Undoubtedly, for most people desert equals sand, and there are few more spectacular examples of sand desert (erg) than the Namib dunes, which stretch for most of Namibia’s Atlantic Coast, pushing south into South Africa, and north into Angola. The remarkableness of the 50,000-square-kilometre Namib Dune Sea within the Namib-Naukluft National Park – about the size of Belgium – has now been internationally recognized in its designation as a UNESCO World Heritage Site. Though the Namib boasts some of the highest dunes in the world, at over 300m, it’s the ever-changing palette of colours that most impresses – from gold to pink, cream to brick-red, apricot to maroon. The coastal dunes are generally paler, with the colouration becoming deeper and redder towards the eastern limits of the sand sea, due to the amount of iron-oxide present in the predominantly quartz sand and the ways in which the dunes have weathered over time. Even so, the dunes magically alter in hue with the changing light.
Dune morphology, on the other hand, depends principally on the strength and the direction of the wind; most kinds of sand dunes are longer on the windward side, where the wind pushes the sand up the dune, with a shorter “slip face” in the lee of the wind, where the blown sand tips over. It’s here that occasional grasses take root, helping to stabilize the dune, and wind-blown detritus collects, providing food for some of the Namib’s extraordinary desert-adapted creatures. The following main dune formations are present in the Namib:
Classic crescent-shaped dunes with two “horns” facing downwind. The most mobile of dunes, forming in strong uni-directional winds; some in the Namib can migrate over 50m per year. They are especially prominent round Lüderitz and Walvis Bay, and up the northern section of the Skeleton Coast. Less common, parabolic dunes are also crescent-shaped but with the horns trailing upwind and the slip face on the inside.
Linear (seif) dunes
Converging winds push the sand into long lines or ridges, running parallel to the prevailing wind; some linear dunes in the Namib are over 32km in length.
Many examples of these giant dunes are found round Sossusvlei. They are formed when several winds blow from different directions, resulting in three or more steep ridges radiating out from a central peak. Star dunes do not migrate, but continue to grow vertically.
Long, asymmetrical dunes that form at right angles to the prevailing wind in conditions of abundant sand, such as on the road between Walvis Bay and the airport; with steep slip faces, they appear like giant ripples from the air.