Coastal Landforms

• What are the landforms formed by erosion in coasts?

  • Headlands and bays
  • Caves, arches, stacks and stumps
  • Wave cut notch and wave cut platforms
• How do Headlands and Bays form?

  1. Coasts have alternating bands of more resistant hard rock e.g. chalk and less resistant soft rock e.g. clay
  2. Where the rock is more resistant, it will be eroded less. This forms a headland which sticks out to sea.
  3. The less resistant soft rock is eroded more quickly by processes e.g. hydraulic action and abrasion- this leads to form a formation of a sheltered bay
  4. In a sheltered bay, sediment from the eroding headland helps to form a beach due to the process of deposition

  
• How does a wave cut notch/platform form?

  1. Destructive waves attack the base of a headland/cliff
  2. Overtime, the base of the cliff is undercut by hydraulic action and abrasion, forming a wave cut notch
  3. Eventually, the wave cut notch will collapse due to gravity and lack of support as well as weathering, causing the headland to retreat
  4. The backwash deposits sediment overtime which builds up to form a wave-cut platform

  
• How do Caves, Arch, Stack, Stump form?

  1. A large crack is opened by hydraulic action
  2. The crack grows into a cave by hydraulic action and abrasion
  3. The cave becomes larger due to hydraulic action and abrasion
  4. The cave breaks through the headland forming a natural arch
  5. The arch is eroded due to weathering and collapses due to gravity
  6. This leaves a tall rock stack
  7. The stack is eroded due to the waves forming a stump

  
• When is deposition likely to occur in a coast?

  • Waves enter an area of shallow water;
  • Waves enter a sheltered area, eg a cove or bay;
  • There is little wind;
  • A river or estuary flows into the sea reducing wave energy;
  • There is a good supply of material and the amount of material being transported is greater than the wave energy can transport.
• Explain longshore drift:

  1. Waves swash up the beach at an angle (45 degrees)
  2. Prevailing wind- most dominant direction, blows at an angle
  3. Backwash occurs at 90 degrees due to gravity
  4. Sediment is transported across the beach

  
• What happens when the longshore drift reaches the edge of the land?

  • Eventually the material being carried by longshore drift will be deposited somewhere
  • It forms 2 key landforms: spits and bars
• Define spits in coasts

  A long finger of sand or shingle jutting out into the sea from the land
• Define bars in coasts

  A ridge of sand or shingle that joins two headlands either side of a bay
• Spit formation:

  This process continues in a zig zag called longshore drift moving the sediment along the beach

  1. The prevailing winds hit the beach at an angle, causing the swash to go up the beach and transport sediment at an angle
  2. When the coastline changes direction, the longshore drift continues
  3. The wave retreats back down the beach (backwash) at a right angle (because of gravity), dragging sediment with It
  4. The sediment builds up over time forming a spit. A coastal ecosystem called a salt marsh forms behind this.

  
• How does a spit become a bar?

  • A bar forms when a spit joins two headlands together.
  • The bar cuts off the bay between the headlands from the sea.
  • This means a lagoon forms behind the bar.

  
• What are beaches made up from?

  Eroded material that have been transported from elsewhere and then deposited by the sea
• Why does this deposition occur at beaches?


  For this to occur, waves must have limited energy,

  so beaches often form in sheltered areas like bays
• Which type of waves are most likely to lead to

  the development of beaches?

  ​Constructive waves build up beaches as they have

  a strong swash and a weak backwash
• Pebble beaches characteristics:

  • Steep gradient
  • Mostly destructive waves
  • Storm beaches with large pebbles
  • Narrow
• Sandy beaches characteristics:

  • Flat gradient
  • Mostly constructive waves
  • Sand dunes are found here
  • Long and wide
• What are sand dunes?

  • Sand dunes are large heaps of sand that form on the dry backshore of a sandy beach.
  • They form when onshore winds carry sand up the beach and deposits it in a heap around an obstacle
• Sand dune characteristics:

  • Formed by deposition and transportation (by the wind)
  • Flat gradient, wide beach, dry sand conditions needed
  • Sub-aerial processes form them
  • Made of a build up of sand around an obstacle and later vegetation in their development
  • Supply of sand and vegetation to stabilise them help them to grow bigger over time
  • Found on a sandy beach
• Formation of a sand dune:

  1. At times of high wind sand gets blown towards the back of the beach.
  2. Sand gets caught and deposited around obstacles such as pieces of wood. These pile up and become embryo dunes
  3. Over time, these develop and become stable by vegetation. These are called fore and yellow dunes
  4. Rotting vegetation adds to the soil making it more fertile. These are called GREY DUNES
  5. Wind can form depressions in the sand called dune slacks- they can have big puddles in if they drop below the water table