Earth's interior consists of four regions: the crust, mantle, outer core, and inner core. Rocks are composed of minerals, and there are three main types of rocks: igneous, sedimentary, and metamorphic. Igneous rocks form from cooling magma, and can be plutonic or volcanic. Sedimentary rocks form from the lithification of sediments, and there are clastic and chemical/organic types. Metamorphic rocks were originally igneous or sedimentary rocks that were changed by heat and pressure. Landforms are shaped by internal and external geomorphic processes over geologic timescales.

1. 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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