Landforms of Coastal Deposition (Cambridge (CIE) IGCSE Geography) : Revision Note

Formation of deposition coastal landforms

Beaches

• Typically, beaches form during the calmer summer months, in sheltered areas such as bays

• Constructive wave action causes deposition, with the swash being stronger than the backwash

• Strong winds can occasionally carry sand from offshore bars onto the shore

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

  1. When a constructive wave carries sediment up the beach, the largest material is deposited along the upper reach of the swash

  2. As the backwash moves back down the beach, it loses water and therefore energy as it travels due to the porosity of the sand

  3. Consequently, the deposition of sediment gets progressively smaller, and the beach is therefore, sorted by wave deposition, with the smallest mud particles settling in the low-energy environment offshore

  4. If a destructive wave forms due to a storm, then large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm

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

1. Sediment is transported by longshore drift

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

3. Due to increased friction, more deposition occurs 

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

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

6. The area behind the spit becomes sheltered

7. Silts are deposited here to form salt marshes or mud flats

Bar

• A bar occurs 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

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

Sand dunes

• Sand dunes are a dynamic environment, changes occur quickly 

• Sandy beaches are usually backed by sand dunes due to strong onshore winds, which transport dried-out, exposed sand

• Sand grains are trapped and deposited against an obstacle (rubbish, rocks, driftwood, etc) to form dunes

• Dune ridges move inland due to onshore winds pushing the seaward side to the leeward side

• It is the interaction of winds and vegetation that help form sand dunes

Formation of a sand dune

• Windblown sand is deposited against an obstruction, such as a pebble or driftwood

• As more sand particles are caught, the dunes grow in size, forming rows at right angles to the prevailing wind

• In a process known as succession, vegetation will eventually colonise and fix the ridges of the dunes

• The first plants (pioneer species) have to cope with:

  • Salinity

  • Lack of moisture as sand drains quickly (highly permeable)

  • Wind

  • Temporary submergence by wind-blown sand

  • Rising sea levels

• Embryo dunes

  • Deposition starts when debris or rubbish traps wind-blown dried sand

  • Pioneer species such as Lyme Grass and Sea Couch Grass begin to colonise

  • There is little soil content and high pH levels (alkaline)

  • Embryo dunes are very fragile and reach a maximum height of 1 metre

• Fore dunes

  • The embryo dunes give some protection against the prevailing wind

  • This allows other species of plant to grow, such as Marram Grass

  • Marram grass begins to stabilise the dune with its root system

  • These plants add organic matter to the dunes, making the dunes more hospitable for plants that later grow

  • A microclimate forms in the dune slack

  • Maximum height is 5 metres

• Yellow dunes

  • These are initially yellow but darken as organic material adds humus to the soil

  • Marram grass still dominates the vegetation, but more delicate flowering plants and insects are found in the dune slacks

  • 20% of the dune is exposed, down from 80% 

  • Height does not exceed 8 metres

• Grey dunes 

  • Grey dunes are more stable, with less than 10% of exposed sand and have a good range of biodiversity

  • Soil acidity and water content increase as more humus is added

  • Shrubs and bushes begin to appear

  • Height is between 8 and 10 metres

• Mature dunes

  • As the name suggests, these are the oldest and most stable of the dunes

  • They are found several hundred metres or more from the shoreline

  • The soil can support a variety of flora and fauna, such as oak trees and alders (climax vegetation)

  • This is the final stage in succession, which is known as the climax community stage