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Deposition Landforms

Characteristics and formation of beaches, spits and bars.


8. Spits by rgamesby

If rocks and cliffs are being continually weathered, eroded and moved then it stands to reason that this will generate a lot of material that will need to be deposited (or laid down) somewhere else along the coastline. The major deposition landforms are beaches, spits and bars. Deposition occurs when wave velocities slow, or when ocean currents slow due to encountering frictional forces such as the sea bed, other counter currents and vegetation.

Beaches are areas of sand, pebbles and shingle that are formed by deposition produced by wave processes.  Beaches are by no means uniform and contain a huge variety of sediment types and sizes, and have many different shapes.

Gently sloping beaches are formed by strong destructive waves that backwash more material away from the beach that they swash up the beach.

Steeply sloping beaches occur by constructive waves that swash more material up the beach than they backwash away, building up a steep beach gradient.

SPITS and BARS

Think about it!

1) Try this landforms identification exercise

2) Try these quizzes from Fife education

3) Try this nice coastal features quiz

4) Coasts questions from s-cool.co.uk

5) Have a go at my Hot Potatoes crossword

6) Half a minute coasts quiz from juicy Geography

7) Coasts penalty shoot out game from juicy Geography

8) Have a try at finishing this passage on Coastal Deposition

Spurn Head, Holderness coastline Spurn head map  
Above is Spurn head, one of the many famous spits found around the UK coastline.

Spits are created by the process of Long shore drift. Some eroded material ends up caught up within the waves and is carried by the sea along the coastline in cells known as littoral cells. Material is carried along the shore in a zigzag fashion by waves as they swash material up the beach at an angle and backwash material down the beach at a right angle. The angle of swash is determined by the prevailing wind (the dominant or main direction in which the wind blows).

Wherever there is a break in the coastline (e.g. across a river or a change in coastline direction) then material is deposited closest to the shore. This is because there are often counter currents and a loss in velocity, so material is dropped or deposited.

Eventually this material builds  up out into sea to form a spit. As seen in the picture opposite of Spurn Head.  The spit often curves inwards towards the land as a result of the prevailing wind directing the waves which push the sediment in towards the shore.

Spits often have salt marshes build up behind them because the spit offers protection from the stronger waves and the wind, allowing salt tolerant plants to grow.

If a spit extends from headland to headland then a bar will be created.  You can see this process on an animation at this link.