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Chapter 15 Weathering, Mass Wasting & Erosion. Preliminaries to Erosion: Weathering and Mass Wasting Weathering Mass Wasting Breaking down of rock

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Text of Chapter 15 Weathering, Mass Wasting & Erosion. Preliminaries to Erosion: Weathering and Mass Wasting...

  • Chapter 15

    Weathering, Mass Wasting & Erosion

  • Preliminaries to Erosion: Weathering and Mass Wasting WeatheringMass WastingBreaking down of rock into smaller components by atmospheric and biotic agentsInvolves the downslope movement of broken rock due to gravity ErosionMore extensive and distant removal of fragmented rock material Denudation

  • Impacts of Weathering & Mass WastingWeathering = fragmentation of rock in place no obvious movementMass Wasting = involves down slope movement empty space above and debris strewn belowErosion = wearing away of the land by the action of water, ice or wind

  • DenudationWeathering followed by mass wasting followed by erosionResults in a lowering of the landscape over millions of years

  • Colorado River is major cause of erosion. Weather and mass wasting have also played a part in the carving of Grand Canyon

  • WeatheringJointingWeathering AgentsMechanical WeatheringChemical WeatheringBiological WeatheringClimate and Weathering

  • Weathering1st step in external process of rock disintegrationThink of weathering as aging of rock surfacesWhere lithosphere and atmosphere meet (land/air interface)Mechanical or chemicalExposed bedrock is prone to weathering its more fragileUnderlying rock is stronger

  • Faults and Jointsfaults = displacement of landjoints = no displacement of landdisplacementno displacement

  • Faults The cracking and displacement of adjacent blocks of rock as a result of the severe stresses set up by tectonic activity

  • JointingVertical

    HorizontalCracks resulting from stress very commonShow no displacement

  • Weathering AgentsMechanicalChemicalBiologicalMost are atmospheric easy for gas to penetrate bedrockWater can also penetrateTemperature changeBiotic influence

  • Mechanical WeatheringDisintegration of rock materialNo change in chemical compositionMostly occurs at or near the surfaceFrost Wedging = freeze/thaw action of waterSalt Wedging = salt crystallizesTemperature change = heat expansion & cold contractionExfoliation = layers peel off

  • Frost WedgingWater permeates cracks/fissures in rocks, then freezes, then melts

  • ExfoliationCurved layers peel off bedrock Occurs at different scalesExfoliation - hillExfoliation - single boulder

  • Impact of Mechanical WeatheringAs rock is fragmented, the amount of rock surface increasesMore surface area exposed = more fragmentation

  • Chemical WeatheringOxidation HydrolosisCarbonationDecomposition of rocks by alteration of mineralsChemical weathering requires moistureMore in humid regions than aridRequires oxygen, water & carbon dioxide3 processes are:

  • OxidationOxidation is the combination of a substance with oxygenCombines with metallic elements to form new compoundsUsually softer and more easily eroded

  • Red Rocks - Oxidation

    Iron oxides are produced Iron oxides are red, orange, or brown in color "Georgia Red Clay" derives its color from the oxidation of iron bearing minerals Oxygen combines with iron-bearing silicate minerals causing "rusting"

  • HydrolysisDecomposition of a chemical compound by reaction with water Igneous rock is very susceptibleIncreases volume of rock and brings on disintegration

  • CarbonationReaction between carbon dioxide in water & carbonate rocksProduces calcium bicarbonate (very soluble)Easily removed by runoff or percolation

  • Biological WeatheringPlants & AnimalsRoots, lichensBurrowing animals

  • Climate and WeatheringWeathering is enhanced by climateMore chemical weathering with high temperatures and lots of rain

  • Mass WastingFallSlideLandslideSlumpFlowEarthflowMudflowDebris FlowCreep

  • Mass Wasting2nd step in external process of rock disintegrationMovement of rock and soil downslope under the influence of gravity Denudation: weathering followed by mass wasting followed by erosion

  • Fall: Falling of pieces of rock downslopeSlide: Landslide instantaneous collapse of a slopeFlow: Gravity impelling force with water to bring section of a slope down i.e. mudflowCreep: Slowest and least perceptible gradual downhill movement

  • Talus SlopePieces of rock become wedged in slope, then are loosened and fall to bottom

  • Visual Evidence of Creep

  • Freeze Thaw ProcessesFreezing lifts particle perpendicular, then melting deposits it further downslope