Mais conteúdo relacionado Mais de lschmidt1170 (20) Ch131. Chapter 13: Introduction to
Landform Study
McKnight’s Physical Geography:
A Landscape Appreciation,
Tenth Edition, Hess
2. Introduction to Landform Study
• The Structure of Earth
• The Composition of Earth
• The Study of Landforms
• Some Critical Concepts
• Scale and Pattern
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3. The Structure of Earth
• Understanding of Earth’s
structure based on minute
fraction of total depth (less
than 8 miles)
• Good deal of understanding
inferred by geophysical
means
• Four regions of Earth’s
interior
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Figure 13-1
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’s
mass
– 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 mantle
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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 volume
and 32% of the Earth’s mass
– Magnetic field of Earth controlled by outer core
– Magnetic poles not the same as the axial poles
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6. The Structure of Earth
• Plate tectonics and the structure of Earth
• “Continental drift”
• Plate tectonics—continental-sized plates slide
along the asthenosphere
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7. The Composition of Earth
• Minerals—naturally
formed compounds and
elements of Earth
• Mineral characteristics
– Solid
– Found in nature
– Inorganic
– Specific chemical
composition
– Contains atoms that
arrange in patterns to
form crystals
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Figure 13-2
8. The Composition of Earth
• Important crustal minerals
– Silicates—combine oxygen
and silicon, the most
common elements in the
lithosphere
– Oxides—elements that are
combined with oxygen
– Sulfides—combination of
sulfur and another element
(i.e., pyrite, Figure 13-3)
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Figure 13-3
9. The Composition of Earth
– Sulfates—contain sulfur and
oxygen
– Carbonates—light-colored
minerals that are composed
of a combination of carbon,
oxygen and an element (i.e.,
limestone)
– Halides—derived from word
“salt”, salty minerals
– Native elements—gold and
silver
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Miami Limestone
Image courtesy of the state
of Florida
10. The Composition of Earth
• Rocks—composed of many
minerals
– Fewer than 20 minerals
make up 95% of the
composition of crustal rocks
– Outcrops
– Bedrock
– Regolith
– Petrology—characteristics of
different rocks
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Figure 13-4
11. The Composition of Earth
• Igneous rocks
– Igneous—“fiery inception”
– Magma—molten rock beneath
Earth’s surface
– Lava—molten rock when it
flows onto Earth’s surface
– Pyroclastics
– Classification of igneous rocks
is based on mineral
composition and texture
– Texture based on how rocks
cool
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Figure 13-8b
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 the
crystals are formed from shattered rock that was explosively
ejected
• Basalt
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13. The Composition of Earth
• Common igneous rocks
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Figure 13-6
14. The Composition of Earth
• Intrusive rock example—granite outcrops
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Figure 13-7a
15. The Composition of Earth
• Extrusive rock example—basalt outcrops
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Figure 13-8a
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 to
large thicknesses
– Exert enormous pressure which causes particles in
sediment to interlock
– Chemical cementation takes place
– Forms sedimentary rock
– Strata—horizontal layers of sedimentary rock; sometimes
tilted into vertical by Earth processes
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17. The Composition of Earth
• Sedimentary rock example
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Figure 13-12
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 complicated
chemical reactions
• Limestone and coal are examples
• Organic sedimentary rocks such as coal form from remains of
dead plants and animals
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19. The Composition of Earth
• The two primary types of sedimentary rocks, white
rock is limestone, dark rock is shale
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Figure 13-11
20. The Composition of Earth
• Metamorphic Rocks
– Rocks which were originally igneous or sedimentary
and 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 is
rearranged
– Regional metamorphism: large volumes of rock are
subjected to heat and pressure over long time scales
– Limestone becomes marble; sandstone becomes
quartzite, shale becomes slate
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21. The Composition of Earth
• Schist—metamorphic
rocks with narrow
foliations
• Gneiss—broad, banded
foliations
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Figure 13-15
Figure 13-16
22. The Composition of Earth
• The rock cycle—processes where rocks can
transition from igneous rocks to sedimentary rocks to
metamorphic rocks
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Figure 13-17
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 continental
lithosphere
– Ocean crust can be subducted into the athenosphere
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24. The Composition of Earth
• Isostasy: recognition of
differences between
oceanic crust, continental
crust, and mantle
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Figure 13-20
25. The Study of Landforms
• Topography—surface
configuration of Earth
• Landform—individual
topographic feature of
any size
• Elements of landform
study
– Structure
– Process
– Slope
– Drainage
– Relief
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Figure 13-22
26. Some Critical Concepts
• Internal and External Geomorphic Processes
– Internal: originate from within Earth, increase relief of land
surface
– External: originate from sources above the lithosphere, such
as the atmosphere or oceans; decrease relief of land surface
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Figure 13-23
27. Some Critical Concepts
• Uniformitarianism
– “The present is the key
to the past”
– Processes which
shaped the landscape
of the past are the
same that will shape
the future
• Geologic time
– Vast periods of time
over which geologic
processes operate
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Figure 13-24
28. Scale and Pattern
• An example of scale—five perspectives Horseshoe Park
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Figure 13-25
29. Scale and Pattern
• The Pursuit of Pattern—major landform assemblages of
the world
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Figure 13-26
30. Summary
• Earth’s structure is presumed based on geophysical
research
• Earth’s interior consists of four regions
• Earth’s composition consists of elements or
compounds of elements called minerals
• Seven primary types of minerals exist
• Rocks are composed of minerals
• Igneous rocks are those formed by cooling and
solidification of molten rock
• Plutonic rocks are those which form within the Earth
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31. Summary
• Volcanic rocks form on the Earth’s surface
• Sedimentary rocks form as a result of transport of
mineral material by water
• Two primary types of sedimentary rocks, clastic and
chemical/organic sedimentary rocks
• Metamorphic rocks are igneous or sedimentary rocks
that have been drastically changed by heat and/or
pressure
• Two primary types, schist and gneiss
• The rock cycle is the transition cycle through the
different rock types
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32. Summary
• Continental and ocean floor rocks possess different
characteristics which are important in geophysical
processes
• Isostasy is the recognition of the differences between
continental crust, oceanic crust, and mantle
• Landforms are characterized by structure, process,
slope, and drainage
• Internal and external geomorphic processes are
responsible for the relief of Earth
• Uniformitarianism allows us to use geologic time to
infer what happened in the past based on the present
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