Sossusvlei, Namibia's highlight in the heart of the Namib Desert, is an enormous clay-pan enclosed by mighty sand dunes. Some of the spectacular hills of sand reach a height of 300 metres and belong therefore to the highest in the world. Only after a heavy rainfall, which is very seldom in this area, does the 'vlei' fill with water. However, as the clay layers are hardly impervious, a turquoise lake remains for quite some time.
During a good rainy season the Tsauchab River flows into the pan, which creates a haven for water birds. Even during the dry season, oryx, springbok and ostriches can be seen feeding off the sparse vegetation along the watercourses.
The dunes of the Namib Desert developed over a period of many millions of years. It is thought that the vast quantities of sand were carried into the Atlantic Ocean by the Orange River. This material was subsequently moved northwards by the Benguela current. The surf pushed the sand back onto land and coastal dunes developed as a result, which were shifted inland more and more by the wind. Wind continuously restacks the sand of the huge shifting dunes of the Namib Desert. It tirelessly forces the grains of sand on the flat windward slope upwards to the crest of the dune. Here they fall down in the wind shade. The leeward slope, therefore, is always considerably steeper than the windward side.