No Stone Unturned

Peter Haff Devotes 25 Years to Studying Nature's Desert Pavement

By Monte Basgall

Traces of Roman roads are still visible millennia after their construction. But desert pavement, Nature’s own handiwork, can last for hundreds of thousands of years. Laid out in segments as long as hundreds of yards on a side, desert pavement has very long-term staying power. It can even repair itself—provided that such forms of human destructiveness as off-road vehicles or military tanks don’t do more damage than Nature can fix, says Peter Haff.

Haff, chair of the Nicholas School’s Earth and Ocean Sciences Division, has spent more than 30 years—off and on— studying desert pavements and how they begin the self-repair process. He sees them almost like living entities, at once simple and complex. When he describes the ways their surfaces are destroyed he makes comparisons to human skin injuries. When he describes their auto-correction process, he talks almost mystically about stones that migrate with the help of animals.

  Formed by dust-laden winds, very occasional rains, and particular kinds of geology and topography, desert pavements are self-deposited mosaics of pebbles overlaying carpets of fine dust. “It’s kind of a dynamic, self-organized structure,” he says. “It takes many thousands of years, perhaps tens of thousands of years, to bring them to the kind of surface we can see today.”

  He and other scientists believe these pebbles eroded from mountain boulders as rare floodwaters washed them down to flatter terrain. The underlying dust gets deposited later than the stones on top, a topsy-turvy scenario scientists think happens for the same reason that Brazil nuts self-migrate above the peanuts and cashews inside homogeneously-packed cans of mixed nuts. Because of this counterintuitive layering, the pebbled surfaces of desert pavement serve as dust covers. And once that rocky protection is removed, self-repair takes many more years than a politician’s term of office—if repairs are possible at all.

  The Jan. 3, 2004, issue of Science News described what happened when the Iraqi version of desert pavement was mauled by the tank treads and Humvee wheels of the United States-led invasion. According to the article, satellite before-and-after comparisons revealed the ruin of more than 950 square kilometers of desert pavement. That contributed to the vast quantities of airborne dust that reduced visibility and fomented breathing problems, the magazine said.

  Haff hasn’t studied desert pavements in other countries. But he has seen plenty of human effects in his baking-hot Mojave Desert field sites in the vicinity of Death Valley. “It is very difficult to find a patch of desert pavement in the Mojave where you cannot find vehicular tracks,” he says.

  An extreme example is one present day hot spot for off-road vehicles at the California landmark Stoddard Wells. There, “no stone has been left unturned,” he adds with a wry chuckle. He knows what happened, and how quickly, because an earlier study he read described “a very beautiful classic pavement cover” as recently as the 1960s, he recalls. “Years later, in the 1980s, I went back and was amazed. Nothing was the same, everything was completely trashed.”

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