Chapter 13: Introduction to Landform Study

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 • 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 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

5. 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

6. The Structure of Earth • “Continental drift” • Plate tectonics—large lithosphericplates 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. 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 beneathEarth’s surface • Lava—molten rock onEarth’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. 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 • ClasticRocks • 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. Slate comes from of shale Quartzite comes from sandstone

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 13-18 & 13-19

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