Themes of the Day:

• Weathering vs. Erosion
• Physical (Mechanical) Weathering
• Chemical Weathering

Weathering vs. Erosion

• The mechanical or chemical breakdown of rocks and minerals
• May occur either in place or in transit
• Differs from erosion in that erosion is the transport process
• Most often acts hand in hand with erosion

Physical (Mechanical) Weathering

• Physical force breaks material into smaller fragments
• Examples:
  • Frost Wedging (ice expands 9% on freezing)
  • Abrasion (fluvial, aeolian, surf zone, glacial, etc.)
  • Biological (burrowing and tree roots)
  • Exfoliation
• Most effective with steep slopes (rugged topography)
• Gravity is the ultimate driving force (for most)

Chemical Weathering

• Most effective in hot, wet climates
• Products of Weathering are both solids (clastic sediments) and dissolved in H₂O (chemical sediments)
• Four basic types of chemical reactions:
  • Oxidation (ex. 4Fe₃O₄ + O₂ = 6Fe₂O₃) Figures 7.8, 7.9
  • Dissolution (ex. NaCl + H₂O = Na⁺ + Cl^- + H₂O)
  • Acid Reaction (Carbonation) (ex. CO₂ + H₂O = H₂CO₃ = H⁺ + (HCO₃)^-
    H⁺ + (HCO₃)^- + CaCO₃ = Ca²⁺ + 2(HCO₃)^-) Figure 7.7
  • Hydrolysis (ex. Fe₂O₃ + H₂O = 2FeO(OH))
• Example: Carbon Cycle - Role of Bicarbonate
• Stability of Minerals during Chemical Weathering