Sailing stones, sliding rocks, and moving rocks all refer to a geological phenomenon where rocks move and inscribe long tracks along a smooth valley floor without human or animal intervention. Tracks from these sliding rocks have been observed and studied in various locations, including Little Bonnie Claire Playa in Nevada, and most notably Racetrack Playa, Death Valley National Park, California, where the number and length of tracks are notable. At Racetrack Playa, these tracks have been studied since the early 1900s, yet the origins of stone movement are not confirmed and remain the subject of research for which several hypotheses exist.
The Racetrack Playa, or The Racetrack, is a scenic dry lake feature with "sailing stones" that inscribe linear "racetrack" imprints. It is located above the northwestern side of Death Valley, in Death Valley National Park, Inyo County, California, U.S..
Located above the northwestern side of Death Valley in Eastern California's Mojave Desert, an exceptionally flat dried lake called Racetrack Playa contains a peculiar phenomenon. Dozens of large stone stabs made of dolomite and syenite - often weighing as much as 318 kilograms - move across the cracked mud, leaving a series of smooth trails behind them.
The Racetrack Playa is 3608 feet (1130 m) above sea level, and 2.8 mi (4.5 km) long (north-south) by 1.3 mi (2.1 km) wide (east-west). The playa is exceptionally flat and level with the northern end being only 1.5 inches (4 cm) higher than the southern. This occurrence is due to major influx of fine-grained sediment that accumulates at the north end.
The highest point surrounding the Racetrack is the 5,678 feet (1731 m) high Ubehebe Peak, rising 1970 feet (571 m) above the lakebed 0.85 mile (1.37 km) to the west.
The playa is in the small Racetrack Valley endorheic basin between the Cottonwood Mountains on the east and Nelson Range to the west. During periods of heavy rain, water washes down from the Racetrack mountain area draining into the playa, forming a shallow, short-lived endorheic lake. Under the hot desert sun, the thin veneer of water quickly evaporates leaving behind a surface layer of soft slick mud. As the mud dries, it shrinks and cracks into a mosaic pattern of interlocking polygons.
The shape of the shallow hydrocarbon lake Ontario Lacus on Saturn's moon Titan has been compared to that of Racetrack Playa. The Milky Way is the visible arc in the center above a sailing stone and tracks from others.
Some of these trails stretch for a whopping 250 metres. They often form a nice, lightly curved line, but sometimes they form sharp, zig-zagging angles, implying a sudden shift to the right or left. These ‘sailing stones’, as they’ve been nicknamed, are so common on the the Racetrack Playa, they make it look like a well-worn racetrack, hence the name. (Playa is another word for ‘dried lake’.)
The stones move only every two or three years and most tracks develop over three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms tend to wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different track in the stone's wake.
Trails differ in both direction and length. Rocks that start next to each other may travel parallel for a time, before one abruptly changes direction to the left, right, or even back to the direction from which it came. Trail length also varies – two similarly sized and shaped rocks may travel uniformly, then one could move ahead or stop in its track.
Racetrack is dry for almost the entire year and has no vegetation. When dry, its surface is covered with small but firm hexagonal mud crack polygons that are typically 3 to 4 inches (7.5 to 10 cm) in diameter and about an inch (2.5 cm) thick. The polygons form in sets of three mud cracks at 120º to each other. A few days after a precipitation event, small mud curls, otherwise known as “corn flakes” form on the playa surface. Absence of these indicates that wind or another object has scraped away the tiny mud curls.
During the bimodal rainy season (summer and especially winter) a shallow cover of water deposits a thin layer of fine mud on and between the polygons of Racetrack. Heavier winter precipitation temporarily erases them until spring when the dry conditions cause new mud cracks to form in the place of the old cracks. Sandblasting wind continually helps to round the edges of exposed polygons. Annual precipitation is 3 to 4 inches (75 to 100 mm) and ice cover can be 1 to 2.5 inches (2.5 to 6.5 cm) thick. Typically only part of the playa will flood in any given year.
According to Marc Lallanilla at LiveScience, while the less informed guesses included everything from aliens and magnetic fields to good old-fashioned pranksters, a popular theory among researchers was that dust devils, which are strong, relatively long-lived whirlwinds, were pushing the stones around as they swept across the playa. But this theory, and others that cropped up, were all disproved.
And then in 2006, planetary scientist Ralph Lorenz from the Johns Hopkins University Applied Physics Laboratory in the US started investigating the sailing stones. He came to the Racetrack Playa with an interest in studying its similarities to a hydrocarbon lake on Saturn’s moon, Titan, and stayed to put an end to a long-standing mystery.
To do so, all he needed was a small rock, some water, and an ordinary Tupperware container. Lorez put the small rock in the bottom of the Tupperware container and filled it with a few centimetres of water. Then he put the whole thing in the freezer.
Marc Lallanilla at LiveScience explains what happened next:
"After putting the container in the freezer, Lorenz ended up with a small slab of ice with a rock embedded in it. By placing the ice-bound rock in a large tray of water with sand at the bottom, all he had to do was gently blow on the rock to get it to move across the water.
And as the ice-embedded rock moved, it scraped a trail in the sand at the tray's bottom. Lorenz devised his clever experiment by researching how the buoyancy of ice can cause large rocks, when encased in ice, to move by floating along tidal beaches in the Arctic Sea."
Calculations by Lorenz and his colleagues of the weather conditions in Death Valley during the winter months appeared to support his theory. "Calculations show that, in this scenario, the ice causes virtually no friction on the water, so the stones are able to glide with just a slight breeze,” Joseph Stromberg reported at Smithsonian Magazine. "The team argues that their model accounts for the movement far better than any other, since it doesn’t require massive wind speeds or enormous ice sheets."
They published their research in the American Journal of Physics.
While the evidence is circumstantial because no one has actually seen it happen, Lorenz's research remains the most likely explaination for the sailing stones of Death Valley.
In this mysterious and desolate corner of the California desert, the stones move by themselves.
There is no doubt that California's Death Valley National Park is an unusual place. Situated in the Mojave Desert, it is the driest location in North America. With one spot at 282 feet (86 m) below sea level, it also has the distinction of being the lowest elevation of any place on the continent. Finally, it also known to be the hottest locale on Earth with temperatures hitting a record high of 134 °F (56.7 °C) in the Furnace Creek section of the park.
While all these features are certainly unusual, there is one more oddity about Death Valley that makes it one of the strangest places in the world. It's a place where the rocks move by themselves.
Now you might argue that there are plenty of places where rocks move without human or animal intervention. During an avalanche, tons of mud, soil and rocks can come tumbling down steep slopes. And during an earthquake, even large boulders can go bouncing around. In Death Valley, however, these stones slide across a nearly-flat, dry, lakebed called Racetrack Playa leaving long, smooth tracks. No avalanches or earthquakes needed. Not just little stones either. Some of the moving rocks are estimated to weigh as much as 700 pounds (318 kilograms).
What's even stranger is that some rocks seem to move in long straight lines, then suddenly change directions. Others look like they've taken a smooth, curved path. Some of the tracks made by the stones are just a couple of yards long, while others run hundreds of feet.
The lakebed is very isolated and rarely visited by people. Nobody has ever been there at the right time to actually see a rock in motion. Because of this, over the years a number of odd theories have been developed about what might be behind the phenomenon. Some of the ideas include magnetism, mysterious energy fields and even pranksters. Some of the more extreme solutions involve flying saucers and aliens.
Scientists Take an Interest
The strange phenomenon was first documented in 1915 when a prospector named Joseph Crook from Fallon, Nevada, visited the area. Crook observed that some of the stones sitting on the lakebed were at the end of long "tracks," giving the impression that they must have moved, scraping up a little less than an inch or so of the soil as they crept along.
In 1948 two geologists, Jim McAllister and Allen Agnew, published the first scientific report of the phenomenon in the Geologic Society of America Bulletin. The two suspected that high winds and wet, slick mud on the lakebed might be behind the odd movements. It also occurred to them that if the effect was due to conditions on the valley floor, they might find rocks that do the same thing in other locations. A similar phenomenon was found to be happening at Little Bonnie Claire Playa in Nye County, Nevada, and later on at Great Slave Lake, in Canada's Northwest Territory.
In 1955 George M. Stanley looked into the mystery. He thought that the stones were too heavy to be moved by the wind alone. He suggested that at times the dry lakebed would flood and if temperatures were low enough, the water would turn to ice. As these ice sheets moved, they would carry the rocks they trapped along with them.
Corralling the Stones
It wasn't until 1972, however, that somebody decided to test Stanley's theory. Researchers Bob Sharp and Dwight Carey went to the valley and picked thirty stones for their test which looked like they had moved in the recent past. They gave each of the stones names and placed stakes in the ground near them to mark their current locations. They then picked a few special stones and created a corral around them using metal stakes made of rebar. The idea was that if a large ice sheet was involved in moving the stones, they would be blocked or deflected by the stakes of the corral. The stones seem to take no notice of the corral, however, and one of them left it that winter only narrowly missing one of the stakes on its way out.
This seemed to indicate that if ice was involved, it was just a small collar of ice around the stone itself, not a large sheet. One of the other things that came out of the seven year study was the observation that none of the stones seemed to move in the summer. Only during the winter.
During the study 28 of the 30 stones originally selected for monitoring moved. The smallest stone (named Nancy) which was only a few inches across, moved the longest distance: 860 feet (260 m). The largest stone to move weighed about 80 pounds. One of the heaviest stones, Karen, which was estimated to weigh 700 pounds, did not move at all.
However, after the test period was over, Karen disappeared. It was rediscovered by San Jose geologist Paula Messina in 1996 about a half mile from its last known location.
In 1995 another scientist, Professor John Reid, and several of his students went to Racetrack Playa to examine the mystery. They found evidence that despite the research done in the seventies at least some of the stones were moving due to being embedded in a large sheet of ice (up to half a mile wide). They based their conclusions on the marks found on the ground after the winter of 1992-1993.
However, there is confirmation that the stones can also move individually. In 2011 a study suggested that the dry lakebed can flood, then freeze. As the water thaws, ice may cling to the stones, floating them like little icebergs. Partly floating in the water with ice to reduce the friction, a strong gust of wind can get even a very heavy stone moving. Once a stone is on the move, the energy it needs to keep going is only half of what is needed to get started, so they can continue for quite a distance even if the wind gust drops.
The Tabletop Experiment
In 2006 Ralph Lorenz, a NASA scientist, developed a tabletop experiment that seemed to confirm the idea of "ice rafts" floating and moving the stones. He was first drawn to the sailing stone mystery because he was interested in meteorological conditions on Saturn's moon of Titan and Racetrack Playa seemed to have some very similar characteristics.
Lorenz put a rock into a Tupperware container and then filled the container with water until the rock was almost covered. He then froze it and let it thaw out a bit until there was just a small raft of ice with the rock caught in it. He then put the rock with its "ice raft" into a tray of water with sand at the bottom. The ice floated the rock so that it only lightly sat on the bottom. Lorenz could then blow on the rock and it would move easily across the sand, leaving a trail behind it.
Scientists would like to confirm the stones' movements by the use of inexpensive time-lapse digital cameras, but so far it's a difficult task to catch the rocks in the act. It is believed that a single stone might not move for years and when it does, the movement might only last about 10 seconds.
Thus though there seems to be a logical mechanism for the movements of the stones, nobody has actually ever seen it happen. So we still can't disprove that it isn't just the result of a group of extraterrestrials out to play a prank on us humans after all.