Racetrack Playa in surface appearance is a place where no movement should take place: a dry, sun-whitened basin in one of the driest regions of North America. Still, upon that plain surface, the rocks produce long marks that are like handwriting, straight strokes, soft curves, sharp turns, and thereby incised in the mud which afterward hardens. Over decades, the tracks challenged visitors and scientists to provide the explanation of the motion without observers.
The scene assists in the explanation of the time the puzzle took too long. The Racetrack Playa is a distant dry lake bed, approximately 3 miles in length, 2 miles in width, which is slickened occasionally following rainfall. The rocks that lie on its surface, some megalithic (as much as 320 kilograms or 700 pounds), may remain where they are in place over years, and then be found elsewhere with tracking wounds stretching hundreds of meters long. The old conceptions were based on absolutes hurricane-force winds, dust devils, magnetic effects and even slippery microbial films. The indications were evident; the mechanism remained unseen.
This was not the case when scientists constructed an experiment patient sufficiently to fit the landscape. My instruments are installed to monitor the playa without having to be there at the correct time of day in winter 2011, as was the case in paleobiology research by Richard Norris. This method consisted of a weather station with the ability to record gusts every one second and 15 rocks fitted with motion-activated GPS units. Since the National park service would not permit the manipulation of native stones, the team employed similar stones that were taken to the area externally. Waiting probably years until the playa fulfills itself that is, when everything is right was the plan. And so the basin turned into a shallow pond.
In December 2013, the playa contained water between 7 and 10cm (three and five inches) deep–enough to cover the surface without being very deep enough to conceal rocks completely. On cold winter nights that water would freeze to such thin, brittle ice, that it would freeze in windowpanes. When the sun melted the surface, the ice broke into broad floating ice-panels. Not gales, but light winds, of the order of 3-5 meters a second (approximately 10 mph), carried those panels over the pond, and the rocks were carried by the panels. The stones were not lubricated, but crawled at 2-6 meters per minute, now only a few seconds, now as many as 16 minutes, so slowly that they would not be noticed without a fixed point to reference them.
A single scene was a capture of the weirdness of the scene in simple terms. On Dec. 21, 2013, the ice began breaking up, around noon, with all types of popping and cracking noises around the entire surface of the frozen pond, said Richard Norris. “I said to Jim, ‘This is it!'” The experiments also described the reason why the trails might seem to be synchronized: in one experiment, rocks which were separated by approximately three football fields started moving simultaneously and traveled over 60 meters (200 feet) before halting.
This process is accurate since the playa is inhospitable. It must have water just enough to house ice but not to an extent that rocks will be floating. The ice has to be light to skate through but strong to serve the purpose of a moving bumper. The mud underneath has to be soft enough to make a track and dry enough to keep it. It is in this respect that movement may be rare measurably rare. According to co-author Ralph Lorenz, the last suspected movement was in 2006, so the frequency of the rocks moving was as low as one millionth of the time, which is then further supported by evidence that the frequency could reduce since the 1970s due to less frequent cold nights.
Racetrack Playa continues to provide mystery, albeit of a different type: not the motion of the stones, but how the slightest alterations in winter water and nocturnal freezing could re-write one of the precision mechanisms of the desert, which remain so delicate and transient.
