What is Weathering?What is Weathering?

Weathering is the Weathering is the chemicalchemical or or physicalphysical breakdownbreakdown of a of a rock or mineral due to rock or mineral due to exposure to the exposure to the atmosphereatmosphere..

Physical or (mechanical Physical or (mechanical Weathering Weathering

Physical or (mechanical) Physical or (mechanical) : : mechanicalmechanical breakdownbreakdown of rock or of rock or minerals.minerals. Just breaks into Just breaks into smaller piecessmaller pieces, , composition of the material is composition of the material is NOTNOT changed!! changed!!

Chemical WeatheringChemical Weathering

Chemical Chemical : : decompositiondecomposition of of material.material.

The composition The composition ISIS Changed!!! Changed!!!

You get something new!You get something new!

Oxidation of Sandstone: turns RED!

Physical (Mechanical) Physical (Mechanical) WeatheringWeathering

There are several different types of There are several different types of physical weathering:physical weathering:

1.) 1.) Frost or Ice WedgingFrost or Ice Wedging –The –The breakingbreaking downdown of rock by the force exerted by of rock by the force exerted by water water expanding as it expanding as it freezesfreezes into ice. into ice.

Frost Wedging Cont….Frost Wedging Cont….

Water Water expandsexpands as it freezes, this breaks the rock into as it freezes, this breaks the rock into angular fragmentsangular fragments..

Occurs Occurs A LOTA LOT in Western New York –Causes most in Western New York –Causes most POTHOLES!!!!POTHOLES!!!!

Will Will ONLYONLY occur in areas where the temperature occur in areas where the temperature alternates alternates aboveabove freezing and freezing and belowbelow freezing!!! freezing!!!

Frost Wedging animation

2.) 2.) ExfoliationExfoliation

ExfoliationExfoliation – – ErosionErosion of upper rock causes of upper rock causes underlying rock to underlying rock to expandexpand resulting in resulting in crackingcracking and and peelingpeeling of rock in slabs. of rock in slabs.

Think of Think of onion skin layersonion skin layers and peeling and peeling them off!!them off!!

PHYSICAL WEATHERING PHYSICAL WEATHERING EXFOLIATION – PEELING AWAY EXFOLIATION – PEELING AWAY

OF ROCKOF ROCKdue to unloading (reduced pressure at earth’s surface) or fluctuations in temperature. Rocks expand and crack

PHYSICAL WEATHERING - PHYSICAL WEATHERING - EXFOLIATIONEXFOLIATION

3.) 3.) Organic ActivityOrganic Activity

3.) 3.) Organic Activity Organic Activity (plant and animal)(plant and animal)

Organic ActivityOrganic Activity – – plant rootsplant roots or or animalsanimals like burrowing worms can cause rock like burrowing worms can cause rock to to breakdownbreakdown..

PHYSICAL WEATHERING – PHYSICAL WEATHERING – ROOT ACTIONROOT ACTION

PLANT ROOTS UPLIFT AND PLANT ROOTS UPLIFT AND FRACTURE ROCKFRACTURE ROCK

4.) Wetting/Drying4.) Wetting/Drying

Wetting and DryingWetting and Drying - - additionaddition of of waterwater to mineral structure causes to mineral structure causes structure to structure to expand.expand.

Mudcracks form from the wetting and drying of clay material.

Important!!!Important!!!What happens to the erosion rate when you What happens to the erosion rate when you

increase the surface area?increase the surface area?

Physical weathering Physical weathering increasesincreases the the surface areasurface area of rocks/minerals.of rocks/minerals.

Taking a rock/mineral and breaking it up into Taking a rock/mineral and breaking it up into smaller piecessmaller pieces causes it to take up causes it to take up more spacemore space (surface area) and will eventually (surface area) and will eventually increaseincrease the the rate of rate of chemical weatheringchemical weathering to occur. to occur.

Physical Weathering

occurs

Let’s Work This Through!

Starting Volume:_______________ Volume:________________________

Total Surface Area:____________ Surface Area:__________________

(2 feet)3 = 8ft3(2 feet)3 = 8ft3

6 x (1foot)2 x 8 = 48ft26 x (2ft)2=24ft2

HydrolysisHydrolysis – the – the chemicalchemical reaction between reaction between waterwater and other substances. and other substances.

Silicate minerals will often form clay from this process.

Kaolin mine, central Georgia (feldspar weathered into clay by hydrolosis)

Chemical WeatheringChemical Weathering

Hydrolysis contHydrolysis cont……HaliteHalite, , gypsumgypsum, and , and limestonelimestone are most are most

susceptible to becoming weathered by susceptible to becoming weathered by water, and most compounds are at least water, and most compounds are at least slightly soluble in water, so water is called slightly soluble in water, so water is called the the UNIVERSAL SOLVENTUNIVERSAL SOLVENT..

Chemically Weathered Limestone

2.) 2.) CarbonationCarbonation

Carbonation (Carbonic Acid)Carbonation (Carbonic Acid) – – dissolvingdissolving of of substances by substances by acidsacids in water often leaving in water often leaving insoluble remainsinsoluble remains..

Carbonic AcidCarbonic Acid can devastate rocks made of can devastate rocks made of calcitecalcite. Rocks such as limestone and . Rocks such as limestone and dolomite can be entirely dissolved, leaving dolomite can be entirely dissolved, leaving extensive caverns.extensive caverns.

Caves formed from

Carbonation

3.) 3.) OxidationOxidationOxidationOxidation – – chemicalchemical reaction of a substance reaction of a substance

with with oxygenoxygen causing a causing a rustrust material to form. material to form.

Note: Most rocks/minerals will appear RED in Note: Most rocks/minerals will appear RED in color after an oxidation reaction.color after an oxidation reaction.

Oxidation of Sandstone

Weathering and Climate Weathering and Climate

So, what effect does climate have on weathering? So, what effect does climate have on weathering?

ClimateClimate plays a very important role in weathering. plays a very important role in weathering.

The The temperaturetemperature and and amount of moistureamount of moisture influences the type of weathering that will occur.influences the type of weathering that will occur.

WarmWarm and and wetwet climates produce mostly climates produce mostly chemical chemical weatheringweathering. . NeverNever any frost wedging. any frost wedging.

CoolCool and and slightly wetslightly wet climates produce mostly climates produce mostly physical weatheringphysical weathering..

Factors Effecting Weathering Factors Effecting Weathering RateRate

Weathering RateWeathering Rate Factors Effecting Weathering RateFactors Effecting Weathering Rate

LowLow Highly resistant mineralsHighly resistant minerals Massive rocks (big blocks)Massive rocks (big blocks) Little to no rainfallLittle to no rainfall Low temperaturesLow temperatures Little or no soilLittle or no soil Little organic activityLittle organic activity

MediumMedium Moderately resistant mineralsModerately resistant minerals Average rock sizeAverage rock size Some rainfallSome rainfall Medium temperaturesMedium temperatures Soil is presentSoil is present Organic activity is moderateOrganic activity is moderate

HighHigh Unstable minerals (easily broken down)Unstable minerals (easily broken down) Small rock particlesSmall rock particles Heavy rainfallHeavy rainfall High temperaturesHigh temperatures Thick soilsThick soils A lot of organic activityA lot of organic activity

Cleopatra’s NeedleCleopatra’s Needle

80 years later: look what’s happened

Cleopatra’s Needle in Egypt: warm, dry climate, little to not weathering occurs.

Cleopatra’s Needle was moved to New York and has weathered significantly on only 80 years due to: cold and wet climate

Weathering and ResistanceWeathering and Resistance

The The harderharder the rock or mineral is, the the rock or mineral is, the moremore resistantresistant it will be to weathering. it will be to weathering.

Any rock with Any rock with quartzquartz will be quite resistant will be quite resistant due to quartz’s due to quartz’s hardnesshardness..

Rocks made mostly of Rocks made mostly of calcitecalcite, a very soft , a very soft mineral, will be mineral, will be easily weatheredeasily weathered..

WHAT KIND OF CLIMATE WHAT KIND OF CLIMATE SUPPORTS WEATHERING?SUPPORTS WEATHERING?

COLD →→→→→→→→→→ HOT

HIGH

PPT

↑

↑

↑

↑

↑

↑

↑

LOW

PPT

CLIMATE CONTROLS WEATHERINGCLIMATE CONTROLS WEATHERING

PHYSICAL WEATHERING:PHYSICAL WEATHERING:

COLD AND MOIST COLD AND MOIST

ALTERNATE FREEZE / THAWALTERNATE FREEZE / THAW

CHEMICAL WEATHERING:CHEMICAL WEATHERING:

WARM AND MOISTWARM AND MOIST

IN BOTH CASES – WATER IS IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THE PRIMARY INGREDIENT THAT PROMOTES WEATHERINGTHAT PROMOTES WEATHERING

How will the landscape be different for arid regions compared to moist regions?

Sketch the diagram.

WHICH LAYER IS MORE WHICH LAYER IS MORE RESISTANT TO WEATHERING?RESISTANT TO WEATHERING?

LEAST RESISTANT?LEAST RESISTANT?

A

BC

D

YOU MIGHT ALSO SEE IT LIKE YOU MIGHT ALSO SEE IT LIKE THIS.THIS.

THE END PRODUCTS OF THE END PRODUCTS OF WEATHERINGWEATHERING

CALLED CALLED SEDIMENTS OR SOILSEDIMENTS OR SOIL

SOIL: a combination of sediment, SOIL: a combination of sediment, rock minerals, and rock minerals, and humus which humus which is organic material.is organic material.

Soil DevelopmentSoil Development Size and thickness of each horizon depends on:

Climate

Vegetation

Slope (gradient or incline)

Time

SOIL HORIZONSSOIL HORIZONS

Layers that develop as a result of the Layers that develop as a result of the weathering processes, biologic weathering processes, biologic activity, and activity, and leachingleaching (flow of water (flow of water through rocks)through rocks)

SOIL – THE PRODUCT OF SOIL – THE PRODUCT OF WEATHERINGWEATHERING

AFTER THOUSANDS OF YEARS…AFTER THOUSANDS OF YEARS…

2 TYPES OF SOIL2 TYPES OF SOILTRANSPORTED SOIL: TRANSPORTED SOIL: SOIL CARRIED SOIL CARRIED

BY EROSION AND DEPOSITED ON THE BY EROSION AND DEPOSITED ON THE BEDROCK (MOST SOIL IS BEDROCK (MOST SOIL IS TRANSPORTED)TRANSPORTED)

RESIDUAL SOIL:RESIDUAL SOIL: SOIL FORMED BY THE SOIL FORMED BY THE WEATHERING OF THE BEDROCK WEATHERING OF THE BEDROCK DIRECTLY BENEATH ITDIRECTLY BENEATH IT

Question Question #25 from #25 from

the August the August ’06 exam’06 exam

WEATHERING SUMMARYWEATHERING SUMMARY

WEATHERING IS WEATHERING IS THE BREAKDOWN OF THE BREAKDOWN OF ROCK INTO SEDIMENTSROCK INTO SEDIMENTS

PHYSICAL WEATHERING – PHYSICAL WEATHERING – INCREASES INCREASES SURFACE AREA - COLD/HUMID CLIMATESURFACE AREA - COLD/HUMID CLIMATE

CHEMICAL WEATHERING – CHEMICAL WEATHERING – WARM/HUMID WARM/HUMID CLIMATECLIMATE

IN BOTH CASES, WATER IS THE PRIMARY IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT INGREDIENT