Chapter 12Tectonics, Earthquakes, and

Volcanism

Geosystems 6eAn Introduction to Physical Geography

Robert W. ChristophersonCharles E. Thomsen

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  

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

 

Earth’s Topographic Regions Plains

High tablelands

Hills and low table lands

Mountains

Widely spaced mountains

depressions

Earth’s Surface Relief Features 

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

Continental Shields

Figure 12.4

Crustal Formation

Figure 12.5

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

Normal Fault

Figure 12.11

Reverse Fault

Figure 12.11

Strike-slip Fault

Figure 12.11

Figure 12.12

San Andreas Fault

Orogenesis:Oceanic-continental

Collision

Figure 12.16

Oceanic-oceanic Collision

Figure 12.16

Continental-continental Collision

Figure 12.16

The Appalachian Mountains

Figure 12.18

EarthquakesForecasting earthquakes

Land uplift and tiltingtiltmeter

Increasing minor tremorsChanges in magnetic fieldPreviously undetected faults Radon monitoringCarbon dioxideForeshocks – tremor preceding the main shock

EarthquakesFocus – subsurface area along a fault plane where the motion of seismic waves is initiated

Epicenter – area at surface directly above the focus

Anatomy of an Earthquake

Figure 12.20

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

Where to find volcanoesSubduction zones, Sea-floor spreading, and Hot spots

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

Composite Volcanoes

Figure 12.35

Shield and Composite Volcanoes

Figure 12.32

White’s Isle, New Zealand

Figure 12.31

CalderasLarge depression formed when a volcanic mountain collapses after eruptingLong Valley Caldera, CaliforniaCarbon dioxide

End of Chapter 12

Geosystems 6eAn Introduction to Physical Geography

Robert W. ChristophersonCharles E. Thomsen