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WEATHERING, EROSION & SOIL FORMATION WEATHERING, EROSION, TRANSPORTATION • Weathering- Physical disintegration and chemical decomposition of rocks • Erosion- Physical removal • Transportation- Movement of eroded particles • Chemical vs. Physical Weathering • Effects of weathering – – – Surface alteration of outcrops Spheroidal weathering Differential weathering Physical Weathering Transport Abrasion WEATHERING, EROSION, TRANSPORTATION • Weathering- Physical disintegration and chemical decomposition of rocks • Erosion- Physical removal • Transportation- Movement of eroded particles • Chemical vs. Physical Weathering • Effects of weathering – – – Surface alteration of outcrops Spheroidal weathering Differential weathering Differential Weathering MECHANICAL WEATHERING • Disintegration of rocks • Frost Action – Frost wedging - rock pried apart along joints • water expands upon freezing (ice wedge) – Frost heaving Frost Action MECHANICAL WEATHERING • Pressure Release – – sheet joint exfoliation • exfoliation domes • Other – – – Plant growth; Burrowing animals Pressure of salt crystals Extreme temperature changes • Mechanical weathering increases surface area facilitating chemical weathering Exfoliation Organic Action Mechanical Weathering Growth of salt crystal in arid/semi-arid regions can split rocks Heat and cold extremes can also cause rock breakage CHEMICAL WEATHERING • Decomposition of rock to form new substances – Equilibrium • Role of Oxygen – Fe in ferromagnesian minerals becomes oxidized • Hematite • Limonite Chemical Weathering • Role of Acid – – Hydrogen ions in water pH=-Log[H+] Acid/Base • Carbonic Acid – – – H2CO3 CO2 + H2O -> H2CO3 H2CO3 -> H+ + HCO3- (in water) Solution weathering- Karstic Features • Calcite (in limestone) dissolves in acidic water • fluted (channeled) rock surface • caves Chemical Weathering • Role of Acid – – Hydrogen ions in water pH=-Log[H+] Acid/Base • Carbonic Acid – – – H2CO3 CO2 + H2O -> H2CO3 H2CO3 -> H+ + HCO3- (in water) Solution weathering- Karstic Features • Calcite (in limestone) dissolves in acidic water • fluted (channeled) rock surface • caves KARST Chemical Weathering • Chemical weathering of feldspar – H+ + feldspar -> clay mineral • Chemical weathering of other minerals • Weathering and climate • Weathering Products Chemical Weathering • Chemical weathering of feldspar – H+ + feldspar -> clay mineral • Chemical weathering of other minerals • Weathering and climate • Weathering Products
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