Coastal Landforms (Edexcel IGCSE Geography)

Erosional Landforms

Headland and bay 

• Found in areas of alternating bands of resistant (hard) and less resistant (soft) rocks running perpendicular to oncoming waves (discordant coastline)

• Initially, less resistant rock (e.g. clay) is eroded back, forming a bay

• A bay is an inlet of the sea where the land curves inwards, usually with a beach

• The more resistant rock (e.g. limestone) is left protruding out to sea as a headland

Cove

• A cove forms where the coastline has bands of resistant and less resistant rock running parallel to the oncoming waves (concordant coastline)

• There is usually a band of resistant rock facing the oncoming waves, with a band of softer rock behind

• Wave processes of abrasion, corrosion and hydraulic action will exploit faults in the resistant rock and erode through to the softer rock 

• Further wave action will erode the softer rock quickly, which will leave behind a circular cove with a narrow entrance to the sea

• Wave refraction within the cove spreads out the erosion in all directions, creating the typical horseshoe shape

• Lulworth Cove in Dorset, UK, is a good example of a cove

Cliff and wave-cut platform

• Cliffs are shaped through erosion and weathering processes

• Less resistant rock erodes quickly and will form sloping cliff faces

• Steep cliffs are formed where there is harder rock facing the sea

• A wave-cut platform is a wide gently sloped surface found at the foot of a cliff:

  • As the sea attacks the base of a cliff between the high and low water mark, a wave-cut notch is formed

  • Abrasion, corrosion and hydraulic action further extend the notch back into the cliff

  • The undercutting of the cliff leads to instability and collapse of the cliff

  • The backwash of the waves, carries away the eroded material, leaving behind a wave-cut platform

  • The process repeats and the cliff continues to retreat, leading to a coastal retreat

Cave, arch, stack and stump

• Found on a headland due to wave action and sub-aerial weathering

• Any weaknesses in the headland are exploited by erosional processes of hydraulic action, abrasion and corrosion

• As the crack begins to widen, abrasion will begin to wear away at the forming cave

• The cave will become larger and eventually break through the headland to form an arch

• The base of the arch continually becomes wider and thinner through erosion below and weathering from above

• Eventually, the roof of the arch collapses, leaving behind an isolated column of rock called a stack

• The stack is undercut at the base by wave action and sub-aerial weathering above until it collapses to form a stump

Depositional Landforms

Beach

• Form in sheltered areas such as bays

• Deposition occurs through constructive wave movement, where the swash is stronger than the backwash

• 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

Spit

• 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 the mouth of a river, which 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 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

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

Lagoon

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

• A lagoon 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 barrier island is that a bar joins two headlands, whereas a barrier island is open at one or both ends