The Sliding Rocks of Death Valley : Facts & Theories
In California, the Death Valley National Park is home to a dry lake called Racetrack Playa. For a long time, rumors have circulated about sailing stones on this allegedly cursed site. Indeed, the regular appearance of traces in the ground suggests that the heavy rocks move spontaneously.
Walking rocks of Racetrack Playa
Racetrack Playa is a dry salt lake 4.5 km long and 2.2 km wide. It only fills with water when it rains, which, as rainfall is extremely rare in the Death Valley, occurs only once or twice a year. On the flat surface of the lake are more than one hundred and sixty large blocks of stone, weighing up to 320 kilos. The ground is regularly marked with traces which suggest that these stones can move at a considerable speed, estimated at 1 meter per second. There is no evidence to suggest that these movements were the result of external intervention. So far, no sliding rocks has been the subject of direct observation. In the 1990s, however, the course of the stones was mapped over several months. This monitoring revealed that the blocks very close to each other follow the same path model, so that scientists believe that these migrations have a common origin.
Explanation attempts
In the past, various theories and explanations have been attempted to find the cause of the sliding rocks phenomena.
One of the advanced possibilities is that the Racetrack Playa is not a flat surface, but a sloping surface, so that the stones slide down the plain. The other theory is that they would react to a magnetic field. However, one and the same argument refutes these two solutions: the traces indicate that some stones have suddenly changed direction, until a 90-degree turn is made in their trajectory. Under the supposed conditions, this reversal would only be possible if the angle of inclination of the plain or its magnetic point had been abruptly altered, which cannot be explained from a physical point of view.
The theory which finds the most followers in the specialized circles starts from the principle that in spite of weak precipitations, the important thermal amplitudes reigning in Death Valley National Park causes the daily formation of gel or even of ice depositing on the surface of the ground. Associated with the fine sand of the desert, this ice forms an extremely slippery surface. If in such a context, a strong wind blows on the Racetrack Playa, it is possible that the stones can move on this base. Then, as the ground dries up, the block stops, while most of the sand that has accumulated in front of the stone during its movement is swept by the wind.
Until today, apart from a few investigations conducted between 1968 and 1974 by geologist Bob Sharp, research has not been carried out further. Therefore, this theory has not yet been able to be supported by direct observations. However, it has been proven that frost and ice formed in the heart of the Death Valley, and various expeditions have witnessed very strong windy passages. However, these findings only concern regions relatively far from Racetrack Playa. It would therefore be necessary to conduct research over a much longer period. But a team, even very interested in the sliding rock phenomenon, will probably think twice before embarking on an extended and demanding stay in the Death Valley, exposed to these extreme conditions.
