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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 processes
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
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

physical weathering
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

physical weathering1
Physical Weathering
  • Ice wedging – water penetrates into cracks, expands when it freezes.
    • cracks grow, new cracks form
physical weathering2
Physical Weathering
  • Root wedging - plant roots penetrate into cracks causing them to widen.
chemical weathering
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)
what is acid rain
What is "Acid Rain"?
  • Additionally acidity added by human activities (burning coal and oil).
    • sulfuric acid (H2SO4)
    • nitric acid (HNO3)
    • also emit mercury
chemical weathering1
Chemical Weathering
  • Minerals are dissolved, creating:
    • ions in solution.
    • secondary minerals.

Fig. 5.4c

Fig. 5.4b

chemical weathering2
Chemical Weathering
  • Some minerals dissolve by hydrolysis.
  • 2KAlSi3O8 + 11H2O 
  • 2K+ +OH- + 4H4SiO4 + Al2Si2O5(OH)4

(feldspar)

(clay mineral)

(ions)

Fig. 5.4

chemical weathering3
Chemical Weathering
  • Other minerals (mainly with iron) dissolve by oxidation.
    • forms “rust” on surface of rocks.
factors affecting weathering
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.
factors affecting weathering1
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.
factors affecting weathering2
Factors Affecting Weathering
  • Rock structure:
  • Joints/fractures expose interior of rock to weathering.
    • cracks for frost/biological wedging
    • more surface area for chemical weathering
factors affecting weathering3
Factors Affecting Weathering
  • Mineral type:
    • Some minerals weather easier than others.
  • Examples:
    • NaCl (halite) dissolves quickly.
    • SiO2 (quartz) dissolves very slowly.
climate and weathering1
Climate and Weathering
  • Describe the type and rate of weathering in:
    • Brazil
    • Illinois