The mysterious phenomenon consists of the stones, which weigh up to 300 kg, that move over the bed of a dry lake in California, apparently without any explanation.
These stones, known as “Sailing Stones”, travel several meters, leaving tracks that reveal their paths along the plain of Racetrack Playa.
Several explanations for the phenomenon have been attributed over the years: from aliens to anomalies in the Earth’s magnetic field.
But now scientists have managed to unravel the mystery behind the walking stones without taking away the charm of the phenomenon.
The walking stones are located in Death Valley, one of the hottest places in the world, north of the Mojave Desert.
The Racetrack Playa plain is the bed of a dry lake with approximately 2.7 square miles in area. Most of the almost perfectly flat landscape is free of any plant or rock formation, except for a few boulders of varying sizes that slide off the slope and stop there.
These stones should be standing still, but this is not what happens, because the stones leave traces of their displacement. Some trails left by the rocks follow straight lines, while others curve and change direction.
The reason for such a mystery is that no one has ever observed the phenomenon happening, and any more obvious natural factor, such as the wind, was not enough to explain it.
The first reports of movement date back to the early 1900s, but it was only in the 1940s that the phenomenon began to draw the attention of the scientific community.
In all this time, any attempt to explain the movement of the stones has failed. It wasn’t until 2014 that Richard Norris and his cousin, James Norris, both researchers at the University of California, witnessed and documented the phenomenon on video.
The Norris began investigating the phenomenon in 2011, when they founded the “Slithering Stones Research Initiative”. For this, they installed a weather station near Racetrack Playa.
They also selected about 15 stones and installed GPS trackers on each to detect and track their movements. The meteorological station would help to understand factors such as wind, temperature and humidity that could be related to the phenomenon.
Between December 4 and 20, 2013, cameras installed by the researchers recorded the movement of the stones, which slid 10 to 16 feet. Some of the tracking rocks moved up to 735 feet between December 2013 and January 2014 in a sequence of events.
In order for the stones to be able to walk, a rather unusual combination of factors that occur during winter in Death Valley is required. At this time of year, rains occur in the region and a shallow layer of water forms on the dry lake bed, where the stones are.
At nigth, temperatures drop enough to freeze the water, forming a thin layer of ice. Then, on a sunny day, the melt breaks up the ice into large slabs. So far, the stones are still standing and it is necessary to add one more element: the wind.
Even weak, the wind propels these ice sheets, which then drag the rocks along. Meanwhile, the rocks leave tracks on the still damp ground. After everything dries up, the trails remain behind the rocks.
The researchers concluded that the rocks move when a layer of ice 3 to 6 millimeters thick breaks up with winds that do not exceed 5 m/s. Thicker plates do not float on liquid water. When displaced by the wind, these plates push the rocks at a speed of 2 to 5 m/s.
Therefore, the trajectory of the stones is determined by the direction and speed of the wind, in addition to the liquid water below the thin layer of ice.
These stones only move once every two or three years, but the tracks left by them remain in the ground for up to four years.
This phenomenon occurs in one of the hottest places on the planet, so the combination of these factors is rare and perhaps unique on the planet.