Coasts

• Coastal processes


  Weathering, erosion, transportation and deposition
• • Destructive waves have high frequency, stronger backwash than swash, result in erosion
  • Constructive waves have low frequency, stronger swash than backwash, result in deposition
• Mechanical weathering

  1. Water enters cracks in rock

  2. Water freezes and expands, putting pressure on rock

  3. Ice thaws, releasing pressure

  4. Repeated freezing and thawing causes rock to break apart
• Chemical weathering


  1. Minerals in rock react with acids in water, forming new chemical compounds

  2. These chemical compounds break down the rock over time
• Mass movement


  Downward movement of rock, mud or soil due to gravity, typically occurs when a lot of water is present
• Types of mass movement

  • Sliding
  • Slumping
  • Rock fall
• Coastal erosion

  • Hydraulic power
  • Abrasion
  • Attrition
• Transportation

  1. Traction

  2. Saltation

  3. Suspension

  4. Solution
• Longshore drift


  1. Swash carries material up beach

  2. Backwash carries material down beach due to gravity

  3. Backwash always moves at 90 degree angle
• Waves approach at angle, moving in same direction as prevailing wind


  Longshore drift occurs
• Deposition


  Occurs when sea loses energy and drops eroded material, most likely with low energy waves, sheltered areas, interrupted longshore drift, little wind, tidal water trapped by spits
• Beaches are formed when deposition level is greater than erosion level
• Waves that deposit more material than they erode are known as constructive waves
• Hydraulic action is the force exerted by water as it hits the coastline, causing waves to break against cliffs or beaches.
• Abrasion occurs when rocks on the seabed rub against one another, creating sand particles that can then wear away the shoreline.
• Solution 


  where rocks and minerals are dissolved within the water
• Suspension 


  where fine material is held within the water mass
• Coastal landforms


  The result of physical processes that have varying effects on different structures and types of rock
• Headlands and bays


  • Form where there are alternating bands of soft and hard rock
  • A discordant coastline is one where bands of soft and hard rock run at right angles to the coast, so the rocks erode at different rates
  • The protruding bands of isolated rock are called headlands
  • The formation of headlands and bays can take thousands of years
• Wave-cut platforms


  1. Waves and rocks crash against the foot of a cliff face

  2. The base of the cliff is eroded away, leaving a wave-cut notch

  3. The unstable cliff collapses

  4. With repeated erosion, the cliff retreats to form a wave-cut platform
• Caves, arches and stacks

  1. Waves crash repeatedly into the headland, causing faults and joints to erode and develop into cracks and small caves

  2. Constant erosion causes the caves to get bigger until their back walls are eroded away completely, creating natural arches

  3. The arches widen as more rock is eroded away through weathering

  4. The arches eventually collapse, leaving an isolated pillar known as a stack. Further erosion of the stack will leave a shorter stump
• Sandy beaches


  • Generally formed from sand or shingle, they are the most common features of deposition found on coasts
• Shingle beaches


  • Occur where there are constructive waves
  • The swash (water moving up the beach) is stronger than the backwash (water moving back down the beach) so sediment builds up on the beach
  • Small sand particles are easily carried back down the beach by the backwash so the beaches are long and shallow
• Sand dunes


  • Mounds of sand that are found behind sandy beaches
  • Require a large, flat beach, a good supply of sand, strong winds and obstacles
  • Sand is deposited by longshore drift and blown to the top of the beach by onshore winds
  • Obstacles, such as driftwood, block sand movement, causing deposits to build over time
  • Vegetation (e.g. marram grass) helps to stabilise and bind the sand together, creating small embryo dunes
  • Over time, the dune migrates inland
• Spits


  • Long stretches of sand or shingle that extend from the land
  • Form where the coastline suddenly changes shape (e.g. at river mouths or estuaries)
  • Sand and shingle are transported by longshore drift past the point where land ends. As the waves lose energy, material is deposited, forming a spit
  • Strong winds can cause the end of the spit to curve towards the land, creating a recurved end
  • In the sheltered area behind the spit, vegetation can grow easily, and a salt marsh may form
• Bars

  • Form when a spit joins two headlands together, trapping the water in a lagoon behind it