Walvis Bay Namibia, is a coastal town situated right on the edge of the Namib Sand Sea. This is made up of a few large tracts of sand dunes which lie along the coastal region.
Images of this landscape abound, it is a very scenic area, with massive majestic sand dunes, it is photographed often and is to be found in many publications, and is the quintessential image that a lot of people have of Namibia.
It is an area approximately 400 kilometeres long and between 100 and 150 kilometres wide, and consists of transverse and barchan dunes.
A barchan dune is one that is roughly arc shaped, and has two long sides with a curved part between them, this part is known as the slip face, which is generally around 32 degrees, which is the angle of repose for dune sand, the other side (the windward side) of the dune is at a much shallower angle of approximately 15 degrees.
The variation in size of sand dunes is considerable, they can be just a few metres, while others are hundreds of metres.
The action of the wind upon the sand causes the sand to ride up on the windward side and when it gets to the top of the dune, it falls over the edge and drops down the other steep side, hence the name, slip face. This way the whole dune is constantly on the move being blown along constantly.
Large dunes often get overtaken by small dunes, this is due to the fact that there is a considerably lesser volume of sand in a smaller dune, therefore it moves quicker.
Inland areas are covered with linear dunes, which run approximately north to south, while nearer the coast, the transverse dune is commonplace. The transverse dune is positioned around 90 degrees to the prevailing wind with a gentle slope on the windward side and a much steeper leeward slope.
These dunes have some vegetation in the form of grasses growing on them, while the more mobile dunes nearer the coast have almost no vegetation whatsoever, but do have a rich variety of small insects and other small animals.
Barchan dunes are also found on Mars, where there are strong winds to move the sand and dust. But that's another story.
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