Weathering Weathering and Soilsand Soils

Marble headstones in Southern Vermont

Weathering Weathering and Soilsand Soils

Granite headstone in Southern Vermont

Weathering and SoilsWeathering and Soils MechanicalMechanical Weathering- the physical Weathering- the physical

breakdown of rocksbreakdown of rocks ChemicalChemical Weathering- reaction of rocks Weathering- reaction of rocks

with water, acids, oxygen, etc. with water, acids, oxygen, etc.

Mechanical Mechanical WeatheringWeathering

Tectonic Tectonic JointingJointing

Mechanical WeatheringMechanical Weathering

ExfoliationExfoliationMechanical WeatheringMechanical Weathering

ExfoliationExfoliationMechanical WeatheringMechanical Weathering

ExfoliationExfoliationMechanical WeatheringMechanical Weathering

Chemical Chemical WeatheringWeathering

Solution:Solution:HH22O + COO + CO22 = =

HH22COCO33 ( H ( H++ + HCO + HCO33-- ) )

in air (acid rain)in air (acid rain) acidacid

gasgasLimestone dissolves readilyLimestone dissolves readily

CaCOCaCO33 + 2 H + 2 H++ (aq) = (aq) =

CaCa+2+2 + CO + CO22 + H + H22OO

Chemical WeatheringChemical Weathering Solution: Karst TopographySolution: Karst Topography

Chemical WeatheringChemical Weathering Solution: Karst TopographySolution: Karst Topography

Chemical WeatheringChemical Weathering Karst Sinkhole- FloridaKarst Sinkhole- Florida

Chemical WeatheringChemical Weathering Karst Sinkhole- FloridaKarst Sinkhole- Florida

Chemical WeatheringChemical Weathering Tower Karst - ChinaTower Karst - China

Chemical WeatheringChemical Weathering

Oxidation:Fe2SiO4 + ½ O2 = Fe2O3 + SiO2

Chemical WeatheringChemical Weathering

Chemical Weathering Chemical Weathering Differential WeatheringDifferential Weathering

Chemical WeatheringChemical Weathering Differential WeatheringDifferential Weathering

Weathering can preferentially dissolve out mafics & increase the sialic component in sediments to yield “granite”

Chemical WeatheringChemical WeatheringWhat happens when granite is weathered?

The biotite and hornblende will undergo hydrolysis to form clay, and oxidation to form iron

oxides.

The feldspars will undergo hydrolysis to form kaolinite (clay) and release Na+ and K+ ions into solution

The quartz (and muscovite, if present) will remain as residual minerals because they are very resistant to weathering.

Idealized soil profile from a humid climate at middle latitudes

Zon

e of

Lea

chin

g

Horizon Development and Horizon Development and Climate Climate

Soil textural classesSoil textural classes

Topsoil ecosystem Topsoil ecosystem in a temperate in a temperate climateclimate

Effect of climate on soil developmentEffect of climate on soil development

Chemical WeatheringChemical Weathering

Transported SoilsTransported Soils

Wind-blown Glacial Wind-blown Glacial LoessLoess Deposits Deposits

Wind-blown Glacial Wind-blown Glacial Loess DepositsLoess Deposits

The Principal Soil TypesThe Principal Soil Types

Effect of climate on soil typesEffect of climate on soil types

tundra soils

Precipitation

Tem

pera

ture

cold

hot hot

coollow high50 cm/yr

pedalferspedocals

laterites

tundra soils

Principal soil types in the USAPrincipal soil types in the USA

Effect of climate on soil typesEffect of climate on soil types

A typical pedocal with A typical pedocal with white white calichecaliche (CaCO (CaCO33) )

deposits in a shallow B deposits in a shallow B horizonhorizon

Effect of climate on soilsEffect of climate on soils

Making Making laterite laterite bricksbricks

Temple at Temple at Angkor Angkor

Wat Wat CambodiaCambodia

(700 yrs (700 yrs old)old)

Laterite

Tundra soil

A Newer A Newer Classification Classification of Soil Typesof Soil Types

Pf

Pc

Pf

Pf, Pc

L

Pf, L

Rates of soil formation:Rates of soil formation:

Central USA: ~ 1 cm/100 years in very porous Central USA: ~ 1 cm/100 years in very porous and permeable rockand permeable rock

Humid N. Carolina: ~ 1 cm/5 yearsHumid N. Carolina: ~ 1 cm/5 years““

Granite may require over 1000 years for a cmGranite may require over 1000 years for a cm

Both Ends of the Erosion ProblemBoth Ends of the Erosion Problem

Serious Serious soil erosionsoil erosion and gully and gully formation related to diversion of formation related to diversion of water runoff over a few months water runoff over a few months in central Californiain central California Sediment pollutionSediment pollution following following

heavy rains in North Carolinaheavy rains in North Carolina

Soil DegradationSoil Degradation ErosionErosion DeforestationDeforestation Agricultural depletionAgricultural depletion Contamination - PollutionContamination - Pollution

SalinizationSalinization PesticidesPesticides Chemical additions and spillsChemical additions and spills

UrbanizationUrbanization DesertificationDesertification OvergrazingOvergrazing

Raindrop impact: Raindrop impact: millions in a single millions in a single shower hit at ~ 30 mphshower hit at ~ 30 mph

Soil ErosionSoil Erosion

Rill-wash and gullying in loose Rill-wash and gullying in loose and poorly-consolidated soilsand poorly-consolidated soils

Soil ErosionSoil Erosion

Soil Lost (tons/km2/yr) % runoffWoods ~ 0 0.12Grass 10 6.5Corn 18087 42Fallow 17050 49

Soil Erosion for Various Uses

Soil ErosionSoil Erosion

Number of dust storms during the month of March, 1936Number of dust storms during the month of March, 1936

Soil ErosionSoil Erosion

Effects of logging in MadagasgarEffects of logging in Madagasgar

Soil ErosionSoil Erosion

Figure 3.12:Figure 3.12: (a) a natural forested slope(a) a natural forested slope(b) the same slope following a clearcut(b) the same slope following a clearcut

Soil ErosionSoil Erosion

Figure 3.12:Figure 3.12: (c) the same slope after conversion to farmland(c) the same slope after conversion to farmland(b) the same slope following urbanization(b) the same slope following urbanization

Soil ErosionSoil Erosion

1968 motorcycles 1968 motorcycles first come to Deer first come to Deer

Creek near Creek near Bakersfield, CABakersfield, CA

1972 after only 4 1972 after only 4 years of ORV use years of ORV use little vegetation or little vegetation or

topsoil remainstopsoil remains

Soil ErosionSoil ErosionORV users increased ORV users increased from 21 to 38 million from 21 to 38 million

between 1982 and 1992between 1982 and 1992

ATVs rip through a marsh in ATVs rip through a marsh in West VirginiaWest Virginia

Great Grizzly Hike, MontanaGreat Grizzly Hike, Montana

Soil ErosionSoil Erosion

1985 photo of bulldozer and jeep tracks in 1985 photo of bulldozer and jeep tracks in Alaskan tundra made in 1946Alaskan tundra made in 1946

Soil ErosionSoil Erosion

Salt accumulation due to irrigation in Salt accumulation due to irrigation in an arid climate: San Fernando Valleyan arid climate: San Fernando Valley

Worldwide Distribution of Salt-affected SoilsWorldwide Distribution of Salt-affected Soils

Chemical Contamination of SoilsChemical Contamination of Soils

Grain production Grain production levels off while levels off while population population continues to growcontinues to grow

Strip-croppingStrip-croppingand and

Contour plowingContour plowing

Combating Soil DegradationCombating Soil Degradation

Rice terraces in Rice terraces in AsiaAsia

Combating Soil DegradationCombating Soil Degradation

No-tillNo-tillFarmingFarming

Combating Soil DegradationCombating Soil Degradation