1. Chapter 13: Introduction to Landform Study

2. 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

3. The Structure of Earth Crust Thinnest layer Base
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)

4. The Structure of Earth Mantle Largest and thickest layer
Makes up 84% of total volume, 67% of total mass
Extends to depth of km (1800 miles)
Magnesium with material from both crust & core
3 sublayers
Lithosphere (upper mantle)
Cool/brittle rock
Asthenosphere
Plastic quality of rocks
Lower mantle
Rigid/brittle rock

5. The Structure of Earth Core Composition: Iron & Nickel Outer core
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

6. The Structure of Earth “Continental drift”
Plate tectonics—large lithospheric plates slide along the top of the asthenosphere

7. 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

8. The Composition of Earth
Figures 13-2 & 13-3
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

9. The Composition of Earth
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

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

11. 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

12. 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

13. 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

14. The Composition of Earth\
Figure 13-6

15. Silica Content of Magma
The Composition of Earth
Silica Content of Magma
Basalt
45-50% SiO2
Andesite
60% SiO2
Rhyolite
70-75% SiO2

16. 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

17. 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

18. Quartzite comes from sandstone
Slate comes from of shale

19. The Composition of Earth
Metamorphic Rocks
hornblende
stress
stress
Granite (igneous)
Gneiss (metamorphic)

20. 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

21. 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 & 13-19

22. The Composition of Earth
Isostasy: equilibrium between gravity & buoyancy
Weight of rocks / glaciers / sediments on continental shelf
Adjustment in the density of the asthenosphere
Earth’s Surface
Figure 13-20

23. 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. The Study of Landforms
Topography – Nebraska

25. The Study of Landforms
Topography – Wyoming

26. Some Critical Concepts
Internal and External Geomorphic Processes
Internal: inside Earth, increase relief
External: outside Earth; decrease relief
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
Geologic time in 1 year
Figure 13-24

28. Scale and Pattern
The Pursuit of Pattern—major landform assemblages of the world
Figure 13-26

29. 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