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  • Ch13

    1. 1. Chapter 13: Introduction toLandform StudyMcKnight’s Physical Geography:A Landscape Appreciation,Tenth Edition, Hess
    2. 2. Introduction to Landform Study• The Structure of Earth• The Composition of Earth• The Study of Landforms• Some Critical Concepts• Scale and Pattern2© 2011 Pearson Education, Inc.
    3. 3. The Structure of Earth• Understanding of Earth’sstructure based on minutefraction of total depth (lessthan 8 miles)• Good deal of understandinginferred by geophysicalmeans• Four regions of Earth’sinterior3© 2011 Pearson Education, Inc.Figure 13-1
    4. 4. The Structure of Earth• Crust– Depth of 5 km below ocean to near 20 km below land– Less than 1% of the Earth’s volume, 0.4% of Earth’smass– Moho discontinuity• Mantle– Extends to depth of 2900 km (1800 miles)– Largest of four shells– Makes up 84% of total volume, 67% of total mass– Three sublayers• Lithosphere• Asthenosphere• Rigid rocks—lower mantle4© 2011 Pearson Education, Inc.
    5. 5. The Structure of Earth• Outer core– Molten, extends to depth of 5000 km• Inner core– Dense mass with radius of about 1450 km– Primarily made of iron/nickel or iron/silicate– Two zones combined make up 15% of the Earth’s volumeand 32% of the Earth’s mass– Magnetic field of Earth controlled by outer core– Magnetic poles not the same as the axial poles5© 2011 Pearson Education, Inc.
    6. 6. The Structure of Earth• Plate tectonics and the structure of Earth• “Continental drift”• Plate tectonics—continental-sized plates slidealong the asthenosphere6© 2011 Pearson Education, Inc.
    7. 7. The Composition of Earth• Minerals—naturallyformed compounds andelements of Earth• Mineral characteristics– Solid– Found in nature– Inorganic– Specific chemicalcomposition– Contains atoms thatarrange in patterns toform crystals7© 2011 Pearson Education, Inc.Figure 13-2
    8. 8. The Composition of Earth• Important crustal minerals– Silicates—combine oxygenand silicon, the mostcommon elements in thelithosphere– Oxides—elements that arecombined with oxygen– Sulfides—combination ofsulfur and another element(i.e., pyrite, Figure 13-3)8© 2011 Pearson Education, Inc.Figure 13-3
    9. 9. The Composition of Earth– Sulfates—contain sulfur andoxygen– Carbonates—light-coloredminerals that are composedof a combination of carbon,oxygen and an element (i.e.,limestone)– Halides—derived from word“salt”, salty minerals– Native elements—gold andsilver9© 2011 Pearson Education, Inc.Miami LimestoneImage courtesy of the stateof Florida
    10. 10. The Composition of Earth• Rocks—composed of manyminerals– Fewer than 20 mineralsmake up 95% of thecomposition of crustal rocks– Outcrops– Bedrock– Regolith– Petrology—characteristics ofdifferent rocks10© 2011 Pearson Education, Inc.Figure 13-4
    11. 11. The Composition of Earth• Igneous rocks– Igneous—“fiery inception”– Magma—molten rock beneathEarth’s surface– Lava—molten rock when itflows onto Earth’s surface– Pyroclastics– Classification of igneous rocksis based on mineralcomposition and texture– Texture based on how rockscool11© 2011 Pearson Education, Inc.Figure 13-8b
    12. 12. The Composition of Earth• Two types of igneous rocks– Plutonic (intrusive)• Rocks cool beneath Earth’s surface• Surrounding rocks insulate the magma intrusion, slowing cooling• Individual minerals in a plutonic rock can grow to large size• Granite– Volcanic (extrusive)• Form on Earth’s surface• Cool rapidly• Generally do not show individual mineral crystals, but can if thecrystals are formed from shattered rock that was explosivelyejected• Basalt12© 2011 Pearson Education, Inc.
    13. 13. The Composition of Earth• Common igneous rocks13© 2011 Pearson Education, Inc.Figure 13-6
    14. 14. The Composition of Earth• Intrusive rock example—granite outcrops14© 2011 Pearson Education, Inc.Figure 13-7a
    15. 15. The Composition of Earth• Extrusive rock example—basalt outcrops15© 2011 Pearson Education, Inc.Figure 13-8a
    16. 16. The Composition of Earth• Sedimentary Rocks– External processes cause rock disintegration– Material transported by water as sediment– Over long periods, large amounts of sediment build tolarge thicknesses– Exert enormous pressure which causes particles insediment to interlock– Chemical cementation takes place– Forms sedimentary rock– Strata—horizontal layers of sedimentary rock; sometimestilted into vertical by Earth processes16© 2011 Pearson Education, Inc.
    17. 17. The Composition of Earth• Sedimentary rock example17© 2011 Pearson Education, Inc.Figure 13-12
    18. 18. The Composition of Earth• Two primary types of sedimentary rocks– Clastic• Composed of fragments of preexisting rocks• Also known as detrital rocks• Shale is an example• Conglomerate; composed of pebble-sized fragments– Chemical and organic sedimentary rocks• Formed by precipitation of soluble materials or complicatedchemical reactions• Limestone and coal are examples• Organic sedimentary rocks such as coal form from remains ofdead plants and animals18© 2011 Pearson Education, Inc.
    19. 19. The Composition of Earth• The two primary types of sedimentary rocks, whiterock is limestone, dark rock is shale19© 2011 Pearson Education, Inc.Figure 13-11
    20. 20. The Composition of Earth• Metamorphic Rocks– Rocks which were originally igneous or sedimentaryand have been changed by heat and pressure– Causes a “cooking” of rocks– Rearranges the crystal structure of the original rock– Contact metamorphism: rock contacts magma and isrearranged– Regional metamorphism: large volumes of rock aresubjected to heat and pressure over long time scales– Limestone becomes marble; sandstone becomesquartzite, shale becomes slate20© 2011 Pearson Education, Inc.
    21. 21. The Composition of Earth• Schist—metamorphicrocks with narrowfoliations• Gneiss—broad, bandedfoliations21© 2011 Pearson Education, Inc.Figure 13-15Figure 13-16
    22. 22. The Composition of Earth• The rock cycle—processes where rocks cantransition from igneous rocks to sedimentary rocks tometamorphic rocks22© 2011 Pearson Education, Inc.Figure 13-17
    23. 23. The Composition of Earth• Continental and ocean floor rocks– Sedimentary rocks make up 75% of the continents– Sedimentary cover is not thick– Continental crust: sial (silicon and aluminum)– Ocean floor crust: sima (silicon and magnesium)– Ocean lithosphere is more dense than continentallithosphere– Ocean crust can be subducted into the athenosphere23© 2011 Pearson Education, Inc.
    24. 24. The Composition of Earth• Isostasy: recognition ofdifferences betweenoceanic crust, continentalcrust, and mantle24© 2011 Pearson Education, Inc.Figure 13-20
    25. 25. The Study of Landforms• Topography—surfaceconfiguration of Earth• Landform—individualtopographic feature ofany size• Elements of landformstudy– Structure– Process– Slope– Drainage– Relief25© 2011 Pearson Education, Inc.Figure 13-22
    26. 26. Some Critical Concepts• Internal and External Geomorphic Processes– Internal: originate from within Earth, increase relief of landsurface– External: originate from sources above the lithosphere, suchas the atmosphere or oceans; decrease relief of land surface26© 2011 Pearson Education, Inc.Figure 13-23
    27. 27. Some Critical Concepts• Uniformitarianism– “The present is the keyto the past”– Processes whichshaped the landscapeof the past are thesame that will shapethe future• Geologic time– Vast periods of timeover which geologicprocesses operate27© 2011 Pearson Education, Inc.Figure 13-24
    28. 28. Scale and Pattern• An example of scale—five perspectives Horseshoe Park28© 2011 Pearson Education, Inc.Figure 13-25
    29. 29. Scale and Pattern• The Pursuit of Pattern—major landform assemblages ofthe world29© 2011 Pearson Education, Inc.Figure 13-26
    30. 30. Summary• Earth’s structure is presumed based on geophysicalresearch• Earth’s interior consists of four regions• Earth’s composition consists of elements orcompounds of elements called minerals• Seven primary types of minerals exist• Rocks are composed of minerals• Igneous rocks are those formed by cooling andsolidification of molten rock• Plutonic rocks are those which form within the Earth30© 2011 Pearson Education, Inc.
    31. 31. Summary• Volcanic rocks form on the Earth’s surface• Sedimentary rocks form as a result of transport ofmineral material by water• Two primary types of sedimentary rocks, clastic andchemical/organic sedimentary rocks• Metamorphic rocks are igneous or sedimentary rocksthat have been drastically changed by heat and/orpressure• Two primary types, schist and gneiss• The rock cycle is the transition cycle through thedifferent rock types31© 2011 Pearson Education, Inc.
    32. 32. Summary• Continental and ocean floor rocks possess differentcharacteristics which are important in geophysicalprocesses• Isostasy is the recognition of the differences betweencontinental crust, oceanic crust, and mantle• Landforms are characterized by structure, process,slope, and drainage• Internal and external geomorphic processes areresponsible for the relief of Earth• Uniformitarianism allows us to use geologic time toinfer what happened in the past based on the present32© 2011 Pearson Education, Inc.