Deep in the California Desert lies a spot known as Death Valley. But unlike ghost towns, dinosaurs,
and other fossils one can find in the desert, in Death Valley rocks seem to have come alive.
For over a century, scientists have been puzzled by the famous Sailing Stones of Racetrack Playa;
rocks that move on their own and leave beautifully smooth tracks behind.
Some are upwards of 500 pounds and still travel more than 15 feet
in a minute. Others leave trails that are thousands of feet long.
However, while it has been confirmed that the rocks do move without human or
animal intervention, no one had ever seen them in action - until a pair of curious
scientists finally got to the bottom of the mystery only a few years ago…
Open Case
Death Valley is the hottest place on the planet.
Named in 1933, the National Park is notably the driest and lowest elevation in North America.
But by any standard, the area on the border of California and Nevada is also
a strange place - home to an eerie and almost haunted site: the infamous Racetrack Playa.
The playa, or dried lakebed, is better known for its bizarre phenomena in
which hundreds of huge rocks have been found to move entirely by themselves.
Known as the Sailing Stones, the inanimate objects drift across the flat desert landscape,
showing no signs of being either pushed or pulled but nonetheless leaving tracks of
their smooth gliding across the dry ground as if propelled by no power other than their own.
And yet, to the naked eye they don’t appear to be moving at all.
Ever since Joseph Crook first documented the baffling case in his account of the sliding
rock phenomenon back in 1915, scientists have been perplexed by the anomaly.
It soon became evident that the rocks were not moved by human or animal intervention,
but it was undeniable that they traveled across the cracked terrain.
In 1948, the Racetrack sparked interest from geologists that mapped the area's bedrock.
In their report, Jim McAllister and Allen Agnew suggested that the tracks could be
scrapers propelled by strong gusts of wind, similar to those that cause dust devils.
Then, in 1952, National Park Service Ranger Louis
G. Kirk thoroughly recorded observations of the furrows’ length, width, and course.
Soon after, scientists and the general public began speculating about the cause.
Patience
Throughout the decades, several explanations have been put forward, ranging from the complex
to the supernatural. It was long thought that strong winds pushed the stones,
and more elaborate theories involved magnetic fields. Some even blamed alien intervention.
However, even the most plausible hypotheses were soon ruled out.
While most geologists reasoned that strong winds and wet mud were at least
partly responsible for the phenomenon, George M. Stanley was not convinced.
In 1955, he published a paper explaining that some rocks weighed as much as a human,
which made them too heavy for the area’s winds to move them. In fact, some weighed up to 700 pounds.
Admittedly, the stones did not seem to move due to any gravitational cause. Varying from
a few ounces to hundreds of pounds, they are basically composed of dolomite and syenite,
minerals not at all uncommon in the surrounding mountains. Naturally, they tumble down due to
the well-known force of erosion and fall onto the flat ground in the valley below.
But once they come to rest at the level surface of the dry lake, the extraordinary happens.
Somehow, the rocks move horizontally. And they not only leave tracks behind,
but their trails are perfectly smooth records of their paths.
Even the largest rocks have left trails as long as 1,500 feet.
Remarkably, rocks with a rough-bottomed surface tend to leave straight tracks,
while those with a smoother bottom surface usually wander.
Even though the rocks change their location periodically, no one had ever seen them move
in person. That is, until a pair of curious and impossibly patient scientists got them on film.
The Most Boring Experiment Ever
The mystery of the Sailing Stones was finally cracked by two cousins in 2014.
Aided by the Scripps Institution of Oceanography and NASA, among others,
Richard and James Norris founded the Slithering Stones Research
Initiative in 2011 and established a weather station near Racetrack Playa.
To conduct the experiment, the team added 15 of their own stones with
embedded GPS tracking units to monitor their movement. And then, they waited.
The stones are immensely difficult to catch in action because they only move
under unique conditions. As the National Park’s personnel ratified, the phenomenon
usually happens in the winter, just after the rain comes. However, the rocks can stay put
for even a decade if the perfect conditions for their sailing adventures are not met.
The researchers did not initially expect to see motion in person, so they settled for remotely
monitoring the area with equipment capable of measuring gusts in one-second intervals.
Not long after, Ralph Lorenz of the Applied Physics Laboratory at Johns
Hopkins University dubbed the whole venture: (QUOTE) “The most boring experiment ever.”
But against all odds, the wait wasn’t long.
In December of 2013, the cousins arrived in Death Valley and found
the normally-barren area covered with a pond of water no deeper than three inches,
and unsuspectingly stumbled upon the perfect balance of factors causing the rare phenomenon.
As fate would have it, they were the first humans to capture it on camera.
Spoiler Alert
From December 4 to 20, the setup captured the
rocks sliding across the playa using time-lapse photography.
The rocks moved as fast as 15 feet per minute, and the cousins finally settled the case. The
combination of winter conditions started with a shallow layer of water in the lake bed,
accumulated from the rains. Later at nighttime, the cold temperatures formed a thin layer of ice.
Even so, it took a precise third requirement for the rocks to change
positions. It was only during a subsequent sunny day that the melting would break the
ice into large floating panels that were, in turn, driven by light winds. As such,
the rocks were nudged into motion by the ice floes and dragged across the desert floor.
Their finding proved previous hypotheses wrong, as the cousins stated in a paper in
the peer-reviewed journal PLOS ONE: (QUOTE) “In contrast with previous hypotheses of powerful
winds or thick ice floating rocks off the playa surface, the process of rock movement
that we have observed occurs when the [...] ‘windowpane’ ice sheet covering the playa pool
begins to melt in late morning sun and breaks up under light winds of [about 10 miles per hour].”
Therefore, the tens-of-yard-wide floating panels push multiple rocks at low speeds
and along trajectories determined by both the direction and the velocity of the wind,
but also that of the water flowing under the ice caps.
If the playa doesn’t get enough rain during a certain season,
the stones can’t move and have to wait until the following year. Thus, Racetrack Playa
stones move once every two or three years, but their tracks remain visible for roughly four.
Since Death Valley is as arid as it gets, the opportunities to see the stones in action are
scarce. However, it is possible to visit the site and hope to catch a glimpse of
the event if all the conditions align. Otherwise, one can also delight in the
wild sight of the mesmerizing trails left behind by the Sliding Stones.
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