coasts by PMT

• Coast


  An open system that receives inputs from outside the system and transfers outputs away from the coast and into other systems (terrestrial, atmospheric or oceanic)
• Sediment cell


  A closed-system in terms of sediment, with sources, through flows, and sinks
• There are eleven sediment cells in England and Wales
• Sources


  Where the sediment originates from (e.g. cliffs, offshore bars)
• Through flows


  The movement of sediment along the shore through longshore drift
• Sinks


  Locations where deposition of sediment dominates (e.g. spits, beaches)
• Dynamic equilibrium


  Where input and outputs of sediment are in a constant state of change but remain in balance
• Sediment cells are not fully closed systems, so actions within one cell may affect another
• Positive feedback


  Mechanisms which enhance changes within a system, taking it away from dynamic equilibrium
• Negative feedback


  Mechanisms which balance changes, taking the system back towards equilibrium
• Littoral zone


  The area of the coast where land is subject to wave action

  
• Littoral zone


  • Constantly changing due to short-term factors like tides and storm surges, and long-term factors like changes in sea level and climate change
• Subzones of the littoral zone


  • Backshore
  • Foreshore
  • Nearshore
  • Offshore
• Advancing coastline


  Due to land emerging or deposition being the prominent process

  
• Retreating coastline


  Due to land submerging or erosion becoming the prominent process
• Emergent or submergent coastlines

  May be due to post-glacial adjustment (the land 'wobbles' as the glacier above it melts, causing isostatic sea level change)
• Abrasion


  Sediment is moved along the shoreline, causing it to be worn down over time
• Attrition


  Wave action causes rocks and pebbles to hit against each other, wearing each other down and becoming round and smaller
• Hydraulic action


  Air is forced into cracks, joints and faults within the rock, causing the cracks to widen and the rock to fracture
• Corrosion (Solution)


  Mildly acidic seawater can cause alkaline rock such as limestone to be eroded, similar to carbonation weathering
• Wave quarrying


  Breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m², directly pulling away rocks from the cliff face or removing smaller weathered fragments
• Erosion rates are highest when waves are high and have a long fetch, approach the coast perpendicular, at high tide, during heavy rainfall, and in winter
• Resistance of rock


  • Determined by whether it is clastic or crystalline, amount of cracks/fractures/fissures, and lithology
• Rock types and erosion rates

  • Igneous (very slow, <0.1cm/year)
  • Metamorphic (slow, 0.1-0.3cm/year)
  • Sedimentary (very fast, 0.5-10cm/year)
• Caves, arches, stacks and stumps

  Sequence of erosional landforms on pinnacle headlands
• Wave-cut notch and platform


  Marine erosion attacks the base of a cliff, creating a notch, leading to cliff face instability and collapse, leaving a platform
• Retreating cliffs


  New cliff faces created through repeat wave-cut notches and platforms, as the land retreats
• Blowhole


  Combination of a pothole on top of a cliff and a cave formed by marine erosion, meeting to create a channel for waves
• Longshore (littoral) drift


  Sediment predominantly transported along the coast, with waves hitting the beach at an angle and pushing sediment in that direction
• Other processes of transportation

  • Traction
  • Saltation
  • Suspension
  • Solution
• Swash-aligned

  Wave crests approach parallel to coast so there is limited longshore drift, sediment doesn't travel up the beach far

  
• Drift-aligned


  Waves approach at a significant angle, so longshore drift causes sediment to travel far up the beach

  
• Deposition


  Occurs when a wave loses energy, meaning the sediment becomes too heavy to carry
• Gravity settling


  The wave's energy becomes very low and so heavy rocks and boulders are deposited followed by the next heaviest sediment
• Flocculation


  Clay particles clump together due to chemical attraction and then sink due to their high density
• Spit


  A long narrow strip of land formed due to deposition from longshore drift, which can develop a hook shape over time

  
• Bar


  A spit which, over time, crosses a bay and links up two sections of coast, with a lagoon within

  
• Tombolo


  A bar or beach that connects the mainland to an offshore island, formed due to wave refraction off the coastal island reducing wave velocity
• Cuspate foreland


  Occurs with triangular shaped headlands, where longshore drift along each side creates beaches that meet to form the foreland

  
• Offshore bars


  A region offshore where sand is deposited, as the waves don't have enough energy to carry the sediment to shore