Transverse and Barchan Dunes
Walvis Bay lies close to the Namib Sand Sea, comprising various significant areas of sand dunes spread down the coast. The actual panorama associated with this distinct region between Luderitz and Walvis Bay, is perhaps just how many people visualize Namibia, the wonderful pictures of enormous sand dunes are very striking and so are photographed as well as published frequently.
It is an area somewhere around four hundred kilometeres in length and somewhere between a hundred and a hundred and fifty kilometres broad, and includes transverse as well as barchan dunes.
A barchan dune is one that is approximately arc shaped, and it has a pair of lengthy sides with a curved component in between these, this specific section is referred to as the slip face, which happens to be in general close to thirty-two degrees, that is actually the angle of repose for dune sand, the other side (the windward aspect) of the dune is a substantially shallower angle of around fifteen degrees.
The word barchan or barkhan, is derived from a Kazakh word, and was first used by Alexander von Middendorf, a Russian naturalist while observing these crescent shaped dunes in Turkestan in 1881.
These types of dunes may vary in proportions from being a few metres to hundreds of metres.
They begin to move because they are continually blown along with the wind flow, which usually blows the fine sand up the windward aspect, when it falls across the slip face, thus resulting in the whole lot moving around with the wind.
More compact barchan dunes proceed more quickly compared to massive ones, and therefore from time to time the smaller sized varieties seem to break through the bigger ones. Transverse dunes further appear along this particular coastal area where the winds tend to be strongest, they are large and also irregular in shape, lying approximately at ninety degrees into the path of the current wind, the windward aspect is usually a moderate incline, although leeward aspect is significantly steeper, whilst inland areas tend to be covered with linear dunes that go approximately north to south.
These types of dunes incorporate some plants such as grasses developing on them, while the far more mobile dunes closer to the seacoast possess hardly any plant life at all, yet really have an abundant selection of small insects along with other small creatures.
Barchan dunes are also found on Mars, where there are strong winds to move the sand and dust.
But that's another story.