Mysterious Rolling Stones of Death Valley

Rolling Stones of Death Valley are strange phenomenon unique to Death Valley in California where the stones mysteriously move by themselves.

Amid the eerie silence and the 50C heat of California's Death Valley these giant boulders appear to move smoothly, and unaided, across the desert.

Imagine it's late evening and you're camping out in the desert. The dried river bed of Racetrack Playa is scattered with rocks and pebbles. As night falls and the valley is shrouded in darkness, you go to sleep. When you wake up in the morning and look out, the stones and rocks strewn across 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?

What Causes the Rolling Stones to Slide in Death Valley?

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.

Scientific Study of the Rolling Stones of Death Valley

One of the first scientific studies, published in 1948, suggested the rock motion was driven by dust devils.

In 1976, 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's study reached three conclusions:

1. Small heaps of the desert were pushed up in front of the stone as it travelled along. This indicated that the ground was wet.
2. The highest recorded numbers of moving rocks occurred during winters of above-average rainfall and strong winds.
3. It would take precisely 0.6 cm 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.

He also wrote in the Bulletin of the 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 fix 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?

Has the Mystery of the Rolling Stones of Death Valley Been Solved?

In 2001 a team led by Richard Norris from the University of California conducted another study into sliding rocks. They selected rocks and monitored their movements remotely using a high-quality weather station. They waited patiently for the sailing stones to move, and in 2013 they noticed the first movements. What they discovered is that before the rocks moved, the dried river bed was underwater, about 7cm deep. They were then able to deduce a timeline of events that led to the Rolling Stones of Death Valley moving.

In 2014, scientists were able to capture the movement of the stones for the first time using time-lapse photography. The results strongly suggest that the sailing stones are the result of a perfect balance of ice, water, and wind.

First, the river bed flooded which was deep enough that ice floats, yet shallow enough that the rocks are not covered. When the temperature at night drops, thin ice forms on the surface of the flooded river. When in the morning when the temperature warms up and the wind blows, ice sheets start floating away and they can bash into rocks as they are blown by the wind. The rocks are resting on a layer of slippery mud which meant that they could be moved up to 5m by a sheet of ice only 3-5mm thick.

The scientists only observed smaller rocks moving in this way so cannot say for certain if this is how the larger rocks move, but it does go some way into explaining these mysterious rolling stones of Death Valley.