Sailing stone at Racetrack Playa in Death Valley National Park, California, USA

© Patrick Walsh/Getty Image

Mystery of the moving rocks. The mystery of the moving rocks

Did that stone in today’s homepage image get there by itself? Not only is Death Valley in the USA one of the hottest places on Earth, it also boasts a mysterious geological phenomenon - rocks that drift across the exceptionally flat desert floor, seemingly under their own power. The rocks here at Death Valley's Racetrack Playa are known as 'sailing stones' and they can vary in size from a few ounces to hundreds of pounds. As seen in our image, the stones leave long trails behind them as they move across the scenic dry lakebed.

When the stone trails were first observed in the early 1900s, no one knew how the stones managed to 'sail' across Racetrack Playa with no-one to push them and they were the subject of many wild theories. Then, in 2014, scientists captured the movement of the stones for the first time using time-lapse photography, and the mystery was finally solved. The stones move only with the perfect balance of melting ice, water and wind. One day in the winter of 2014, rain had formed a shallow pond that froze overnight. When it thawed in the next day's sun, the very thin ice sheet melted and cracked into floating panels. Driven by a light wind, these sheets accumulated behind the stones, and very slowly pushed them forward.