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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 MechanicalWeathering1) Frost wedging- most effective in climates with freeze/thaw cyclesEx: high altitudes, mid-latitudes
  4. 4. Granite boulder
  5. 5. Talus slope
  6. 6. Types of MechanicalWeathering2) Unloading- caused by a decrease in pressure- effective on large bodies of intrusive igneous rocks
  7. 7. UnloadingRocks expand & crack parallel to surface (“sheeting”)- produce rounded mountains called exfoliation domesEx: Yosemite National Park, CA Stone Mountain, GA
  8. 8. Unloading
  9. 9. Sheeting Frost Wedging Sheeting
  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. Types of WeatheringProcesses2) Chemical Weathering- alters crystalline structure and/or composition of minerals- new minerals formed or minerals dissolve
  15. 15. Chemical WeatheringAgents:1)Oxygen - abundant and reactive Atomic Number = 8
  16. 16. OxygenEx: Mafic mineral + oxygen = iron oxideHornblende + Oxygen = Hematite
  17. 17. Agents of Chemical Weathering2) Acid – destroys crystalline structureEx: How granite weathers (p. 89)Feldspar + acid = clay mineralClay minerals = most common weathering product of silicates
  18. 18. Clay MineralsFamily of mineralsMicroscopic sheet silicates (like mini-micas)Ex: kaolinite
  19. 19. Sources of Acid:a) Volcanic eruptions
  20. 20. Volcanic acidsHot springs where water circulates near magma chambersEx: YellowstoneNational Park
  21. 21. Sources of Acidb) Mine Drainage- sulfur-bearing minerals react with water to form sulfuric acidEx: Pyrite = FeS2 (iron sulfide) Galena = PbS (lead sulfide)
  22. 22. Open Pit Mine
  23. 23. Sources of Acidc) Air pollutionCoal-burning power plants release sulfur into atmosphere- produce sulfuric acid (acid rain)
  24. 24. 1990 Clean Air Act AmendmentsRequires power plants to reduce pollutants1) Install “scrubbers” in smokestacks2) Burn lower sulfur-content coal
  25. 25. Map of U.S. coal deposits
  26. 26. Chemical WeatheringEnvironmental conditions that enhance chemical weathering:1)2)
  27. 27. Chemical WeatheringWhere would it be most significant?a) Amazon Rain Forestb) Peoria, ILc) North Pole
  28. 28. Working together:Mechanical weathering creates smaller pieces w/ larger surface areas
  29. 29. Weathering ProductsOriginal Mineral ProductHornblende Clay mineralsFeldspar Clay mineralsBiotite/muscovite Clay mineralsQuartz Quartz
  30. 30. Stable minerals at surface1) _______________________2) _______________________
  31. 31. Factors controlling rate ofweathering1) Particle size_________ particles = faster chemical weathering_________ particles = faster mechanical weathering
  32. 32. Factors controlling rate ofweathering2) CompositionWhich weathers faster in warm humid climate: basalt or granite?Basalt = _____; Granite = _____
  33. 33. Factors controlling rate ofweathering3) ClimateEx: Limestone in humid climate- chemical weathering dominates- rolling hills- lots of caves & sinkholes
  34. 34. ClimateEx: Limestone in arid climate- mechanical weathering dominates- steep cliffs with talus slopes