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Lecture 6 Weathering and Soil Physical Geology Lecture Outline I Weathering A) B) Definitions Mechanical Weathering C) Chemical Weathering i. ii. iii. Frost Action Pressure Release Other Mechanical Processes i. Agents a) Acids b) Oxidation c) Solution Weathering Examples ii. II Soils A) B) C) D) E) F) III Definitions Soil Horizons and Classification Soil Character and Thickness Organic Activity and Soil Development Soils and Climate Paleosols Conclusions Physical Geology Weathering Definition weathering: the destructive processes by which rocks are changed on exposure to atmospheric agents at or near the earth's surface, with little or no transport of the altered material. Specifically, it is the physical disintegration and chemical decomposition of rock that produce an in-situ layer of waste and prepare sediments for transportation. Physical Geology Weathering Definition Physical Geology Weathering Results Smaller Pieces of Rock Increased Surface Area Conduits for Water Physical Geology Weathering Processes Physical Geology Mechanical Weathering Frost Action Physical Geology Mechanical Weathering Pressure Release - Exfoliation Physical Geology Mechanical Weathering Other Processes Salt Crystal Plant Growth Burrowing Animals Physical Geology Chemical Weathering chemical weathering: the process of weathering by which chemical reactions(hydrolysis, hydration, oxidation, carbonation, ion exchange and solution) transform rocks and minerals into new chemical combinations that are stable under conditions prevailing at or near the earth's surface. Physical Geology Chemical Weathering Agents Acids Oxidation Solution Weathering Physical Geology Chemical Weathering Agents - Acids acid: chemical compound that gives off hydrogen ions (H+) when they dissociate in water Physical Geology Chemical Weathering Agents - Oxidation oxidation: the process of combining w/ oxygen Hematite Limonite 4Fe + 3O2 -----> 2Fe2O3 Physical Geology Chemical Weathering Agents - Solution Weathering Physical Geology Chemical Weathering Products Physical Geology Chemical Weathering Chemical Weathering of Feldspar Physical Geology Weathering Factors That Influence Weathering Physical Geology Weathering Climate and Weathering Physical Geology Soil Definitions (1): any kind of loose, unconsolidated earth material (engineering/construction) (2): layer of weathered, unconsolidated material on top of bedrock (geology) (3): horizons of weathered, unconsolidated material that contains organic matter and is capable of supporting plant growth (soil science) Physical Geology Soils Soil Horizons and Classification Physical Geology Soils Character and Thickness Slope Age Climate Physical Geology Soils Organic Activity Physical Geology Soils Paleosols