Sand Dunes (DP IB Geography)

Coastal Processes & Sand Dune Formation

• 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