Introduction to Geography People, Places, and Environment, 4e Edward F. Bergman William H. Renwick

1. Introduction to GeographyPeople, Places, and Environment, 4eEdward F. BergmanWilliam H. Renwick Chapter 3 Landforms: The Dynamic Earth Victoria Alapo, Instructor Geog 1010

2. Geomorphology • Study of landforms and processes that create them • Lithosphere comprises of: • Rocks and soil • Surface landforms • Plains, hills, valleys, depressions

3. Landform Processes • Endogenic • Internal forces beneath or at Earth’s surface • Mountain building • Earthquakes • Exogenic • External forces • Erosion, water, wind, chemical

4. Plate Tectonics • Fixed Earth Theory • States that continents and oceans have always been fixed in place • Plate Tectonics Theory • Proposed by Alfred Wegener, 1900s • Became popular in the 1960s • Pangaea Hypothesis • First a supercontinent, and the tectonic plates moved (see next slide – plate boundaries)

5. Plate Boundaries

7. Earthquakes • Focus • Place of actual movement • Epicenter • Surface directly above focus • See next slide – epicenters • Seismic waves • Recordable vibrations • Seismograph • Recording device for seismic waves • Richter Scale, 1935

8. Earthquakes

9. Volcanoes • Magma • Molten rock underneath the earth • Lava • Molten rock reaching Earth’s surface • Volcano • Surface vent for lava

10. Volcano Types • Shield volcanoes • Sedate • Runny lava • The Hawaiian Islands: Mauna Loa, Hawaii (still active, but not explosive) • Composite cone volcanoes • Explosive • Pyroclasts – this explosive material includes sticky lava, hot ash, sulfurous gas, rock bombs, etc – e.g. Pompei • Krakatau in Indonesia, largest recorded eruption.

12. Plate Boundaries • Divergent • Plates spreading apart, leading to: • Seafloor spreading • Rift Valleys in Africa • Convergent • Plates push together, leading to: • Mountain building • Volcanic eruptions as dense plates dive below • Transform • Grinding of plates past each other, leading to: • Offset sidewalks • E.g. along the San Andreas Fault, CA

13. Rock Formation • Igneous • Cooled molten crustal material (magma) • E.g. Basalt, granite • Sedimentary • Sediments laid down in layers and from high pressure • E.g. Sandstone, shale, limestone • Metamorphic • The 2 rocks above can be later compacted again, by heat & pressure, and so undergo further change • E.g. Marble derived from limestone

14. Weathering • Process of breaking rock into pieces • The first step in the formation of soil • Mechanical weathering • Process of rocks breaking down by physical force, e.g. tree roots, freezing & thawing - pot holes. See next slide. • Chemical weathering • Process of breaking down rock by: • Exposure to air and water • Acids released by decaying vegetation • Oxidation (rust due to iron content) • Leaching (nutrients being washed downwards beyond plant roots) • Decomposition of calcium carbonate

15. Mechanical Frost Wedging: the most important type of mechanical weathering; freeze-thaw repetition. Also responsible for city pot-holes. Personal home experiment Fig. 15-7 and 15-8

16. Movement of Weathered Material • Mass movement could be: • Slow gradual movement occurring near the surface, like soil creep • Or in dramatic movements such as rock slides, landslides and mudflows

17. Glaciers • Slow moving “rivers of ice” flowing from colder to warmer regions. They move only a few feet per year. • They act like conveyor belts, picking up sediment and dropping it in depositional areas • These glacial sediments are called, Moraines • Terminal moraines – found at the very end of glacier • Lateral moraines – found along the sides • Medial moraines – found in the middle • See next slide

18. Moraines

19. Impact of Past Glaciations • Soils & Landforms • Advance and retreat of glaciers leave behind highly fertile soil and various landforms (see next slide). • Water supply & Transportation routes • Retreating glaciers left sand and gravel deposits yielding large supplies of ground water • Also, water transport is heavily influenced by glacial melt water channels left behind by receding glaciers. E.g. Great Lakes, Hudson Bay, etc. See pg 117.

20. U-shaped valleys & jagged/rugged landscapes

21. Coastal Erosion • Longshore currents: • Currents traveling parallel to the shore, caused by repeated breaking of waves. Capable of carrying enormous amounts of sediment, and changing the form of beaches.

22. Coastal Erosion Effects of longshore currents:

23. Rate of Landform Change

24. Environmental Hazards • Environmental processes • Natural • Tornadoes, landslides, earthquakes • Human vulnerability • Rebuilding after natural disaster e.g. Pompeii, Italy; New Orleans, hurricane areas of Florida, California, etc • Trusting in Seawalls & Levees, instead of living elsewhere