Coastal weathering and erosion

  • Mechanical weathering
  • The breakdown of rock without changing its chemical composition
  • Freeze-thraw weathering-
  • when the temperature above or below 0 degrees (the freezing point of water)
  • Water freezes - expands and puts pressure on the rock
  • Water thraws - contracts and releases the pressure on the rock
  • Repeated freezing and thrawing widens the cracks - casues the rock to break up

Chemical weathering

  • Breakdown of rock by changing its chemical composition
  • Carbonation weathering-
  • happens in warm and wet conditions
  • rainwater has carbon dioxide dissolved in it - weak carbonic acid
  • carbonic acid reacts with rock that contains calcium carbonate
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The 4 processes of erosion

Hydraulic power

  • Waves crash against rock and compresses the air in the cracks - puts pressure on the rock
  • Repeated compression - widens the cracks and makes bits of rock break off


  • Eroded particles in the water scrape against rock - removes small pieces


  • Eroded particles in the water smash into each other and break into smaller fragments
  • Their edges also get rounded off as they rub together


  • Weak carbonic acid in sea water dissolves rock like chalk and limeston
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Eroding the coastline

  • The waves that carry out erosional processes are called destructive waves

  • Destructive waves have a high frequency (10-14 waves per minute)

  • They're high and steep
  • Their backwash is more powerful than their swash - material is removed from the coast
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Coatsal landforms

Cliff retreat

  • Waves cause the most erosion at the foot of a cliff - forms a wave-cut notch (erosion makes it unstable over time)
  • The part of the cliff above sea level is also affected by mechanical and chemical weathering - makes the cliff unstable and collapse
  • The collasped material is washed away and a new wave-cut notch starts to form
  • Repeated collapsing results in the cliff retreating
  • The rate of retreat depends on lots of things;
  • geology - soft rock retreats quickly and hard rock can be eroded over thousands of years
  • vegetation - cliffs covered in vegetationa are more stable and retreat slowly
  • Ciff collapses are mass movements - happen when the force of gravity acting on a slope is greater than the force supporting it
  • 3 types of mass movements;
  • Slides - material shifts in a straight line
  • Slumps - material shifts with a rotation
  • Rockfalls - Material shifts vertically
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Headlands and Bays

  • Headlands and Bays form where there are alternating bands of resistant and less resistant rock along a coast
  • The less resistant rock (e.g. clay) is eroded away quickly - forms a bay (have a gentle slope)
  • The resistant rock (e.g. chalk) is eroded away more slowly - forms a headland (steep sides)
  • For example, the Foreland and Swanage Bay in Dorset
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