EXTERNAL FORCESEXTERNAL FORCESPART 1PART 1

IN THIS CHAPTER YOU WILL IN THIS CHAPTER YOU WILL STUDY:STUDY:

SOME KEY DEFINITIONSSOME KEY DEFINITIONS

DIFFERENT TYPES OF WEATHERINGDIFFERENT TYPES OF WEATHERING

(I)PHYSICAL(I)PHYSICAL

(II) CHEMICAL(II) CHEMICAL

(III) BIOLOGICAL(III) BIOLOGICAL

SOME KEY DEFINITIONSSOME KEY DEFINITIONS

DENUNDATIONDENUNDATION

THE WEARING AWAY OF THE LAND BY THE WEARING AWAY OF THE LAND BY WEATHERING AND EROSION. IT WEATHERING AND EROSION. IT INCLUDES ALL NATURAL AGENCIES INCLUDES ALL NATURAL AGENCIES LIKE THE SUN, RAIN, FROST, WIND, LIKE THE SUN, RAIN, FROST, WIND, RIVERS, SEA, ICE, TEMPERATURE RIVERS, SEA, ICE, TEMPERATURE CHANGE AND EVEN THE ACTION OF CHANGE AND EVEN THE ACTION OF PLANTS AND ANIMALS.PLANTS AND ANIMALS.

WEATHERINGWEATHERINGTHE WEARING AWAY THE WEARING AWAY (DISINTEGRATION AND (DISINTEGRATION AND DECOMPOSITION) OF ROCKS BY THE DECOMPOSITION) OF ROCKS BY THE EFFECTS OF THE WEATHER AND THE EFFECTS OF THE WEATHER AND THE ATMOSPHERE.ATMOSPHERE.EROSIONEROSIONTHE WEARING AWAY OF THE EARTH’S THE WEARING AWAY OF THE EARTH’S SURFACE BY WATER, ICE AND WIND.SURFACE BY WATER, ICE AND WIND.

THE DIFFERENCE BETWEEN THE DIFFERENCE BETWEEN WEATHERING AND EROSIONWEATHERING AND EROSION

THE KEY DIFFERENCE HERE ISTHE KEY DIFFERENCE HERE IS

MOVEMENTMOVEMENT

IN THE CASE OF WEATHERING, NO IN THE CASE OF WEATHERING, NO MOVEMENT IS INVOLVED. HOWEVER, MOVEMENT IS INVOLVED. HOWEVER, IN EROSION, THE AGENT BREAKING IN EROSION, THE AGENT BREAKING UP THE ROCK ALSO MOVES THE UP THE ROCK ALSO MOVES THE DEBRIS ALONG WITH IT.DEBRIS ALONG WITH IT.

MASS WASTINGMASS WASTING

ALSO KNOWN AS MASS MOVEMENT; ALSO KNOWN AS MASS MOVEMENT; FOLLOWS WEATHERING. IT IS THE FOLLOWS WEATHERING. IT IS THE DOWNHILL MOVEMENT OF ROCK DOWNHILL MOVEMENT OF ROCK DEBRIS AND SOIL DUE TO THE FORCE DEBRIS AND SOIL DUE TO THE FORCE OF GRAVITY. WATER ACTS AS A OF GRAVITY. WATER ACTS AS A LUBRICANT, MAKING THE DEBRIS LUBRICANT, MAKING THE DEBRIS MORE SLIPPERY AND EASY TO MOVE.MORE SLIPPERY AND EASY TO MOVE.

TYPESTYPESOFOF

WEATHERINGWEATHERING

PHYSICAL WEATHERINGPHYSICAL WEATHERING

THE BREAKING UP OF ROCK THAT THE BREAKING UP OF ROCK THAT DOES NOT CAUSE THE CHEMICAL DOES NOT CAUSE THE CHEMICAL COMPOSITION OF THE ROCK TO COMPOSITION OF THE ROCK TO CHANGE.CHANGE.

TYPES OF PHYSICAL TYPES OF PHYSICAL WEATEHRINGWEATEHRING

FROST SHATTERINGFROST SHATTERING

FOR THIS TYPE OF WEATHERING TO FOR THIS TYPE OF WEATHERING TO OCCUR THE TEMPERATURE MUST OCCUR THE TEMPERATURE MUST FLUCTUATE (CHANGE/VARY). THERE FLUCTUATE (CHANGE/VARY). THERE MUST ALSO BE BARE ROCK EXPOSED MUST ALSO BE BARE ROCK EXPOSED TO THE SURFACE, WITH LITTLE TO THE SURFACE, WITH LITTLE VEGETATION TO PROTECT THE ROCK VEGETATION TO PROTECT THE ROCK FROM THE WEATHER CONDITIONS.FROM THE WEATHER CONDITIONS.

IF IT RAINS DURING THE DAY, OR THERE IS IF IT RAINS DURING THE DAY, OR THERE IS MOISTURE FROM DEW OR MELTING ICE OR MOISTURE FROM DEW OR MELTING ICE OR FROST, WATER CAN TRICKLE INTO CRACKS FROST, WATER CAN TRICKLE INTO CRACKS IN THE ROCK. IF AT TNIGHT THE IN THE ROCK. IF AT TNIGHT THE TEMPERSATURE DROPS BELOW OTEMPERSATURE DROPS BELOW O00C, THE C, THE WATER IN THE CRACKS FREEZES, AND THE WATER IN THE CRACKS FREEZES, AND THE ICE TAKES UP MORE SPACE, AND SO ICE TAKES UP MORE SPACE, AND SO EXERTS PRESSURE ON THE ROCK. EXERTS PRESSURE ON THE ROCK. REPEATED FREEZE-THAW WEATHERING REPEATED FREEZE-THAW WEATHERING SLOWLY WIDENS THE CRACKS IN THE SLOWLY WIDENS THE CRACKS IN THE ROCK UNTIL PIECES OF ROCK BREAK OFF.ROCK UNTIL PIECES OF ROCK BREAK OFF.

FROST SHATTERINGFROST SHATTERING

EXFOLIATION OR ONION-EXFOLIATION OR ONION-PEELINGPEELING

ROCKS ROCKS EXPANDEXPAND WHEN HEATED AND WHEN HEATED AND CONTRACTCONTRACT WHEN COOLED. IN WHEN COOLED. IN DIURNAL DIURNAL TEMPERATURES (WHERE THERE IS TEMPERATURES (WHERE THERE IS CONSTANT HEATING AN COOLING) SUCH CONSTANT HEATING AN COOLING) SUCH AS IN THE DESERT, THIS TYPE OF AS IN THE DESERT, THIS TYPE OF WEATHERING TAKES PLACE. THE OUTSIDE WEATHERING TAKES PLACE. THE OUTSIDE LAYER OF THE ROCK EXPANDS AND LAYER OF THE ROCK EXPANDS AND CONTRACTS REGULARLY. THIS WEAKENS CONTRACTS REGULARLY. THIS WEAKENS IT AND EVENTUALLY IT PEELS OFF. WHEN IT AND EVENTUALLY IT PEELS OFF. WHEN THIS LAYER FALLS OFF, THE OTHER LAYER THIS LAYER FALLS OFF, THE OTHER LAYER IS ATTACKED, AND IT PEELS OFF LIKE THE IS ATTACKED, AND IT PEELS OFF LIKE THE SKIN OF AN ONION.SKIN OF AN ONION.

EXFOLIATIONEXFOLIATION

THERMAL EXPANSIONTHERMAL EXPANSION

GRANULAR DISINTEGRATIONGRANULAR DISINTEGRATION

ROCKS ARE MADE UP OF DIFFERENT ROCKS ARE MADE UP OF DIFFERENT YYPES OF MINERALS AND THESE YYPES OF MINERALS AND THESE MINERALS EXPAND AND CONTRACT MINERALS EXPAND AND CONTRACT AT DIFFERENT RATES, AND THIS AT DIFFERENT RATES, AND THIS CAUSES THE ROCK TO CAUSES THE ROCK TO DISINTEGRATE.DISINTEGRATE.

PRESSURE RELEASEPRESSURE RELEASE

ROCKS DEEP UNDERGROUND HAVE ROCKS DEEP UNDERGROUND HAVE THE WEIGHT OF OTHER ROCKS THE WEIGHT OF OTHER ROCKS PRESSING DOWN ON THEM. OVER PRESSING DOWN ON THEM. OVER TIME THE UPPER ROCKS ARE TIME THE UPPER ROCKS ARE ERODED AWAY, SO THE PRESSURE IS ERODED AWAY, SO THE PRESSURE IS REDUCED AND THE STRESSES ARE REDUCED AND THE STRESSES ARE LESS. THE ROCK EXPANDS AND LESS. THE ROCK EXPANDS AND CAUSES THE CRACKS TO OPEN UP, CAUSES THE CRACKS TO OPEN UP, ALMOST AS IF THEY ARE BREATHING ALMOST AS IF THEY ARE BREATHING A SIGH OF RELIEF!A SIGH OF RELIEF!

PRESSSURE RELEASEPRESSSURE RELEASE

SALT CRYSTAL GROWTHSALT CRYSTAL GROWTH

THE WATER FROM SLAT WATER THE WATER FROM SLAT WATER EVAPORATES AND LEAVES THE SALT EVAPORATES AND LEAVES THE SALT CRYSTALS BEHIND. WHEN THEY ARE CRYSTALS BEHIND. WHEN THEY ARE HEATED, THEY EXPAND, CAUSING HEATED, THEY EXPAND, CAUSING STRESS IN THE ROCK AND CRACKS STRESS IN THE ROCK AND CRACKS FORM. THIS CAUSES THE ROCKS TO FORM. THIS CAUSES THE ROCKS TO BREAK UP OVER TIME.BREAK UP OVER TIME.

SALT CRYSTAL GROWTHSALT CRYSTAL GROWTH

CHEMICAL WEATHERINGCHEMICAL WEATHERING

CHEMICAL WEATHERING IS THE CHEMICAL WEATHERING IS THE CHEMICAL DECOMPOSITION OF CHEMICAL DECOMPOSITION OF ROCKS AS THEIR MINERALS REACT ROCKS AS THEIR MINERALS REACT WITH RAINWATER, GASES AND WITH RAINWATER, GASES AND MINERALS. CHEMICAL WEATHERING MINERALS. CHEMICAL WEATHERING ALTERS THE MINERALS WHICH MAKE ALTERS THE MINERALS WHICH MAKE UP THE ROCK, IT MAY PRODUCE A UP THE ROCK, IT MAY PRODUCE A CHANGE IN COLOUR AND TEXTURE. CHANGE IN COLOUR AND TEXTURE.

PROCESSES OF CHEMICAL PROCESSES OF CHEMICAL WEATHERINGWEATHERING

CARBOBNATION & SOLUTIONCARBOBNATION & SOLUTION

OXIDATION AND REDUCTIONOXIDATION AND REDUCTION

HYDRATIONHYDRATION

HYDROLYSISHYDROLYSIS

CARBONATION & SOLUTIONCARBONATION & SOLUTION

IS THE MOST COMMON PROCESSIS THE MOST COMMON PROCESS

CARBON DIOXIDE IS ABSORBED BY BOTH RAIN CARBON DIOXIDE IS ABSORBED BY BOTH RAIN WATER AND GROUND WATER, AND WHEN WATER AND GROUND WATER, AND WHEN DISSOLVED IN WATER FORMS A WEAK ACID DISSOLVED IN WATER FORMS A WEAK ACID SOLUTION (CARBONIC ACID). THE WEAK ACID SOLUTION (CARBONIC ACID). THE WEAK ACID SOLUTION SOAKS THROUGH THE ROCKS SOLUTION SOAKS THROUGH THE ROCKS REMOVING THE SOLUBLE PARTICLES AND REMOVING THE SOLUBLE PARTICLES AND LEAVING THE INSOLUBLE PARTICLES BEHINDLEAVING THE INSOLUBLE PARTICLES BEHIND

IN THE CARIBBEAN CARBONATION AND SOLUTION IN THE CARIBBEAN CARBONATION AND SOLUTION ARE MOST COMMON IN LIMESTONE AREASARE MOST COMMON IN LIMESTONE AREAS

OXIDATION & REDUCTIONOXIDATION & REDUCTION

OXIDATION OS THE REACTION OF OXIDATION OS THE REACTION OF MINERALS WITH OXYGEN IN THE AIR MINERALS WITH OXYGEN IN THE AIR AND WATER, TO FORM MINERAL AND WATER, TO FORM MINERAL OXIDES. THE MAIN MINERAL INVOLVE OXIDES. THE MAIN MINERAL INVOLVE IS IRON. SINCE IRON IS FOUND IN IS IRON. SINCE IRON IS FOUND IN MOST ROCKS, THIS PROCESS IS MOST ROCKS, THIS PROCESS IS COMMON. THE IRON-OXIDE CRUST COMMON. THE IRON-OXIDE CRUST CRUMBLES EASILY AND WEAKENS CRUMBLES EASILY AND WEAKENS THE ROCK.THE ROCK.

OXIDATION IS VERY COMMON IN HOT OXIDATION IS VERY COMMON IN HOT WET AREAS SUCH AS THE WET AREAS SUCH AS THE CARIBBEAN, AND ROCKS THAT ARE CARIBBEAN, AND ROCKS THAT ARE AFFECTED OFTEN HAVE A YELLOW, AFFECTED OFTEN HAVE A YELLOW, BROWN OR REDDISH COLOUR, FORM BROWN OR REDDISH COLOUR, FORM THE “RUSTING” OF THE IRON THE “RUSTING” OF THE IRON COMPOUNDS.COMPOUNDS.

HYRDRATIONHYRDRATION

IN WET AREAS, MINERALS OFTEN IN WET AREAS, MINERALS OFTEN ABSORB WATER AND SWELL. THE ABSORB WATER AND SWELL. THE ROCK MINERALS ARE ALTERED BY ROCK MINERALS ARE ALTERED BY THE PHYSICAL STRESSES , AND THIS THE PHYSICAL STRESSES , AND THIS MAY CASUE THE ROCK TO BREAK UP MAY CASUE THE ROCK TO BREAK UP INTO FINER PARTICLES.INTO FINER PARTICLES.

IN CONTRAST WITH MECHANICAL IN CONTRAST WITH MECHANICAL WEATHERING, CHEMICAL WEATHERING, CHEMICAL WEATHERING TENDS TO BE MORE WEATHERING TENDS TO BE MORE ACTIVE INAREAS WHICH HAVE A ACTIVE INAREAS WHICH HAVE A WARM, HUMID CLIMATEWARM, HUMID CLIMATE, WHILE , WHILE MECHANICAL WEATHERING TENDS MECHANICAL WEATHERING TENDS TO TAKE PLACE IN MORE TO TAKE PLACE IN MORE DRY AREASDRY AREAS..

HYDROLYSISHYDROLYSIS

HYDROLYSIS IS THE BREAKING DOWN OF HYDROLYSIS IS THE BREAKING DOWN OF ROCK MINERALS BY HYDROGEN IONS ROCK MINERALS BY HYDROGEN IONS FOUND IN WATER. THE MINERALS COMBINE FOUND IN WATER. THE MINERALS COMBINE WITH WATER AND BREAK DOWN WITH WATER AND BREAK DOWN CHEMICALLY. MINERALS SUCH AS CHEMICALLY. MINERALS SUCH AS CALCIUM, SODIUM AND POTASSIUM ARE CALCIUM, SODIUM AND POTASSIUM ARE REPLACED BY THE HYDROGEN IONS. THE REPLACED BY THE HYDROGEN IONS. THE ROCKS IN WHICH THESE MINERALS WERE ROCKS IN WHICH THESE MINERALS WERE FOUND BECOME WEAKER SINCE THEY ACT FOUND BECOME WEAKER SINCE THEY ACT AS BINDING PARTICLES.AS BINDING PARTICLES.

FOR EXAMPLE, FELDSPARS, BY THE FOR EXAMPLE, FELDSPARS, BY THE PROCESS OF HYDROLYSIS, ARE PROCESS OF HYDROLYSIS, ARE DECOMPOSED INTO FINE CLAYS. (AS DECOMPOSED INTO FINE CLAYS. (AS SEEN IN THE NEXT SLIDE)SEEN IN THE NEXT SLIDE)

BIOLOGICAL WEATHERINGBIOLOGICAL WEATHERING

THE BREAKING DOWN OF ROCKS BY THE BREAKING DOWN OF ROCKS BY PLANTS AND ANIMALSPLANTS AND ANIMALS

PHYSICAL BIOLOGICAL PHYSICAL BIOLOGICAL WEATHERINGWEATHERING

CERTAIN ANIMALS BURROW INTO THE CERTAIN ANIMALS BURROW INTO THE GROUND (RABBITS AND GROUND (RABBITS AND EARTHWORMS) AND CAUSE THE EARTHWORMS) AND CAUSE THE ROCKS TO BECOME WEAKER OR ROCKS TO BECOME WEAKER OR LOOSER. SOMETIMES THE ROCKS LOOSER. SOMETIMES THE ROCKS AND THE PLANTS GET INTO CRACKS AND THE PLANTS GET INTO CRACKS AND THE PLANT GROWS. THE AND THE PLANT GROWS. THE CRACKS BECOME LARGER AND CRACKS BECOME LARGER AND WIDER, EVENTUALLY CAUSING THE WIDER, EVENTUALLY CAUSING THE ROCK TO BREAK UP.ROCK TO BREAK UP.

CHEMICAL BIOLOGICAL CHEMICAL BIOLOGICAL WEATHERINGWEATHERING

WHEN VEGETATION DECAYS, HUMUS WHEN VEGETATION DECAYS, HUMUS IS FORMED. WATER DRAINING IS FORMED. WATER DRAINING THROUGH THE HUMUS BECOMES THROUGH THE HUMUS BECOMES ACIDIC, RESULTING IN THE ACIDIC, RESULTING IN THE WEATHERING OF ROCK BELOW.WEATHERING OF ROCK BELOW.

QUESTIONSQUESTIONS

ON THE WORLD MAP PROVIDED NAME ON THE WORLD MAP PROVIDED NAME ONE AREA WHERE WEATHERING BY ONE AREA WHERE WEATHERING BY TEMERATURE CHANGETEMERATURE CHANGE WILL TAKE WILL TAKE PLACE AND ONE AREA WHERE PLACE AND ONE AREA WHERE FREEZE-THAW WEATHERINGFREEZE-THAW WEATHERING WILL WILL TAKE PLACETAKE PLACE

EXPLAIN 2 WAYS IN WHICH EXPLAIN 2 WAYS IN WHICH WEATHERING IS AFFECTED BY WEATHERING IS AFFECTED BY CLIMATECLIMATEEXPLAIN WHY A ROCK WITH MANY EXPLAIN WHY A ROCK WITH MANY JOINTS OR CRACKS WILL BE JOINTS OR CRACKS WILL BE AFFECTED BY AFFECTED BY

(A)(A) FROST SHATTERINGFROST SHATTERING(B)(B) CHEMICAL WEATHERINGCHEMICAL WEATHERING(C)(C) BIOTIC WEATHERINGBIOTIC WEATHERING