Ch4_Weathering_students
- 1. CH. 4 - WEATHERING Chapter 2
- 2. Types of Weathering Processes 1) Mechanical Weathering - rx break down into smaller pieces - little or no chemical alteration
- 3. Types of Weathering Processes 2) Chemical Weathering - alters crystalline structure and/or composition of minerals - new minerals formed or minerals dissolve
- 4. Types of Mechanical Weathering 1) Frost wedging Water expands as it freezes - most effective in climates with freeze/thaw cycles Ex: high altitudes, mid-latitudes
- 5. Types of Mechanical Weathering 2) Unloading - caused by a decrease in pressure - effective on large bodies of intrusive igneous rocks
- 6. Unloading Rocks expand & crack parallel to surface (“sheeting”) - produce rounded mountains called exfoliation domes Ex: Yosemite National Park, CA Stone Mountain, GA
- 7. Types of Mechanical Weathering 3) Abrasion - grinding by friction - usually done by water: rivers, waves, glaciers - process by which rivers & glaciers carve their own valleys
- 8. Types of Mechanical Weathering 4) Organic Activity - root wedging
- 9. Mechanical Weathering Where would it be most significant? a) Amazon Rain Forest b) Peoria, IL c) North Pole
- 10. Chemical Weathering New minerals formed or old ones dissolve Agents: 1)Oxygen - abundant and reactive Atomic Number = 8
- 11. Oxygen Ex: Mafic mineral + oxygen = iron oxide Hornblende + O = Hematite
- 12. Agents of Chemical Weathering 2) Acid – destroys crystalline structure Ex: How granite weathers (p. 89) Feldspar + acid = clay mineral
- 14. Clay Minerals Most common weathering product of silicates Family of minerals microscopic sheet silicates (like mica structure)
- 16. Sources of Acid: a) Volcanic eruptions
- 17. Volcanic acids Hot springs where water circulates near magma chambers Ex: Yellowstone National Park
- 18. Sources of Acid b) Mine Drainage - sulfur-bearing minerals react with water to form sulfuric acid Ex: Pyrite = FeS 2 Galena = PbS
- 19. Sources of Acid c) Air pollution Coal-burning power plants release sulfur into atmosphere - produce sulfuric acid (acid rain)
- 20. Clean Air Act (1990) Requires power plants to reduce pollutants 1) Install “scrubbers” in smokestacks 2) Burn lower sulfur-content coal
- 21. Chemical Weathering Environmental conditions that enhance chemical weathering: 1) 2)
- 22. Chemical Weathering Where would it be most significant? a) Amazon Rain Forest b) Peoria, IL c) North Pole
- 23. Working together: Mech. weathering creates smaller pieces w/ larger surface areas - inside of rock is exposed
- 24. Weathering Products Original Mineral Product Hornblende Clay minerals Feldspar Clay minerals Biotite/muscovite Clay minerals Quartz Quartz
- 26. Stable minerals at surface 1) _______________________ 2) _______________________
- 27. Factors controlling rate of weathering 1) Particle size Smaller particles = faster chemical weathering Larger particles = faster mechanical weathering
- 28. Factors controlling rate of weathering 2) Composition Which weathers faster in warm humid climate: basalt or granite? Basalt = _____ ; Granite = _____
- 30. Factors controlling rate of weathering 3) Climate Ex: Limestone in humid climate - chemical weathering dominates - rolling hills - lots of caves & sinkholes (Ex: Florida)
- 31. Climate Ex: Limestone in arid climate - mechanical weathering dominates - steep cliffs with talus slopes Ex: Carlsbad Caverns, NM