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


• 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)


• 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


• 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


• “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


• 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



• Composition of Earth’s crust is significantly different from Earth as a whole.


• 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


• 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


Figure 13-6

Rhyolite70-75% SiO2

Andesite60% SiO2

Basalt45-50% SiO2

Silica Content of Magma



• 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


• 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

18

Quartzite comes from sandstone Slate comes from of shale

Gneiss (metamorphic)Granite (igneous)

stress stress

hornblende

Metamorphic Rocks



• Rock cycle—processes where rocks transition from igneous rocks to sedimentary rocks to metamorphic rocks– Not a linear path

Figure 13-17


• 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


• 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

24

Topography – Nebraska


25


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

http://www.uky.edu/KGS/education/geologictimescale.pdf

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

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Chapter 13: Introduction to Landform Study