Depositional landforms

When water loses its energy, any sediment it is carrying is deposited. The build-up of deposited sediment can form different features along the coast.

Beaches

Beaches are made up from eroded material that has been transported from elsewhere and then deposited by the sea. For this to occur, waves must have limited energy, so beaches often form in sheltered areas like bays. Constructive waves build up beaches as they have a strong swash and a weak backwash.

Sandy beaches are usually found in bays where the water is shallow and the waves have less energy. Pebble beaches often form where cliffs are being eroded, and where there are higher energy waves.

A cross-profile of a beach is called the beach profile. The beach profile has lots of ridges called berms. They show the lines of the high tide and the storm tides. A sandy beach typically has a gentle sloping profile, whereas a shingle beach can be much steeper. The size of the material is larger at the top of the beach, due to the high-energy storm waves carrying large sediment. The smallest material is found nearest the water as the waves break here and break down the rock through attrition.

Spits

A spit is an extended stretch of sand or shingle jutting out into the sea from the land. Spits occur when there is a change in the shape of the landscape or there is a river mouth.

Longshore drift occurs along a beach, due to the prevailing wind and wave direction. The secondary wind and wave direction causes a sandspit with a hooked end. Salt marshes form behind the sandspit.

This is how spits are 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.

Bars

Longshore drift occurs along a beach, due to the prevailing wind and wave direction. The sand covers the entrance to an old bay, leaving behind a lagoon. This sand is called a bar.

Sometimes a spit can grow across a bay, and joins two headlands together. This landform is known as a bar. They can trap shallow lakes behind the bar, these are known as lagoons. Lagoons do not last forever and may be filled up with sediment.