Coastal Landforms: Erosion & Deposition (Edexcel GCSE Geography A)

Coastal Landforms - Erosion

Headlands and bays

• These occur along discordant coastlines

  • Alternating bands of hard and soft rocks run perpendicular to oncoming waves 

• The soft rock (e.g. clay) is eroded backward, forming an inlet

• As the inlet continues to erode it curves inward, and a bay is formed, usually with a beach

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

• A headland usually:

  • Has cliffs along its sides

  • Projects out to sea

  • Is longer than it is wide

  • Has geology is of resistant rock

• A bay usually has:

  • A wide, open entrance from the sea

  • A roughly semi-circular shape extending into the coastline

  • Land that is lower than the headlands surrounding it

  • A bay may or may not have a beach

The formation of headlands and bays on discordant coastlines

Cliffs 

• Cliffs are shaped through erosion and weathering processes

• Soft rock erodes quickly, forming sloping cliff faces

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

Wave-cut platforms

• 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

The process of cliff retreat and wave-cut platform formation

Caves, arches, and stacks 

• These features form in a headland because of wave action and sub-aerial weathering

• The erosional processes of hydraulic power, abrasion and some corrosion begin to attack weaknesses in the headland

• Cracks in the headland begin 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

• The stack eventually collapses to form a stump

The formation of a cave, arch, stack and stump

Coastal Landforms - Deposition

Beaches

• Beaches usually form in summer months when the weather is calmer

• There are two main types of beaches:

  • Sandy

  • Pebble (shingle)

• Sandy beaches form in sheltered areas, such as bays, through deposition

  • This occurs due to constructive wave movement, where the swash is stronger than the backwash

  • Sandy beaches are usually:

    • Wider than shingle beaches

    • Gently sloping

• Pebble or shingle beaches are more likely to form in areas where there are high-energy waves

  • Pebble beaches are usually:

    • Narrower than sandy beaches 

    • Steeply sloping

• Beaches often have a combination of shingle and sand

• The beach cross-sections are not smooth

• Beaches have a number of features, including:

  • Storm beaches form at the top of the beach, furthest from the sea

    • These are created by storm waves depositing larger materials 

  • A ridge of shingle and sand called a berm marks the normal high tide level

  • The smallest sediment, which is sand, is deposited nearest to the sea

Spits

• An extended stretch of sand or shingle that extends out to sea from the shore

• Spits occur when there is either:

  • A change in the shape of the coastline

  • The mouth of a river, which prevents a spit 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 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 or there is a river mouth, a shallow, sheltered area leads to the 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. This results in a hooked end

• The area behind the spit becomes sheltered

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

Spit formation

Bars

• Bars form due to the same process as a spit 

• A bar joins two headlands together

• A bar of sand is formed (sandbar)

• Freshwater is trapped behind to form a lagoon

Image showing how longshore drift contributes to spit and bar formation