Weathering, ch. 6 (113-125)
Mechanical weathering: rock broken into smaller pieces
Chemical weathering: composition is altered.
Different from erosion, the removal of the weathered materials
 

Mechanical Weathering
• Exfoliation: fractures due to pressure release.
• Frost wedging: caused by expansion of water when it freezes.
                Talus: rock pieces accumulate at base of slope
• Organisms
• Salt crystal growth
• Thermal expansion

Chemical Weathering

  • Dissolution (or solution)

    • In pure water, halite (salt) dissolves.
    Rain water (water + CO2) acidic, dissolves calcite
    Acid rain
    • natural: volcanoes
    • human-caused: burning of oil/coal

    • Oxidation (“rust”):mineral reacts with O2

  • Hydrolysis

    •     Hydrogen ions replace other ions (common in feldspars).
        Produces clay minerals and releases ions into water
     

    Weathering rate:
    1. particle size: weathering highest on surfaces and in fractures
    2. Climate: high T and water
    3.Parent material
    – limestones, rock salt weather quickly (in humid environments)
    – chemical weathering of silicates depends on mineral

    Short web pages on geology of Arches, Natural Bridges, and needles

    Regolith: rock fragments
    Soil: supports plant life
    – humus
    – air and water
    – mineral grains
    –  clay minerals