Landforms of the Coast (AQA A Level Geography)

• Erosion causes a range of landforms at the coast including:
  • Wave cut platforms
  • Caves, arches and stacks

Wave cut platform formation

• At high-energy coastlines, hydraulic action and abrasion can cause the formation of wave-cut platforms 
  • Powerful destructive waves attack the base of  the cliff at high tide 
  • The hydraulic action and abrasion create a wave-cut notch which over time increases in size 
  • This is called undercutting 
  • Eventually the overhang created by the undercutting collapses due to weathering and gravity 
  • The cliff retreats, leaving a wave cut platform that is exposed at low tide

A wave cut platform in Portugal

Diagram to show the formation of a wave cut platform 

Cave, arch and stack formation

• At a headland, where the rock is hard, erosion is slow and can lead to a variety of landforms
• Wave refraction concentrates wave energy onto the headland and can contribute to the formation of caves, arches, stacks and stumps
  • Joints in the headland are susceptible to erosion by hydraulic action
  • Over time the joints widen forming a cave which is enlarged by hydraulic action and abrasion
  • Eventually erosion cuts through the headland forming an arch
  • The roof of the cave will eventually collapse due to gravity and the lack of support
  • This leaves a stack which will over time be eroded by weathering, abrasion and hydraulic action to form a stump

 

Erosional features at Durdle Door on the Dorset Coast

Erosional landforms, cave, arch and stack

• Depositional landforms occur at low-energy coastlines when the waves do not have enough energy to carry a large sediment load
• Deposition leads to the formation of a range of coastal features and landforms including:
  • Beaches
  • Spits
  • Tombolos
  • Bars or barrier beaches
  • Salt marshes
  • Sand dunes

Beach formation

• The most common depositional landform is a beach
  • Beaches build up due to constructive waves
• Beaches can be drift-aligned or swash-aligned 
  • Drift-aligned beaches form where longshore drift moves the sediment along the beach as waves approach at an oblique angle 
  • This will often culminate in a spit where the coastline changes direction 
  • Swash-aligned beaches form where the energy is low 
  • The waves are more parallel to the shore in swash-aligned environments so there is very little horizontal or lateral movement of sediment

Spit formation

• Spits are created due to longshore drift
  • Sediment is transported by waves along a coastline
  • When the coastline changes direction the waves no longer have the energy to carry the sediment and it is deposited 
  • The build up of deposited sediment out to sea, often into an estuary, is called a spit 
  • The spit often has a curved end or hooks due to a secondary prevailing wind

Formation of spit

Tombolo and bar formation

• As spits form across an estuary or around a headland there can also be the formation of tombolos and bars where the sediment meets either an island or the opposite side of a headland respectively 
  • These are formed in the same way, through longshore drift and deposition
  • Bars can also form offshore
  • These are raised ridges of sediment away from the shore 
  • They form where the sediment level is high and the sea is shallow 
• Bars that form as spits extend to join two headlands are also known as barrier beaches
  • Water trapped behind the barrier beach is called a lagoon

Depositional landforms

Salt marshes

• Behind spits and barrier beaches the area is very sheltered, tidal currents and river currents meet leading to lots of deposition 

• This can lead to the formation of salt marshes 
• Salt-tolerant species colonise these sheltered, flat muddy areas 
• They are covered at high tide and exposed at low tide 

Sand dunes

• Deposition can also lead to the formation of sand dunes 
• Sand dunes are formed in areas where there is a large quantity of sand, a large tidal range and onshore prevailing winds 
• When sand is trapped towards the back of the beach due to an obstacle dunes will develop 
• Pioneer plant species hold the sand together and stabilise the dune 
• Other plants are then able to thrive in the environment which leads to the development of the dune ecosystem, this is called plant succession