Weathering and mass movement

• Weathering processes have a significant impact on the coastline
• Weathering


  The breaking down of rock in situ, caused by the weather (e.g. changes in temperature and levels of precipitation) or animals and plants
• Types of weathering


  • Biological weathering
  • Chemical weathering
  • Mechanical weathering
• Biological weathering


  • Caused by animals or birds burrowing into the cliff face and weakening the rocks, or by plant roots getting into cracks and making them bigger
  • Puffins are a good example, using their bills to cut into the soil and then shoveling away loose material with their feet
• Chemical weathering


  1. Rainfall creates a chemical reaction when it hits rocks

  2. Carbonation: rainfall contains carbonic acid which can react with calcium carbonate in limestone, forming calcium bicarbonate which is soluble and gets dissolved and carried away

  3. Hydrolysis: acid from rainfall breaking down rock and making it rot

  4. Oxidation: oxygen and water react to break down rocks
• Mechanical weathering


  • Also known as physical weathering, caused by extremes of temperature or changes in moisture which cause rocks to become disintegrated
• Freeze-thaw weathering


  Water enters cracks in the rock, freezes at night, expands and puts pressure on the rock, then thaws and relieves the pressure. The repetition of this causes the rock to break away, collecting as scree at the cliff base.
• Onion skin weathering


  Also known as exfoliation, caused by temperature changes - rocks expand when heated during the day and contract when cooled at night, applying stress to the outer layers and causing them to peel away or flake off over time.
• Salt weathering


  Salt from sea spray enters cracks in the rock, then evaporates and crystallizes, expanding and putting pressure on the rock to make it weaker, similar to freeze-thaw weathering.
• Mass movement


  Rock, soil or mud moving down a slope due to gravity, usually caused by heavy rainfall
• Types of mass movement


  • Rock falls
  • Landslides
  • Slumping
• Rock falls


  Fragments of rock break away from the cliff base, often due to freeze-thaw weathering, collecting at the bottom to form a fan-shaped scree slope.
• Landslides


  Downhill movement of large volumes of rock, soil and mud, caused by heavy rainfall weakening the slope - the saturated rock can then slide down along a weak bedding plane, taking vegetation with it.
• Landslides


  • Rock slides: large amounts of rock sliding down a cliff as a block
  • Mud flows: wet and rapid slides on steep slopes lacking vegetation, where the saturated soil spreads out over a large area at the base of the cliff
• Slumping


  Material moves down a concave cliff face, rotating backwards into the cliff face as it slips down - caused by waves eroding the base of the cliff, leaving it unsupported.