Rolling Stones of Death Valley
Dancing rocks, rolling stones and boogie boulders, these are all names for a strange phenomenon unique to Death Valley in California.
Imagine this, its late evening and the long since dried river bed is scattered with rocks and pebbles. As night falls and the valley is shrouded in darkness, you go to sleep. When you wake up to the warm Sun in the morning and look out, the stones and rocks littering the riverbed have moved, leaving a trail behind them.
American Indians, five centuries ago, would stand out in the freezing night standing guard and watching for anyone moving the rocks. They saw no one - but by morning the rocks had moved. Is it any wonder that the Indians attributed mystical status to these rocks?
Death Valley is the lowest and hottest place in the Western hemisphere and as such, it is subject to quickly changing atmospheric conditions. Several theories have been suggested including vibrations from earthquakes, swelling clay that pushes up on the rocks, the combination of high winds and wet clay and even Aliens.
The most popular theory is the combination of high winds and slippery clay. After a rain storm, a fine, slippery layer of clay forms across the clay, reducing friction. When two columns of strong wind whip through the valley, they may push the rocks across the lake bed. Crosscurrents formed in the valley could create mini tornadoes which would move the rocks around. This could account for the apparent randomness of the trails.
Dr Robert Sharp of the geology department of the California Institute of Technology conducted a study of the area and the rocks. He selected 25 rocks between one kilogram and 450 kilograms. Sharps study reached three conclusions:
- Small heaps of the desert were pushed up in front of the stone as it travelled along. This indicated that the ground was wet.
- The highest recorded numbers of moving rocks occurred during winters of above average rainfall and strong winds.
- It would take precisely 0.6 cms of water to put the surface into a delicate balance. Any more and the rocks would sink into the mud, any less and there would be too much friction.
In 1976 he wrote in the Bulletin of Geological Society of America and stated that:
The secret is to catch the play of wind and water at precisely the right moment.
Not everybody is convinced of this though... Two years after the results were published, there was a severe frost after a week of heavy rain. Surely this would 'glue' the rocks in place? In the morning they found that several rocks had moved.
If it's not nature, what then can be the secret of these rocks?