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Weathering And Erosion

Learn about weathering and erosion, two natural processes that break down rock and transport earth materials. Discover the types and agents of mechanical and chemical weathering, as well as the factors that affect weathering rates.

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Weathering And Erosion

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  1. Weathering And Erosion -

  2. Weathering- the break-up of rock due to exposure to the atmosphere (H2O + gases) • Erosion - removal and transport of earth materials by natural agents (glaciers, water, winds)

  3. Types of Weathering • Mechanical Weathering- rock is broken down into smaller pieces of the same material • No change in the composition • Ex. Rock cliffpebbles and boulders same as cliff

  4. Agents of Mechanical Weathering: • Abrasion – rocks hitting other rocks • Frost Action (Ice Wedging) – water seeps into cracks in rocks, then freezesexpandsmeltsrefreezes • Wetting and Drying – effective in breaking up rocks containing clay) Clay swells up when wet and shrinks when dry causing rocks to fall apart

  5. Agents of Mechanical Weathering: • Plant and Animal Action – (mosses, ants, earthworms, moles�) • plant roots grow into cracks  wedging rock apart; animals dig into the earth • Exfoliation – peeling of rock layers due to gravity (sheet of rock peels away) Happens to granite

  6. Types of Weathering • Chemical Weathering - rock’s minerals are changed into different substances • change in composition and appearance • occurs when a chemical reaction takes place between the rock and H2O, CO2, O2, or acid

  7. Agents of Chemical Weathering • Hydrolysis – Chemical reaction of water and minerals • EX. Feldspar + H2O  Kaolin (clay) • Oxidation – Chemical reaction of oxygen + minerals (occurs in rocks with iron) • Ex. Fe + O2  FeO2 (iron oxide) Hematite or rust

  8. Agents of Chemical Weathering • Carbonation – chemical reaction of CO2 (dissolved in water) and minerals produces carbonic acid and results in a mineral changing • Acids – (plant decay, industrial runoff, and acid rain) acid seeps into rocks and produces cracks rocks break apart • These two processes rarely occur alone! Mechanical and chemical weathering almost always act together.

  9. Factors that affect Weathering Rates: • Amount of rock surface exposed: faster weathering with more surface area • Climate: Rainfall, alternating freeze/thaw cycles • ***Warm, humid climates More chemical weathering • ***Cool, dry climates More mechanical weathering

  10. Factors that affect Weathering Rates: • Type of Rock: all rocks do not weather at the same rate • EX. Marble tombstones weather faster than granite or slate because of acid rain.

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