Weathering

Definition Weathering is the breakdown of rock without transport. NO movement!!!!!

types of weathering Physical / MechanicalChemical Definition:  Disintegration / breaking of rocks into smaller pieces Needs large temperature change or pressure E.g.: Hot deserts (large day/night temperature change) Definition:  Decomposition of rocks by changing their chemical composition Needs water / rain E.g.: humid tropical areas (lots of water and warm)

Physical Weathering Types Thermal Stress Rocks heat up during the day and expand They cool and contract during the cold night The movement causes the rock to break Salt - Crystal Very high temperature causes high evaporation Salts in the rocks begin to crystallise The growing salt crystals break the rock apart Pressure release Rocks deep in the earth are under a lot of pressure and squeezed together If the rocks and soil on top are removed the rock expands and breaks apart Freeze-Thaw action Water moves into cracks and between layers of rock When it gets cold the water freezes and expands The pressure from the frozen water breaks the rocks apart

Physical Weathering Types Salt - Crystal Very high temperature cases high evaporation Salts in the rocks begin to crystallise The growing salt crystals break the rock apart

Physical Weathering Types Freeze-Thaw action Water moves into cracks and between layers of rock When it get’s cold the water freezes and expands The pressure from the frozen water breaks the rocks apart

Physical Weathering Types Pressure release Rocks deep in the earth are under a lot od pressure and squeezed together If the rocks and soil on top are removed the rock expands and breaks apart

Physical Weathering Types Thermal Stress Rocks heat up during the day and expand They cool and contract during the cold night The movement causes the rock to break

Physical Weathering Types Thermal Stress Rocks heat up during the day and expand They cool and contract during the cold night The movement causes the rock to break Salt - Crystal Very high temperature cases high evaporation Salts in the rocks begin to crystallise The growing salt crystals break the rock apart Pressure release Rocks deep in the earth are under a lot od pressure and squeezed together If the rocks and soil on top are removed the rock expands and breaks apart Freeze-Thaw action Water moves into cracks and between layers of rock When it get’s cold the water freezes and expands The pressure from the frozen water breaks the rocks apart

Chemical Weathering Types Dissolution & carbonation Water & CO 2 combine to form a weak acid Carbonic acid This acid attacks the rock and dissolves it Oxidation Oxygen and metals combine (especially iron) The reaction forms a new material – oxide (rust) The oxide breaks down easily Hydration Water and minerals combine (chemical reaction) A new material is formed – hydride Volume increases and the rock breaks easier because of more pressure

Chemical Weathering Types Dissolution & carbonation Water & CO 2 combine to form a weak acid Carbonic acid This acid attacks the rock

Chemical Weathering Types Oxidation Oxygen and metals combine (especially iron) The reaction forms a new material – oxide (rust) The oxide breaks down easily

Chemical Weathering Types Hydration Water and minerals combine (chemical reaction) A new material is formed – hydride Volume increases and the rock breaks easier because of more pressure

Chemical Weathering Types Dissolution & carbonation Water & CO 2 combine to form a weak acid Carbonic acid This acid attacks the rock and dissolves it Oxidation Oxygen and metals combine (especially iron) The reaction forms a new material – oxide (rust) The oxide breaks down easily Hydration Water and minerals combine (chemical reaction) A new material is formed – hydride Volume increases and the rock breaks easier because of more pressure

Special Weathering Types Biological Plants (and animals) weaken the rock to break it apart or help penetration of water E.g. physical: roots of a tree grow into a crack in the rock and push it apart E.g. chemical: rabbits make a burrow; water can get to the rocks underneath and cause dissolution Physical action Wind, waves and rivers push rocks against other rocks so they break apart Attention! Don’t confuse with erosion … it does not include the transport by water, wind … Gravity (helps, no type!) Rocks fall down so the chemicals and mechanics can work on the next layer

Special Weathering Types Biological Plants (and animals) weaken the rock to break it apart or help penetration of water E.g. physical: roots of a tree grow into a crack in the rock and push it apart E.g. chemical: rabbits make a burrow; water can get to the rocks underneath and cause dissolution

Special Weathering Types Physical action Wind, waves and rivers push rocks against other rocks so they break apart NOT the transport!

Special Weathering Types Gravity (helps!) Rocks fall down so the chemicals and mechanics can work on the next layer

Special Weathering Types Biological Plants (and animals) weaken the rock to break it apart or help penetration of water E.g. physical: roots of a tree grow into a crack in the rock and push it apart E.g. chemical: rabbits make a burrow; water can get to the rocks underneath and cause dissolution Physical action Wind, waves and rivers push rocks against other rocks so they break apart Attention! Don’t confuse with erosion … it does not include the transport by water, wind … Gravity (helps, no type!) Rocks fall down so the chemicals and mechanics can work on the next layer

Where and when? Subarctic  freeze - thaw Tropical  oxidation Wet Continental  mix Deserts  little weathering Catania: Rainfall: 50 cm Temperature: 17° Calcutta: Rainfall: 180 cm Temperature: 27°