Every year, twice a year if he's lucky, Hans-Joachim Pachur leaves his office in a pleasant villa opposite the Berlin botanical garden, leaves the exuberant plant life that shades the streets and pushes through fences and sidewalk cracks, and catches a plane for, say, Libya. In Tripoli he meets up with several colleagues and gets ready for the desert. A geographer at the Free University of Berlin, Pachur has been exploring the Sahara for the last quarter century, and he has been known to do it on camelback. These days, though, he mostly chooses Land Rovers. Supplies gathered and gear checked, the team drives south, away from the Mediterranean; they head out onto the sea of sand, where the waves crest at 600 feet.
To cross those dunes, Pachur and his group let most of the air out of their tires for better traction. When a dune is very steep ...
