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
Diagram of dune succession
