Coasts

• Waves

  Formed by the wind blowing over the water's surface
• Wind duration

  • Longer time
  • More powerful wave
• Swash


  Water rushes up the beach
• Backwash


  Water flows back towards the sea
• Constructive waves


  • Build up a beach deposit material
• Destructive waves


  • Remove material from beach erosion.
• Characteristics of destructive waves

  • Low frequency
  • Low
  • Long waves
• Characteristics of constructive waves

  • High frequency
  • High
  • Steep waves
• Mechanical weathering

  1. Freeze-thaw

  2. Salt crystallisation
• Chemical weathering

  Changing chemical composition of rock
• Biological weathering

  1. Plants growing in cracks

  2. Animals burrowing into rocks
• Mass movement

  Shifting of rocks and loose material down a slope
• Landslide

  Material shifts in a straight line along a slide plane
• Slump

  Material rotates along a curved slip plane
• Rockfall

  Fragment of rock breaks up away from the cliff
• Mudflow

  Saturated soil and debris flow down a slope
• Erosion


  • Hydraulic power
  • Abrasion
  • Corrosion
• Longshore drift


  1. Waves follow the direction of the prevailing wind

  2. Material zigzags along the coast
• Traction


  Large particles are pushed along the sea bed
• Suspension


  Small particles are carried/floated along in the water
• Solution


  Some materials dissolve in the water and are carried along
• Deposition


  Occurs when water carrying sediment loses energy and slows down
• Concordant coastline

  • Alternating bands of hard and soft rock are parallel to the coast
• Discordant coastline


  • Alternating bands of hard and soft rock are at right angles to the coast
• Headlands

  Alternating bands of resistant and less resistant rock eroded faster
• Bays

  Formed where less resistant rock is eroded faster, creating a gentle slope
• Headland formation

  1. Resistant rock juts out, forming a headland

  2. Less resistant rock erodes faster, forming a bay with steep sides
• Caves

  • Formed by erosion enlarging cracks in the headland
  • Continued erosion deepens the cave until it breaks through the headland
• Arch formation

  1. Erosion continues to wear away the rock supporting the arch

  2. Arch eventually collapses
• Stacks

  Isolated rock formations separate from the headland, formed by erosion around the base and collapse
• Examples of coastal features

  • Durdle Door, Dorset
  • Old Harry, Dorset
• Wave-cut platforms


  Formed by erosion of the cliff face, creating a notch that becomes unstable and collapses, leaving a wave-cut platform
• Beaches


  • Formed by constructive waves depositing material
  • Sand beaches have low energy waves and are flat and wide
  • Shingle beaches have high energy waves and are steep and narrow
• Spit formation


  1. Longshore drift transports sand around a sharp bend in the coastline, depositing it in the sea

  2. Strong winds and waves can curve the end of the spit

  3. Area behind the spit is sheltered, allowing material to accumulate and plants to grow
• Bars


  Formed when a spit joins two headlands, cutting off a bay from the sea and allowing a lagoon to form
• Offshore bar formation


  Friction with the sea bed causes waves to slow down and deposit sediment offshore, creating a bar not connected to the coast
• Sand dune formation


  1. Sand deposited by longshore drift is moved up the beach by the wind

  2. Vegetation decreases wind speed, causing sand to be deposited and dunes to form

  3. Vegetation roots stabilise the sand, encouraging more accumulation and the formation of mature dunes
• Coastal management strategies

  • Hard engineering (sea walls, groynes, rock armour, gabions)
  • Soft engineering (beach nourishment, dune regeneration, managed retreat)
• Sea walls


  • Concrete walls that reflect waves back to sea, preventing erosion and flooding
  • Can cause erosion under the wall due to strong backwash
• Groynes


  • Wooden/stone fences built at right angles to the coast, trapping material transported by longshore drift and creating wider beaches