For decades, scientists could not understand what sets the stones in motion, leaving traces at the bottom of the dried lake. Racetrack Playa is a dry lake surrounded by mountains in Death Valley National Park. In summer, its bottom is covered with cracks, in winter it is either ice or snow.
But the most entertaining part of the landscape is dozens of scattered stones, each of which has a furrow. Some of the tracks are a straight meter line, others are zigzag and have a length of more than 120 meters.
Scientists have tried many times to find a scientific explanation for the movement of stones. In 1948, geologists Jim McAlister and Allen Agnew decided that the movement was caused by dust storms combined with the periodic flooding of a dry lake. Another popular theory was the appearance of an ice sheet at the bottom of a dry lake in winter. In the early 1970s, geologists Robert Sharp and Dwight Carey surrounded rocks with wooden pegs, suggesting that ice would freeze to them and immobilize the rocks. Nevertheless, some stones managed to "bypass" obstacles.
Despite the fact that geologists often visited Racetrack Playa, they could not catch the process of moving stones. From 1987 to 1994, Hampshire College professor John Reid brought groups of students to Death Valley every year to study the stones. He had his own theory about them: since many of the tracks were parallel, he believed that the stones moved inside large layers of ice, which slid under the influence of strong winds. This theory was shattered by the arguments of a geologist from California State University in San Jose Pola Messina. After creating a digital map of the tracks using GPS, she found that most of the tracks were not actually parallel.
The search for the reasons for the movement of the stones still got off the ground when a specialist from Johns Hopkins University Ralph Lorenz got involved. Having studied the cases of the movement of stones in other parts of the Earth, Lorenz learned about the huge boulders that were carried to the Arctic tidal beaches due to the lifting force of the ice. To test the connection between this phenomenon and what happens on a dry lake from year to year, he conducted an experiment right in his kitchen. He took a small stone, put it in a plastic container, which he filled with water a couple of centimeters, so that a small part of the stone sticks out of it, and put it in the freezer; then, turning the piece of ice over so that the stone peeping out of it looked down, he let it go over a tray of water, at the bottom of which lay sand. As expectedfrom the slightest breeze, the stone frozen into the ice slid, leaving traces on the sand.
In 2011, a new model was described in a scientific report. “Basically, a chunk of ice forms around the rock and the liquid level changes, causing the rock to float out of the mud,” Lorenz explained. "It's a small piece of floating ice with the keel pointing down, which gives it the ability to cut a furrow in soft mud." Calculations show that in this scenario, the ice has virtually no friction and rocks can slide even in the lightest breeze.
However, among the visitors of Racetrack Playa there are those who oppose such a prosaic explanation - people like secrets, they like unanswered questions.