Erosion and transportation

Processes of erosion at the coast

Coastal erosion is the process of the sea wearing away the land. There are four processes which could cause erosion on a cliff:

  • Hydraulic action – air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
  • Abrasion – bits of rock and sand in waves grind down cliff surfaces like sandpaper.
  • Attrition – waves smash rocks and pebbles on the shore into each other, and they break and become smoother.
  • Solution – acids contained in sea water will dissolve some types of rock such as chalk or limestone.

Transportation at the coast

Sediment is carried by the waves along the coastline. The movement of the material is known as longshore drift. Waves approach the coast at an angle because of the direction of the prevailing wind. The swash will carry the material towards the beach at an angle. The backwash then flows back to the sea, down the slope of the beach. The process repeats itself along the coast in the zig-zag movement.

Waves approach a beach at an angle - determined by prevailing wind direction. Waves push rocks up the beach, roll back down and are pushed back up in a zig-zag pattern.

Beach material can be moved in four different ways. These are:

  • Solution – when minerals in rocks like chalk and limestone are dissolved in sea water and then carried in solution. The load is not visible.
  • Suspension – small particles such as silts and clays are suspended in the flow of the water.
  • Saltation – where small pieces of shingle or large sand grains are bounced along the sea bed.
  • Traction – where pebbles and larger material are rolled along the sea bed.