Sand Dunes (SL IB Geography)

• The coastal processes of erosion and deposition generate sediment for dune building
• Dunes form primarily by prevailing winds blowing sediment up the beach
• Plant succession stabilises sediment, which is vital for dune formation
• Dune formation requires:
  • Lots of sediment
  • Continuous wind 
  • Large beaches
  • Large tidal range, so sand sediment has time to dry
  • Obstacles for the dune to form over
  • Hardy, pioneer species to bind the sand

Formation of a sand dune

• The wind blows up the beach, transporting sediment
• When sediment reaches an obstacle, large pieces settle in front of it to create a ridge
• Behind the obstacle, smaller pieces of sediment settle
• This will build up over time, forming a sand dune
• The sand dune is steeper on the windward side, and more gentle on the other
• A psammosere is the plant succession of a sand dune

Embryo dunes

• These are young, very small sand dunes (only a few metres)
• Pioneer species colonise in embryo dunes and stabilise the sand e.g. lime grass or saltwort
• Sand accumulates around the newly colonised plant
• These dunes are fragile and tides can easily wash them away

Foredune

• Further up the beach, behind the embryo dune, a foredune develops
• Foredunes form as embryo dunes build up 
• Marram grass begins to grow, stabilising the dune further
• Sea holly grows on the sheltered side of the dune
• Species start to become more diverse and cover the ground

Yellow dune

• These dunes sit above the beach level
• These are mainly made of sand rather than soil
• The diversity of organisms increases, e.g. ragwort
• Marram grass (dead leaves) incorporate organic matter (humus), into the dune, creating soil:
  • This makes the sand/soil more nutrient-rich – a perfect environment for further plants to develop

Grey dune

• Grey dunes have more protection from the other dunes in front 
• Sand is more protected from the wind and stabilised by vegetation
• These dunes are fixed dunes 
• Gorse and heather can grow as soils improve

Dune slack

• The dip between sand dunes is the dune slack
• They may be moist or entirely filled with water
• They are nutrient-rich and home to a variety of plants and animals 

Mature dune

• This is the last stage of dune succession, reaching the climax community
• Conditions are much more favourable, with moisture and nutrient-rich soils
• They are far above the high-tide level
• These could be brambles, pine or birch trees
  

Diagram of dune succession

Diagram of dune succession