Barkan in the wind

Heading out from the Gorge we encountered concrete mile-stones marking the progress of one particular sand dune over the years. Actually, more of like 17m-stones, since that is the average distance moved annually since 1969. It is about 9m high and 100m along its curve.
The local Maasai believe the black sands originated from Ol Doinyo Lengai or “Mountain of God”, an ex-volcano which is just visible on the horizon.
An significant peculiarity is that the sand has a very high iron content and has become magnetised. The compulsory tour guide insists on chucking handfuls up to prove that it prefers to clump and drop rather than be dispersed by the wind. Unfortunately, thanks to the mornings rainfall, the sand is saturated and really solid underfoot; my footsteps on the dune leave no imprint. So the animated demonstration merely proved to me that mud drops in the wind.
This type of dune is called a barchan or barkan and is begun by sand clumping around a stone as it is blown by the wind which comes predominantly from the East. Sand grains are blown up the gentle, windward slope in the usual way, but instead of flying through the air like spume off a wave, tumbles down the leading edge owing to each grains affection for its neighbour - magnetic attraction. As they are blown up, gravity tempts them to take a less vertical line. Over time this results in more sand on the sides than in the centre and thus the crescent shape.Read more