DENUDATION:DENUDATION:

Erosion Erosion andand

WeatheringWeathering

IntroductionIntroduction

DENUDATIONDENUDATION refers to the wearing down refers to the wearing down and stripping and leveling of the earths and stripping and leveling of the earths surface.surface.

They are also They are also gradationalgradational because they because they grade/level grade/level the earth’s surface.the earth’s surface.

2 processes: 2 processes: weathering and erosionweathering and erosion.. WeatheringWeathering is the is the breakdownbreakdown of rock and of rock and

minerals.minerals. ErosionErosion is the is the movementmovement of these of these

weathered materials.weathered materials.

ErosionErosion

The The removalremoval of weathered sediment or rock of weathered sediment or rock by the forces of by the forces of wind, water and icewind, water and ice. .

This is a two-fold process:This is a two-fold process:

- - TransportationTransportation which is the which is the movement of sediment or movement of sediment or

weathered weathered material away from its material away from its source to source to another location.another location.

- - DepositionDeposition which is dropping or which is dropping or settling of sediments.settling of sediments.

WeatheringWeathering

Weathering is the Weathering is the breakdownbreakdown of rocks and of rocks and minerals by minerals by physical physical pressures and chemical pressures and chemical reactions.reactions.

There are two types : There are two types : physical and chemicalphysical and chemical..

Physical WeatheringPhysical Weathering Physical weatheringPhysical weathering is the is the

breakdown of rock and minerals bybreakdown of rock and minerals by mechanical stressesmechanical stresses. .

4 types to be discussed…4 types to be discussed…

Physical weathering prevails in:  Physical weathering prevails in:  cold and wet climates cold and wet climates high altitudes and high latitudeshigh altitudes and high latitudes hot/dry regionshot/dry regions

1.1. Physical Weathering - Frost fracture Physical Weathering - Frost fracture water gets into the cracks of rocks, freezes water gets into the cracks of rocks, freezes and expands causing rocks to crack.and expands causing rocks to crack.

2.2. Physical Weathering – Physical Weathering – Heat or Thermal ExpansionHeat or Thermal Expansion

Repeated daily heating and cooling of Repeated daily heating and cooling of rock results in rock results in expansionexpansion during during heating and heating and contractioncontraction during cooling. during cooling.

Different materials expand and contract Different materials expand and contract at different rates, resulting in stresses at different rates, resulting in stresses along mineral boundaries.along mineral boundaries.

Heat or Thermal ExpansionHeat or Thermal Expansion

3.3. Physical Weathering - ExfoliationPhysical Weathering - Exfoliation

is the breaking off of rocks in curved is the breaking off of rocks in curved sheets or slabs along joints that are sheets or slabs along joints that are parallel to the ground surface.parallel to the ground surface.

Most commonly the release of stress Most commonly the release of stress upon a rock occurs when overlying upon a rock occurs when overlying rock is eroded awayrock is eroded away . .

ExfoliationExfoliation

4.4. Physical Weathering – Physical Weathering – Plants and Plants and

animalsanimals

ROOTS grown into the rock

Expansion due Expansion due to root growth.to root growth.

Animals that Animals that burrow in the burrow in the ground.ground.

Could be considered Biological weathering!!!!

Chemical WeatheringChemical Weathering

Chemical weathering is the Chemical weathering is the breakdown of rocks and minerals by breakdown of rocks and minerals by chemical reactionschemical reactions and usually and usually involves the involves the action of rainwateraction of rainwater..

This involves three processes:This involves three processes:

1.1. Chemical Weathering – Chemical Weathering – Solution/DissolutionSolution/Dissolution

The formation of solutions as The formation of solutions as rainwater rainwater absorbs absorbs COCO2 2 , SO, SO22, and , and other chemicals from the atmosphere other chemicals from the atmosphere along with along with organic acidsorganic acids from the soil from the soil

Which then Which then reacts with rock and reacts with rock and minerals causing some to dissolveminerals causing some to dissolve and move away.and move away.

2.2. Chemical Weathering –Chemical Weathering –HydrolysisHydrolysis

Hydrolysis like the first process Hydrolysis like the first process involves the involves the minerals in solutionminerals in solution. .

In this case, In this case, carbonic acid reacts with carbonic acid reacts with silicatessilicates in some rocks in some rocks leaving a soft leaving a soft clayclay from which potassium, sodium from which potassium, sodium and magnesium are subsequently and magnesium are subsequently leachedleached..

3.3. Chemical Weathering –Chemical Weathering –OxidationOxidation

OxidationOxidation is the reaction of is the reaction of metallic metallic minerals to oxygen (mainly in water.minerals to oxygen (mainly in water.

This results in the formation of This results in the formation of oxides, which tend to be oxides, which tend to be softersofter than than the original mineral. the original mineral.

For example, For example, rust rust on iron.on iron.

Relate environmental conditions & rate Relate environmental conditions & rate of physical & chemical weatheringof physical & chemical weathering

•Freezing temperatures and moisture?

•Frost Fractures

•Variation/fluctuations in H/C temperatures?

•Thermal Expansion

•Presence of vegetation?

•Roots expanding cracks

•Heavy precipitation?

•Accelerates dissolving of rocks/minerals

Relate environmental conditions & rate Relate environmental conditions & rate of physical & chemical weatheringof physical & chemical weathering

CO2 and SO2 in the humid air? Creates solutions that dissolve some rock and

minerals O2, Moisture and metallic minerals?

Chemical reaction-oxidation, ie. rust Carbonic Acid?

Hydrolysis, transform rock into soft clay-like..leach away

High Temperatures? Accelerates oxidation

Oceans and Salt? Accelerates oxidation

PracticePractice

Figure 2.5, TextFigure 2.5, Text Page 25Page 25