If a stone sails across the desert and no one is there to see it, did it really move?

The Daily Mail revisits the phenomenon of “sailing stones”—stones that apparently move without the aid of wildlife, human, or hoaxist help.

These stones, which range in size from pebbles to boulders heavier than you or I in a post-Thanksgiving dinner state, have been studied by geologists for decades. Many of the stones can be found in Death Valley’s cheekily named Racetrack Playa (dry lakebed), where they leave a distinct trail in their wake, etched into the desert floor. They appear capable of turning on a dime and abruptly changing direction. Mysteriously, stones that had been traveling in a parallel direction, may suddenly inexplicably diverge paths. (Some may idly remark on such similarities in certain human relationships.)

http://www.flickr.com/photos/yathin/ / CC BY-NC-ND 2.0

Science has put forth more than a few theories of how these stones slide, glide, and scoot. One involves ice. The weather in Death Valley is punishing, reaching daytime highs of over 120°F and freezing winter night lows. Throw in 90mph winds and thin sheets of clay, and you may have the right mixture for a stone to set sail.

Wikipedia gives an account of a multi-year study undertaken in the 1970s. Each of the twenty-five stones monitored was assigned an alphabet letter, as well as a nickname. Mary Ann (aka, stone A), Nancy (aka, stone H), and Karen (aka, stone J) were among those who found their unpredictable movements closely scrutinized through the seasons. Mary Ann moved over 200 feet the first winter, with the more petite Nancy traveling more than four times that distance over the years. At some point, Karen somehow up and left the study, only to be possibly sighted decades later half a mile down the playa. Foul play was unlikely given that the heavy equipment needed to transport Karen’s 700lbs would have left tracks of its own. Alien abduction or a mistaken identity, however, are entirely possible.

The sailing stones are notoriously shy. Through the numerous scientific studies and visits from curious onlookers, no one has actually seen them move. The lonely, meandering scars carved into the desert floor are the only trace left behind of their silent travels.

Readers interested in detailed analysis on the stones can find more information in a write-up on the USGS website, as well as in various scientific papers.

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