Sand Dunes are mounds or ridges of drifted sand. Sand dunes can form both at the coast and in inland areas where there is sufficient sand and wind. However, the shape (morphology) of coastal dunes and inland dunes differ considerably even though the process of formation is very similar.
They are unique as coastal features as they are formed by air movement rather that water movement. There are several basic requirements for the formation of sand dunes, these are:
A supply of dry sand over a wide beach
An area of low lying land behind the beach
Predominantly onshore winds
Dunes normally form at the top of a beach, when the onshore winds blow sand from the lower shore to the top of the shore. The sand builds up at the top of the shore, especially around small objects such as strandline material. These small objects slow the speed of the wind so that it is no longer able to blow the sand.
These mounds of sand are colonised by salt tolerant plants, which further reduce the wind speed and increase sand deposition. With increased dropping of sand the height of these 'embryo dunes' increases. These embryo dunes are less frequently covered by the tide and waves and subsequently more plant species are able to grow here. The embryo dunes continue growing, unless they are destroyed by waves or storms.
I think that covers it.