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Weathering

Weathering. Weathering Processes. All rock types (ig., meta. and sed.) can be weather. Physical weathering: breaking of rocks into smaller pieces Chemical weathering: dissolving minerals. Benefits of Weathering. Creates soil, an essential ingredient for abundant plant life.

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Weathering

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  1. Weathering

  2. Weathering Processes • All rock types (ig., meta. and sed.) can be weather. • Physical weathering: breaking of rocks into smaller pieces • Chemical weathering: dissolving minerals

  3. Benefits of Weathering • Creates soil, an essential ingredient for abundant plant life. • Releases nutrients (Ca, K, Fe). • Produces clay, sand, and gravel – building blocks for our society. • Produces mineral deposits – aluminum and iron. Fig. 14.16

  4. Physical Weathering • Rocks always contain cracks (called joints or fractures). • Cracks formed by: • stresses during tectonics. • daily heating and cooling. • layers in sedimentary rocks. Fig. 11.6

  5. Physical Weathering • Ice wedging – water penetrates into cracks, expands when it freezes. • cracks grow, new cracks form

  6. Physical Weathering • Root wedging - plant roots penetrate into cracks causing them to widen.

  7. Chemical Weathering • Water is essential to chemical weathering. • Acids or oxygen (O2) are usually necessary. • Rain water is naturally acidic. • H2O + CO2 (carbon dioxide)  H2CO3 (carbonic acid)

  8. What is "Acid Rain"? • Additionally acidity added by human activities (burning coal and oil). • sulfuric acid (H2SO4) • nitric acid (HNO3) • also emit mercury

  9. Chemical Weathering • Minerals are dissolved, creating: • ions in solution. • secondary minerals. Fig. 5.4c Fig. 5.4b

  10. Chemical Weathering • Some minerals dissolve by hydrolysis. • 2KAlSi3O8 + 11H2O  • 2K+ +OH- + 4H4SiO4 + Al2Si2O5(OH)4 (feldspar) (clay mineral) (ions) Fig. 5.4

  11. Chemical Weathering • Other minerals (mainly with iron) dissolve by oxidation. • forms “rust” on surface of rocks.

  12. Factors Affecting Weathering • Precipitation: • As precipitation increases, rate of chemical weathering increases. • Temperature: • As temperature increases, chemical reaction rate increases. • As number of freeze/thaw cycles increases, physical weathering increases.

  13. Factors Affecting Weathering • Biological Activity: • Physical weathering caused by plant roots. • Plants produce organic acids that increase chemical weathering. • Burrowing animals expose rocks to chemical weathering.

  14. Factors Affecting Weathering • Rock structure: • Joints/fractures expose interior of rock to weathering. • cracks for frost/biological wedging • more surface area for chemical weathering

  15. Factors Affecting Weathering • Mineral type: • Some minerals weather easier than others. • Examples: • NaCl (halite) dissolves quickly. • SiO2 (quartz) dissolves very slowly.

  16. Climate and Weathering

  17. Climate and Weathering • Describe the type and rate of weathering in: • Brazil • Illinois

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