You are here: AQA GCSE Geography PLCs > Coasts > C4 Example Answer

Explain how hydraulic action / abrasion / attrition causes coastal erosion.

The command is “explain”, so your answer should provide a reasoned account of how the process causes coastal erosion.

Possible answers include:

  • Corrasion is when destructive waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff. Over time this can loosen cliff material forming a wave-cut notch.
  • Abrasion occurs as breaking waves, concentrated between the high and low watermarks, which contain sand and larger fragments that wear away the base of a cliff or headland. It is commonly known as the sandpaper effect. This process is particularly common in high-energy storm conditions.
  • Waves hitting the base of a cliff causes air to be compressed in cracks, joints and folds in bedding planes, causing repeated changes in air pressure. As air rushes out of the cliff when the wave retreats, it creates an explosive effect as pressure is released. This process is supported further by the weakening effect of weathering. The material breaks off cliffs, sometimes in huge chunks. This process is known as hydraulic action.
  • Attrition is when waves cause rocks and pebbles to bump into each other and break up.
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