Depositional landforms

What is a beach?

Beach

• Beaches are made up from eroded material that has been transported from elsewhere and then deposited by the sea

• 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

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

Illustration showing spit formation

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

Illustration showing bar formation

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 showing the formation of a tombolo and barrier island