Weathering D. Crowley, 2008

Weathering To know how rocks are weathered

Shape & Size F Rocks are different shapes and sizes because they are changed by the conditions in their environment F Rocks gradually wear away – this is known as weathering F There are three types of weathering: - 1.Physical weathering 2.Chemical weathering 3.Biological weathering

Expanding F What happens to objects when they are heated (think about the particle model) F Heating an object causes it to expand F However water also expands as it freezes (turning into ice) – 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 turns to ice F Watch the bursting bolt demo…

Physical Weathering F Physical weathering is caused by changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves… F Temperature - 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 cooled many times, cracks form and pieces of rock fall away (this type of physical weathering happens a lot in deserts, because it is very hot during the day but very cold at night) F Watch the glass rod demo…

Physical Weathering F Freezing and thawing – water expands when it freezes F If water gets into a crack in a rock and then freezes, it expands and pushes the crack further apart F When the ice melts later, water can get further into the crack F When the rock freezes again, it expands and makes the crack even bigger - this process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off

Physical Weathering Freezing and thawing

Physical Weathering F Wind, rain and waves – the wind can blow tiny grains of sand against a rock wearing the rock away and weathering it F The rain can lash against a rock and wear it away F Waves can crash against a rock and wear it away

Chemical Weathering F Rainwater is naturally slightly acidic because carbon dioxide from the air dissolves in it F Minerals in rocks may react with the rainwater, causing the rock to be weathered – this is chemical weathering F Some types of rock are easily weathered by chemicals, such as limestone and chalk F Some types of rock are not easily weathered by chemicals, such as granite and gabbro

Chemical Weathering Chemical weathering

Chemical Weathering F The burning of fossil fuels produces oxides of sulphur and nitrogen, causing rain to become more acidic (acid rain) F This type of acid rain reacts more quickly with rock minerals, weathering them more rapidly…

Biological Weathering F Animals and plants can wear away rocks – this is biological weathering F Burrowing animals such as rabbits can burrow into a crack in a rock, making it bigger and splitting the rock F Plant roots can grow in cracks – as they grow bigger, the roots push open the cracks and make them wider and deeper, eventually causing pieces of rock to fall away F People can cause biological weathering by walking. Over time, paths in the countryside become damaged due to the boots wearing them away

Biological Weathering

After Weathering F Transportation is the movement of rock fragments (this can be via strong winds; rivers; glaciers etc…) F Deposition occurs when pieces of rock sink to the bottom of a river bed / lake/ sea eventually forming sedimentary rocks… F This then completes our rock cycle…

Rock Cycle

Rock Bingo F Create a table as shown, and choose any 9 of the following words F Write these in your table, and cross them off if you hear them… F Sedimentary F Igneous F Metamorphic F Erosion F Transportation F Deposition F Minerals F Acid F Fossils F Crystals F Interlocking F Non-interlocking F Weathering F Particle theory F Melting F Compaction F Porous F Grains

Rock Bingo 1. The wearing away of rocks 2. The process of breaking rocks up (via physical, chemical, or biological means) 3. The carrying of rock fragments 4. Process by which rocks can no longer be carried due to insufficient energy 5. A rock which lets water pass through it is 6. A rock type which cannot contain fossils as they have melted 7. Rocks which often contain fossils 8. Expansion due to heat can be explained by the 9. This type of rain increases the rate of chemical weathering Weathering Erosion Transportation Deposition Porous Acid Particle theory Sedimentary Igneous