wave erosion processes

• what are the 4 main processes

  -hydraulic action

  -corrosion

  -abrasion

  -attrition
• what influences erosion

  wave type

  wave size

  lithology
• what is hydraulic action

  the force of the water itself breaks up rocks

  - may occur through direct impact of the water itself or by compressing air in cracks of rock
• how can hydraulic action take place

  - a plunging destructive wave can exert enough force (50kg/cm^2) to break off material from unconsolidated sources

  
  

  - force of breaking wave compresses air into cracks in the rock, when the wave energy is exhausted the compressed air explodes, causing micro-fractures in the rock and expanding the main crack
• what is hydraulic action the most effective to

  most effective water erosion for igneous rocks due to its cooling joints
• how to speed up hydraulic action/ make it more effective


  bigger waves

  -more power and exert a greater force upon impact = fastest rate of erosion by hydraulic action

  
  

  remove debris from the foot of the cliff

  -debris absorbs some wave energy and protects the cliff base
• what is abrasion

  wave picks up sediment and throws the load items against rock
• how does abrasion take place

  repeated impact chips away the rock face until small fragments break away
• what is abrasion most effective to

  soft sedimentary rock are eroded rapidly by abrasion
• how to speed up abrasion/make it more effective

  high energy destructive waves with a large wave height have a greater force to throw rocks with = faster rate of erosion

  
  

  for it to be effective, abrasion needs a supply of hard load items close to the foot of the cliff
• what is corrosion


  where water dissolves rock minerals
• what is corrosion most effective on

  limestones or sedimentary rocks with calcite cement are eroded rapidly by corrosion
• what is the most effective wave for corrosion


  constructive waves as the force of the impact is not relevant and their prolonged contact between water and material with a slow and low wave increases the time for a chemical reaction to occur
• what is attrition


  where material transported by waves are eroded through collisions with other load items (bash together in the wave)
• where does attrition occur

  foreshore and nearshore zones
• what does attrition do


  breaks down sediment into smaller sized particles

  
  

  blunts any sharp edges of particles, making them increasingly round
• effect of attrition on different rocks


  soft rocks: (eg poorly cemented sandstones and chalk)

  - broken down quickly into silt and sand

  
  

  hard rocks: (eg granite and flint)

  - form larger shingle pebbles
• when are wave erosion processes most effective


  during high energy storm events with large destructive waves

  
  

  erosion is faster when wind is blowing directly onshore and the tide is high (deeper water closer to the cliff = less energy loss)

  
  

  heavy rainfall can weaken the cliff through pore water pressure lubricating and increasing the weight of the cliff which encourages mass movement which can increase the rate of erosion