70.%20Weathering%20Erosion%20Transport

70.%20Weathering%20Erosion%20Transport - Weathering Erosion...

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Unformatted text preview: Weathering Erosion Transport Lecture 7 Weathering-Erosion-Transport Lecture 7: Weathering, Erosion, Transport Page 1 of 21 Lecture 7: Weathering Erosion Transport Physical Weathering Ice Ice Vegetation Vegetation Mechanical Mechanical Freeze-Thaw Frost Heave & Ice Wedging Lecture 7: Weathering, Erosion, Transport Page 2 of 21 Lecture 7: Weathering Erosion Transport Vegetation Biochemical Processes Root Penetration & Up-rooting Mechanical Weathering Rock Fall & Impact Lecture 7: Weathering, Erosion, Transport Page 3 of 21 Lecture 7: Weathering Erosion Transport Chemical Weathering Water is the MOST SIGNIFICANT AGENT Chemical Weathering HYDROLYSIS: with water HYDROLYSIS: – M+ + H2O = MOH + H+ OXIDIZATION: with oxygen OXIDIZATION: – M+ + O= = MnOm CARBONATION: with carbonic acid CARBONATION: – CO2 + H2O = H2CO3 – H2O3 + CaCO3 = Ca++ + 2HCO3 Lecture 7: Weathering, Erosion, Transport Page 4 of 21 Lecture 7: Weathering Erosion Transport Chemical Weathering CHELATION: with organics CHELATION: CATION EXCHANGE: with H+ CATION DIALYSIS: removal of an ion DIALYSIS: HYDRATION: addition of water HYDRATION: – M+ + H2O = M H2O Hydrolysis Lecture 7: Weathering, Erosion, Transport Page 5 of 21 Lecture 7: Weathering Erosion Transport Organic Weathering Lecture 7: Weathering, Erosion, Transport Page 6 of 21 Lecture 7: Weathering Erosion Transport Oxidation - Carbonation Human Activities Agricultural Chemicals & Irrigation Lecture 7: Weathering, Erosion, Transport Page 7 of 21 Lecture 7: Weathering Erosion Transport Most Weatherable Relative Weathering Resistance of Minerals Gypsum, Halite (salts) Calcite Olivine Amphibole/Pyroxene/Mica Na/Ca-Feldspar (Plagioclase) Na/CaK-Feldspar (Orthoclase) Quartz Clay Oxides Least Weatherable Weathering Chart Lecture 7: Weathering, Erosion, Transport Page 8 of 21 Lecture 7: Weathering Erosion Transport Weathering Products CHEMICAL Ions (Ca++, Na+, K+, Cl-, etc) Secondary Minerals Clays Oxides CLASTIC PARTICLES Boulders…………………………………>6 in Boulders…………………………………>6 Cobbles………………………………….2-6 in Cobbles………………………………….2Gravel…………………………….2 mm-2 in Gravel…………………………….2 mmSand……………………………..0.05-2 mm Sand……………………………..0.05Silt……………………….0.002 –0.05 mm Silt……………………….0.002 Clay……………………………..<0.002 mm Clay……………………………..<0.002 Particle Size Classification Lecture 7: Weathering, Erosion, Transport Page 9 of 21 Lecture 7: Weathering Erosion Transport Erosion GRAVITY GRAVITY – Drives all erosion processes WATER WATER – Most significant WIND WIND – Arid regions, dominant MECHANICAL MECHANICAL – Impact between particles Function of: Slope Material Water/moisture Mechanical process Gravity Lecture 7: Weathering, Erosion, Transport Page 10 of 21 Lecture 7: Weathering Erosion Transport Detachment Erosion Raindrop Erosion Raindrop QR = K(E)a QR = Raindrop Erosion K = Material Coefficient E = Kinetic energy of drops a = Constant for each soil type Soil Erosion Universal Soil Loss Equation Universal A = RK(LS)CP A = Average soil loss R = Rainfall factor K = Soil-erodibility LS = Slope Length/Steepness C = Cropping P = Conservation practice Lecture 7: Weathering, Erosion, Transport Page 11 of 21 Lecture 7: Weathering Erosion Transport Soil Loss Factors Moving Water Lecture 7: Weathering, Erosion, Transport Page 12 of 21 Lecture 7: Weathering Erosion Transport Flowing Water Erosion Boundary Shear Boundary τ = Boundary shear τ = γdS (force/area) γ = Density of the fluid Density d = depth of water S = Channel slope (ratio) Critical Tractive Force Boundary shear that just moves the Boundary most exposed particle τc = (π/6)cD(ρs – ρ)g(tanα) c = packing coefficient of grains D = mean grain diameter ρs = density of grains ρ = density of the fluid α = angle of repose of the grains Lecture 7: Weathering, Erosion, Transport Page 13 of 21 Lecture 7: Weathering Erosion Transport Smooth Sand/fine-gravel Bed Critical Tractive Force reduces to: Critical τc = 4D D = median grain size in feet Wind Erosion E = f(I, K, C, L, V) E = Wind erosion I = Soil and Slope erodibility K = Soil ridge roughness C = Wind erosion factor L = Surface length, fetch V = Vegetative cover Lecture 7: Weathering, Erosion, Transport Page 14 of 21 Lecture 7: Weathering Erosion Transport Wind Erosion Factors Mechanical Erosion Lecture 7: Weathering, Erosion, Transport Page 15 of 21 Lecture 7: Weathering Erosion Transport Human Activities Sediment Transport Lecture 7: Weathering, Erosion, Transport Page 16 of 21 Lecture 7: Weathering Erosion Transport Sorting Transport of sedimentary particles Transport leads to sorting/grading of the deposit All particles the same size All – Well Sorted = Poorly Graded Particle sizes well mixed Particle – Poorly Sorted = Well Graded Lecture 7: Weathering, Erosion, Transport Page 17 of 21 Lecture 7: Weathering Erosion Transport Grain Shape Rounding increases with transport distance Erosion-Particle Size Inertia Lecture 7: Weathering, Erosion, Transport Page 18 of 21 Lecture 7: Weathering Erosion Transport Erosion-Cohesion Cohesion Erosion: Inertia + Cohesion Lecture 7: Weathering, Erosion, Transport Page 19 of 21 Lecture 7: Weathering Erosion Transport Transport-Deposition Erosion-Transport-Deposition Lecture 7: Weathering, Erosion, Transport Page 20 of 21 Lecture 7: Weathering Erosion Transport Hjülstrom Diagram Break Lecture 7: Weathering, Erosion, Transport Page 21 of 21 Lecture 7: Weathering Erosion Transport ...
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This note was uploaded on 04/16/2011 for the course GEOL 320 taught by Professor Mathewson during the Spring '11 term at Texas A&M.

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