Weathering and Erosion

• Definition: Weathering is the interaction of atmosphere, hydrosphere and biosphere with rocks exposed at the earths surface to produce regolith



• Why? Rocks and minerals are physically and chemically altered so that they are more nearly in equilibrium with a new set of environmental conditions



• Process: Parent material is eroded, transported, deposited as sediment.



• Types of weathering
• decomposition
• disintegration



• Differential weathering

• Physical (Mechanical) Weathering
• Natural weakness of parent rock
• Frost action
• freeze heaving
• frost wedging (talus)
• Pressure release
• sheet joints
• thermal expansion and contraction
• exfoliation and spheroidal weathering
• plants and animals



• Chemical Weathering
• chemical reactions between minerals in rocks and air and water
• solution
• hydrolysis
• oxidation



• Rates of chemical weathering
• particle size
• climate: dry vs. wet, warm vs. cold
• parent material
• solubilities
• structure: granite vs. shale
• soils
• time
• comparison to Bowen's reaction series
• Soils
• Regolith vs. soil
• Profiles and horizons
• O-Horizon: humus
• A-Horizon
• B-Horizon
• C-Horizon
• Bedrock



• Factors controlling soil formation
• climate
• tropical humid: laterites
• dry: pedocals (caliche)
• temperate: pedalfer
• parent material
• organic activity
• relief and slope
• time



• Paleosols