In a land far far away (for most of us), lies a desert valley that has kept a tantalizing secret for at least centuries, if not longer. The place is called the Racetrack Playa in the northwest part of Death Valley, which is part of the Mojave Desert. Racetrack Playa is 4.5 miles (7.3 km) long by 2 miles (3.2 km) wide, with an elevation 3,707 feet (1130 meters) above sea level.
The mystery is the Sailing Stones, big pieces of rock, mostly dolomite, that travel seemingly on their own, across the desert floor leaving long tracks behind them.
Western man has been aware of the phenomenon since the 1940s and many speculated as to how the stones could move, and how did they leave such big long, and often crazily angled tracks? Let’s explore the phenomenon and see what science can offer by way of explanation.
My first thought was about the nature of the stones. Did they share some kind of geological properties that may account for their ability to move? I looked up dolomite (the predominant stone in that area), and learned a few things. Its colors can range from white, pink, green, gray, to brown and black. The stones are often streaked with white. On the hardness scale, they rate 3.5 – 4. Compare that to a diamond, the hardest mineral, which is a 10. Dolomite can form beautiful crystals too – see photo below.
But none of these facts seems to be out of the ordinary. None of it would account for the stones’ ability to move.
Weather conditions on the playa surprised me, especially considering it’s in a desert. Ground temperatures have been recorded as high as 201 degrees F (94 C). However, in early Spring, temperatures cool down thanks to a combination of snow melt from surrounding mountains and below freezing temperatures at night.
NASA Goddard Space Flight Center geophysicist Gunther Kletetschka buried a large quantity of sensors around the playa in the summer of 2010. The sensors were called Hydrochrons and they measured the temperature and water content around them. Kletetschka buried the sensors at depths of ¾ of an inch (1.9 cm) up to 3 inches (7.6 cm) deep.
He and his colleagues returned at a later date and retrieved the sensors. What they learned confirmed their suspicions. In March, freezing temperatures were recorded IN the top layer of soil. But in April, the soil was revealed to be wet down to 3 inches below the surface.
What this meant was the snow runoff from the surrounding mountains flooded the playa and at night, in the sub freezing temperatures, it froze into thin sheets of ice. The ice that surrounded each stone formed what scientists call an “ice collar” . As more snow melt arrived in April, that water lifted the frozen parts already in place, including the “ice collars” and caused the stones to slide along the desert floor for long and often crazily angled distances.
The amazing part is that some of these stones are quite heavy, weighing as much as 700 pounds. Because the surface of the desert floor was saturated with water/ice, the stones left long, wide tracks in it (between 3 [7.6 cm) and 12 inches [30 cm] wide), as they were slid along by the action of the melting ice.
Researchers pointed out that the reason the tracks seem to be wider than the stones that left them is because the ice collars around each stone contributed to the width of the tracks. Once they melted, there was no evidence of them, just the mystery of big stones seeming to move on their own.
Throughout the years, several explanations have been offered for the ability of the stones to move and leave tracks without anyone ever having witnessed them moving:
- Animal activity
- Student pranks
- Earthquake activity
- Magnetic field action
Animal activity: There aren’t many animals that can move upwards of 700 pound rocks and why would they?
Gravity: The floor of the desert is at an incline – of one inch. So that hardly accounts for anything and gravity wouldn’t have much to do there.
Aliens: Why? If they exist, WHY would they scratch off the surface and move stones around? None of the stones seem to go missing, and people do track them, including scientists. So the aliens don’t seem to be interested in them.
Student pranks: Though a good theory, one glaring problem sticks out. No footprints are left behind. If the stones can leave a track in the moistened surface, footprints would appear as well.
Earthquake activity: Scientists already record all seismic activity in that area, and they’ve been able to correlate that activity with the movement of the stones they study, and there is no match.
Magnetic Field action: Students working with the researchers tested the area for magnetic activity, thinking fluctuations in that might account for the stones moving. However, no magnetic fields were found in that area.
Scientists are now placing cameras around the area to monitor the activity of the weather conditions and the stones. They hope to finally get video evidence of the stones moving and the conditions under which they move. They believe the results will confirm their theory that a combination of meltwater, frost, and wind is causing the stones to move.
I think the NASA scientists are on the right track with their theory. It would be far more mysterious and exciting to never figure out this mystery, but let’s not lose sight of the fact that this theory is actually amazing! If you were designing a planet, would you think to put in this much detail, this much mystery, and pardon me for saying so, awesomeness? I sure wouldn’t, so this mystery, now potentially solved, is still a wondrous thing and we can all be excited and delighted by it.
What’s also important – the scientists are going to use the lessons they’ve learned from nature in this investigation in Microelectromechanical systems (MEMS) technology. This technology is used in many different industries, so who knows how our lives will be enhanced just by uncovering the intricacies of this wonderful mystery!
Til the next time!
Sailing Stones Update – September 2, 2014
Finally, a scientist has witnessed the stones actually moving! Paleobiologist Richard Norris (from Scripps Institute of Oceanography, UC San Diego) published his account in a journal named Plos One from August 27, 2014.
Because no one has enough time to sit and wait for these rocks to move, Norris and his team attached specialized GPS units to 15 of the rocks in the winter of 2011. Then they added some high-resolution weather monitors that could detect gusts of wind to one-second intervals. After that it was a waiting game.
Norris and one team member returned to the area in December 2013 and discovered the area awash in 3 inches of water. Soon after the rocks began moving. In an article for Science Daily, Norris said, “Science sometimes has an element of luck. We expected to wait five or ten years without anything moving, but only two years into the project, we just happened to be there at the right time to see it happen in person.”
So it seems the original theory was correct. During those times when the basin is somewhat awash in water, the stones begin moving due to a delicate dance of specialized weather conditions. Basically, it goes like this:
Water fills the playa on those rare occasions and forms floating ice in cold winter weather (mostly at night). The ice has to be highly specific: deep enough so it floats on the ground but shallow enough so the rocks are exposed. When the sun comes up the next day and warms the ice enough that it starts to melt, it has to be just the right kind so it forms almost floating “rafts,” if you will, thereby carrying the rocks a certain distance. Light winds play a role in that they provide the push to move the rocks.
The scientists were able to determine that the movement of the rocks occurred in just a few seconds in some cases, while others took up to 16 minutes to move. The scientists observed rocks that were a distance of three football fields from each other began moving at the same time and together moved 200 plus feet (60 meters) before stopping. Other rocks moved several times before coming to a complete stop.
Prior to this discovery, park rangers thought people must be stealing some of the rocks because they would find the typical scarred trails on the playa floor minus the rock at the end. Turns out, Norris and his team discovered these “empty” trails were actually caused by the ice as well.
The scientific team were rightly pleased with their results. Norris said, “We documented five movement events in the two and a half months the pond existed and some involved hundreds of rocks. So we have seen that even in Death Valley, famous for its heat, floating ice is a powerful force in rock motion. But we have not seen the really big boys move out there …. Does that work the same way?”
As per usual, inquiring minds want to know! LOL!! I guess the scientists will eventually figure out how these larger rocks move. But I’m suspecting, it’s much along the same lines, no pun intended!