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Weathering and Soils

Weathering and Soils. The Rock Cycle. The Rock Cycle. Weathering Breakdown of Rock near the Surface Due to Surface Processes. Chemical Alteration Solution & Leaching Biological Action Hydration Mechanical Impact

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Weathering and Soils

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  1. Weathering and Soils

  2. The Rock Cycle

  3. The Rock Cycle

  4. WeatheringBreakdown of Rock near the Surface Due to Surface Processes Chemical Alteration • Solution & Leaching • Biological Action • Hydration Mechanical • Impact • Wedging: Frost, Plant Roots, Salt Crystal Growth, Expansion of Hydrated Minerals

  5. Never Safe From Weathering

  6. Weathering Rates

  7. Differential Weathering and Erosion

  8. Differential Weathering and Erosion

  9. Mass-WastingMovement of Large Amounts of Material Downhill under Gravity • Creep • Mudflows • Slump • Rockfalls • Avalanches

  10. Surface Area and Weathering

  11. Surface-Volume Effects

  12. Spheroidal Weathering

  13. Spheroidal Weathering and Exfoliation

  14. Spheroidal Weathering

  15. Joints and Spheroidal Weathering

  16. What Determines Soil Type • Climate • Vegetation • Drainage • Time • Parent Material • Residual - Transported • Least Important Factor for Mature Soils

  17. Soil Formation Young Soils • Strongest Influence Is Parent Material Mature Soils • Strongest Influences: Climate, Vegetation, Drainage

  18. Soil Formation Processes Leaching from Surface • K, Mg, Na • Ca • Si • Al, Fe Accumulation beneath Surface • Al, Fe in Humid Climates • Ca in Arid Climates

  19. Soil Horizons and Profiles Soil Horizons • Layers in Soil • Not Deposited, but Zones of Chemical Action Soil Profile • Suite of Layers at a Given Locality

  20. Principal Soil Horizons • O - Organic (Humus) Often Absent • A – Leaching • K, Mg, Na, Clay Removed • E - Bleached Zone - Present Only in Certain Soils • B – Accumulation • Absent in Young Soils • Distinct in Old Soils • Al, Fe, Clay (Moist) • Si, Ca (Arid) • C - Parent Material

  21. Limits of Soil Formation Balance Between: • Downward Lowering of Surface • Downward Migration of Horizons If erosion rapid or soil evolution slow, soils may never mature beyond a certain point. Extremely ancient soils may have lost everything movable

  22. This may be the most difficult classification problem in science because of the many factors involved. Varied Bases for Classification Parent Material Special Constituent Materials Maturity Structure Climate & Vegetation Multiple Objectives Scientific Genesis & Evolution Agricultural Fertility Most Effective Use Engineering Slope Stability Expansion and Shrinkage Stability of Excavations Soil Classification

  23. "The 7th Approximation" • U.S. Soil Conservation Service • 12 Soil Orders

  24. "The 7th Approximation"

  25. Soils of the U.S.

  26. Typical Soil Profile (Spodosol)

  27. Aridisol, Kuwait

  28. Ultisols:AlabamaTennessee

  29. Oxisol, California (a Paleosol)

  30. Paleosol, Scotland

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