This story appears in the November 2012 issue of National Geographic magazine.
I got my first lesson in the physics of sand dunes in 1998 on an expedition into the Sahara. In order to take aerial photos in this remote part of the world, I had learned to fly a motorized paraglider, one of the lightest and slowest aircraft in the world. It weighs a little under a hundred pounds; its top airspeed is 30 miles an hour. And it has no wheels.
I mastered new skills to fly (and land) the paraglider. But there was one I hadn’t realized I’d need to survive the Sahara: reading sand dunes. Just as the sailor watches whitecaps for the sudden squall, I had to learn to anticipate the invisible currents of air that created the dunes. If I wasn’t paying attention, I could get caught in turbulence—or even a fatal downdraft.
The Sahara is traversed by endless rows of dunes called barchans. The word means “crescent-shaped dune” in the Turkic languages of eastern Europe and Central and northern Asia. I had become intrigued with them while reading a book by Ralph Bagnold, a British Army officer who pioneered motorized travel in the Libyan Desert in the 1920s and ’30s. Bagnold described barchans as life-forms—they move, multiply, maintain structure, and adapt to their environment. I thought they might be interesting to photograph from above.
But first I had to reach the dunes. I traveled to the region with France’s Alain Arnoux, a champion of motorized paragliding. I was counting on him to help me fly safely. Getting to the barchans took us four days in a four-wheel drive, traveling from N’Djamena, the capital of Chad, to the far north. The sand that makes up the dunes had traveled too, migrating west from Egypt and Sudan. We were guided by an old French map that depicted the dunes as right parentheses, all pointing into the wind.
I did not realize the difficulties that awaited. Nor did I realize the allure of dunes. Once I started flying in the desert, I came under its spell and began what turned out to be a 15-year project to photograph the world’s most extreme deserts.
When we got to the Mourdi Depression, my traveling companion had bad news. Shouting to be heard over the gale, Alain told me there was no way even he could fly in such wind. So we drove out into the middle of the broad stony basin until we found a 50-foot-tall barchan to give us some shelter for the night.
We awoke before dawn. The wind on the dune crest had died down to a breeze. I took off at sunrise, running down the windward slope of the dune. After gaining 500 feet, I felt like an insect flying over an enormous conveyor belt in a croissant factory. The barchans stretched to the horizon as they combined, separated, and spawned progeny.
I soon became nervous. The wind was much faster than I was, so I was being pushed backward while heading into it. It was like trying to swim up a river against a current that’s moving faster than you can swim. That’s a frightening experience for a pilot. You can’t see what’s behind you, and when you land, you have a hundred pounds on your back and a large sail over your head that wants to keep moving backward.
Ground friction slows the wind, especially in the morning, so I dropped to within 50 feet of the dune crests to advance. After an hour even the wind down low began to increase and become turbulent. The sun was heating up the dark ground, creating bubbles of rising hot air that broke up the smooth flow of wind across the surface. When I gained altitude to find our dune camp, I began flying with the wind instead of against it and suddenly found myself moving ahead at more than 70 miles an hour—an alarming speed. I turned into the wind and hovered like a kite 200 feet above camp. Alain came zooming in underneath me. Landing in such a gale made me anxious, and I watched to see what the champion would do.
He read the dune like an open book: The wind was rushing over the top of its crest and then doubling back. To try and land near our cars, parked in the dune’s inner arc, would be fatal. The paraglider is an inflated wing; in turbulent air it could lose rigidity and crumple. Landing on the dune’s windward slope was a better option, but a gust could push us back into the whirlpool of wind—and a nasty mess. As I watched, Alain made the prudent choice and landed in the gravel plains beside the dune, avoiding the turbulence. I soon came down to join him.
Alain had given me a great lesson in reading the winds. After 26 desert flying expeditions, I’ve had a lot of postgraduate training. I have found that dunes are both flyable and beautiful in the calm first hours of morning.
And I’ve learned to be patient and to pick my seasons carefully. In the Sahara, for example, fall is best because the winds are relatively light and the weather is cool.
I still fear sandstorms, which can come up with little notice. I’ve even learned how to land in them: as soon and as quickly as possible. With an aircraft that flies faster than I can run, I have also learned that dunes are my friends. They’re soft and always point the direction to a safe landing. You don’t need a weatherman to know which way the wind blows when you have dunes to inform you.
I have developed a few simple rules. The smallest dunes are the ones most affected by the wind, so their direction indicates the way the wind is blowing. If at all possible, land on the sunny side of a sand dune; the shady side usually has downdrafts, so you just drop like a stone. White sand is safer to fly over than dark sand. Dark sand absorbs the heat, then releases it in big bubbles of hot air, like a lava lamp. When the sand is blowing off the dune crests, it’s a good time to be on the ground. And last, it’s always better to be on the ground wishing you were in the sky than in the sky wishing you were on the ground.