coasts

• 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)

  -considered closed system during scientific research and coastline management planning
• sediment cell =

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

  -11 in England and Wales

  -not fully closed so actions within one cell may affect another
• components of a sediment cell - 


  • sources - where sediment originates from (eg cliffs, offshore bars)
  • through flows - movement of sediment along the shore through longshore drift
  • sinks - locations where deposition of sediment dominates (eg spits, beaches)
• dynamic equilibrium =

  a state where the input and outputs of sediment in a coastal system/ sediment cell are in a constant state of change but remain in balance

  -physical and human actions can change this equilibrium

  
• negative feedback loop =

  a mechanism that balances changes, taking the coastal system back towards dynamic equilibrium

  -lessens change which has occurred within the system

  -eg a storm erodes a large amount of beach:

  1.destructive waves from storm lose energy and excess sediment is deposited as an offshore bar

  2.bar dissipates waves energy which protects beach from further erosion

  3.overtime bar gets eroded instead of beach until bar is gone and normal conditions of dynamic equilibrium ensue
• positive feedback -

  a mechanism that exaggerates change, taking the coastal system away from dynamic equilibrium

  -eg people walking over sand dunes destroys vegetation growing and causes erosion:

  1.roots from vegetation hold the sand dunes together -damaging vegetation makes sand dunes more susceptible to erosion - increases rate of erosion

  2.eventually sand dunes will be completely eroded leaving more of the beach open to erosion taking the beach further away from dynamic equilibrium
• littoral zone -

  the area of the coast where land is subject to wave action -constantly changing due to:

  • short-term factors like tides and storm surges
  • long-term factors like changes in sea level and climate change

  
• subzones of the littoral zone -

  • backshore - area above high tide level
  • foreshore - land where most wave processes occur
  • offshore - the open sea

  
• advancing coastline -

  coastline may be due to the land emerging or deposition being the prominent process

  
• retreating coastline -

  coastline may be due to the 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)
• 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 over time

  
• 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

  
• Resistance of rock


  • Determined by whether rocks are clastic or crystalline, the amount of cracks/fractures/fissures, and the lithology of the rock
• Types of rock and their 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


  A sequence of erosional landforms formed on pinnacle headlands
• Wave-cut notch and platform


  Marine erosion attacks the base of a cliff, creating a notch, causing the cliff face to become unstable and fall, leaving behind a platform
• Retreating cliffs


  New cliff faces are created through the process of repeat wave-cut notches and platforms, as the land retreats

  
• Blowhole


  A combination of a pothole on top of a cliff, created by chemical weathering, and a cave formed by marine erosion, meeting to create a channel for incoming waves
• Longshore (littoral) drift


  Sediment is predominantly transported along the coast, with waves hitting the beach at an angle and pushing sediment in that direction up the beach, then gravity carrying it back down in the backwash
• Other processes of sediment transportation


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


  Wave crests approach parallel to coast so there is limited longshore drift, sediment doesn't travel up 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
• Processes of deposition


  • Gravity settling (heavy rocks/boulders deposited first)
  • Flocculation (clay particles clump together and sink)
• Spit


  A long narrow strip of land formed due to deposition from longshore drift, can develop a recurved end
• Bar


  A spit that 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 island reducing velocity and leading to deposition

  
• Cuspate foreland


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

  
• Offshore bars


  A region offshore where sand is deposited as waves don't have enough energy to carry sediment to shore
• Sand dunes


  Formed when prevailing winds blow sediment to the back of the beach, with a process of vegetation succession from embryo dunes to yellow dunes to grey dunes
• Sand deposition


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

  2. Sand deposited as the wave breaks early, scouring the seabed and instantly depositing its 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


  1. Requires large quantities of sand and a large tidal range

  2. Sand dries so it is light enough to be picked up and carried by the wind to the back of the beach

  3. Frequent and strong onshore winds are necessary
• Stages of sand dune succession


  • Embryo dunes
  • Yellow dunes
  • Grey dunes
  • Dune slack
  • Heath and woodland