1. Earth & Space Science Chapter 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 – CO 2 + H 2 O  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