So, I ask myself, how could this blog possibly miss the “dune week” celebration on the geoblogosphere, an arenaceous festival if ever there was one? The great thing about asking yourself is that a credible answer should be forthcoming – feeble though it may be in this instance: “distracted, pressures of work, general indolence… but better late than never, eh?” I am not convinced, but, anyway, offer this:
In the great deserts of the world, the sand seas made up of the long, towering edifices of seif dunes, elongate, shape-shifting mountainous ribbons of sand, named after the Arabic word for “sword,” are invariably characterised by intervening “streets.” These are the lanes between the long dunes, mysteriously swept free of sand, covered instead in pebbles and cobbles – as in my example from Egypt’s Western Desert, above. There are, at least, two explanations for these “streets”:
1. Ralph Bagnold, the man who figured out how deserts work, offered a clear model, based on physics, experiment, and meticulous science, that showed how the saltation of sand grains driven by the wind was much more energetic over pebbles (bouncing) than over a sand surface (splashing). This led to a removal of sand from a rocky surface and, inevitably, to its self-accumulation into dunes.
2. The Walmajarri people of Australia’s Great Sandy desert believe that their streets (below) were swept clean by mythical snakes journeying westward.
[For some great dune reading, see Dana Hunter’s post and round-up of the geoblogosphere’s eponymous week.]