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  1. 1. Chapter 14: The InternalProcessesMcKnight’s Physical Geography:A Landscape Appreciation,Tenth Edition, Hess
  2. 2. The Internal Processes• The Impact of Internal Processes on theLandscape• From Rigid Earth to Plate Tectonics• Plate Tectonics• Volcanism• Diatrophism• Folding• Faulting• The Complexities of Crustal Configuration2© 2011 Pearson Education, Inc.
  3. 3. The Impact of Internal Processeson 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 volcanoes3© 2011 Pearson Education, Inc.
  4. 4. From Rigid Earth to PlateTectonics• Continents seem fixed fromhuman perspective• Until midtwentieth century,scientists believed Earth’scontinents were rigid• Continental drift—Pangaea• Evidence includes similargeologic features on coasts ofdifferent continents• Continents fit together4© 2011 Pearson Education, Inc.Figure 14-1
  5. 5. From Rigid Earth to PlateTectonics• Paleontology supportscontinental drift• Glaciated continentsreconstructed made sense• Rejected by most scientistsat the time (1920s), butaccepted today5© 2011 Pearson Education, Inc.Figure 14-5
  6. 6. Plate Tectonics• The evidence– Plate boundaries• Earthquakes occuralong lines• Correspond withlocations of trenchesand ridges in theseafloor6© 2011 Pearson Education, Inc.Figure 14-7
  7. 7. Plate Tectonics– Seafloor spreading• Midocean ridges formedby magma rising up fromthe mantle• New basaltic ocean floorcreated, moves away fromridge• At trenches, olderlithosphere descends intothe asthenosphere whereit is recycled—subduction7© 2011 Pearson Education, Inc.Figure 14-8
  8. 8. Plate Tectonics– Paleomagnetism• Iron in cooled magmaorients itself with themagnetic poles of Earth• Provides a record of pastmagnetic fields• Magnetic field haschanged orientation atleast 170 times• Should be symmetry inmagnetic orientation• Used to verify age ofocean floor rock andseafloor spreading8© 2011 Pearson Education, Inc.Figure 14-10
  9. 9. Plate Tectonics• Plate tectonics– Theory behind motion oflithospheric plates– Plates float onasthenosphere– 7 major plates,7 intermediate plates,12 smaller plates– Smaller plates are largeplates that are beingsubducted9© 2011 Pearson Education, Inc.Figure 14-11
  10. 10. Plate Tectonics• Driving plate tectonics– Slow convection inEarth’s mantle– Convection can pushplates away from eachother– Most motion results fromplates pulled bysubduction of denseoceanic lithosphere– Ongoing area ofresearch10© 2011 Pearson Education, Inc.Figure 14-11
  11. 11. Plate Tectonics• Plate boundaries– Divergent boundaries• Plates move away fromeach other• Asthenosphere wells up inthe plate opening• Represented by amidocean ridge• Associated with shallow-focus earthquakes andvolcanic activity• Constructive• Continental rift valley, proto-ocean11© 2011 Pearson Education, Inc.Figure 14-13
  12. 12. Plate Tectonics• Convergent boundaries– Collisions between plates– Destructive– Three primary collisions:• Oceanic-continental—oceanic plate sinks since moredense; 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)12© 2011 Pearson Education, Inc.
  13. 13. Plate Tectonics– Three primary collisions (cont.)• Oceanic-oceanic– Subduction results in underseatrench formation– Deep and shallow earthquakes– Island volcanic arc• Continental-continental– No subduction since two platesare highly buoyant– Builds huge mountain ranges– Volcanoes are rare– Shallow earthquakes arerelatively common13© 2011 Pearson Education, Inc. Figure 14-15
  14. 14. Plate Tectonics• Transform boundaries– Two boundaries slippast each other laterally– Transform faults– Neither creates nordestroys crust– Commonly produceshallow focusearthquakes– San Andreas fault14© 2011 Pearson Education, Inc.Figure 14-18
  15. 15. Plate Tectonics• The rearrangement– 450 million years ago,one supercontinentexisted– Broke up 200 millionyears ago• Laurasia• Gondwanaland– Arrangement to thecurrent continentalconfiguration15© 2011 Pearson Education, Inc.Figure 14-19
  16. 16. Plate Tectonics• The Pacific Ring of Fire– Plate boundaries existall around the PacificRim– Primarily subductionzones– 75% of all volcanoes liein the Ring of Fire16© 2011 Pearson Education, Inc.Figure 14-20
  17. 17. Plate Tectonics• Additions to basic platetectonic theory– Mantle plumes• localized hot areas notassociated with plateboundaries• Move with the plate, soeventually becomeinactive• Hot spot trail• Hawaiian islands17© 2011 Pearson Education, Inc.Figure 14-22
  18. 18. Plate Tectonics– Accreted Terranes– Piece of lithospherecarried by a plate thateventually collides andfuses (accretes) withanother plate18© 2011 Pearson Education, Inc.Figure 14-24
  19. 19. Plate Tectonics• The questions– Midcontinental mountain range formation (i.e., theAppalachians)– Number of plates and plate sizes have changed overEarth’s history– Why are there earthquakes in the middle of continentalplates?– Why are plates different sizes?– Why do plates form where they do?19© 2011 Pearson Education, Inc.
  20. 20. Volcanism• Definition—all phenomenaconnected to the origin andmovement of molten rock• Extrusive volcanism—occurs on Earth’s surface,often shortened tovolcanism• Intrusive volcanism—occurs below surface,plutonic activity20© 2011 Pearson Education, Inc.Figure 14-26
  21. 21. Volcanism• Volcanism– Magma versus lava– Violent or gentle eruptions– Pyroclastic material– Some self destruct (i.e.,Krakatau in 1883)21© 2011 Pearson Education, Inc.Figure 14-26
  22. 22. Volcanism• Global volcano distribution22© 2011 Pearson Education, Inc.Figure 14-27
  23. 23. 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 two23© 2011 Pearson Education, Inc.
  24. 24. Volcanism• Volcanic activity– Relatively temporaryfeatures on the landscape– Much of Earth’s wateroriginated from water vaporfrom volcanic eruptions– Magma contains majorelements required for plantgrowth– Provides soil fertility24© 2011 Pearson Education, Inc.Figure 14-29
  25. 25. Volcanism• Lava flows– Lava generally flows horizontally,parallel to the surface alongwhich it flows– Eventually cools in horizontalorientation, strata– Streams flowing through lavaflows result in irregular orfragmented surface– Uniform cooling results inhexagonal structure25© 2011 Pearson Education, Inc.Figure 14-30
  26. 26. Volcanism• Flood basalt– Most extensive lava flowscome from hot spots– Flood basalt is a vastaccumulation of lavabuild up– Correlated with massextinctions26© 2011 Pearson Education, Inc.Figure 14-31
  27. 27. Volcanism• Volcanic peaks– Shield volcanoes• Layer upon layer ofsolidified lava flows• Little pyroclastic material• Hawaiian islands are anexample27© 2011 Pearson Education, Inc.Figure 14-32
  28. 28. Volcanism• Volcanic peaks (cont.)– Composite Volcano• Emit higher silica lavas(andesite lava)• Form symmetric, steepsided volcanoes• Pyroclastics from explosivelava flows alternate withnonexplosive flows• Pyroclastic flows producesteep slopes, lava holds ittogether28© 2011 Pearson Education, Inc.Figure 14-34
  29. 29. Volcanism• Volcanic peaks (cont.)– Lava domes• Masses of very viscouslava that do not flow far• Lava bulges from the vent,dome grows by expansionfrom below and lava within• Some lava domes forminside of compositevolcanoes29© 2011 Pearson Education, Inc.Figure 14-36
  30. 30. Volcanism• Volcanic peaks (cont.)– Cinder cones• Smallest volcanicmountains• Basaltic magma iscommon• Slopes form frompyroclastic materials• Generally found inassociation with othervolcanoes30© 2011 Pearson Education, Inc.Figure 14-38
  31. 31. Volcanism• Volcanic peaks (cont.)– Calderas• Result from a volcano thatexplodes, collapses, orboth• Immense, basin-shapeddepression; larger thanoriginal crater• Crater Lake in Oregon isan example– Volcanic necks• Pipe or throat of an oldvolcano that filled with solidlava31© 2011 Pearson Education, Inc.Figure 14-40
  32. 32. Volcanism• Volcanic hazards– Volcanic gases—mainlywater vapor, but can causeacid rain and alter globalclimate– Lava flows—causeimmense property damage– Eruption clouds—gas andash material clouds thatextend up to 16 km into theatmosphere, drop large rockfragments called “bombs”32© 2011 Pearson Education, Inc.Figure 14-45
  33. 33. Volcanism• Volcanic hazards (cont.)– Pyroclastic flows—avalanche of hot gasesand material, up to 100mph– Volcanic mud flows(lahars)—result fromheavy rain and/or snowmelt during an eruption33© 2011 Pearson Education, Inc.Figure 14-44
  34. 34. 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 activity34© 2011 Pearson Education, Inc.
  35. 35. Volcanism• Igneous features– Igneous intrusion—rockformed beneath theEarth’s surfacepenetrates the crust—pluton– Stoping– Scheme for classifyingigneous intrusions35© 2011 Pearson Education, Inc.Figure 14-48
  36. 36. Volcanism• Igneous features (cont.)– Batholiths—large,subterranean body ofindefinite depth; important inmountain building– Stocks—similar to a batholithbut much smaller– Laccoliths—slow-moving,viscous magma forcedbetween horizontal layers ofrock; builds up a mushroomshaped mass36© 2011 Pearson Education, Inc.Figure 14-49
  37. 37. Volcanism• Igneous features (cont.)– Dikes—vertical sheet ofmagma thrust upward intopreexisting rock; long andnarrow– Sills—long, thin body whoseorientation is determined bypreexisting rocks– Veins—molten materialforces itself into smallerfractures in preexisting rock,takes irregular shapes37© 2011 Pearson Education, Inc.Figure 14-50
  38. 38. Diatrophism• Refers to the deformationof Earth’s crust• Two primary types ofdiatrophism, folding andfaulting38© 2011 Pearson Education, Inc.Figure 14-53
  39. 39. Folding• Results when rock issubjected to lateralcompression• Can take place on anyscale• Can vary in complexity• Two types– Anticline/upfold, can beforced to have reverseorientation, an overturnedfold– Syncline/downfold—overthrust fold 39© 2011 Pearson Education, Inc.Figure 14-51
  40. 40. Faulting• Occurs when rock breaksaccompanied by displacement• Occurs along zones ofweakness in the crust, faultzones• Fault lines• Begin as sudden ruptures, butcan result in large (hundredsof km) faults over millions ofyear• Fault scarps40© 2011 Pearson Education, Inc.Figure 14-54
  41. 41. Faulting• Four primary fault types41© 2011 Pearson Education, Inc.Figure 14-55
  42. 42. Faulting• Fault-produced landforms– Tilted fault-blockmountains; one side of thefault block is tilted steeplyrelative to the other– Horst: uplift of a land blockbetween two parallel faults– Graben: downthrown landblock between two parallelfaults42© 2011 Pearson Education, Inc.Figure 14-59Figure 14-57
  43. 43. Faulting• Strike-slip faultinglandforms– Linear fault trough• Small depressions in thetrough known as sags• Sag ponds• Offset drainage channels• Shutter ridge43© 2011 Pearson Education, Inc.Figure 14-60
  44. 44. Faulting• Earthquakes– Vibration in Earth resulting from sudden displacementalong a fault• Earthquake waves– Energy released by earthquakes moves in several typesof seismic waves that originate at the center of faultmotion, the origin– Ground above origin experiences strongest jolt, theepicenter– P-waves versus S-waves44© 2011 Pearson Education, Inc.
  45. 45. Faulting• Earthquake magnitude—relativeamount of energy released duringan earthquake– Logarithmic scale, 32nd power– Richter scale– Strongest recordedearthquake—9.5 in Chile• Shaking intensity– Intensity of ground shaking notconsistent during an earthquake– Mercalli intensity scale45© 2011 Pearson Education, Inc.
  46. 46. Faulting• Earthquake hazards– Most damage from groundshaking– Liquefaction of moistsediments– Landslides– Water movements in lakesand oceans (i.e., tsunamis)46© 2011 Pearson Education, Inc.Tsunami damage in Kodiak, AKImage courtesy of NOAA
  47. 47. The Complexities of CrustalConfiguration• 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 upliftcombined with lateral pressure from the west resulted in avast rupture and faulting– Whole block moved by Lewis Overthrust– Had Precambrian sedimentary rock over Cretaceousstrata47© 2011 Pearson Education, Inc.
  48. 48. The Complexities of CrustalConfiguration• Mountains without roots, Chief Mountain48© 2011 Pearson Education, Inc.Figure 14-64
  49. 49. 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 occurwithin lithospheric plates• The continents have rearranged themselves from asingle supercontinent, Pangaea, to the arrangementtoday• Volcanism describes the motions of molten rock• The chemistry of magma changes the type of eruptionthat takes place49© 2011 Pearson Education, Inc.
  50. 50. Summary• There are four primary types of volcanic mountains• Numerous volcanic hazards are a great threat to life andproperty• In addition to volcanoes, numerous intrusive processesmodify the landscape• Diatrophism refers to the modification of Earth’s crust• Folding is the bending of rock over long time scales dueto continuous external pressure• Faulting is a weakness in the crust50© 2011 Pearson Education, Inc.
  51. 51. Summary• There are four primary types of faults• Different landforms result from each of these four typesof faults• Earthquakes result from a sudden displacement along afault• There are numerous hazards associated withearthquakes• While the processes were considered individually, theyare all interrelated51© 2011 Pearson Education, Inc.