Coasts

• Waves


  Form when wind blows over the sea, causing friction with the surface of the water and creating ripples that grow into waves
• Fetch


  The distance the wind blows across the water, the longer the fetch the more powerful the wave
• Tsunamis


  Form when earthquakes or volcanic eruptions shake the seabed
• Wave action at the coast

  1. Waves approach the shore, breaking up and surging up the beach (swash)

  2. Water then comes back down the beach (backwash)
• Constructive waves


  • Low waves that surge up a beach with a powerful swash, usually formed by distant storms
• Destructive waves


  • High-energy waves with a larger backwash than swash, formed by local storms
• Coastal erosion processes


  • Hydraulic power
  • Abrasion
  • Attrition
  • Solution
• Coastal weathering processes


  • Chemical weathering (carbonation, hydration)
  • Mechanical weathering (freeze-thaw)
• Mass movement processes


  • Sliding landslides
  • Slumping
• Longshore drift


  The movement of sediment along the coast by waves approaching at an angle
• Deposition


  Occurs when waves lose energy and drop sediment, e.g. in sheltered bays
• Erosional coastal landforms


  • Cliffs and wave-cut platforms
  • Headlands and bays
  • Caves, arches, stacks
• Depositional coastal landforms


  • Beaches
  • Sand dunes
  • Spits
  • Tombolos and sandbars
• Seawalls


  • Concrete barriers placed at the coast to reflect waves, can have walkways but are expensive and obtrusive
• Groynes


  • Timber or rock structures built out from the coast to trap sediment, can interrupt longshore drift
• Rock armour


  • Large boulders dumped at the coast to break and absorb wave energy, can be expensive to transport
• Gabions


  • Wire cages filled with rocks, support cliffs and act as a buffer, can become vegetated but rust over time
• Beach nourishment


  • Adding sand or shingle to beaches, needs constant maintenance and works with other structures
• Dune regeneration


  • Replanting marram grass and using fences to protect dunes, time-consuming but natural
• Waves


  Caused by friction between the wind and water causing the water to swell
• Factors influencing wave size and energy

  • How long the wind has been blowing
  • Strength of the wind
  • How far the wave has travelled (the fetch)
• Destructive waves


  Created in storm conditions, from big, strong waves when the wind is powerful and has been blowing for a long time, when wave energy is high and the wave has travelled with great force
• Destructive waves


  • Have a stronger backwash than swash
  • Have a short wave length and are high and steep
  • Tend to erode the coast
• Constructive waves


  Created in calm weather, less powerful than destructive waves, break on the shore and deposit material, building up beaches
• Constructive waves


  • Have a swash that is stronger than the backwash
  • Have a long wavelength, and are low in height
• Types of weathering


  • Chemical
  • Physical
  • Biological
• Chemical weathering


  Weak acids like rain dissolve the rocks
• Physical weathering


  Temperature, frost, water etc. freeze thaw weathering is when the constant freezing of water and then melting again causes cracks in the rocks
• Biological weathering


  Rocks are broken up by living things e.g. plant routes or burrowing animals
• Types of mass movement

  • Rock fall
  • Landslide
  • Cliff collapse
  • Mudflow
  • Rotational slip
• Rock fall


  When rocks fall from a cliff
• Landslide


  When a large amount of material slides down a slope
• Cliff collapse


  When a cliff falls away
• Mudflow


  A flow of mud down a slope
• Rotational slip


  A slump-rotational slide where material slides along a curved surface
• Hydraulic action


  Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion
• Abrasion


  Bits of rock and sand in waves grind down cliff surfaces like sandpaper
• Attrition


  Waves smash rocks and pebbles on the shore into each other, and they break and become smoother
• Solution


  Acids contained in sea water will dissolve some types of rock such as chalk or limestone
• Coastal transport processes

  • Traction
  • Saltation
  • Suspension
  • Solution