Have you heard of “sliding stones”? These are moving rocks that mysteriously move across the surface of the Racetrack Playa, a seasonally dry lake (or playa) in the Panamint Mountains, Death Valley National Park. Most of the racetrack rocks originate from the nearby hillside of a dark dolomite on the south end of the playa. As they move without human intervention, the rocks leave long tracks behind them, often tens of hundreds of feet and typically less than an inch deep. The rocks move once every two or three years and most tracks last for just three or four years. Rocks with rough bottoms leave straight striated tracks while those with smooth bottoms wander.
During periods of heavy rain, water washes down from the nearby mountain slopes onto the playa and form a shallow short-lived lake. Soon, the thin veneer of water evaporates and leaves behind a layer of soft gooey slippery mud. As it dries the mud shrinks and cracks into a mosaic of interlocking polygons.
Geologists have long speculated on the explanations of this interesting phenomenon. Most favor the idea that strong winds (nearing 90 mph) push the rocks along the playa’s muddy bottom left at the end of the rainy period. However, some of the stones are thought to be too heavy (weighing as much as a human) for the area’s wind to move. Some geologists maintain that ice sheets around the stones may help to catch the wind or move in ice flows. Neither theory explains how two rocks right next to one another can move in opposite directions or one can stay put while another three times its size doesn’t.
The mysteries of Nature… I guess you can’t judge a rock by its mantle.
Nina Munteanu is an ecologist, limnologist and internationally published author of award-nominated speculative novels, short stories and non-fiction. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books.