coasts

• mechanical weathering is the breakdown of rock without changing its chemical composition
• freeze thaw weathering is mechanical
• freeze thaw weathering- water goes in rock. water freezes. water expands. this widens the cracks in the rock. repeat
• chemical weathering is the breakdown of rock by changing its chemical composition
• carbonation weathering is a type of chemical weathering that happens in warm and wet conditions
• carbonation weathering- rainwater has dissolved carbon dioxide dissolved in it, witch makes it a weak carbonic acid. carbonic acid reacts with rock that contains calcium carbonate, so the rocks are dissolved by the rainwater
• mass movement is where material falls down a slope
• slides- material shifts in a straight line down the slope
• slumps- material rotates along a curved slip plane
• rockfalls- material breaks up, often along bedding planes and falles down a slope
• when wind blows over the suface of the sea it creates waves
• destructive waves- have a high frequency and are high and steep. backwash is more strong than the swash so material is removed
• constructive waves- low frequency, low and long. swash more powerful than backwash so material is deposited
• hydraulic action- waves crash against rock and push air into the gaps
• abrasion- rocks scrape against side of cliff
• attrition- rocks bang into each other making them smaller and rounder
• longshore drift- prevailing wind is the direction of the swash, gravity is the direction of the backwash
• desposition is the dropping of material
• traction- rolling
• saltation- bouncing
• suspension- carried along (suspended in water)
• solution- dissolved
• discordant coastlines are made of alternating bandsof soft and hard rock at right angles to the coast
• concordant coastlines are where the bands of rock are parallel to the coastline
• a bar formes when a spit joins two headlines together
• wave cut platform:

  1. erosion at the foot of a cliff forming a wave cut notch
  2. rock above becomes unstable and collapses
  3. collapsed material is washed away and ew notch forms
  4. process repeats and cliff retreats
• sand beaches are created by low energy waves
• shingle beaches are created by high energy waves
• sand dune order: embryo dune, foredune, mature dune
• sand dunes are formed when sand is moved up the beach by wind sand collects around obstacles because they decrease wind speed forming embryo dunes.
• embryo dunes are colonized by plants. the roots of the plants stabilize the dune sand encourage more sand to accumulate this formes fore dunes and eventually mature dunes
• hard engineering strategies:

  sea wall

  gabions

  rock armour

  groynes
• soft engineering strategies:

  beach nourishment and reprofiling

  dune regeneration

  managed retreat
• in lyme regis powerful waves from the south west erode the sea cliffs
• in may 2008, 400m of cliff collapsed
• lyme regis depends on tourism
• in 1990 west Dorset coast district council began a scheme to provide long term protection for the coast
• phase 1 was building rock armour
• phase 3 was never carried out because of the cost
• positive: new beaches increased trade up to 70 percent