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Earth & Space Science Chapter 7

Earth & Space Science Chapter 7. Weathering , Erosion, and Soil. Mechanical/Physical Weathering. Changes size and shape of rocks, not composition Temperature Water freeze/thaw cycle (water expands when it freezes): frost wedging Pressure Plant roots enlarge cracks in rocks

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Earth & Space Science Chapter 7

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  1. Earth & Space ScienceChapter 7 Weathering, Erosion, and Soil

  2. Mechanical/Physical Weathering Changes size and shape of rocks, not composition • Temperature • Water freeze/thaw cycle (water expands when it freezes): frost wedging • Pressure • Plant roots enlarge cracks in rocks • Exfoliation of layers

  3. Examples: Frost wedging, exfoliation, and root wedging

  4. Chemical Weathering Changes the chemical identity of the rock • Water • Dissolves minerals • Chemical reaction: hydrolysis (decomposes silicates) • Oxygen • Chemical reaction: oxidation (especially iron) • Carbon dioxide • CO2 + H2O  Carbonic acid (dissolves calcite) • Acid precipitation • Nitric and sulfuric acid from air pollution

  5. Examples:

  6. Effect of temperature and rainfall

  7. What affects the rate of weathering? • Climate • Warm/rainy = more chemical weathering • Cool/dry = more physical weathering • Rock type/composition • Sedimentary = most weathering • Exposed surface area • Greater surface area = greater weathering • Topography: slope of the land • Steeper = greater weathering

  8. Exposed surface area affects weathering

  9. Erosion and Deposition • Erosion transports weathered material until it is deposited in a new location. • Wind, running water, glaciers, glaciers, ocean currents, and waves • The importance of gravity: • Loose rock falls downhill • Water flows downhill • Glaciers flow downhill

  10. Water Erosion • Greatest when water is moving rapidly • Rivers/streams: billions of tons of sediment carried downstream, deposited at deltas • Waves: erosion and deposition of sand forms barrier islands

  11. Glacial Erosion • Move as dense rivers of ice • Grind up, transport and deposit large amounts of rock and debris • Much of the northern U.S. landscape has been shaped by glaciers

  12. Wind Erosion • Especially important in arid (dry) locations and coastal regions without much vegetation

  13. Soil Formation • Soil consists of weathered rock and organic material • Soil texture is determined by the amount and type of different sized particles

  14. Soil Horizons • O: organic material and leaf litter • A: weathered rock and organic material • B: zone of accumulation/ clay and minerals • C: broken down bedrock

  15. Factors in Soil Formation • Climate—rock weathers more rapidly in humid, temperate climates • Topography—slope affects deposition of soil • Parent material—type of rock that forms the soil • Biological organisms—help break down soil and add to humus • Time—soil is renewable, but can take long periods of time

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