It is a mystery that has hovered for nearly a century: the phenomenon of the moving rocks of Racetrack Playa also called “sailing stones”. In this desert place, we find rocks weighing from a few grams to hundreds of kilos having left behind traces of several meters, suggesting that they moved without human or animal intervention.
Racetrack Playa is a dry lake in the middle of the Death Valley in California. Devoid of relief and vegetation, the first theory was that it was the wind that managed to push the rocks.
But in 2014, a new discovery called everything into question. American researchers have indeed found that in winter, Racetrack Playa could partly cover itself with ice. This ice comes from intense rain and freezing temperatures overnight.
However, this ice does not last long: it melts during the day, creating patches of ice floating above a layer of water thin enough to leave the rocks partly emerged. Pushed by the wind, these ice sheets carry the rocks in their path. Once melted and evaporated, the ice leaves as the only trace of its existence these mysterious rock displacements.
To observe the phenomenon, specific conditions must be met and the rocks moving only 3-4 meters per minute, you need constant monitoring and close enough to see it. This explains why it took several decades to arrive at this explanation.
Another factor which could complicate this discovery: since the 1970s, the formation of ice and therefore the movements of rocks have become more rare due to global warming.