A Couple Of Things You Should Know About Sand Dunes But Were Afraid To Ask
Right at the edge of the Namib Sand Sea, lies Walvis Bay, a coastal town in the west of Namibia, this sand sea is in fact a few very large areas of sand which has blown into huge dunes that lay along the coastal region.
The image of the landscape of this particular area between Luderitz and Walvis Bay, is possibly how most people think of Namibia, the pictures of massive sand dunes are quite impressive and are photographed and published often.
It is an area approximately 400 kilometeres long and between 100 and 150 kilometres wide, and consists of transverse and barchan dunes.
The roughly arc shaped dune is known as a barchan dune, and has two long sides connected with a curved part forming the arc, the slip face is what this section is known as, which happens to be 32 degrees which is the maximum angle that sand can rest at, this is also known as the angle of repose. On the other side os the dunes, the sand is at a much shallower angle due to this being the windward side and rests at around 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.
Smaller barchan dunes move faster than large ones, and sometimes the smaller ones appear to break through the larger ones.
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
The more static dunes can be found to be growing some vegetation, mostly short hardy grasses, while the dunes nearer the coastal region are completely vegetation free, mainly due to the fact that they’re moving the whole time so nothing has a chance to grow on them. Even though there is no grass on these dunes, they do posess a surprisingly large number and variation of small animals and insects.
They say that there is a very similar type of dune to the barchan dune here and you can find it on Mars due to there being strong winds blowing, acting in a similar way with the sand and dust up there. But that’s another story.
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