Classic sand grains of the desert dunes: fine-grained, some rounded, some quite angular, but all smoothed and frosted by, of course, the process of sand-blasting; and all with that veneer of iron mineral colouring. These are typical of virtually all desert dunes, but they come from, what is for me at least, a special place.
A couple of years ago, I wrote a piece about Ralph (pronounced, as is common in the UK, “Rafe”) Bagnold, and called it “The man who figured out how deserts work.” An explorer, soldier and scientist, he was an extraordinary individual, in the late 1920s and early 1930s pioneering long-range motorised desert travel, before laying the foundations of today’s understanding of desert sands, helping turn the tide of the war in North Africa, and then turning his attention to sand transport by water.
Having established the quantitative basis of wind-blown sand transport in the laboratory, in 1938 Bagnold set off on an expedition to revisit one of his old haunts in the Libyan Desert of southwest Egypt and test his lab results in the field. His base camp was set up beneath the cliffs of the vast plateau of the Gilf Kebir, the border of Libya just to the west and that of Sudan not far to the south. He chose an ideal field lab, camping along the flanks of a huge lee, or falling, dune, where the sand blows southward from the Great Sand Sea, and spills over the edge of a row of cliffs to form a long and elongate dune:
I was lucky enough, on what can honestly be described as a trip of a lifetime, to join an expedition in the footsteps of Bagnold’s 1938 venture and we visited the site of his base camp. In the top picture you can see the dune streaming off to the south, where, at its tip, it breaks up into smaller dunes (see the Google Earth image above, right). My colleagues are clustered around what are clearly the remains of a shelter that Bagnold’s team built (bottom, left), somewhat the worse for wear some seventy years on, but still not covered in sand – the dune largely passes them by. And the Shell kerosene cans used by the expedition are still lying around. Was this one opened by Ralph Bagnold? It’s from here, a special place, that the grains at the head of this post come. The sand grains that Bagnold slept on and worked with are likely long blown off on their travels to the south, but even so….
Some of Bagnold’s most important field measurements at the Gilf Kebir were wind velocities and the associated sand movement under different conditions. Here are a couple of photos of him at work there (courtesy of Stephen Bagnold), the one at left taken in a slight sandstorm:
My work necessitated waiting for a sand storm to blow up.….A heavy one blew up within a few days. I was well prepared for it except, alas, I had lost my sand goggles. I spent some very uncomfortable hours sitting in the open, directly exposed to a violent sand blast, trying to keep my eyes open while taking readings from an array of gauges and sand traps. The purpose of eyelashes was very evident. Fortunately, I managed to get some reliable measurements which nicely confirmed my wind-tunnel measurements made in London.
This was Bagnold’s last desert expedition – he had other things to keep him busy - but he wrote of being at home in England:
And then comes some trivial sense-impression—the hot-varnish smell of a car standing in the sun, a cloudless sunset, the finding of sand grains in the pocket of an old coat. Out comes the map again; and the eye hovers over some blank space still father away which nobody has yet reached. Happy calculations follow about petrol and distances—dreams of just one more desert trip.
I know what he meant – after all, where else can you wake up in the morning to a view like this?