Sand dunes are formed by the action of wind. The wind moves small particles of sand upward and as particles fall they collect at the base of the dune. This action is repeated until a dune as we know it is formed.
Dunes in deserts can be several hundred of meters high. Some are smooth and conical others develop a mosaic of ripples. Colour too can vary from gold yellow to deep reds and orange.
The sand dunes found at the beach are formed in a different way to the stereotypical dune found in the desert. On the shore, sand is pushed along by a process known as ‘long shore drift’. This is a process where sand and gravel is moved sideways along the beach, then deposited by wind and wave action up the onto the beach above the high tide mark. Sand deposited in the sea by eroding cliffs can be swept to form dunes many miles away from their destination.
Sand is pushed up the beach by action of waves, wind and tide. Some of the sand collects around obstructions like flotsam and jetsam, tree stumps etc. Here the sand settles, collects and becomes dunes. As these sand dunes grow in size some plants can take a hold like Marram Grass, Bent Grass and Beach Grass. These grasses have long, trailing stems which root and help bind the dune causing more sand to build up behind it, thus allowing the creation of new dunes which in turn allow more grasses to establish themselves. These sand dune systems in some locations can spread many miles inland. Sand dunes are a diverse ecosystem allowing many species of plants to thrive, like the rare Yellow Horned Poppy, Sea Beet, and Sea Purslane. In these habitats are also found Sand Lizards, Grass Snakes and many species of bird life. Often salt marsh and woodland can form and survive behind a sand dune system.
Sand dunes can take many, many years to establish themselves and sadly they can be completely destroyed in a single storm. This phenomenon is known as a ‘blow out’ and in the right conditions can occur at any time. A ‘blow out’ occurs when a patch of vegetation is lost through fire or drought. Some erosion can be caused by trampling of humans or cattle over a period of time allowing a depression to be formed by strong winds. Usually ‘blow outs’ are small in size but this is not always the case. Under a extreme conditions they have been known to spread for several miles.
Sand dune systems are relatively rare ecosystems. They are a pleasure to visit and should be protected and preserved for all to enjoy.
http://www.bbc.co.uk/nature/blueplanet/factfiles/plants/marram_bg.shtml
http://www.geography-site.co.uk/pages/physical/coastal/dunes.html
http://members.multimania.co.uk/WoodyPlantEcology/sanddune/index.html
