Earth Science Unit 1.4: Weathering and Soils

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Earth Science Unit 1.4Weathering and Soils
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The Rock Cycle
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WeatheringThe breakdown of rock near the surface
due to surface processes, such as

• Chemical Alteration
• Solution leaching of water
• Biological action
• Hydration
• Mechanical
• Impact
• Wedging Frost, Plant Roots, Salt Crystal
  Growth, Expansion of Hydrated Minerals

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Weathering Rates
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Differential Weathering and Erosion
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Differential Weathering and Erosion
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Mass-WastingMovement of Large Amounts of
Material Downhill under Gravity

• Creep
• Mudflows
• Slump
• Rockfalls
• Avalanches

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Surface Area and Weathering
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Spheroidal Weathering
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Spheroidal Weathering and Exfoliation
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Spheroidal Weathering
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Joints and Spheroidal Weathering
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What Determines Soil Type

• Climate
• Vegetation
• Drainage
• Time
• Parent Material
• Residual - Transported
• Least Important Factor for Mature Soils

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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

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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

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Principal Soil Horizons

• O - Organic (Humus) Often Absent
• A Leaching (Clay Removed)
• E - Bleached Zone - Only in Certain Soils
• B Accumulation
• Absent in Young Soils
• Distinct in Old Soils
• Al, Fe, Clay (Moist)
• Si, Ca (Arid)
• C - Parent Material (bedrock)

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Soil Classification

• 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

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"The 7th Approximation"

• U.S. Soil Conservation Service
• 12 Soil Orders

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"The 7th Approximation"
Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development Degree of Weathering and B Horizon Development
Little Slight Slight Moderate Large Extreme
Entisols Aridisols Aridisols
Inceptisols Inceptisols Alfisols
Spodosols Ultisols
Mollisols Oxisols
Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials Soils Defined by Special Constituent Materials
Andisols Andisols Volcanic Ash Volcanic Ash Volcanic Ash Volcanic Ash
Histosols Histosols Peat, Organic Matter Peat, Organic Matter Peat, Organic Matter Peat, Organic Matter
Vertisols Vertisols Self-Mixing Clay Soils Self-Mixing Clay Soils Self-Mixing Clay Soils Self-Mixing Clay Soils
Gelisols Gelisols Soils on Permafrost Soils on Permafrost Soils on Permafrost Soils on Permafrost
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Soils of the U.S.
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Typical Soil Profile (Spodosol)
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Aridisol, Kuwait
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UltisolsAlabamaTennessee
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Oxisol, California (a Paleosol)
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Paleosol, Scotland