deposition

• When does deposition occur?

  Deposition occurs when the sea loses energy and drops eroded material.
• Describe how sandy beaches form.

  • These occurs where there are constructive waves.

  • The swash is stronger than the backwash so sediment builds up on the beach.

  • Small sand particles are easily carried back down by the backwash so the beaches are long and shallow.
• Describe how shingle beaches form.

  • These occur where there are high energy waves.

  • The backwash is stronger than the swash so smaller sand particles are washed away, leaving larger sediment on the beach.

  • The weak swash does not move the sediment far up the beach. This creates short and steep beaches.
• What are sand dunes and what do they require to form?

  Sand dunes are mounds of sand that are found behind sandy beaches. To form, they require a large, flat beach, a good supply of sand, strong winds and obstacles.
• Describe the formation of sand dunes.

  1. Sand is deposited by longshore drift and blown to the top of the beach by onshore winds.

  2. Obstacles, such as driftwood, block sand movement, causing deposits to build over time.

  3. Vegetation (e.g. marram grass) helps to stabilise and bind the sand together, creating small embryo dunes.

  4. Over time, the dune migrates inland.
• What are spits?

  Spits are long stretches of sand or shingle that extend from the land. They form where the coastline suddenly changes shape (e.g. at river mouths or estuaries).
• Describe how spits form.

  Sand and shingle are transported by longshore drift past the point where land ends. As the waves lose energy, material is deposited, forming a spit. Strong winds can cause the end of the spit to curve towards the land, creating a recurved end.
• Explain how salt marshes may form.

  In a sheltered area behind a spit, vegetation can grow easily, and a salt marsh may form.
• Explain how bars form.

  Bars form when a spit joins two headlands together, trapping the water in a lagoon behind it.