Ch14

Chapter 14: The Internal Processes

McKnight’s Physical Geography: A Landscape Appreciation,

Tenth Edition, Hess

The Internal Processes

• The Impact of Internal Processes on the Landscape

• From Rigid Earth to Plate Tectonics• Plate Tectonics• Volcanism• Diatrophism• Folding• Faulting• The Complexities of Crustal Configuration

2© 2011 Pearson Education, Inc.

The Impact of Internal Processes on the Landscape

• Internal processes build terrain• Reshape the crustal surface of Earth• Have been taking place for billions of years• Typically the effects do not act independently• Earthquakes and volcanoes


From Rigid Earth to Plate Tectonics

• Continents seem fixed from human perspective

• Until midtwentieth century, scientists believed Earth’s continents were rigid

• Continental drift—Pangaea• Evidence includes similar

geologic features on coasts of different continents

• Continents fit together


Figure 14-1

From Rigid Earth to Plate Tectonics

• Paleontology supports continental drift

• Glaciated continents reconstructed made sense

• Rejected by most scientists at the time (1920s), but accepted today


Figure 14-5

Plate Tectonics

• The evidence– Plate boundaries

• Earthquakes occur along lines

• Correspond with locations of trenches and ridges in the seafloor


Figure 14-7

Plate Tectonics

– Seafloor spreading• Midocean ridges formed

by magma rising up from the mantle

• New basaltic ocean floor created, moves away from ridge

• At trenches, older lithosphere descends into the asthenosphere where it is recycled—subduction


Figure 14-8

Plate Tectonics

– Paleomagnetism• Iron in cooled magma

orients itself with the magnetic poles of Earth

• Provides a record of past magnetic fields

• Magnetic field has changed orientation at least 170 times

• Should be symmetry in magnetic orientation

• Used to verify age of ocean floor rock and seafloor spreading


Figure 14-10

Plate Tectonics

• Plate tectonics– Theory behind motion of

lithospheric plates– Plates float on

asthenosphere– 7 major plates,

7 intermediate plates, 12 smaller plates

– Smaller plates are large plates that are being subducted


Figure 14-11

Plate Tectonics

• Driving plate tectonics– Slow convection in

Earth’s mantle– Convection can push

plates away from each other

– Most motion results from plates pulled by subduction of dense oceanic lithosphere

– Ongoing area of research


Figure 14-11

Plate Tectonics

• Plate boundaries– Divergent boundaries

• Plates move away from each other

• Asthenosphere wells up in the plate opening

• Represented by a midocean ridge

• Associated with shallow-focus earthquakes and volcanic activity

• Constructive• Continental rift valley, proto-

ocean


Figure 14-13

Plate Tectonics

• Convergent boundaries– Collisions between plates– Destructive– Three primary collisions:

• Oceanic-continental—oceanic plate sinks since more dense; subduction

– Forms oceanic trench and continental mountains (i.e., Cascades, Andes)

– Earthquakes occur along margin– Volcano formation along the plates—continental volcanic arc– Forms metamorphic rocks—blueschist (above)


Plate Tectonics

– Three primary collisions (cont.)• Oceanic-oceanic

– Subduction results in undersea trench formation

– Deep and shallow earthquakes– Island volcanic arc

• Continental-continental– No subduction since two plates

are highly buoyant– Builds huge mountain ranges– Volcanoes are rare– Shallow earthquakes are

relatively common

13© 2011 Pearson Education, Inc. Figure 14-15

Plate Tectonics

• Transform boundaries– Two boundaries slip

past each other laterally– Transform faults– Neither creates nor

destroys crust– Commonly produce

shallow focus earthquakes

– San Andreas fault


Figure 14-18

Plate Tectonics

• The rearrangement– 450 million years ago,

one supercontinent existed

– Broke up 200 million years ago

• Laurasia• Gondwanaland

– Arrangement to the current continental configuration


Figure 14-19

Plate Tectonics

• The Pacific Ring of Fire– Plate boundaries exist

all around the Pacific Rim

– Primarily subduction zones

– 75% of all volcanoes lie in the Ring of Fire


Figure 14-20

Plate Tectonics

• Additions to basic plate tectonic theory– Mantle plumes

• localized hot areas not associated with plate boundaries

• Move with the plate, so eventually become inactive

• Hot spot trail• Hawaiian islands


Figure 14-22

Plate Tectonics

– Accreted Terranes– Piece of lithosphere

carried by a plate that eventually collides and fuses (accretes) with another plate


Figure 14-24

Plate Tectonics

• The questions– Midcontinental mountain range formation (i.e., the

Appalachians)– Number of plates and plate sizes have changed over

Earth’s history– Why are there earthquakes in the middle of continental

plates?– Why are plates different sizes?– Why do plates form where they do?


Volcanism

• Definition—all phenomena connected to the origin and movement of molten rock

• Extrusive volcanism—occurs on Earth’s surface, often shortened to volcanism

• Intrusive volcanism—occurs below surface, plutonic activity


Figure 14-26

Volcanism

• Volcanism– Magma versus lava– Violent or gentle eruptions– Pyroclastic material– Some self destruct (i.e.,

Krakatau in 1883)


Figure 14-26

Volcanism

• Global volcano distribution

22© 2011 Pearson Education, Inc.Figure 14-27

Volcanism

• Magma chemistry and styles of eruption– Nature of eruption determined by magma chemistry,

also by confining pressure– Quantity of silica in magma is critical

• High silica magma—felsic magma—granite• Intermediate silica—andesitic magma—diorite• Low silica—mafic magma—basalt

– High silica eruptions—pyroclastic– Low silica eruptions—quiet, nonexplosive– Intermediate—some combination of the two


Volcanism

• Volcanic activity– Relatively temporary

features on the landscape– Much of Earth’s water

originated from water vapor from volcanic eruptions

– Magma contains major elements required for plant growth

– Provides soil fertility


Figure 14-29

Volcanism

• Lava flows– Lava generally flows horizontally,

parallel to the surface along which it flows

– Eventually cools in horizontal orientation, strata

– Streams flowing through lava flows result in irregular or fragmented surface

– Uniform cooling results in hexagonal structure


Figure 14-30

Volcanism

• Flood basalt– Most extensive lava flows

come from hot spots– Flood basalt is a vast

accumulation of lava build up

– Correlated with mass extinctions


Figure 14-31

Volcanism

• Volcanic peaks– Shield volcanoes

• Layer upon layer of solidified lava flows

• Little pyroclastic material• Hawaiian islands are an

example


Figure 14-32

Volcanism

• Volcanic peaks (cont.)– Composite Volcano

• Emit higher silica lavas (andesite lava)

• Form symmetric, steep sided volcanoes

• Pyroclastics from explosive lava flows alternate with nonexplosive flows

• Pyroclastic flows produce steep slopes, lava holds it together


Figure 14-34

Volcanism

• Volcanic peaks (cont.)– Lava domes

• Masses of very viscous lava that do not flow far

• Lava bulges from the vent, dome grows by expansion from below and lava within

• Some lava domes form inside of composite volcanoes


Figure 14-36

Volcanism

• Volcanic peaks (cont.)– Cinder cones

• Smallest volcanic mountains

• Basaltic magma is common

• Slopes form from pyroclastic materials

• Generally found in association with other volcanoes


Figure 14-38

Volcanism

• Volcanic peaks (cont.)– Calderas

• Result from a volcano that explodes, collapses, or both

• Immense, basin-shaped depression; larger than original crater

• Crater Lake in Oregon is an example

– Volcanic necks• Pipe or throat of an old

volcano that filled with solid lava


Figure 14-40

Volcanism

• Volcanic hazards– Volcanic gases—mainly

water vapor, but can cause acid rain and alter global climate

– Lava flows—cause immense property damage

– Eruption clouds—gas and ash material clouds that extend up to 16 km into the atmosphere, drop large rock fragments called “bombs”


Figure 14-45

Volcanism

• Volcanic hazards (cont.)– Pyroclastic flows—

avalanche of hot gases and material, up to 100 mph

– Volcanic mud flows (lahars)—result from heavy rain and/or snow melt during an eruption


Figure 14-44

Volcanism

• Monitoring volcanic hazards– Research to locate previous pyroclastic flows and lahars– Tiltmeters, measure the slope of a volcano to look for swelling– Monitor earthquake activity


Volcanism

• Igneous features– Igneous intrusion—rock

formed beneath the Earth’s surface penetrates the crust— pluton

– Stoping– Scheme for classifying

igneous intrusions


Figure 14-48

Volcanism

• Igneous features (cont.)– Batholiths—large, subterranean

body of indefinite depth; important in mountain building

– Stocks—similar to a batholith but much smaller

– Laccoliths—slow-moving, viscous magma forced between horizontal layers of rock; builds up a mushroom shaped mass


Figure 14-49

Volcanism

• Igneous features (cont.)– Dikes—vertical sheet of

magma thrust upward into preexisting rock; long and narrow

– Sills—long, thin body whose orientation is determined by preexisting rocks

– Veins—molten material forces itself into smaller fractures in preexisting rock, takes irregular shapes


Figure 14-50

Diatrophism

• Refers to the deformation of Earth’s crust

• Two primary types of diatrophism, folding and faulting


Figure 14-53

Folding

• Results when rock is subjected to lateral compression

• Can take place on any scale• Can vary in complexity• Two types

– Anticline/upfold, can be forced to have reverse orientation, an overturned fold

– Syncline/downfold— overthrust fold


Figure 14-51

Faulting

• Occurs when rock breaks accompanied by displacement

• Occurs along zones of weakness in the crust, fault zones

• Fault lines• Begin as sudden ruptures, but

can result in large (hundreds of km) faults over millions of year

• Fault scarps


Figure 14-54

Faulting

• Four primary fault types


Figure 14-55

Faulting

• Fault-produced landforms– Tilted fault-block

mountains; one side of the fault block is tilted steeply relative to the other

– Horst: uplift of a land block between two parallel faults

– Graben: downthrown land block between two parallel faults


Figure 14-59

Figure 14-57

Faulting

• Strike-slip faulting landforms– Linear fault trough

• Small depressions in the trough known as sags

• Sag ponds• Offset drainage channels• Shutter ridge


Figure 14-60

Faulting

• Earthquakes– Vibration in Earth resulting from sudden displacement

along a fault• Earthquake waves

– Energy released by earthquakes moves in several types of seismic waves that originate at the center of fault motion, the origin

– Ground above origin experiences strongest jolt, the epicenter

– P-waves versus S-waves


Faulting

• Earthquake magnitude—relative amount of energy released during an earthquake– Logarithmic scale, 32nd power– Richter scale– Strongest recorded

earthquake—9.5 in Chile• Shaking intensity

– Intensity of ground shaking not consistent during an earthquake

– Mercalli intensity scale


Faulting

• Earthquake hazards– Most damage from ground

shaking– Liquefaction of moist

sediments– Landslides– Water movements in lakes

and oceans (i.e., tsunamis)


Tsunami damage in Kodiak, AKImage courtesy of NOAA

The Complexities of Crustal Configuration

• All these processes are interrelated• An example: Glacier National Park

– Was below sea level for millions of years– Vast amounts of sedimentary rock– Igneous activity added variety to the sedimentary rock– Igneous intrusions created a sill and numerous dikes– Tremendous mountain building and associated uplift

combined with lateral pressure from the west resulted in a vast rupture and faulting

– Whole block moved by Lewis Overthrust– Had Precambrian sedimentary rock over Cretaceous strata


The Complexities of Crustal Configuration

• Mountains without roots, Chief Mountain


Figure 14-64

Summary

• Internal processes build terrain and modify terrain• Plate tectonics describe the motion of lithospheric plates• There is widespread evidence of plate tectonics• There are three primary types of collisions that occur within

lithospheric plates• The continents have rearranged themselves from a single

supercontinent, Pangaea, to the arrangement today• Volcanism describes the motions of molten rock• The chemistry of magma changes the type of eruption that

takes place


Summary

• There are four primary types of volcanic mountains• Numerous volcanic hazards are a great threat to life and

property• In addition to volcanoes, numerous intrusive processes

modify the landscape• Diatrophism refers to the modification of Earth’s crust• Folding is the bending of rock over long time scales due

to continuous external pressure• Faulting is a weakness in the crust


Summary

• There are four primary types of faults• Different landforms result from each of these four types

of faults• Earthquakes result from a sudden displacement along a

fault• There are numerous hazards associated with

earthquakes• While the processes were considered individually, they

are all interrelated


Ch14

Technology

Transcript of Ch14