Depositional landforms

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4 Terms

1
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What is a beach?

Beach

  • Beaches form in sheltered areas such as bays

  • Deposition occurs through constructive wave movement, where the swash (water that rushes up the beach) is stronger than the backwash (water that flows back towards the sea)

  • Beach formation usually occurs in the summer months when the weather is calmer

  • Sometimes sand from offshore bars can blow onto the shore by strong winds

  • Blown sand can create sand dunes at the backshore of a beach

2
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What is a spit?

  • A spit is an extended stretch of sand or shingle that extends out to sea from the shore

  • Spits occur:

    • when there is a change in the shape of the coastline

    • OR

    • when the mouth of a river prevents a spit from forming across the estuary

  • A spit may or may not have a 'hooked' end, depending on opposing winds and currents

  • A good example is Spurn Point, which stretches for three and a half miles across the Humber Estuary in the northeast of England

Stages of spit formation

  • Sediment is transported by longshore drift

  • Where the coastline changes direction, a shallow, sheltered area allows for deposition of sediment

  • Due to increased friction, more deposition occurs 

  • Eventually, a spit slowly builds up to sea level and extends in length

  • If the wind changes direction, then the wave pattern alters and results in a hooked end

  • The area behind the spit becomes sheltered

  • Silts are deposited here to form salt marshes or mud flats

Diagram of coastal spit formation with labels: prevailing winds, zig-zag material movement, coastline change, salt marsh development, and spit curvature.

Illustration showing spit formation

3
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What is a bar?

Bar

  • When a spit grows across a bay, and joins two headlands together

  • A bar of sand is formed (sandbar)

  • Sandbars can also form offshore due to the action of breaking waves from a beach

Diagram illustrating coastal features with longshore drift, spit, bay, old bay, bar, and lagoon depicted, showing sediment movement and landform changes.

Illustration showing bar formation

4
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What is a lagoon, tombolo and barrier island?

Lagoon

  • A lagoon is where a small body of water is cut off from the sea 

  • They may form behind a bar or tombolo

  • Lagoons do not last forever and may fill with sediment and form new land

Tombolo  

  • A tombolo is formed when a spit joins the mainland to an island

  • Chesil Beach in Dorset is a tombolo, as the mainland is joined to the Isle of Portland 

Barrier Island

  • Barrier islands form parallel to the coast 

  • The main difference between a bar and a barrier island is that a bar joins two headlands, whereas a barrier island is open at one or both ends

Illustration of coastal features: island, tombolo, spit, barrier island, and coastline shown in green and beige, surrounded by blue water.

Illustration showing the formation of a tombolo and barrier island