An interesting geological phenomenon has been discovered on the dried-up Lake Racetrack Playa in Death Valley in the United States. The stones at the bottom of the lake move spontaneously, and over long distances, as evidenced by the long traces that remain behind them. The stones move on their own without the help of living beings, however, until Christmas 2013, no one had ever seen or recorded the movement on camera.
Most of the sliding rocks fall to the bottom of the dried-up lake from a 260 m high dolomite hill at the southern end of Racetrack Playa. The weight of the stones reaches several hundred kilograms. The tracks following them are several tens of meters long, 8 to 30 cm wide and less than 2.5 cm deep.
The stones come into motion only once every two or three years, and most of the tracks last for 3-4 years. Stones with a ribbed bottom surface leave straighter footprints, while stones on the flat side wander from side to side. Sometimes the stones turn over, which is reflected in the size of their footprint.
In 1948, geologists Jim McAlister and Allen Agnew mapped the location of the rocks and marked their footprints. A little later, the staff of the US National Park Service compiled a detailed description of the site and Life magazine published photos from Racetrack Playa. Most of the hypotheses agreed that the wind at a wet surface of the bottom of the lake at least partly explains the phenomenon.
In 1955, geologist George Stanley of the University of Michigan published an article in which he argued that the rocks were too heavy to be moved by the local wind. He and his associate proposed a theory according to which, during the seasonal flooding of a dried-up lake, an ice crust forms on the water, which facilitates the movement of stones.
In May 1972, Robert Sharp (Caltech) and Dwight Carey (University of California, Los Angeles) launched a rock tracking program. Thirty stones with relatively fresh footprints were marked, and their starting position was indicated with pegs.
Ten of the marked stones moved during the first winter of exploration. After 7 years, only two of the 30 observed stones have not changed their location. The smallest of the stones was 6.5 cm in diameter, and it moved to the maximum total distance - 262 m and further in just one winter - 201 m. The most massive stone, the movement of which was recorded, weighed 36 kg.
In 2014, a work was published in PLOS, the authors of which describe the mechanism of the movement of stones. Scientists placed several of their stones weighing 5-15 kg on the bottom of the lake, equipping them with navigation sensors and surrounding them with cameras. The reason for the movement was large (tens of meters), but thin (3-6 mm) areas of ice formed after freezing in the previous frosty nights. This floating ice, carried away by the wind and under-ice currents, moved stones at a speed of 2-5 m / min.
However, there is still no theory that would explain why nearby stones can move in different directions when others are standing still. It is also unclear why the stones move in different directions and are "scattered" all over the bottom of the lake, while regular winds would move all the stones to one of the edges of the lake. In general, the next explanation of the phenomenon does not stand up to criticism and leaves the researchers room for a flight of imagination.