How does deposition form coastal features?

Deposition is the laying down of material in a new location. It occurs when waves lose energy to transport rocks, pebbles and sand.

Longshore drift is the process where particles moves along the shoreline over and over again, due to the strength and angle of waves.

Deposition features include:

• spits
• sandbars

Spits are formed when the coastline changes direction and material is deposited over time due to longshore drift.

A sandbar occurs when deposited material eventually joins up with the other side of the bay - the area behind the newly formed bar is known as a lagoon.

Transportation is the movement of material along the coast from areas of erosion to areas of deposition. The main process that transports material along the coastline is longshore drift.

Transportation of particles along a coastline is influenced by:

• the strength of waves
• the angle at which the waves strike the shoreline

This is determined by the direction from which the prevailing wind blows.

• A pebble or sand particle moves from point A to B, carried by the swash up the beach, the angle determined by the wave and wind direction.
• It is then pulled down the beach from B to C, carried by gravity and the wave's backwash.
• This process is repeated over and over again and the particle moves along the shoreline. This process is called longshore drift.

There are different depositional features produced by longshore drift. This video explains how deposition forms spits, sandbars and lagoons.

Spits form where the coastline changes direction and longshore drift continues to move material along the beach.

• Longshort drift moves material along a beach in the direction of the prevailing wind.
• When the coastline changes direction, longshore drift continues to deposit material in the sea, extending the line of the beach.
• Over time the level of the sand deposited will build up until it is above sea level.
• The beach appears to extend out into the sea and is known as a spit or sandspit.
• Secondary wind and wave direction causes waves to strike the spit from a different direction.
• This changes the line of the spit, giving it a curved or hooked end.
• The spit creates an area of sheltered calmer water.
• The flow of river water into the sea can prevent a spit developing right across an estuary.
• The mixing of salt water fresh water and sediment carried into an estuary can form a salt marsh.
• Sediment can build up to form dry land.

A sandbar is formed when a spit extends across a bay from one headland to another.

• Longshore drift moves sand out across the bay, forming a spit.
• Where there is no river estuary or slow flow of water, the sand can be deposited faster than it is removed.
• The deposited material eventually joins up with the other side of the bay and a strip of deposited sand blocks off the water in the bay from the sea.
• This feature is called a sandbar and the area behind the newly formed bar is known as a lagoon.

Deposition is the laying down of material in a new location. It occurs when waves lose energy to transport rocks, pebbles and sand.

Longshore drift is the process where particles moves along the shoreline over and over again, due to the strength and angle of waves.

Deposition features include:

• Spits
• Sandbars

Spits are formed when the coastline changes direction and material is deposited over time due to longshore drift.

A sandbar occurs when deposited material eventually joins up with the other side of the bay - the area behind the newly formed bar is known as a lagoon.