It is one of Death Valley’s most intriguing geological whodunits — the sliding rocks of the Racetrack Playa.
On an ancient lakebed located on the western side of Death Valley National Park, boulders that weigh up to 700 pounds sail across the almost perfectly flat terrain, leaving grooved trails in their wake. As NATURE’s Life in Death Valley shows, each of these furrows chronicles a rock’s journey, ranging from a mere few inches to nearly 3,000 feet. Some tracks manifest in straight bold lines, while others coil back on themselves in sinuous arcs.
Despite a century of scientific investigation, this curious phenomenon has confounded the geological community and park visitors alike. To this day, no one has ever seen the rocks move. But in lieu of eyewitnesses, countless theories have been put forward over the years in an effort to explain the reasons behind the migrations.
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One early suggestion was that the rocks were driven by gravity, sliding down a gradual slope over a long period of time. But this theory was discounted when it was revealed that the northern end of the playa is actually several centimeters higher than the southern end and that most of the rocks were in fact traveling uphill.
Though no one has yet been able to conclusively identify just what makes the rocks move, one woman is coming closer to solving the mystery. For the past ten years, Dr. Paula Messina, professor of geology at San Jose State University in California, has made it her quest to understand what has bewildered geologists for decades. “It’s interesting that no one has seen them move, so I am kind of sleuthing to see what’s really going on here,” says Dr. Messina.
Many scientists had dedicated much of their careers to the racing rocks, but the remoteness of the area kept their research limited in scope. No one had been able to map the complete set of trails before the advent of a quick, portable method known as global positioning. Dr. Messina was the first to have the luxury of this high technology at her fingertips.
In 1996, armed with a hand-held GPS unit, she digitally mapped the location of each of the 162 rocks scattered over the playa. “I’m very fortunate that this technology was available at about the same time the Racetrack captured my interest,” she says. “It took only ten days to map the entire network — a total of about 60 miles.” Since then, she has continued to chart the movements of each rock within a centimeter of accuracy. Walking the length of a trail, she collects the longitude and latitude points of each, which snap into a line. She then takes her data back to the lab where she is able to analyze changes in the rocks’ positions since her last visit.
She has found that two components are essential to their movement: wind and water. The fierce winter storms that sweep down from the surrounding mountains carry plenty of both.
The playa surface is made up of very fine clay sediments that become extremely slick when wet. “When you have pliable, wet, frictionless sediments and intense winds blowing through,” offers Dr. Messina, “I think you have the elements to make the rocks move.”
At an elevation of 3,700 feet, strong winds can rake the playa at 70 miles per hour. But Dr. Messina is quick to point out that sometimes even smaller gusts can set the rocks in motion. The explanation for this lies in her theory, which links wind and water with yet another element: bacteria.
After periods of rain, bacteria lying dormant on the playa begin to “come to.” As they grow, long, hair-like filaments develop and cause a slippery film to form on the surface. “Very rough surfaces would require great forces to move the lightest-weight rocks,” she says. “But if the surface is exceptionally smooth, as would be expected from a bio-geologic film, even the heaviest rocks could be propelled by a small shove of the wind. I think of the Racetrack as being coated by Teflon, under those special conditions.”
In science, hypotheses are often based on logic. But over the years, Dr. Messina has discovered that on the Racetrack, logic itself must often be tossed to the wind. “Some of the rocks have done some very unusual things,” she says.
In her initial analysis she hypothesized that given their weight, larger rocks would travel shorter distances and smaller, lighter rocks would sail on further, producing longer trails. It also seemed reasonable that the heavier, angular rocks would leave straighter trails and rounder rocks would move more erratically.
What she discovered surprised her. “I was crunching numbers and found that there was absolutely no correlation between the size and shape of the rocks and their trails. There was no smoking gun, so this was one of the big mysteries to me.” What appears as a very flat, uniform terrain is in fact a mosaic of microclimates. In the southeastern part of the playa, wind is channeled through a low pass in the mountains, forming a natural wind tunnel. This is where the longest, straightest trails are concentrated. In the central part of the playa, two natural wind tunnels converge from different directions, creating turbulence. It’s in this area that the rock trails are the most convoluted. “What I think is happening,” proposes Dr. Messina, “is the surrounding topography is actually what is guiding the rocks and telling them where to go.”
Some people have suggested attaching radio transmitters to the rocks or erecting cameras to catch them “in the act” in order to put an end to the speculation. But as Death Valley National Park is 95 percent designated wilderness, all research in the park must be noninvasive. It is forbidden to erect any permanent structures or instrumentation. Further, no one is permitted on the playa when it is wet because each footprint would leave an indelible scar.
As for Dr. Messina, she is content in the sleuthing. “People frequently ask me if I want to see the rocks in action and I can honestly answer that I do not,” she says. “Science is all about the quest for knowledge, and not necessarily knowing all the answers. Part of the lure of this place is its mystery. It’s fine with me if it remains that way.”
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ummmm…. a time-lapse camera????
Dear Logical Dude,
In case you missed this part of the above article…
“Some people have suggested attaching radio transmitters to the rocks or erecting cameras to catch them “in the act” in order to put an end to the speculation. But as Death Valley National Park is 95 percent designated wilderness, all research in the park must be noninvasive. It is forbidden to erect any permanent structures or instrumentation. Further, no one is permitted on the playa when it is wet because each footprint would leave an indelible scar.”
I wonder if there’s also not some hydraulics involved. Presumably water is being pushed around on the playa as well. Might that create some kind of sucking force on the rocks? I like the teflon analogy as well. Even I can push around a heavy boulder over ice. And don’t forget Newton; objects in motion tend to stay in motion absent any resistance. Very curious.
how about when it is dry to place a small gps system on all the rocks to prove that they move
I have researched pans (playas) in the Karoo of South Africa and I have had a similar problem where large dolerite (basalt) boulders (50 x 50 x 50 cms and greater up to 0.5 cu. m) out in the middle of one flat surface pan in particular. I have no modern day trail as at Racetrack Playa. Any modern day trail would be obliterated by weather conditions shortly after they would appear. The large boulders at this pan arrived at some time in the distant past, however smaller cobbles and small boulders may still be moving. This one particular pan is about 0.70 sq. km in size, not nearly as large as “Racetrack Playa,” but possibly the same forces as work. I have no definite answers just hypotheses an empirical observations. The elevation of the pan (Haaskraal Pan Complex, HPC) is approximately 1,478 masl (4,850 ft. asl), and is in an arid area that receives 100m to the center over a flat surface.
At first I thought that the floodwaters from the stream played some role in moving the boulders. I excavated cross-sections of the stream channel, terrace deposits south of the pan, and walked up and down the exposed stream banks but did not find any boulders approaching the sizes of the boulders on the pan surface. There were no boulders in the upper stratigraphy of excavations of adjacent terrace deposits outside of the pan that in the past were above today’s pan surface indicating deflation of the terraces and the pan surface. In the upper layers of one terrace deposit I found convoluted drainage patterns indicative of frozen ground.
A combination of physical occurrences combined to move these large boulders. In a rather fast flip flop of weather conditions cold dry late Pleistocene conditions with frozen ground gave way to saturated montmorillonite sediments as convoluted patterns began to thaw, combined with heavy prevalent northwest winds and high rainfall that made the boulders move slowly toward the center of the pan. Repeated drying and large dessication cracks on the surface followed by high winds and the right amount of moisture from rainfall moved the boulders over the slick clay surface additionally over time.
From Antarctic ice cores during the late Pleistocene ca. 25-35 kyr there were frequent cold/dry conditions followed by wet/warm conditions during this period. This may be the time when the boulders moved. It seems the Racetrack Playa boulder paths are more current, but is there any evidence for these pathways in the past? What is the mineralogy of the soil? Do dust devils occur? How much patination occurs on the boulder surfaces? How embedded in the surface are the different boulders? I find this an intriguing problem. A waiver and permit from the Park Service to study the problem in a minimalist invasive approach worked out with them through their permit process would seem possible and should be attempted. Believe it or not this is a sedimentological scientific problem that occurs in various parts of the world that needs further research.
someone needs to walk out there without permission at the edge fo the mountian side with a high zoom time laps camra and leave it there all camo like and come back one week later and see if the 700 lb. roock moved if the tripod legs of the camra “scars” the land so be it it’s in the act of science then u can go back to your computer and see if it moved.
i think magnetic pulls have something to do with it but a camra will see the forces acting on it.
The answer, I believe, is that the Playa stones do not actually move but rather the earth moves under them. The Playa surface is flat and riddled with “viens”, providing reduced resistance in the form of “drag.” The more important force at work here is Magnetic Fields. The rocks have a magnetic field which may have become polarized upon formation or by a electrostactic fields generated by friction or by laying in the same position in relation to the earth’s magnetic field for eons coupled with repeated cycles of extreme heat and cooling. Even moderately polarized material of the smallest size are “acted upon” my the Earth’s magnetic field, by aligning itself with the magnetic poles of the earth or in this case retaining a certain “sweet spot” where the magnetic field of the Earth exercizes a greater force on the stones than does the friction of the soil that the stones are “defying.” The soil, most likely “flows” around the rock much the way water does but without the ripples.
This can be demonstrated by lightly covering a paper plate with sand, sugar, flour or actual soil about 1/16″ deep. Carefully shake the plate back an forth while holding it level to create smooth horizontal “Playa” surface.
Gently place your “Playa Stone,” (a small piece of iron, metal or a magnet,) atop the “soil.” Finally, take a magnet and hold it under the plate directly below, but not in contact with your “Playa Stone.” Holding the magnet in place, pull the plate horizontally in only one direction. Your “Playa Stone should have created a trail through your “soil” much like the above picture.
This may or may not be what is happening in Death Valley.
Additionally, I propose that if it is the case that magnetic fields are working to hold the stones in place, the tracks have and will again stop and then change direction as the Earth’s magnetic field changes over time.
It may also be that Playa surface has a very slight incline and that seismic activity of the right magnitude is creating vibrations which act upon larger solids more intensely by transfering that vibrational energy into the solid which uses that energy to vibrate as well, gravity comes into play pulling the stones down the incline as they vibrate.
The theories of Dr. Paula Messina which include wind water and bacteria do not hold true
Have you ever seen wind blow even a small piece of gravel across a road, sidewalk or even ice. If it were water that was causing the movement, the raised “wake” of the soil, (pictured above,) left on either side of the stone’s trail would wash away when created.
Additionally, wind is not constant either in intensity nor direction. The change in direction and intensity of the wind would serve only to keep the stone in place, as all efforts over time would not amount to a consistant direction.
As I proposed above, magnetic fields would act on the stones equally despite the size or shape of the stone. The stones are not moving, the Earth is moving under it, so all trails should be basically uniform. The rocks should all move the same distance and the trail should be constant in the distance of it’s cross-section.
I have spent quite some time trying to get people to listen to my theory, and I am getting somewhat frustrated. The simple fact is that the rocks are sliding downhill. I know that observations by many individuals suggest that the rocks are moving uphill, but those observations are not being made while the rocks are moving. The quite common phenomena that is responsible for the movement of the rocks is frost heave, and ice lens formation. The rocks are NOT sliding uphill, they are sliding downhill along with the surface layer of the playa. As the weather warms, and people make their observations, it would appear as though they are sliding uphill, but the surface has settled back with the melting of the lenses leaving the Southern end of the Playa lower. This is a somewhat simplistic explanation, but I doubt that anyone is going to pay attention anyway.
I KNEW that noone would pay attention to this. Unfortunately, for the scientific community, this is the actual answer to this mystery. There is far too much evidence in my favor to argue otherwise.