offers an excellent article on the sliding rocks. Includes a Real
Media Sound Clip.
The book Exploring Death Valley by Ruth Kirk also offers a nice overview on the moving rocks, although it is a bit outdated (1965, Stanford University Press, pages 57-59).
case of the creepy crawlies.
There are some things in nature that you can't argue with. Rocks are heavy. Rocks are inanimate. Rocks are just plain stone-dead.
Yet, there is a place in the world where the rocks seem to just get up and move when no one is looking.
If you wish to visit this strange place you better be well prepared. These rocks with legs are located on the Racetrack Playa in Death Valley, California. Yes, you read it right. Death Valley. At nearly 300 feet below sea level, Death Valley has the honor of being the lowest, hottest, and driest point in the United States. Downright deadly.
Racetrack Playa is actually a three-mile long dried up lake. Surrounding the lakebed are fairly rugged mountains, which help to channel the winds at high speeds through the valley below.
Okay, I can hear your brain screaming all the way over here - What about those moving rocks?
The rocks range in size from small pebbles to large boulders. Some of these dolomite rocks can weigh up to 700 pounds. Not exactly something the average human being can lift (I'll assume that you are not related to Hercules or Charles Atlas).
These rocks definitely move. Since the playa lakebed is essentially dried mud, the trails of these buggers can be clearly seen. As the rocks move, they create long, shallow furrows that trail behind. The larger boulders can form trails that are up to 200 feet long. The smaller, more lightweight rocks can move over 600 feet in a single advance.
So what is causing these rocks to move?
Many would guess that it was aliens from outer space or divine intervention, but there is no reputable person that has ever put forward either of these theories. We'll leave the Martian theory for the crop circle fanatics.
Sorry, but when it comes to these moving chunks of calcium magnesium carbonate, we have to depend on legitimate scientific theories and experimentation.
At first thought, one would tend to think that gravity is simply pulling these rocks downhill. But this theory can be quickly ruled out. The playa is so flat that just two inches of rainwater will cover the entire lakebed on a calm day.
Way back in the 1950's, when the scientists started to study this phenomenon, it was believed that the rocks moved due to the combination of high-speed winds coupled with a slick, muddy lakebed (only two inches or less of rain is received each year). The mud becomes so slick that it acts like it is treated with WD-40 lubricant. Couple that with the howling winds and those rocks will just glide across that playa.
One scientist, Dr. Robert P. Sharp, supports this theory. Sharp, a professor of geology at the California Institute of Technology embarked on a seven-year study of this curious wonder. He tagged the positions of thirty stones and watched them for about one year. He recorded the weather conditions after each move. To no one's surprise, all but two of them moved in the directions of the prevailing winds. A nine-ounce stone moved 690 feet in one giant slide. Another stone moved 860 feet in a series of moves.
Another geologist, John Reid, has come up with an alternative theory. Reid was out on a field trip with a group of students back in 1991. They arrived to Racetrack Playa right after melting snows had left about five centimeters of water on the lakebed. The mud formed from this meltwater was downright slippery - one of his students slid between five and six meters. But when Reid tried to move modest sized rocks (25 kg), they wouldn't budge. From this he concluded that the wind could not solely move the rocks (yet a 200 pound person easily slides along with no wind?).
Back at his lab at Hampshire College in Amherst, Massachusetts, Reid put forward an alternative theory. He proposes that the meltwaters form a thin layer of ice at its surface. Of course, this ice freezes to the rock surface. Friction due to the wind blowing over the large surface area of the frozen water causes both the ice and the rocks to move together.
So which theory is correct? No one knows. Remember, no human has ever seen these rocks in actual motion - they have only seen the end result. It is clear, however, that the conditions needed to get these rocks moving are very extreme in terms of climate. Therefore, it is possible that no one will ever be around when one of these rocks decides to get up and speed away.
Of course, maybe it was the Martians...
Useless? Useful? I’ll leave that for you to decide.
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