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Weathering vs. ErosionWeathering vs. Erosion
• What is weathering?What is weathering?– Breakdown of earth materialsBreakdown of earth materials
• What is erosion?What is erosion?– Removal of earth material Removal of earth material
• GlaciersGlaciers• WindWind• WaterWater
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Types of WeatheringTypes of Weathering
• There are two primary types of There are two primary types of weathering:weathering:– Physical – Breaking a material into Physical – Breaking a material into
smaller particlessmaller particles– Chemical – Changing the materials Chemical – Changing the materials
compositioncomposition
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Physical WeatheringPhysical Weathering
• Physical or Physical or mechanical mechanical weatheringweathering– Breaking a rock or Breaking a rock or
mineral into mineral into smaller piecessmaller pieces
– No change in No change in compositioncomposition
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Physical WeatheringPhysical Weathering
• There are six types of physical There are six types of physical weatheringweathering– AbrasionAbrasion– Frost wedgingFrost wedging– Salt crackingSalt cracking– Organic activityOrganic activity– Pressure reliefPressure relief– Thermal expansionThermal expansion
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Physical WeatheringPhysical Weathering
1)1) Abrasion – Abrasion – – A rock is pelted by a stream of small A rock is pelted by a stream of small
particlesparticles– Particles carried by wind or waterParticles carried by wind or water– Think of sandblastingThink of sandblasting
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Physical WeatheringPhysical Weathering
2)2) Frost Frost wedging – wedging – – Water fills a crackWater fills a crack– Freezing water Freezing water
expands cracksexpands cracks– Destroys rockDestroys rock
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Physical WeatheringPhysical Weathering
3)3) Salt cracking – Salt cracking – – Similar to frost wedgingSimilar to frost wedging– Most common in coastal regionsMost common in coastal regions
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Physical WeatheringPhysical Weathering
4)4) Organic Organic activity – activity – – Animals burrowingAnimals burrowing– Plants grow and the Plants grow and the
roots spread roots spread
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Physical WeatheringPhysical Weathering
5)Pressure relief 5)Pressure relief cracking – cracking – – Depth equals Depth equals
higher pressurehigher pressure– Pressure makes a Pressure makes a
rock smallerrock smaller– Pressure is Pressure is
released, and the released, and the rock expands and rock expands and crackscracks
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Physical WeatheringPhysical Weathering
• Pressure relief Pressure relief (cont’d)(cont’d)– Cracks are called Cracks are called
jointsjoints– Joints - Joints - rocks rocks
separate but don’t separate but don’t movemove
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Physical WeatheringPhysical Weathering
• Pressure relief Pressure relief (cont’d)(cont’d)– Within igneous Within igneous
bodies, the joints bodies, the joints tend to form tend to form parallel to the parallel to the surfacesurface
– This is called This is called exfoliationexfoliation
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Physical WeatheringPhysical Weathering
6)6) Thermal expansion – Thermal expansion – – Heating and cooling = expansion and Heating and cooling = expansion and
contractioncontraction– Different minerals expand and contract Different minerals expand and contract
differentlydifferently– Weakens a rockWeakens a rock
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Chemical WeatheringChemical Weathering
• Chemical weathering – Chemical weathering – – A rock is broken down and it’s A rock is broken down and it’s
composition changescomposition changes– Exposure to air or water initiate Exposure to air or water initiate
chemical changeschemical changes
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Chemical WeatheringChemical Weathering
• Chemical weathering can be broken Chemical weathering can be broken into a number of categoriesinto a number of categories– OxidationOxidation– HydrolysisHydrolysis– Weathering by solutionWeathering by solution
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Chemical WeatheringChemical Weathering
1)1) Oxidation – Oxidation – – Elements reacting with free oxygenElements reacting with free oxygen– Oxygen combines with elements, Oxygen combines with elements,
removing them from the mineralremoving them from the mineral– RustingRusting
• 4 Fe (+3) + 3 O4 Fe (+3) + 3 O22 (-4) = 2 Fe (-4) = 2 Fe22OO33 (Hematite) (Hematite)
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Chemical WeatheringChemical Weathering
• Oxidation (cont’d) Oxidation (cont’d) – – – Pyrite (FeSPyrite (FeS22) is ) is
commonly oxidized commonly oxidized when exposed to when exposed to oxygen at the oxygen at the surfacesurface
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Chemical WeatheringChemical Weathering
2)2) Hydrolysis – Hydrolysis – – Hydrogen ions (H+) replaces other Hydrogen ions (H+) replaces other
positively charged ions positively charged ions – Happens within slightly acidic waterHappens within slightly acidic water
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Chemical WeatheringChemical Weathering
• Hydrolysis (cont’d) – Hydrolysis (cont’d) – – Acidic water travels across a rock, Acidic water travels across a rock,
replacing cations with hydrogen replacing cations with hydrogen – Common reaction:Common reaction:
• Potassium feldspar + hydrogen ions + Potassium feldspar + hydrogen ions + water = Muscovite mica + potassium ions + water = Muscovite mica + potassium ions + dissolved silica dissolved silica
• 12H12H22O + O + 2H2H++ + 3KAlSi + 3KAlSi33OO88 = = KAlKAl33SiSi33OO1010(OH)(OH)22 + + 2K2K++ + 6H + 6H44SiOSiO44
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Chemical WeatheringChemical Weathering
3)3) Weathering by solution –Weathering by solution –– Also called dissolutioningAlso called dissolutioning– Ions pulled into solutionIons pulled into solution– Halite (salt) and calciteHalite (salt) and calcite
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Chemical WeatheringChemical Weathering
• Weathering by Weathering by solution (cont’d) –solution (cont’d) –– Water is dipolar Water is dipolar – Pure, neutral water Pure, neutral water
can weather by can weather by solutionsolution
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Chemical WeatheringChemical Weathering
• Weathering by Weathering by solution (cont’d) –solution (cont’d) –– Water attaches to Water attaches to
the ionsthe ions– The salt is The salt is
dissolveddissolved
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Chemical WeatheringChemical Weathering
• Weathering by solution (cont’d) –Weathering by solution (cont’d) –– Water isn’t normally neutralWater isn’t normally neutral– Natural water is usually slightly acidicNatural water is usually slightly acidic
– HH22O + COO + CO22 = H = H22COCO33 = H = H++ ion + HCO ion + HCO3)3)
• Excess HExcess H++
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Chemical WeatheringChemical Weathering
• Weathering by Weathering by solution (cont’d) –solution (cont’d) –– Carbonic acid Carbonic acid
reacts with calcite reacts with calcite (CaCO(CaCO33)) in in limestones limestones
– Calcite dissolves Calcite dissolves into solutioninto solution
– CaCOCaCO33 + H + H22COCO33 = = Ca + 2HCOCa + 2HCO33
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Chemical WeatheringChemical Weathering
• Acid Rain – Acid Rain – – Defined – Precipitation with a pH < 5.0Defined – Precipitation with a pH < 5.0– Excess acid rain can:Excess acid rain can:
• Rapidly weathers certain rock types Rapidly weathers certain rock types • Effects groundwater qualityEffects groundwater quality
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Chemical WeatheringChemical Weathering
• Acid rain (cont’d) – Acid rain (cont’d) – – Result of water and Result of water and
industrial wastes industrial wastes mixingmixing
– Wastes from Wastes from burning fossil fuelsburning fossil fuels
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Chemical WeatheringChemical Weathering
• Acid rain (cont’d) - Acid rain (cont’d) - – Waste products include:Waste products include:
• SO2SO2• NO2NO2
– These wastes create:These wastes create:• Nitric acid - Nitric acid - NONO22 + O + O22 + H + H22O = HNOO = HNO33
• Sulfuric acid -Sulfuric acid - SO SO22 + O + O22 + H + H22O = HO = H22SOSO44
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Chemical WeatheringChemical Weathering
• Acid rain (cont’d) –Acid rain (cont’d) –– Acid rain dissolves marble or limestone Acid rain dissolves marble or limestone
(weathering by solution)(weathering by solution)– Excess acid rain pollutes ponds, lakes Excess acid rain pollutes ponds, lakes
or reservoirs or reservoirs – Acid rain can leach into the Acid rain can leach into the
groundwatergroundwater
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Rate of WeatheringRate of Weathering
• Variables influencing the rate of Variables influencing the rate of weathering include weathering include – ClimateClimate– Rock typeRock type– Particle sizeParticle size– Particle shapeParticle shape
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Rate of WeatheringRate of Weathering
1)1) Climate – Climate – – Very important Very important
consideration re: consideration re: weatheringweathering
– MoistureMoisture
Physical weathering
Chemical weathering
Cool, dry climate
Cool, moist climate x xWarm, dry climate xWarm, moist climate x x
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Rate of WeatheringRate of Weathering
2)2) Rock type – Rock type – – Different rock weather at different ratesDifferent rock weather at different rates– Granite weathers slowlyGranite weathers slowly
• Mineral strengthMineral strength
– Limestone weathers quicklyLimestone weathers quickly• CalciteCalcite
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Rate of WeatheringRate of Weathering
3)3) Particle size – Particle size – – Rock or particle size influences rate of Rock or particle size influences rate of
weatheringweathering– More surface area exposed = quicker More surface area exposed = quicker
weatheringweathering
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Rate of WeatheringRate of Weathering
• Particle size Particle size (cont’d) – (cont’d) – – Small particles Small particles
have more surface have more surface area exposed area exposed
– More surface area More surface area = faster weathering= faster weathering
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Rate of WeatheringRate of Weathering
4)4) Particle shape –Particle shape –– A particle with numerous edges or A particle with numerous edges or
corners will weather quicklycorners will weather quickly– A particle with few edges or corners A particle with few edges or corners
will weather slowlywill weather slowly
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Rate of WeatheringRate of Weathering
• Particle shape Particle shape (cont’d)(cont’d)– A corner weathers A corner weathers
quickestquickest– An edge weathers An edge weathers
slowerslower– A face weathers A face weathers
slowestslowest
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