Coastal formations

• How are wave-cut platforms formed?

  1. The sea attacks the base of the cliff between the high and low water mark.
  2. A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action
  3. As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
  4. The backwash carries away the eroded material, leaving a wave-cut platform.
  5. The process repeats. The cliff continues to retreat.
• How are caves, arches, stacks and stumps formed?

  1. Cracks are widened in the headland through the erosional processes of hydraulic action and abrasion.
  2. As the waves continue to grind away at the crack, it begins to open up to form a cave.
  3. The cave becomes larger and eventually breaks through the headland to form an arch.
  4. The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock).
  5. The stack is undercut at the base until it collapses to form a stump.
• How are spits formed?

  1. Sediment is carried by longshore drift.
  2. When there is a change in the shape of the coastline, deposition occurs. A long thin ridge of material is deposited. This is the spit.
  3. A hooked end can form if there is a change in wind direction.
  4. Waves cannot get past a spit, therefore the water behind a spit is very sheltered. Silts are deposited here to form salt marshes or mud flats.
• Swanage bay case study

  The area around Swanage is made up of bands of hard and soft rock. The soft rock is made of clay and sands, and the hard rock is chalk and limestone. As erosion processes take place, the clay erodes away quicker than the limestone and chalk. This forms headlands and bays, creating Swanage Bay and two headlands - Ballard Point and Durlston Head.