IGCSE Geography / Coastal environments

Weathering and mass movement on the coast revision notes

Edexcel International GCSE Geography (4GE1), chapter 2: Coastal environments, specification point 2.1a. Free lesson.

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Weathering, erosion and mass movement are different processes that shape coastal cliffs. Knowing what causes each process helps explain how cliffs weaken and retreat.

How weathering, erosion and mass movement differ

These processes can happen on the same cliff, but they do different things. Weathering breaks rock down where it stands, so it does not carry the pieces away. Erosion wears rock away and removes it. Mass movement moves rock and soil down a slope under gravity. Weathering is caused by weather, chemicals, plants and animals. It acts on the cliff face and top. Erosion is caused by waves, which attack the base of the cliff. Mass movement is caused by gravity and affects the whole slope. Weathering and mass movement are sub-aerial processes. They act on the land surface…

How the three types of weathering break rock

All weathering breaks rock down in place. The pieces stay where they are until another process moves them. Mechanical weathering does not change what the rock is made of, while chemical weathering changes the rock itself. Biological weathering is caused by living things. Freeze-thaw is mechanical weathering. Water enters a crack, freezes and expands, forcing the crack wider. Repeated freezing can break off pieces of rock. Salt crystallisation is mechanical weathering. Sea spray enters cracks and dries, leaving salt crystals. As the crystals grow, they force the rock apart.…

How sliding, slumping and rockfall happen

Mass movement is rock and soil moving down a slope under gravity. The forms are distinguished by how the material moves and the shape of the surface it moves along. Sliding happens when a whole block moves straight down a flat slip plane inside the cliff. Slumping happens when saturated soft clay rotates down a curved slip plane, leaving steps in the cliff. Rockfall happens when weathered pieces drop from a steep rock face and pile up at the bottom. For sliding and slumping, rain is a trigger. Saturated rock or soil becomes heavier, and water makes the slip plane slippery.…

How the processes make a cliff retreat

Weathering, erosion and mass movement work together on the same cliff. Weathering widens cracks and weakens the cliff. Waves erode the base, removing support from the rock above. The weakened, unsupported cliff can then slide or slump. Waves carry the fallen material away and attack the base again, so the cliff retreats.

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