Sand Dunes - slides

• Sand dunes


  Accumulations of sand shaped into mounds by the wind
• Sand dunes are a system that needs to be thought of as such

  
• Important inputs for sand dunes

  • A plentiful supply of sand
  • Strong onshore winds
  • A large tidal range
  • An obstacle to trap the sand
  • Vegetation growth to encourage further growth of the dune

  
• Sand movement


  Sand is mostly moved inland via the process of saltation
• Sea breeze


  A wind blowing from the water onto the land, arising due to differential heating between land and water surfaces
• Beach with large tidal range


  • Weston-super-Mare in Somerset, UK
• Sand dune formation - First Stage/Embryo Stage

  1. Dried sand reaches top of beach and is trapped by debris

  2. Sand may become colonised by small plants or trap other windblown debris, increasing its size and trapping even more sand

  3. First dunes formed are embryo dunes

  4. Alkaline sand only allows hardy plants like lyme grass and sand couch to colonise

  5. These plants add organic matter to the dunes making them more hospitable for later plants
• Sand dune formation - Second Stage/Formation of Foredunes

  1. Foredunes or yellow dunes form

  2. Dunes darken as organic material adds humus to the soil

  3. Dunes remain slightly alkaline

  4. Foredunes tend to grow to around 5m in height with 20% of sand exposed

  
• Sand dune formation - Third Stage/Formation of grey dunes and dune ridges

  1. Dunes become more fixed

  2. Soil becomes increasingly acidic as more humus forms, increasing water retention

  3. This allows new species of plants to thrive like creeping willow and dewberry

  4. Less than 10% of sand is exposed on these 8-10m high dunes

  
• Sand dune formation - Fourth Stage/Formation of wasting dunes

  1. Very little sand from the beach accumulates beyond the grey dunes and dune ridges

  2. Soil is more acidic, water retentive and rich in humus

  3. Typical vegetation includes heather and gorse

  4. Dune height is usually between 6-8m high

  
• Stages of dune formation

  • Embryo dunes, foredunes and grey dunes
• Dune slacks can develop, which are depressions within the dunes where the water table is on or near the surface and conditions are often damp
• Blowouts can form where wind has removed the sand, or due to wildlife or human activity
• Depositional coastal features like sand dunes should be thought of as systems with inputs, processes and outputs