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Science Frontiers ONLINE No. 114: Nov-Dec 1997 |
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The world's largest "playa-slider" furrow
Most studies of playa sliders ("moving rocks") have been conducted at Racetrack Playa, near Death Valley, California. There one finds good-sized rocks at the ends of long tracks they have made when some force has propelled them across the flat playa surface. What has moved these rocks, some of which weigh 700 pounds? The current consensus holds that wind is the motive force, but that it is inadequate to move the rocks directly. Instead, the wind acts upon sheets of ice in which the rocks are frozen. As these sheets of ice are moved across the playa, the keels of the frozen-in rocks leave those curious trails that have intrigued Forteans for many decades. (SF#109)
Playa sliders have also been found at Magdalenasmeer Playa in South Africa, and in Nevada and Tunisia. In a recent issue of Geology Today, C.C. Reeves, Jr., Texas Tech University, adds to the list a playa at Double Lakes, Texas.
Of special interest at Double Lakes is not the rocks and other debris blown across the playa but a discarded hotwater tank. It, too, is a playa slider. It first left a trail a few hundred meters long when it was frozen in an ice sheet spigot down, with the spigot furrow quite obvious. The ice sheet then melted, and the tank was blown over spigot-up. Another ice sheet formed, and the tank was off across the playa again. This time the keel of the tank excavated a furrow as wide as the tank's length, 91 centimeters, several centimeters deep, and 122 meters long. Reeves contends that this is the world's largest playaslider furrow!
(Reeves, C.C., Jr.; "Unusual Playa Sliders at Double Lakes, Texas," Geology Today, 12:207, 1996.)
Comment. Now that science has finally stooped to study this mundane phenomenon and has come up with some answers, we are inclined to remove it from the rolls of Fortean phenomena!