PowerPoint PresentationWeathering: the disintegration, or breakdown of rock materialSlide 3Slide 4Mechanical WeatheringSlide 6WeatheringSheet Joints (Exfoliation)Slide 9Exfoliated Domes, YosemiteSlide 11Frost Wedging: rock breakdown caused by expansion of ice in cracks and jointsSlide 13Slide 14Role of Physical WeatheringSurface Area and WeatheringRates of weatheringChemical WeatheringSlide 19Slide 20Slide 21Slide 22Solution: process by which rock is dissolved in waterSlide 24Olivine/pyroxene to clayFeldspars to clayQuartz to quartz (!)Calcite to …….Slide 29Biological WeatheringSlide 31Mechanical and Chemical WeatheringSlide 33Slide 34WeatheringWeathering: the disintegration, or breakdown of rock materialMechanical Weathering: no change in chemical composition--just disintegration into smaller piecesChemical Weathering: breakdown as a result of chemical reactionsCaCO3+CO2+H2O ---> Ca2+ + 2HCO3-Mechanical WeatheringPhysical breakup• pressure release• water: freeze - thaw cycles• crystallization of salt in cracks• thermal expansion and contractionAll this increases the total surface area exposed to weathering processes.Mechanical WeatheringExfoliation:Rock breaks apart in layers that are parallel to the earth's surface; as rock is uncovered, it expands (due to the lower confining pressure) resulting in exfoliation.WeatheringMechanical WeatheringSheet Joints(Exfoliation)Stone Mountain, GAHalf Dome, Yosemite, CAExfoliated Domes, YosemiteStone Mountain, GAStone Mountain, Georgia, showing the product of exfoliation due to unloadingFrost Wedging: rock breakdown caused by expansion of ice in cracks and jointsShattered rocks are common in cold and alpine environments where repeated freeze-thaw cycles gradually pry rocks apart.WeatheringThermal expansion due to the extreme range of temperatures can shatter rocks in desert environments.Repeated swelling and shrinking of minerals with different expansion rates will also shatter rocks.Role of Physical Weathering1) Reduces rock material to smaller fragments that are easier to transport2) Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weatheringSurface Area and WeatheringJoints in a rock are a pathway for water – they can enhance mechanical weatheringRates of weatheringChemical WeatheringDefinition: transformation/decomposition of one mineral into anotherMineral breakdown• carbonate dissolves• primary minerals --> secondary minerals (mostly clays)Net loss of elements retained in the soil.•Water is the main operator:–Dissolution•Many ionic and organic compounds dissolve in water–Silica, K, Na, Mg, Ca, Cl, CO3, SO4–Acid Reactions•Water + carbon dioxide <---> carbonic acid•Water + sulfur <---> sulfuric acid•H+ effective at breaking down mineralsChemical WeatheringDissolutionH2O + CO2 + CaCO3 --> Ca+2 + 2HCO3-water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion Biological activity in soilsgenerates substantial CO2Bicarbonate is the dominant ion in surface runoff.•Oxidation–Oxygen dissolved in water promotes oxidation of sulfides, ferrous oxides, native metals•Organic Activity–Plant material makes H+ ions availableChemical Weathering•Hydration: attachment of water molecules to crystalline structure of a rock, causing expansion and weakness•Hydrolysis: combination of hydrogen and oxygen in water with rock to form new substancesChemical WeatheringSolution: process by which rock is dissolved in water•Is strongly influenced by pH and temperature•When water becomes saturated, chemicals may precipitate out forming evaporite deposits.•Calcium carbonate (calcite, limestone), sodium chloride (salt), and calcium sulfate (gypsum) are particularly vulnerable to solution weathering.Chemical WeatheringBowen’sReactionSeriesGoldrichStabilitySeriesFirst toCrystallizeLast toCrystallizeSlowWeatheringFastWeatheringResistance to WeatheringOlivine/pyroxene to clay+ H2CO3 (acid)Feldspars to clay+ H2CO3 (acid)Quartz to quartz (!)+ anythingCalcite to …….nothing+ anythingThis photo of Lime Sink was taken on 20 July 1932, over a week after the drawdown, which occurred over the night of 9-10 July.‘Karst’ landforms develop in areas underlain with limestoneBiological WeatheringCan be both chemical and mechanical in nature.• roots split rocks apart• roots produce acids that dissolve rocks.• tree throw• burrowing animalsRates of weathering•Climate–Temperature and moisture characteristics–Chemical weathering•Most effective in areas of warm, moist climates – decaying vegetation creates acids that enhance weathering•Least effective in polar regions (water is locked up as ice) and arid regions (little water)–Mechanical weathering•Enhanced where there are frequent freeze-thaw cyclesWeatheringMechanical and Chemical Weathering–Fracturing, disintegration caused by mechanical weathering exposes more surface area.–Greater surface area, means more places for chemical action to
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