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Ch4_Weathering_students

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Power point packet notes on weathering

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Ch4_Weathering_students

  1. 1. CH. 4 - WEATHERING <ul><li>Chapter 2 </li></ul>
  2. 2. Types of Weathering Processes <ul><li>1) Mechanical Weathering </li></ul><ul><li>- rx break down into smaller pieces </li></ul><ul><li>- little or no chemical alteration </li></ul>
  3. 3. Types of Weathering Processes <ul><li>2) Chemical Weathering </li></ul><ul><li>- alters crystalline structure and/or composition of minerals </li></ul><ul><li>- new minerals formed or minerals dissolve </li></ul>
  4. 4. Types of Mechanical Weathering <ul><li>1) Frost wedging </li></ul><ul><li>Water expands as it freezes </li></ul><ul><li>- most effective in climates with freeze/thaw cycles </li></ul><ul><li>Ex: high altitudes, mid-latitudes </li></ul>
  5. 5. Types of Mechanical Weathering <ul><li>2) Unloading </li></ul><ul><li>- caused by a decrease in pressure </li></ul><ul><li>- effective on large bodies of intrusive igneous rocks </li></ul>
  6. 6. Unloading <ul><li>Rocks expand & crack parallel to surface (“sheeting”) </li></ul><ul><li>- produce rounded mountains called exfoliation domes </li></ul><ul><li>Ex: Yosemite National Park, CA </li></ul><ul><li>Stone Mountain, GA </li></ul>
  7. 7. Types of Mechanical Weathering <ul><li>3) Abrasion </li></ul><ul><li>- grinding by friction </li></ul><ul><li>- usually done by water: rivers, waves, glaciers </li></ul><ul><li>- process by which rivers & glaciers carve their own valleys </li></ul>
  8. 8. Types of Mechanical Weathering <ul><li>4) Organic Activity </li></ul><ul><li>- root wedging </li></ul>
  9. 9. Mechanical Weathering <ul><li>Where would it be most significant? </li></ul><ul><li>a) Amazon Rain Forest </li></ul><ul><li>b) Peoria, IL </li></ul><ul><li>c) North Pole </li></ul>
  10. 10. Chemical Weathering <ul><li>New minerals formed or old ones dissolve </li></ul><ul><li>Agents: </li></ul><ul><li>1)Oxygen - abundant and reactive </li></ul><ul><li>Atomic Number = 8 </li></ul>
  11. 11. Oxygen <ul><li>Ex: Mafic mineral + oxygen = iron </li></ul><ul><li>oxide </li></ul><ul><li>Hornblende + O = Hematite </li></ul>
  12. 12. Agents of Chemical Weathering <ul><li>2) Acid – destroys crystalline structure </li></ul><ul><li>Ex: How granite weathers (p. 89) </li></ul><ul><li>Feldspar + acid = clay mineral </li></ul>
  13. 13. Bowen’s Reaction Series
  14. 14. Clay Minerals <ul><li>Most common weathering product of silicates </li></ul><ul><li>Family of minerals </li></ul><ul><li>microscopic sheet silicates (like mica structure) </li></ul>
  15. 16. Sources of Acid: <ul><li>a) Volcanic eruptions </li></ul>
  16. 17. Volcanic acids <ul><li>Hot springs where water circulates near magma chambers </li></ul><ul><li>Ex: Yellowstone National Park </li></ul>
  17. 18. Sources of Acid <ul><li>b) Mine Drainage </li></ul><ul><li>- sulfur-bearing minerals react with water to form sulfuric acid </li></ul><ul><li>Ex: Pyrite = FeS 2 </li></ul><ul><li> Galena = PbS </li></ul>
  18. 19. Sources of Acid <ul><li>c) Air pollution </li></ul><ul><li>Coal-burning power plants release sulfur into atmosphere </li></ul><ul><li>- produce sulfuric acid (acid rain) </li></ul>
  19. 20. Clean Air Act (1990) <ul><li>Requires power plants to reduce pollutants </li></ul><ul><li>1) Install “scrubbers” in smokestacks </li></ul><ul><li>2) Burn lower sulfur-content coal </li></ul>
  20. 21. Chemical Weathering <ul><li>Environmental conditions that enhance chemical weathering: </li></ul><ul><li>1) </li></ul><ul><li>2) </li></ul>
  21. 22. Chemical Weathering <ul><li>Where would it be most significant? </li></ul><ul><li>a) Amazon Rain Forest </li></ul><ul><li>b) Peoria, IL </li></ul><ul><li>c) North Pole </li></ul>
  22. 23. Working together: <ul><li>Mech. weathering creates smaller pieces w/ larger surface areas </li></ul><ul><li>- inside of rock is exposed </li></ul>
  23. 24. Weathering Products <ul><li>Original Mineral Product </li></ul><ul><li>Hornblende Clay minerals </li></ul><ul><li>Feldspar Clay minerals </li></ul><ul><li>Biotite/muscovite Clay minerals </li></ul><ul><li>Quartz Quartz </li></ul>
  24. 25. Bowen’s Reaction Series
  25. 26. Stable minerals at surface <ul><li>1) _______________________ </li></ul><ul><li>2) _______________________ </li></ul>
  26. 27. Factors controlling rate of weathering <ul><li>1) Particle size </li></ul><ul><li>Smaller particles = faster chemical weathering </li></ul><ul><li>Larger particles = faster mechanical weathering </li></ul>
  27. 28. Factors controlling rate of weathering <ul><li>2) Composition </li></ul><ul><li>Which weathers faster in warm humid climate: basalt or granite? </li></ul><ul><li>Basalt = _____ ; Granite = _____ </li></ul>
  28. 30. Factors controlling rate of weathering <ul><li>3) Climate </li></ul><ul><li>Ex: Limestone in humid climate </li></ul><ul><li>- chemical weathering dominates </li></ul><ul><li>- rolling hills </li></ul><ul><li>- lots of caves & sinkholes (Ex: Florida) </li></ul>
  29. 31. Climate <ul><li>Ex: Limestone in arid climate </li></ul><ul><li>- mechanical weathering dominates </li></ul><ul><li>- steep cliffs with talus slopes </li></ul><ul><li>Ex: Carlsbad Caverns, NM </li></ul>

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