Not all features you see on the coast are created by powerful erosion by waves. Some features are created by the sea depositing material and sometimes it may be a combination of erosion and deposition.
Coastal deposition is the laying down or dumping of material by wave action.
Coastal deposition occurs in sheltered areas where the sea can no longer erode or transport material. This often happens in a bay where wave action is at its most gentle. The most common type of deposition feature is the beach, which is made up of either sand or shingle.
Beaches are created initially by erosion when waves wear away material from the cliff face they are breaking on. However, this eroded material will be deposited and may eventually build to create a pebble beach in front of the cliff. These pebbles will be drawn up and down the beach in front by the action of the waves. Attrition will occur and, depending on the rock type, the pebbles may be worn down to sand.
Beaches are not permanent features. Their size and shape changes every time the tide comes in and goes out. Storm conditions, when huge waves crash against the shore, can also alter beaches considerably.
Spits are features of coastal deposition. An example is Hurst Castle spit in Hampshire.
1. A spit is created when longshore drift transports pebbles and sand towards a corner in a coastline. At the point where there is change in the direction of the coastline and shallow water with weak currents, the pebbles and sand are deposited.
2. Over time the deposition will extend into the sea in the direction of the longshore drift.
3. A salt marsh will then develop on the sheltered side of the spit. The spit may develop a hooked end if there is a secondary wind direction or wave refraction.
When a spit begins to grow across a river mouth, a salt marsh often develops on the sheltered(inland) side of the spit. Fine sediment builds up in this shallow water and this environment offers an ideal habitat for waders and other migrant birds.
Spits that continue to grow across a river estuary, or a bay, are known as bars, and a lagoon often forms behind the bar. Like all coastal landforms, bars are temporary features in the landscape. Eventually, either the sea currents change direction and break through, or the lagoon fills with sediment deposited by a river flowing into it.
Like spits and bars, tombolos are low-lying ridges of deposited material; however, they link offshore islands to the mainland. A tombolo forms a causeway which can give access to the island at low tide but is submerged at high tide.