The Living World
21 Topics | 21 Quizzes

Coastal Processes: Deposition

Deposition is a process that involves the ocean depositing or dropping the material it carries. Deposition occurs on coastlines that have constructive waves.

This process happens because the velocity or speed of the water flow slows down. When the velocity slows, there is not enough force to hold the material in the water anymore and it is dropped onto the ground. Deposition can be increased by a lack of wind and by areas that offer shelter, such as bays and shallow waters, which reduce wave energy.

The Effect of Deposition

When waves lose energy, they are less able to carry and maintain sediment. Therefore, these sediments settle and accumulate, forming depositional landforms. Two examples of depositional landforms are spits and bars.

Spits are created through deposition and are striking landforms on the coastline. Longshore Drift brings material along the coast until it runs out of energy, and the material is deposited. This often occurs when the wind direction changes or when the flow of water is disrupted by another body of water, such as a river, causing a decrease in energy and resulting in deposition. The deposited material builds up over time and forms a spit.

Bars are created in a similar fashion by deposition. Longshore Drift transports sediment along the coastline and reaches a bay. The bay causes the waves to lose their energy due to increased shelter from the wind and lower energy levels in the water. Material is deposited by the waves between the two headlands, which can form a bar over time. 

Deposition can also lead to the growth and creation of beaches, which are on the receiving end of an increased amount of material dropped by the waves.

Key Terms

SpitAn extended stretch of beach material that sticks out into the sea and is joined to the mainland at one end.
BarA ridge of sand or shingle that joins two headlands on either side of a bay.
Longshore DriftThe process by which sediment is transported along the coastline by the action of waves that approach at an angle to the shore but recede directly away from it.

The movement of sediment is generally sideways due to the angle of the swash and is followed by a straight backwash, creating a zigzag pattern of sediment transport.
Constructive WavesWaves that carry material, with a strong swash and weak backwash. Material is deposited to a coastline by the swash and isn’t removed by the backwash.

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