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  1. 1. CH. 4 - WEATHERING Chapter 2
  2. 2. Types of WeatheringProcesses1) Mechanical Weathering- rx break down into smaller pieces- little or no chemical alteration
  3. 3. Types of WeatheringProcesses2) Chemical Weathering- alters crystalline structure and/or composition of minerals- new minerals formed or minerals dissolve
  4. 4. Types of MechanicalWeathering1) Frost wedging- most effective in climates with freeze/thaw cyclesEx: high altitudes, mid-latitudes
  5. 5. Granite boulder
  6. 6. Talus slope
  7. 7. Types of MechanicalWeathering2) Unloading- caused by a decrease in pressure- effective on large bodies of intrusive igneous rocks
  8. 8. UnloadingRocks expand & crack parallel to surface (“sheeting”)- produce rounded mountains called exfoliation domesEx: Yosemite National Park, CA Stone Mountain, GA
  9. 9. Unloading
  10. 10. YosemiteHalf Dome isan exfoliationdome cut inhalf by largeglaciersduring the IceAge
  11. 11. Types of MechanicalWeathering3) Abrasion- grinding by friction- usually done by water: rivers, waves, glaciers- process by which rivers & glaciers carve their own valleys
  12. 12. Types of MechanicalWeathering4) Organic ActivityEx: root wedging
  13. 13. Mechanical WeatheringWhere would it be most significant?a) Amazon Rain Forestb) Peoria, ILc) North Pole
  14. 14. Chemical WeatheringNew minerals formed or old ones dissolveAgents:1)Oxygen - abundant and reactive Atomic Number = 8
  15. 15. OxygenEx: Mafic mineral + oxygen = iron oxideHornblende + Oxygen = Hematite
  16. 16. Agents of Chemical Weathering2) Acid – destroys crystalline structureEx: How granite weathers (p. 89)Feldspar + acid = clay mineralClay minerals = most common weathering product of silicates
  17. 17. Clay MineralsFamily of mineralsMicroscopic sheet silicates (like mini-micas)Ex: kaolinite
  18. 18. Sources of Acid:a) Volcanic eruptions
  19. 19. Volcanic acidsHot springs where water circulates near magma chambersEx: YellowstoneNational Park
  20. 20. Sources of Acidb) Mine Drainage- sulfur-bearing minerals react with water to form sulfuric acidEx: Pyrite = FeS2 (iron sulfide) Galena = PbS (lead sulfide)
  21. 21. Open Pit Mine
  22. 22. Sources of Acidc) Air pollutionCoal-burning power plants release sulfur into atmosphere- produce sulfuric acid (acid rain)
  23. 23. 1990 Clean Air Act AmendmentsRequires power plants to reduce pollutants1) Install “scrubbers” in smokestacks2) Burn lower sulfur-content coal
  24. 24. Map of U.S. coal deposits
  25. 25. Chemical WeatheringEnvironmental conditions that enhance chemical weathering:1)2)
  26. 26. Chemical WeatheringWhere would it be most significant?a) Amazon Rain Forestb) Peoria, ILc) North Pole
  27. 27. Working together:Mechanical weathering creates smaller pieces w/ larger surface areas
  28. 28. Weathering ProductsOriginal Mineral ProductHornblende Clay mineralsFeldspar Clay mineralsBiotite/muscovite Clay mineralsQuartz Quartz
  29. 29. Stable minerals at surface1) _______________________2) _______________________
  30. 30. Factors controlling rate ofweathering1) Particle size_________ particles = faster chemical weathering_________ particles = faster mechanical weathering
  31. 31. Factors controlling rate ofweathering2) CompositionWhich weathers faster in warm humid climate: basalt or granite?Basalt = _____; Granite = _____
  32. 32. Factors controlling rate ofweathering3) ClimateEx: Limestone in humid climate- chemical weathering dominates- rolling hills- lots of caves & sinkholes
  33. 33. ClimateEx: Limestone in arid climate- mechanical weathering dominates- steep cliffs with talus slopes