Earth’s Surface Relief Features Crustal Formation Processes Crustal Deformation Processes Orogenesis (Mountain Building) Earthquakes Earthquakes and the San Andreas Fault Volcanism
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Earth’s Surface Relief Features Relief – vertical elevation differences in the landscapeTopography – the characteristics of the Earth’s surfaceCrustal Orders of Relief
First Order – continental landmasses and ocean basinsSecond Order – mountain chains, plains, lowlands, mid-ocean ridges, oceanic trenches Third Order – individual mountains, cliffs, valleys, hills
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Earth’s Topographic Regions Plains
High tablelands
Hills and low table lands
Mountains
Widely spaced mountains
depressions
Earth’s Surface Relief Features
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Crustal Formation Processes Continental Shields - region where a craton is exposed at the surface
Craton – the heart of continental crust
Terranes – slowly migrating crustal pieces which have become part of a plate
Appalachian Mountains
Folding – convergent plate boundary where rocks are compressed and deformed
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Continental Shields
Figure 12.4
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Crustal Formation
Figure 12.5
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FaultsRocks on either side of a fracture in Earth’s crust displace relative to the other side in a process known as faulting.
Earthquakes occur at the moment of fracture and represent a sharp release of energy
The basic types of faults: normal fault, reverse (thrust) fault, and strike-slip fault
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Normal Fault
Figure 12.11
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Reverse Fault
Figure 12.11
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Strike-slip Fault
Figure 12.11
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Figure 12.12
San Andreas Fault
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Orogenesis:Oceanic-continental
Collision
Figure 12.16
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Oceanic-oceanic Collision
Figure 12.16
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Continental-continental Collision
Figure 12.16
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The Appalachian Mountains
Figure 12.18
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EarthquakesForecasting earthquakes
Land uplift and tiltingtiltmeter
Increasing minor tremorsChanges in magnetic fieldPreviously undetected faults Radon monitoringCarbon dioxideForeshocks – tremor preceding the main shock
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EarthquakesFocus – subsurface area along a fault plane where the motion of seismic waves is initiated
Epicenter – area at surface directly above the focus
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Anatomy of an Earthquake
Figure 12.20
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VolcanismVolcano – form at the end of a central vent or pipe that rises from the astenosphere and upper mantle through the crust into a volcanic mountain
Geothermal energy – boiled groundwaterLava – molten rockPyroclastics – pulverized rock and clastic materials ejected during an eruption
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Where to find volcanoesSubduction zones, Sea-floor spreading, and Hot spots
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VolcanoesEffusive eruption – gentler eruptions that produce enormous volumes of lava
Hawaii and Iceland
Shield volcanoes
Explosive eruptions – volcanic activity inland from subduction zones
Composite (strato) volcanoes
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Composite Volcanoes
Figure 12.35
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Shield and Composite Volcanoes
Figure 12.32
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White’s Isle, New Zealand
Figure 12.31
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CalderasLarge depression formed when a volcanic mountain collapses after eruptingLong Valley Caldera, CaliforniaCarbon dioxide
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End of Chapter 12
Geosystems 6eAn Introduction to Physical Geography
Robert W. ChristophersonCharles E. Thomsen