marine erosion

• What is the main source of energy at the coast?

  waves, which are generated by wind

  the friction between wind and the water surface which transfers energy from the wind to the water
• Why does wind occur?

   because of the rotation of the earth and differences in atmospheric pressure when different parcels of air are heated differently by the sun
• What features of wind affect the energy of a wave?


  fetch

  duration

  strength of wind
• What is wave height?

  the distance from the peak to the trough
• What is wave length?

  the distance from crest to crest
• What is wave frequency?

  the number of waves which pass a specific point over a given time
• What are the break characteristics of constructive waves?


  strong swash

  weak backwash
• What are the break characteristics of destructive waves?


  weak swash

  strong backwash
• How are destructive waves formed?

  Local storms, strong winds, high fetch 
• How are constructive waves formed?

  Distant weather systems, calm local weather, short fetch 
• Constructive waves on beaches?

  Build up the beach with a gentle beach profile
• Destructive waves on beaches?


  Beach is limited. Steeper beach profile is likely in the short term 
• What is abrasion?

  sediment and stones are picked up by the waves and wear away at the cliff/headland
• What is hydraulic action?

  this is the shear force of the waves forcing air at high pressure into cracks in the cliff over time this weakens the rock and causes the joint to widen
• What is corrosion?

  weak acids in seawater dissolve the rock particles
• What is attrition?

   as rocks are moved around by the water they knock into each other gradually becoming smaller and rounder
• What factors influence erosion?

  wave type

  wave size

  lithology
• How do wave size and wave type affect erosion?


  • Wave type and size affects the seasonal changes in the amount of erosion 
  • Erosion tends to happen more during the winter due to a greater number of destructive waves
  • The size and type of waves affects the amount of hydraulic action and abrasion
• How does lithology affect erosion?

  Lithology affects erosion by determining the resistance of rocks to weathering and erosion processes.

  • Weaknesses in rocks erode more quickly
  • More resistant rocks erode more slowly
• How are wave-cut platforms formed?

  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 (undercutting)

  eventually, the overhang created by the undercutting collapses due to weathering and gravity

  the cliff retreats, leaving a wave-cut platform that's exposed at low tide
• How do caves, arches, stacks and stumps form?

  • At a headland, where the rock is hard, erosion is slow
  • Wave refraction concentrates wave energy onto the headland
  • Joints in the headland are susceptible to erosion by hydraulic action. Over time the joints widen forming a cave that 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 that will over time be eroded by weathering, abrasion, and hydraulic action to form a stump
• When does most erosion happen?

  during winter storms when destructive waves are at their largest and most powerful
• What is differential erosion?

  when bands of more-resistant rock between weaker joints and cracks erode more slowly

  the selective erosion of areas of weakness- as opposed to more resistant areas and types of rock
• The type of wave that strikes the shore can have a big impact on erosion. For example, constructive waves tend to deposit sediment on the shore, reducing erosion, while destructive waves tend to erode the shore by pulling sediment away.