WeatheringWeathering

D. Crowley, 2008D. Crowley, 2008

Weathering

To know how rocks are To know how rocks are weatheredweathered

Shape & Size

Rocks are different shapes and sizes because they are Rocks are different shapes and sizes because they are changed by the conditions in their environmentchanged by the conditions in their environment

Rocks gradually wear away – this is known as Rocks gradually wear away – this is known as weatheringweathering

There are three types of weathering: -There are three types of weathering: -

1.1. Physical weatheringPhysical weathering

2.2. Chemical weatheringChemical weathering

3.3. Biological weatheringBiological weathering

Expanding

What happens to objects when they are heated (think about the What happens to objects when they are heated (think about the particle model)particle model)

Heating an object causes it to Heating an object causes it to expandexpand

However water also However water also expands as it freezes expands as it freezes (turning into ice) – (turning into ice) – this is why putting a bottle of liquid in the freezer causes it to this is why putting a bottle of liquid in the freezer causes it to break / water pipes can burst during winter as the water within break / water pipes can burst during winter as the water within turns to iceturns to ice

Watch the bursting bolt demo…Watch the bursting bolt demo…

Physical Weathering

Physical weathering is caused by changes such as changes in Physical weathering is caused by changes such as changes in temperaturetemperature, , freezing and thawingfreezing and thawing, and the effects of , and the effects of windwind, , rain rain and and waveswaves……

Temperature Temperature - when a rock gets hot it expands a little, and when - when a rock gets hot it expands a little, and when a rock gets cold it contracts a little. If a rock is heated and a rock gets cold it contracts a little. If a rock is heated and cooled many times, cracks form and pieces of rock fall away cooled many times, cracks form and pieces of rock fall away (this type of physical weathering happens a lot in deserts, (this type of physical weathering happens a lot in deserts, because it is very hot during the day but very cold at night)because it is very hot during the day but very cold at night)

Watch the glass rod demo… Watch the glass rod demo…

Physical Weathering

Freezing and thawingFreezing and thawing – water – water expands expands when it freezeswhen it freezes

If water gets into a crack in a rock and then freezes, it expands If water gets into a crack in a rock and then freezes, it expands and pushes the crack further apartand pushes the crack further apart

When the ice melts later, water can get further into the crackWhen the ice melts later, water can get further into the crack

When the rock freezes again, it expands and makes the crack When the rock freezes again, it expands and makes the crack even bigger - this process of even bigger - this process of freezing and thawing freezing and thawing can continue can continue until the crack becomes so big that a piece of rock falls off until the crack becomes so big that a piece of rock falls off

Physical Weathering

Freezing and thawingFreezing and thawing

Physical Weathering

WindWind,, rain rain and and waves waves – the – the wind wind can blow tiny grains of sand can blow tiny grains of sand against a rock wearing the rock away and weathering itagainst a rock wearing the rock away and weathering it

The The rain rain can lash against can lash against a rock and wear it awaya rock and wear it away

Waves Waves can crash against can crash against a rock and wear it away a rock and wear it away

Chemical Weathering

Rainwater is naturally slightly acidic because carbon dioxide Rainwater is naturally slightly acidic because carbon dioxide from the air dissolves in itfrom the air dissolves in it

Minerals in rocks may react with the rainwater, causing the rock Minerals in rocks may react with the rainwater, causing the rock to be weathered – this is to be weathered – this is chemical weatheringchemical weathering

Some types of rock are easily weathered by chemicals, such as Some types of rock are easily weathered by chemicals, such as limestone and chalklimestone and chalk

Some types of rock are not easily weathered by chemicals, Some types of rock are not easily weathered by chemicals, such as granite and gabbrosuch as granite and gabbro

Chemical Weathering

Chemical weatheringChemical weathering

Chemical Weathering

The burning of fossil fuels produces oxides of sulphur and The burning of fossil fuels produces oxides of sulphur and nitrogen, causing rain to become more acidic (acid rain)nitrogen, causing rain to become more acidic (acid rain)

This type of acid rain reacts more quickly with rock minerals, This type of acid rain reacts more quickly with rock minerals, weathering them more rapidly…weathering them more rapidly…

Biological Weathering

Animals and plants can wear away rocks – this is Animals and plants can wear away rocks – this is biological biological weatheringweathering

Burrowing animals such as rabbits can burrow into a crack in a Burrowing animals such as rabbits can burrow into a crack in a rock, making it bigger and splitting the rockrock, making it bigger and splitting the rock

Plant roots can grow in cracks – as they grow Plant roots can grow in cracks – as they grow bigger, the roots push open the cracks and make bigger, the roots push open the cracks and make them wider and deeper, eventually causing pieces them wider and deeper, eventually causing pieces of rock to fall awayof rock to fall away

People can cause biological weathering by walking. People can cause biological weathering by walking. Over time, paths in the countryside become Over time, paths in the countryside become damaged due to the boots wearing them away damaged due to the boots wearing them away

Biological Weathering

Biological WeatheringBiological Weathering

After Weathering

Transportation is the movement of rock fragments (this can be Transportation is the movement of rock fragments (this can be via strong winds; rivers; glaciers etc…)via strong winds; rivers; glaciers etc…)

Deposition occurs when pieces of rock sink to the bottom of a Deposition occurs when pieces of rock sink to the bottom of a river bed / lake/ sea eventually forming sedimentary rocks…river bed / lake/ sea eventually forming sedimentary rocks…

This then completes our rock cycle… This then completes our rock cycle…

Rock Cycle

Rock Bingo

Create a table as shown, and choose any 9 of the following wordsCreate a table as shown, and choose any 9 of the following words Write these in your table, and cross them off if you hear them…Write these in your table, and cross them off if you hear them…

SedimentarySedimentary IgneousIgneous MetamorphicMetamorphic ErosionErosion TransportationTransportation DepositionDeposition

MineralsMinerals AcidAcid FossilsFossils CrystalsCrystals InterlockingInterlocking Non-interlockingNon-interlocking

WeatheringWeathering Particle theoryParticle theory MeltingMelting CompactionCompaction PorousPorous GrainsGrains

Rock Bingo

1.1. The wearing away of rocksThe wearing away of rocks

2.2. The process of breaking rocks up (via physical, The process of breaking rocks up (via physical, chemical, or biological means)chemical, or biological means)

3.3. The carrying of rock fragmentsThe carrying of rock fragments

4.4. Process by which rocks can no longer be carried due Process by which rocks can no longer be carried due to insufficient energyto insufficient energy

5.5. A rock which lets water pass through it isA rock which lets water pass through it is

6.6. A rock type which cannot contain fossils as they A rock type which cannot contain fossils as they have meltedhave melted

7.7. Rocks which often contain fossilsRocks which often contain fossils

8.8. Expansion due to heat can be explained by theExpansion due to heat can be explained by the

9.9. This type of rain increases the rate of chemical This type of rain increases the rate of chemical weatheringweathering

WeatheringWeathering

ErosionErosion

TransportationTransportation

DepositionDeposition

PorousPorous

AcidAcid

Particle theoryParticle theorySedimentarySedimentary

IgneousIgneous