Unit 4: Weathering, Unit 4: Weathering, Erosion, Deposition Erosion, Deposition

(WED)(WED)

Destructive ForcesDestructive Forces

DESTRUCTIVE FORCES!DESTRUCTIVE FORCES!

Plate tectonics builds the earth Plate tectonics builds the earth surface upsurface up

But what goes up, must come down!But what goes up, must come down! Once exposed to the air, water or Once exposed to the air, water or

wind, rock will begin its destructive wind, rock will begin its destructive cyclecycle

It will weather down!It will weather down!

What is weathering?What is weathering?

The breaking down of rock due to The breaking down of rock due to physical and/or chemical changes in physical and/or chemical changes in the rock as it is exposed to the the rock as it is exposed to the atmosphereatmosphere

Occurs at the interface between the Occurs at the interface between the atmosphere and the lithosphereatmosphere and the lithosphere

Results in smaller pieces of rock Results in smaller pieces of rock called sedimentscalled sediments

Physical weatheringPhysical weathering

Results in a change in appearance of Results in a change in appearance of rock (size, shape, state)rock (size, shape, state)

Types include: frost action, plant Types include: frost action, plant action, pressure unloadingaction, pressure unloading

Frost actionFrost action

Occurs in a cold and moist climateOccurs in a cold and moist climate Alternating freezing and melting of water Alternating freezing and melting of water

in the rock cracks the rockin the rock cracks the rock

Plant actionPlant action

Plant roots grow into small cracks in rock Plant roots grow into small cracks in rock and widen themand widen them

Pressure unloadingPressure unloading

Rock cracks when pressure over the rock Rock cracks when pressure over the rock is removedis removed

Chemical WeatheringChemical Weathering

Results in a change in chemical Results in a change in chemical composition of the rockcomposition of the rock

Types include: oxidation, acid Types include: oxidation, acid reactions, and hydrolysisreactions, and hydrolysis

OxidationOxidation

Addition of oxygen to metal…results in Addition of oxygen to metal…results in rust (iron oxide)rust (iron oxide)

HydrolysisHydrolysis

Chemical weathering by reaction of Chemical weathering by reaction of water with other substanceswater with other substances

When certain minerals are exposed When certain minerals are exposed to water they dissolve into ions…ex: to water they dissolve into ions…ex: feldsparfeldspar

Feldspar will chemically weather into Feldspar will chemically weather into clay (kaolinite)clay (kaolinite)

Water will help any chemical reactionWater will help any chemical reaction

AcidsAcids

Gases such as sulfur dioxide, nitrogen Gases such as sulfur dioxide, nitrogen dioxide, carbon dioxide will dissolve in dioxide, carbon dioxide will dissolve in rainwater forming acid rain (sulfuric acid, rainwater forming acid rain (sulfuric acid, nitric acid, and carbonic acid -a weak acid)nitric acid, and carbonic acid -a weak acid)

Calcite will dissolve completely in carbonic Calcite will dissolve completely in carbonic acid-thus chemically weather any rock acid-thus chemically weather any rock containing this mineral easilycontaining this mineral easily

Acid rain which forms naturally, for Acid rain which forms naturally, for example volcanic activity, or by pollutants, example volcanic activity, or by pollutants, harms any exposed rock, buildings and harms any exposed rock, buildings and monumentsmonuments

Caves Form!Caves Form!

End RESULT of Weathering:End RESULT of Weathering:

SEDIMENTS!SEDIMENTS! INCLUDES-CLAY, SILT, SAND, INCLUDES-CLAY, SILT, SAND,

PEBBLES AND COBBLESPEBBLES AND COBBLESSEE ESRT P6,7SEE ESRT P6,7

What can affect the rate of What can affect the rate of weathering?weathering?

Size of the sedimentSize of the sediment Type of mineral (hardness)Type of mineral (hardness) Temperature Temperature Humidity (amount of moisture Humidity (amount of moisture

present)present)

How does weathering connect How does weathering connect to the rock cycle?to the rock cycle?

Sediments form sedimentary Sediments form sedimentary rocks…rocks…

What is soil?What is soil?

A mixture of weathered rock and A mixture of weathered rock and organic remains (humus)organic remains (humus)

Forms at interface between the Forms at interface between the atmosphere and the lithosphereatmosphere and the lithosphere

How does soil form?How does soil form? 11stst: rocks weathers: rocks weathers 22ndnd: leaching of minerals adds : leaching of minerals adds

nutrients to lower layers from top nutrients to lower layers from top layerlayer

33rdrd: biological activity such as : biological activity such as decomposition add organic matter decomposition add organic matter (humus) to soil, soil is mixed by (humus) to soil, soil is mixed by earthwormsearthworms

Takes 500 to 1000 years to formTakes 500 to 1000 years to form

Soil HorizonsSoil Horizons

A=topsoil (fertile layer)A=topsoil (fertile layer) B=SubsoilB=Subsoil C=Parent RockC=Parent Rock

Types:Types:

Residual or Residual or

transportedtransported

What measure can be done to What measure can be done to conserve Soil?conserve Soil?

Soil is a natural resource and must Soil is a natural resource and must be protected!be protected!

Several methods exist to protect soil Several methods exist to protect soil such as contour farming, no-till such as contour farming, no-till farming, terracing, and crop rotationfarming, terracing, and crop rotation

These all prevent erosion of the These all prevent erosion of the topsoil by wind or watertopsoil by wind or water

Why is it important to protect?Why is it important to protect?

We need it to sustain ecosystemsWe need it to sustain ecosystems Producers take nutrients from the Producers take nutrients from the

soil and convert it to food with the soil and convert it to food with the help of sunlighthelp of sunlight

Basis of the food chainBasis of the food chain