Coastal Landscapes

• Coast


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


  A section of coast that is considered a closed-system in terms of sediment

  
• Components of a sediment cell


  • Sources (where sediment originates from)
  • Through flows (movement of sediment along the shore through longshore drift)
  • Sinks (locations where deposition of sediment dominates)
• Dynamic equilibrium


  A state where the input and outputs of sediment in a coastal system 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 that exaggerate changes within the coastal system, taking it away from dynamic equilibrium

  
• Negative feedback


  Mechanisms that balance changes within the coastal system, taking it back towards equilibrium

  
• Littoral zone


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

  
• Subzones within the littoral zone


  • Backshore (area above high tide level)
  • Foreshore (land where most wave processes occur)
  • Nearshore (shallow water areas close to land)
  • Offshore (the open sea)
• Advancing coastline


  A coastline where the land is emerging or deposition is the prominent process

  
• Retreating coastline


  A coastline where the land is submerging or erosion is the prominent process
• Corrasion


  Sand and pebbles are picked up by the sea from an offshore sediment sink or temporal store and hurled against the cliffs at high tide, causing the cliffs to be eroded

  
• 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


  As a wave crashes onto a rock or cliff face, 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, waves approach the coast perpendicular to the cliff, at high tide, during heavy rainfall, and in winter
• Factors affecting rock resistance to erosion

  • Whether rocks are clastic or crystalline
  • Amount of cracks, fractures and fissures
  • Lithology of the rock
• Erosional landforms


  • Caves, arches, stacks and stumps
  • Wave-cut notch and platform
  • Retreating cliffs
  • Blowhole

  
• Longshore (littoral) drift


  The process where sediment is predominantly transported along the coast
• Processes of sediment transportation


  • Traction (large, heavy sediment rolls along the sea bed)
  • Saltation (smaller sediment bounces along the sea bed)
  • Suspension (small sediment is carried within the water column)
  • Solution (dissolved material is carried within the water)
• Swash-aligned


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

  
• Drift-aligned


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

  
• 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
• Depositional landforms


  • Spits
  • Bars
  • Tombolos
  • Cuspate forelands
  • Offshore bars
  • Sand dunes
• The formation of sand dunes requires large quantities of sand, a large tidal range, frequent and strong onshore winds, and a process of vegetation succession (embryo dunes, yellow dunes, grey dunes)
• Sand deposition


  1. Waves don't have enough energy to carry the sediment to shore

  2. Sand is deposited
• Formation of offshore bar


  1. Wave breaks early

  2. Scouring the seabed

  3. Instantly depositing sediment as a loose-sediment offshore bar

  
• Sand dunes

  Sand accumulates at the back of the beach due to prevailing winds
• Formation of sand dunes

  • Requires large quantities of sand and a large tidal range
  • Sand needs to dry so it can be picked up and carried by the wind
  • Frequent and strong onshore winds are necessary
• Vegetation succession in sand dunes


  1. Embryo dunes

  2. Yellow dunes

  3. Grey dunes

  4. Dune slack

  5. Heath and woodland
• Embryo dunes


  Sand starts to accumulate around a small obstacle (driftwood, wooden peg, ridge of shingle) in the upper beach area
• Yellow dunes


  More sand accumulates and vegetation may develop on the upper and back dune surfaces, stabilising the dune
• Grey dunes


  Sand develops into soil with lots of moisture and nutrients as vegetation dies, enabling more varied plant growth
• Dune slack


  Water table rises closer to the surface or water is trapped between hollows between dunes during storms, allowing the development of moisture-loving plants
• Depositional landforms

  • Consist of unconsolidated sediment and are vulnerable to change
  • Depend on a continuous supply of sediment to balance erosion
  • Their dynamic equilibrium can shift
• Weathering


  Breakdown of rocks over time, leading to the transfer of material into the littoral zone where it becomes an input to sediment cells
• Mechanical (physical) weathering


  1. Freeze-thaw (frost-shattering)

  2. Salt crystallisation

  3. Wetting and drying