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Chapter 13: Introduction to Landform Study

McKnight’s Physical Geography: A Landscape Appreciation,

Tenth Edition, Hess

Introduction to Landform Study

• The Structure of Earth• The Composition of Earth• The Study of Landforms• Some Critical Concepts• Scale and Pattern

2© 2011 Pearson Education, Inc.

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


Figure 13-1


• 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



• 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



• Plate tectonics and the structure of Earth • “Continental drift”• Plate tectonics—continental-sized plates slide

along the asthenosphere


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


Figure 13-2


• 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)


Figure 13-3


– 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


Miami LimestoneImage courtesy of the state

of Florida


• 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


Figure 13-4


• 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


Figure 13-8b


• 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



• Common igneous rocks


Figure 13-6


• Intrusive rock example—granite outcrops


Figure 13-7a


• Extrusive rock example—basalt outcrops


Figure 13-8a

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



• Sedimentary rock example


Figure 13-12

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



• The two primary types of sedimentary rocks, white rock is limestone, dark rock is shale


Figure 13-11

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


The Composition of Earth• Schist—metamorphic rocks with narrow foliations

• Gneiss—broad, banded foliations


Figure 13-15

Figure 13-16

The Composition of Earth• The rock cycle—processes where rocks can transition from igneous rocks to sedimentary rocks to

metamorphic rocks


Figure 13-17

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


The Composition of Earth• Isostasy: recognition of differences between

oceanic crust, continental crust, and mantle


Figure 13-20

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


Figure 13-22

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


Figure 13-23

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


Figure 13-24

Scale and Pattern

• An example of scale—five perspectives Horseshoe Park


Figure 13-25

Scale and Pattern

• The Pursuit of Pattern—major landform assemblages of the world

29© 2011 Pearson Education, Inc.Figure 13-26

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


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


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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Technology

sedimentary

primary types

depth

earth

limestone

form

study

structure