Among the many things that are intoxicating about the desert, the things that draw us back, I find the silence perhaps the most compelling. In a world where noise bombardment is the norm, the complete absence of sound is a shock and a fascination, the auditory equivalent of turning off your headlamp deep underground and experiencing, literally, a complete inability to see your hand held up in front of your face. Sit in the desert in the morning or at night and you can sense yourself straining to detect a sound, any sound - but there is nothing. Wilfred Thesiger, one of the great desert explorers and writers, wrote of “a silence in which only the winds played, and a cleanness that was infinitely remote from the world of men.” It is only the wind that breaks the silence, gently and subtly as the day warms up and the air is on the move, sometimes expressing itself with the fury of a sandstorm. Watching the first breaths of wind gather momentum and begin their game with the sand is hypnotizing - at first a few tumbling grains, then more, gathering themselves into swirling, shape-shifting, fluid sheets dancing over the desert surface. This is the desert at work, the wind is the engine and the sculptor, and, as Thesiger observed, the only thing that breaks the silence.
We can wonder at the glorious diversity of the results of the engine’s efforts - ripples, ridges, dunes in all their variety, sand seas, sandstorms, sand blasting - but our understanding of how the engine works is owed to one man, Ralph Bagnold. 
, and, later, Model A’s. He pioneered the means for extended automobile expeditions, desert navigation, and driving across sand - including the giant dunes of the Great Sand Sea. As a civilian in the late 1920s and early 1930s, he accomplished journeys that no-one had thought possible, and, along the way, became fascinated by what we didn’t know about the desert:
“In 1929 and 1930, during my weeks of travel over the lifeless sand sea in North Africa, I became fascinated by the vast scale of organization of the dunes and how a strong wind could cause the whole dune surface to flow, scouring sand from under one’s feet. Here, where there existed no animals, vegetation or rain to interfere with sand movements, the dunes seemed to behave like living things. How was it that they kept their precise shape while marching interminably downwind? How was it they insisted on repairing any damage done to their individual shapes? How, in other regions of the same desert, were they able to breed “babies”, just like themselves that proceeded to run on ahead of their parents? Why did they absorb nourishment and continue to grow instead of allowing the sand to spread out evenly over the desert as finer dust grains do? More basically, what kind of upward physical force must be exerted on the mineral grains to make them rise against the force of gravity, lifting them to such a height that they can strike one’s face like little hammers? No satisfactory answers to these questions existed. Indeed, no-one had investigated the physics of blown sand. So here was a new field, I thought, one that could be explored at home in England under laboratory-controlled conditions.”
And explore under laboratory-controlled conditions is exactly what he did. He was a highly-skilled engineer and designed and built his own wind tunnels and delicate measuring apparatus from scratch. He meticulously measured sand, its ranges of grain sizes and how they influenced (and were influenced by) transportation by his laboratory winds. He documented saltation, the process by which flying sand grains land and kick yet more grains into the air, and demonstrated that this is the main way in which desert sand moves, quantifying the physics and the aerodynamics. In 1938, he returned to the Sahara as a leader of a multi-disciplined expedition to the Gilf Kebir in the southwesternmost corner of Egypt, an area he and his colleagues had explored earlier. His aim was to take field measurements of moving sand and dune dynamics to test his laboratory results, an aim he accomplished with dramatic success. This was the first time that the desert’s engine had been scientifically measured and documented - many questions remain today, but the basis was set out by Bagnold.
A couple of years ago, I was lucky enough to be invited to join an expedition retracing, as far as we could, Bagnold’s 1938 itinerary - I was the sort of token geologist. And what an extraordinary experience that was - I became completely hooked on the desert. A visit to the site of his base camp revealed the extent to which his much-studied dune had overridden the scene. Challenges of logistics, navigation and vehicle travel in 2007 only emphasized how extraordinary had been Bagnold’s achievements nearly eighty years previously.
The Second World War saw Ralph Bagnold back in his military role. Exploiting his desert expertise, he established the legendary Long Range Desert Group, a highly mobile raiding force that wrought havoc by appearing out of nowhere behind enemy lines after journeys that were thought impossible. After the war, he returned to refining and compiling his work on desert sand, the result being The Physics of Blown Sand and Desert Dunes, a work which remains a classic reference today. He later published with Carl Sagan on the sands of Mars and provided advice to NASA in preparations for the first mission to the Red Planet. And, having exhausted what could be done at the time on windblown sand without reliable long term wind data, now Brigadier Bagnold turned his attention to revolutionizing our understanding of sand transport by rivers and waves.
There is much to say about Ralph Bagnold, and I shall say more in later posts. But for now to conclude with a return to the engine, the desert wind… I took Bagnold’s writing with me through the Gilf Kebir and across the Great Sand Sea - an inspiration in an inspirational landscape, not just the science and the observations, but the resonance of his palpable love of the desert. I watched sand on the move, skittering across the desert floor under a gathering wind, avalanching spontaneously down the steep slope of a dune - and hurtling chaotically, viciously in a raging sandstorm. We had experienced minor sandstorms already, but the one that hit us in the White Desert was a monster. I have just now opened my notebook from that evening, scribbled in pencil because a pen became instantly non-functional, and some sand grains fell from between the pages. As I was blasted by the onslaught of flying sand, I felt a resonance with Ralph Bagnold who had written:
"A dense, stinging fog of low-flying sand grains wholly obscured not only our cars but ourselves up to our shoulders, while our heads stuck out against a clear blue sky. One after the other, our feet dropped an inch as sand was scoured from beneath.
The whole landscape was on the move."
On this occasion, my head did not stick out above the sand and there was no blue sky visible - until the following, incredible, morning which revealed “a cleanness that was infinitely remote from the world of men.”
[For further reading, Ralph Bagnold’s autobiography, Sand, Wind, and War - Memoirs of a Desert Explorer is fascinating and characteristically modest - but, sadly, out of print. The Physics of Blown Sand and Desert Dunes was reprinted in paperback by Dover in 2005. Bagnold photographs above by kind permission of Stephen Bagnold; other photographs are my own. More can be found on Bagnold throughout my own book, Sand: The Never-Ending Story, University of California Press - just published - only a few remaining - hurry!]
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