Weathering Erosion & SoilsWeathering is the the breakdown ofsolid rock at or near the Earth'ssurface.Weathering may bemechanical or chemical• Mechanical weathering is the physicalabrasion due to the action of– Water (Streams, Rivers and Surf)– Ice (Frost, Snow, Glaciers)–Wind• Chemical weathering is the chemicalreaction of minerals with the water andoxygen of our atmosphere.Chemical Weathering• Increases with Temperature• Increases with Moisture (Rainfall)• Increases with Acidity• Decreases with Silica Polymerization(Bowen’s Reaction Series)Chemical Weathering ofIgneous Rock Minerals• Oxides > Hydroxides• Ferromags > Mg-Fe Clay• Feldspar > Al-Clay + Na+ + K+ + Ca++• Mica > Al-Fe Clay + Na+ + K+ + Ca++•Quartz > Quartz SandErosion and Transport• Erosion is the reduction of exposed landforms.• Transport is the movement of eroded materialdownslope.• Transport by water sorts the particles by size.• Because different minerals dominate differentsize fractions, the deposited material differs fromthe parent rock in mineralogy and chemistry.Weathering Products AreSorted by Size• Coarse particles require moving water or wind– Rock grains: Pebbles, Cobbles, Boulders– Quartz: Pebbles and Sand• Fine particles require standing water.– Clays Very fine (<10 µm)• Dissolved ions require evaporation–Na+ + K+ + Ca++DissolvedSoilsSoils•A regolith is any accumulation of fine rockmaterial on a planetary surface.•A soil is the accumulation of weathered rockmaterial together with organic matter.•A pedocal is a dry-climate soil containing solublecalcium minerals (calcite).•A pedalfer is a humid-climate soil rich in Al andFe.•A laterite is an extreme pedalfer in tropicalclimates.Acid Rain• Results from burning of sulfur-rich fossilfuels.• Is mainly a problem in humid temperateclimates (NE US, Europe).Acid Mine Drainage• Results from oxidation of sulfide minerals (pyrite)in unsaturated rock.•2FeS2 +7H2O + 2O2 > 2Fe(OH)3 + 4H2SO4• Pyrite + water + oxygen > limonite + sulfuric acid• Big Problem in
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