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Did you know that Death Valley National Park is considered the lowest point in the United States? Located in the northern Mojave Desert bordering the Great Basin Desert in California, Death Valley features a narrow stretch of flat, cracked, dry lakebed nicknamed Racetrack Playa. It's not a racetrack for vehicles though. It's a racetrack for massive stones.
The stones move mysteriously on their own around the desert floor and leave long trails behind in the sand. This natural phenomenon has left researchers puzzled for decades, but geologists have finally gotten to the bottom of the mystery. Here’s how the bizarre sailing stones of Death Valley actually move.
Where Is the Racetrack Playa?
Racetrack Playa is nestled between the Cottonwood and Chance mountain ranges of Death Valley. If you look across the playa, you’ll see nothing but cracked dirt with hundreds of rocks scattered about. You might notice that some of the rocks have long trails following them in the mud. Given the massiveness of the rocks (some weigh up to 700 pounds!), there’s no way that they can be simply blown around by the wind.
These stones that seem to move by themselves are known as sailing stones. They were first discovered in the early 1900s. Throughout the decades, people have invented many different theories ranging from strong winds to involvement with extraterrestrials.
The most popular theory was that strong wind gusts moved the sailing stones. Since the region is so flat and bordered by mountains, it’s not uncommon for strong winds to create a wind tunnel. Dust devils (mini tornados) are a common occurrence in Death Valley. Scientists disproved this theory, however, due to the large size of the rocks in addition to the curved paths, which aren't characteristic of objects moved from wind. With the wind theory debunked, it didn’t seem like the mystery would ever be solved.
A New Theory
For almost 100 years, scientists failed to solve the mystery. In 2006, NASA scientist Ralph Lorenz made a breakthrough after conducting an experiment at his home. He believed that the unique weather and climate conditions of Death Valley were similar to those of Ontario Lacus, a lake on Saturn’s moon Titan.
He proposed that ice was behind the strange movement. To prove his hypothesis, Lorenz filled a Tupperware container with an inch of water and placed a rock in the container so that it was barely sticking out above the water. He put the container in the freezer. When the water froze, he took the entire block with the stone still embedded in the ice and put it in a larger tray of water with sand at the bottom. With the ice just barely floating on top of the thin sheet of water, he was able to move the rock around by simply blowing on it. As the rock moved, it left a trail in the sand below.
Not only is Death Valley the lowest point in the United States, but it’s also the hottest. In 1913, Death Valley officially became the hottest place on Earth after recording a temperature of 134 degrees Fahrenheit! The average temperature in the summer is an unbearable 108 degrees. With such a hot reputation, how could ice even form there?
In the winter, it’s still rare for Death Valley to experience below-freezing temperatures, but at lower elevations, it’s not impossible. In the unlikely event that it rains, which happens very infrequently, a small layer of water can form on the surface of the usually dry lakebed and create small ponds. If the conditions are just right, that surface water can freeze around the rocks and create a situation similar to the one in Lorenz’s experiment.
When ice forms around the rocks and the water begins to melt, the rocks start to float on top of the ponds. As the ice sheets break up behind the rocks, the force of the ice sheets combined with the wind pushes the rocks forward. By the time anyone gets to the playa to catch the rocks in action, the ice has since melted, the water has evaporated, and the rocks are sitting peacefully in the mud with long trails behind them. Some of the trails are over 1,500 feet long! After decades of research and hypothesizing, scientists finally believe that they have a decent grasp on how the mysterious sailing stones move along the desert floor.