Coasts

• How wind creates waves


  1. Blowing wind creates ripples

  2. Ripples turn into waves

  3. Lower part of wave slows down due to friction

  4. Upper part of wave falls forward and breaks onto beach
• Destructive waves


  High frequency waves (10-15 times per minute), tall, crash onto beach and scour away land, swash less powerful than backwash, cause erosion by abrasion
• Constructive waves


  Low energy, less frequent (6-9 times per minute), roll onto beach, lose energy when rolling up beach so deposit material, forward swash more powerful than backwash, cause deposition
• Fetch


  Longer fetch leads to destructive waves, shorter fetch leads to constructive waves
• Wind strength


  Stronger winds lead to destructive waves, weaker winds lead to constructive waves
• Coriolis force


  Earth's rotation affects the way winds travel, deflecting them clockwise in northern hemisphere and counter-clockwise in southern hemisphere
• How tides are created

  1. Gravitational pull of moon and sun creates high and low tides

  2. High tide when area points towards moon

  3. Low tide at 90-degree angle to moon

  4. Spring tides when sun, earth and moon aligned

  5. Neap tides when sun and moon at right angles to earth
• Tidal range


  Higher tidal range leads to increased coastal erosion
• How ocean currents work

  1. Surface currents wind-driven, include rip, longshore and tidal currents

  2. Upwelling currents bring cold water to surface, creating cycle of upwelling and downwelling

  3. Deep currents density-driven

  4. Global conveyor belt circulates heat, nutrients and gases around the world
• Sediment sources


  • Rivers bringing clastic sediments
  • Mass movement of cliffs
  • Onshore currents excavating sea floor sediment
  • Biogenic sediments from dead sea creatures
• Sediment cells


  Areas where sediment movement is largely self-contained, bounded by headlands and peninsulas, can have smaller sub-cells
• Sediment budgets


  • Balance between changes in sediment volume held within the system and volume entering or leaving the system
  • Positive budget = more inputs than outputs
  • Negative budget = more outputs than inputs
  • Affected by changes in inputs (e.g. river damming, coastal defences) and outputs (e.g. sediment removal, sea level rise)
• Coastal landform


  Characteristic feature that has developed as a result of high energy conditions operating on coastal material (erosion feature) or low energy conditions following a period of high energy (deposition feature)
• Coastal landscape


  A section of coastline that has a range of coastal features; some erosional, some depositional, that is distinguishable from neighbouring coastal landscapes by prevailing characteristics that dominate the form of the coastline there
• Weathering


  1. Thermal expansion/extraction

  2. Wetting/drying

  3. Freeze-thaw action

  4. Chemical solution

  5. Biological weathering
• Erosion


  1. Abrasion/corrasion

  2. Hydraulic action

  3. Cavitation

  4. Attrition
• Mass movement


  1. Run-off

  2. Landslide

  3. Slumping

  4. Soil creep
• Coastal erosion features


  • Headlands and bays
  • Caves
  • Arches
  • Stack
  • Stump
  • Wave-cut (marine) platform
  • Wave-cut notch
• Coastal deposition features


  • Beaches
  • Spit
  • Bar
  • Tombolo
  • Offshore bar
  • Barrier islands
• The degree of natural erosion is affected by the components, processes and energy: Lithology, Rock structure, Climatic environment, Energy inputs
• Coastal landscapes


  Interaction between: Nature and structure of the rock or materials, Climate component determining weathering processes, Marine processes of erosion and deposition, Input of energy and sediment, Amount of time for processes to operate
• Factors involved in sand dune formation


  • Gradient of ground inland adjacent to beach is relatively flat
  • Strong onshore winds provide energy to move sand inland
  • Beach composed of fine sand particles
  • Large area of beach exposed at low tide
• Types of coastal landscapes


  • High energy coastal environment dominated by developing features of erosion
  • Low energy coastal environment dominated by relatively stable features of deposition
  • Variable energy (dynamic) coastal environment dominated by transfers of sediment between phases of erosion and periods of deposition
  • Coastal environment with little long-term change and time for full evolution of coastal landforms into a state of stable equilibrium
  • Metastable coastal environment where processes (and thus, features) change rapidly
  • Historic coastal environment with evidence of ancient processes, sea levels and features with more recent features superimposed
• Sand dune succession: psammosere development


  1. Sand accumulates against a feature and builds upper beach height

  2. Wind speed drops behind accumulation resulting in more sand deposition

  3. Marram grass colonises embryo dunes stabilizing further dune migration

  4. Marram leaves further reduce wind speed and capture more blown sand

  5. Decaying plants add humus

  6. Microclimate and soil conditions change allowing colonisation by additional species
• Mudflat/saltmarsh succession: halosere development


  1. Marine algae and sea lettuce are early colonizers of nearly permanently submerged mudflat

  2. Pioneer species trap sediment and calm tidal waters

  3. Colonisation by hardy grass species that can tolerate high saline and pH conditions

  4. Vegetation dominated by low-growing flowering plants

  5. Deciduous woodland develops that shades and dominates competition
• Psammosere


  The characteristic plant succession that develops on a new sand dune ecosystem and achieves, or is on the way to achieving a climax community
• Halosere


  A sub-set of hydrosere (plant succession occurring in water conditions) that occurs in salt (as opposed to fresh) water
• Climatic climax community


  The dominant plant species at the end of a phase of plant succession that reaches a state of ecological equilibrium appropriate to the climate experienced there
• Seral community


  One or more of the intermediate stages of dominant vegetation stages on the way to a climatic climax community
• Primary succession (prisere)


  Uninterrupted development from first colonisation to climax vegetation
• Secondary succession


  A succession that takes over once natural conditions have changed and replaces a primary succession sequence
• Plagioclimax


  Where human intervention has interrupted the natural succession that would have taken and delivered an alternative climax of vegetation
• Rates of succession may be relatively rapid (measured in centuries) or take longer (over thousands of years) depending on growth rates and abundance of colonising species, but many environments are interrupted before attaining climax stability as conditions change
• Factors involved in sand dune formation


  • Gradient of ground inland adjacent to beach is relatively flat
  • Strong onshore winds provide energy to move sand inland
  • Beach composed of fine sand particles
  • Large area of beach exposed at low tide
• Sand dune succession: psammosere development


  1. Sand accumulates against a feature and builds upper beach height

  2. Wind speed drops behind accumulation resulting in more sand deposition

  3. Marram grass colonises embryo dunes stabilizing further dune migration

  4. Marram leaves further reduce wind speed and capture more blown sand

  5. Decaying plants add humus

  6. Microclimate and soil conditions change allowing colonisation by additional species
• Mudflat/saltmarsh succession: halosere development


  1. Marine algae and sea lettuce are early colonizers of nearly permanently submerged mudflat

  2. Pioneer species trap sediment and calm tidal waters

  3. Colonisation by hardy grass species that can tolerate high saline and pH conditions

  4. Vegetation dominated by low-growing flowering plants

  5. Deciduous woodland develops that shades and dominates competition
• Psammosere


  The characteristic plant succession that develops on a new sand dune ecosystem and achieves, or is on the way to achieving a climax community
• Halosere


  A sub-set of hydrosere (plant succession occurring in water conditions) that occurs in salt (as opposed to fresh) water
• Climatic climax community


  The dominant plant species at the end of a phase of plant succession that reaches a state of ecological equilibrium appropriate to the climate experienced there
• Seral community


  One or more of the intermediate stages of dominant vegetation stages on the way to a climatic climax community