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A Look at the Playa |
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Exciting things happen on dry lake beds. But why do dry lake beds occur?
Everywhere there are deserts, you'll find dry lake beds. They are stark and deadly places, best avoided by travelers. But they're the best setting in the world for certain activities: Launching rockets. Landing the Space Shuttle. Doing secretive military tests. Breaking land speed records. And all this week in Nevada's Black Rock Desert, celebrating the
Burning Man arts festival. What creates these remarkable features?Black Rock Desert as seen by the Earth Observing System. NASA photo STS039-80-096.
To start, you need a desert. In the driest places, permanent rivers are rare, and the kind of stream networks that we're used to in temperate regions are slow to take form. Where mountains are actively growing, as in the American West, the basins between ranges tend to be bowls, with closed drainage. Where the landscape is old and flat, as in Arabia and southern Africa, the movements of sand dunes create many closed basins. Either way, these basins hold shallow lakes during parts of the year.
Only the finest sediment reaches the center of a desert basin: particles of silt and clay size. Both wind and water carry this material. Water also brings with it dissolved minerals, and as the desert lakes dry up these minerals come out of solution. Among these are calcite and gypsum, which tend to cement the lakebed mud and turn it hard.
Other minerals are salts, mostly halitethe same substance as table salt. Where halite is abundant, dry lake beds turn into salt flats. The world's largest salt flat is the Salar de Uyuni in Bolivia, where a thick layer of salt supports a local mining industry. Out in its center, the landscape resembles a salt Antarctica. And in America there's the Bonneville Salt Flats in Utah, a place so flat that you can see the Earth's curvature as you look across it.
A C-5 Galaxy crash-lands at Rogers Dry Lake Bed on May 2, 2001. U.S. Air Force photo.
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Not every dry lake bed is a salt flat. Many are paved with silt and clay, like Rogers Dry Lake Bed in southern California. Its surface is so perfect that aircraft runways can be created by simply painting an outline on the ground. The U.S. Air Force tests experimental aircraft there, and the Space Shuttle lands there when conditions are poor in Florida. It's also a well-known site for emergency crash landings, such as the time in May 2001 when a huge C-5 transport with broken landing gear diverted its flight there to come down safely.
Dry lake beds have many different names around the world: they are salars in Latin America, sabkhas in north Africa, vloers in south Africa, faydah in Arabia, takirs or bahirs in central Asia, and kavirs in Iran. But in the deserts of the United States the most common term is playa, the same word that Spanish speakers use to refer to the beach.
It would seem like the seashore is the opposite of a totally flat expanse of dry dust. You might think of the playa as a kind of beach without an ocean. Perhaps this usage of "playa" is an example of wry frontier humor; that's not out of character. But I prefer to think that the beach and the playa share something deep: they're the kind of place where you feel free to move, where your sight expands, where the immensity of the space prompts you to respond in vigorous and creative ways. And I like to think that Burning Man, the annual art encampment on the great playa in Black Rock Desert, may be the purest use of a space like that.
