Chapter 13: Introduction to Landform Study
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Transcript of Chapter 13: Introduction to Landform Study
Chapter 13: Introduction to Landform Study
The Structure of Earth
• Understanding of Earth’s structure based on minute fraction of total depth (<8 miles)
• Good deal of understanding inferred by geophysical means
• 4 regions of Earth’s interior
Figure 13-1
The Structure of Earth
• Crust– Thinnest layer
• Depth of 5 km below ocean to near 20 km below land
• < 1% of Earth’s volume, 0.4% of Earth’s mass
– Base• Moho discontinuity
– Composed of mostly silicate material
– Part of lithosphere– Ocean crust (basalt) vs.
Continental crust (granite)
The Structure of Earth
• Mantle– Largest and thickest layer
• Makes up 84% of total volume, 67% of total mass• Extends to depth of
2900 km (1800 miles)– Magnesium with
material from bothcrust & core
– 3 sublayers• Lithosphere (upper mantle)
– Cool/brittle rock• Asthenosphere
– Plastic quality of rocks• Lower mantle
– Rigid/brittle rock
The Structure of Earth
• Core Composition: Iron & Nickel • Outer/inner core combined = 15% of
Earth’s volume & 32% of Earth’s mass• Outer core
– Molten (liquid), extends to depth of 5000 km
– Generates Earth’s magnetic field
• Magnetic poles not the same as the axial poles
• Inner core– Solid, dense mass– Rotates independently
The Structure of Earth
• “Continental drift”• Plate tectonics—large lithospheric plates slide along the
top of the asthenosphere
The Composition of Earth
• Minerals—naturally formed compounds & elements of Earth
• Characteristics– Solid– Found in nature– Inorganic– Specific chemical
composition– Specific crystal
structure• Atoms arrange in
patterns to form crystals
The Composition of Earth
• Important crustal minerals– Silicates—oxygen + silicon
• Most common elements in the lithosphere– Oxides—oxygen + another element– Sulfides—sulfur + another element– Sulfates—sulfur + oxygen– Carbonates—light-colored minerals
composed of carbon, oxygen + another element (i.e., limestone)
– Halides—derived from word “salt”, salty minerals
– Native elements—gold and silver• Also appear as elements
Figures 13-2 & 13-3
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• Earth’s composition as a whole– Primarily iron & oxygen.– Silicon is abundant in the
crust– Iron & Magnesium are more
abundant in the lower mantle & core due to density
The Composition of Earth
The Composition of Earth
• Composition of Earth’s crust is significantly different from Earth as a whole.
The Composition of Earth
• Rocks—composed of 2 or more minerals– Fewer than 20 minerals make up 95% of the composition
of crustal rocks– Bedrock
• Solid rock; no weathering– Outcrop
• Bedrock exposure– Regolith
• Partially weathered rock– Petrology—
characteristics of different rocks
Figure 13-4
The Composition
of Earth
• Igneous rocks– Igneous—“fiery
inception”• Crystallized magma/lava
– Magma—molten rock beneath Earth’s surface
– Lava—molten rock on Earth’s surface
– Pyroclastics
The Composition of Earth
• Igneous Rock Classification– 2 Compositions
• Light colored (felsic)• Dark colored (mafic)
– 2 Textures • Plutonic (intrusive)
– Rocks cool slowly beneath Earth’s surface
– Coarse-grained• Volcanic (extrusive)
– Rocks cool rapidly on Earth’s surface
– Fine-grained
The Composition of Earth
Figure 13-6
Rhyolite70-75% SiO2
Andesite60% SiO2
Basalt45-50% SiO2
Silica Content of Magma
The Composition of Earth
The Composition of Earth
• Sedimentary Rocks– Sediments– Lithification
• Putting fragments back together • Compaction• Cementation
– Iron oxide, silica & calcium carbonate
– Deposited in layers – Clastic Rocks
• Pieces of other rock– Chemical Rocks
• Precipitated materials– Organic Rocks
• Plant or animal parts
Figures 13-9 & 13-13
The Composition of Earth
• Metamorphic Rocks– Re-crystallizing pre-existing
rock– Heat and pressure– Foliation
• Banded, layered, or wavy characteristic after extreme pressure
– Types• Contact metamorphism• Regional metamorphism• Burial metamorphism• Shock metamorphism• Pyro-metamorphism
Figure 13-16b
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Quartzite comes from sandstone Slate comes from of shale
Gneiss (metamorphic)Granite (igneous)
stress stress
hornblende
Metamorphic Rocks
The Composition of Earth
The Composition of Earth
• Rock cycle—processes where rocks transition from igneous rocks to sedimentary rocks to metamorphic rocks– Not a linear path
Figure 13-17
The Composition of Earth
• Continental rocks– Sedimentary rocks =
75% of continents– Continental crust: sial
• Granite
• Ocean floor rocks– Ocean floor crust: sima
• Basalt– More dense than
continental rocks = subduction
Figures 13-18 & 13-19
The Composition of Earth
• Isostasy: equilibrium between gravity & buoyancy
Figure 13-20
Weight of rocks / glaciers / sediments on continental shelf
Adjustment in the density of the asthenosphere
Earth’s Surface
The Study of Landforms
• Topography vs. Landform• Elements of landform study
– Structure• Geology
– Process• Actions creating landforms
– Slope– Drainage– Relief
• Change in elevation in an area
• Fundamental questions of geographic inquiry:– What, where, why, and so what?
Figure 13-22
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Topography – Nebraska
The Study of Landforms
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The Study of Landforms
Topography – Wyoming
Some Critical Concepts
• Internal and External Geomorphic Processes– Internal: inside Earth, increase relief– External: outside Earth; decrease
relief
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
– Geologic time in 1 year Figure 13-24
Scale and Pattern
• The Pursuit of Pattern—major landform assemblages of the world
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• 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• The rock cycle is the transition cycle through the different rock types• 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