The Sliding Stones of (Not) Racetrack Playa, and One of the Less Important Consequences of Climate Change

UNR field studies stop on the Carson Sink and Highway 50, circa 1983

There are lots of mystery spots in the world. My garage is one of them. Over the decades it has collected the flotsam and jetsam of our lives, and it hasn't happened in any kind of organized manner. The last few weeks of this summer has seen one of our most ambitious attempts yet to clear out the debris and preserve the important records of our lives. I even had a yard sale! There have been lots of precious little discoveries, and one of them was the snapshot above, of another mystery spot in the world. It was taken in 1983 or 1984 when I was attending grad school at the University of Nevada, Reno.

I know that for some of you, seeing the tracks across the playa surface can only mean one place on the planet: Racetrack Playa in Death Valley National Park. For years and years geologists and others noted the strange trackways made by pebbles and boulders and pondered how in the world they happened. There have been the "boring" scientific hypotheses involving wind, water and ice, and the more exotic fringe ideas like weird magnetic currents and aliens. I took the picture, but I've never been to Racetrack Playa and therefore am not guilty of tampering with the stones (the National Park Service and geologists take a very dim view of such things). It turns out the strange sliding stones have been found in other places. I know of at least three of them.

Paul is going to solve the mystery of Bonnie Claire Playa, no matter the cost.

There seem to be at least three important factors to get sliding stones: a flat playa surface, a nearby source of rocks, and the possibility of freezing windy conditions. The Racetrack has the Grandstand, an island of rock in the midst of the playa and a high enough altitude to get freezing conditions once in awhile. Bonnie Claire Playa in the vicinity of Death Valley has an active alluvial fan and similar elevation. And Highway 50 in the Carson Sink of Nevada has Highway 50. The highway has to cross the playa and to prevent flooding it has been built on a roadway of stones brought in from elsewhere. That's where I was when I snapped the opening picture of this post. Some of the stones escaped from the highway and set off across the playa surface. My fellow students were trying to suggest an origin of the trackways as being the result of high winds and too many drunk geologists being blown across the dry lake surface.

Moving stones on Bonnie Claire Playa

Some hypotheses involved only extreme winds blowing over a very slick muddy playa surface. Some experiments suggested that pebbles could be set in motion by hurricane force winds, but wind by itself cannot explain the fact that some of the moving stones weigh hundreds of pounds. The fact that some rock trails run parallel to each other suggest that they were locked together. A sheet of ice covering the playa provides a possible explanation. It the ice were to break up into smaller sheets, the ice could presumably act as a sail. Most observers figured that high winds were still a necessity.

Stone tracks on Bonnie Claire Playa

In 2013 cameras caught the movement of the stones (see it here). Ice was indeed involved, but hurricane force winds weren't required. The sheets of ice were pushing the rocks around in winds as little as 10 miles per hour. It's not clear if this process can explain the movement of the larger boulders.

The greatest irony of the mystery of the sliding stones is that they might soon no longer move at all. As the climate changes and warms over the coming decades, the required conditions, particularly that of ice formation, will no longer exist.

Here is one more mystery for you. When we last visited Bonnie Claire Playa, we found this circular structure. I welcome any explanation you can provide for this one! UFOs need not apply, even though Area 51 is only a few hundred miles away. You can see some more pictures of the strange feature in my post here: https://geotripper.blogspot.com/2015/02/a-little-mystery-to-accompany-moving.html

Learn more about the research on the sliding stones of Racetrack Playa here:
https://scripps.ucsd.edu/news/mystery-solved-sailing-stones-death-valley-seen-action-first-time

A Little Mystery to Accompany the Moving Stones of the Basin and Range

I'm back from an intense journey through Death Valley National Park and surrounding regions. Much photography and commentary can be expected in the next few weeks, but for today, I'll just lay out a bit of a mystery.

The sliding stones of Racetrack Playa in Death Valley are justly famous, and the mystery of their mode of movement has recently been made clear. But the Racetrack isn't the only place where the stones slide. Bonnie Claire Playa, close to the California-Nevada border, also shows the phenomena. We headed up there on our field studies class. The stones are fascinating, but something else caught my eye while exploring the playa surface.

I don't know what this circle is. It was there by itself, and had no obvious tracks leading to it. Because of its singular nature, I strongly suspect human intervention (SBCC, did you have anything to do with this??). But who knows? If some folks dragged something in a circle, how did they not leave tracks around the edge? Did someone leave a large tire for awhile and retrieve it later?

I even found the circle on Google Earth (below). Again it seems to be all by itself, with no tracks leading to and from.

What do you think is going on here?

One of Geology's Little Mysteries Solved: The Sliding Stones of Racetrack Playa in Death Valley

Bonnie Claire Playa in Nevada

There are side shows that happen in the sciences. There are the big mysteries of the cosmos and earth history that take many years and the work of dozens or hundreds of the greatest minds to solve: atomic theory, quantum physics, plate tectonics, DNA sequencing and so on. In geology, there are the big picture mysteries of how the continents have moved through time, the patterns of evolution of life on the planet, the origins of rock sequences. It's the great human adventure of exploration that carries us into a fascinating future.

And then there are those nagging little mysteries. Why does bread fall with the buttered side down? Why do cats land right side up? It's the kinds of things that have kept the Mythbusters at work for years. Well, it seems that one of those nagging little mysteries in geology has been solved. For years, stones have left mysterious trackways on the surface of Racetrack Playa in Death Valley National Park. They have been noted more than half a century, and have been the subject of a number of studies, but in all those years no one has seen it happen, or provided a convincing explanation of how it could happen. There have been numerous hypotheses, and of course outlandish ideas like magnetic force lines and alien interventions.

Bonnie Claire Playa, Nevada

But now, we are learning that Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, and Brian Jackson have shed light on the mystery, and produced digital images of the rocks in action. In their just released article, Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion, they document the conditions that resulted in the movement of numerous stones on the playa, especially during the winter of 2013-2014. The article can be read in its entirety here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0105948 (and thank you for the open access!).

In essence, the researchers marked the location of stones, and outfitted many with GPS trackers. When storms filled part of the playa surface, a thin sheet of ice formed on the water. As the ice began to melt during the day, large sheets of ice were seen moving and pushing the stones.  The winds recorded were not nearly as powerful as expected, as stones were moved when the winds were no more than 4-5 meters per second (9-11 mph). You can see the process happening in the video here:



I was sure all along that UFOs were swooping down and playing a form of ice hockey with complicated rules, but actually the phenomenon the researchers described made good sense. Racetrack Playa is not the only place where rocks have left trails. I've not been to Racetrack Playa yet, but I've seen tracks on Bonnie Claire Playa northeast of Death Valley National Park, and along Highway 50 in the Carson Sink of western Nevada. There were certain factors in common with each site: relatively high altitude, a source of rocks (the roadbed of Highway 50 was one source), and winters that occasionally have freezing conditions and high winds. Ice was suggested as a factor because many of the trails were parallel to each other as if the rocks were locked together.

I've been joking all day that my life feels empty now that the stones have been explained. But does solving the mystery of the sliding stones take away from our sense of wonder at the world? No, it doesn't. It is a marvelous example of how science works. I love to see mysteries solved by good old-fashioned hard work and persistence. 

This also allows me to say to the vandals and felons who have stolen the sliding stones from the surface of the Racetrack, thinking they have some taken possession of a magical key to the supernatural worlds encompassed within: "Guess what, moron! You've stolen a rock. You are an idiot".

Citation: Norris RD, Norris JM, Lorenz RD, Ray J, Jackson B (2014) Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion. PLoS ONE 9(8): e105948. doi:10.1371/journal.pone.0105948

Strangers in a Strange Land: Just how flat is flat?

We've looked at two playa surfaces now in the series Strangers in a Strange Land, our tour of Death Valley and the Mojave Desert of eastern California. The first was the salt pan at Badwater, the lowest point in North America at minus 282 feet, and Bonnie Claire Playa, where rocks seem to have a mind of their own.

Playas have to be counted as pretty much the flattest places on Earth (abyssal plains on the deep ocean floor are pretty flat, too, but aren't exactly accessible). And they are flat. When rare flash floods bring clay-rich water onto the playa surface, the water spreads out, and the clay stays in suspension long enough to be spread evenly across the lake.

I was thinking about flatness today when I was running errands at the department. Topographic maps are the tool of choice for geologists for mapping and plotting. They are also used by anyone who really wants to know where they are when backpacking, hiking, camping, hunting, or whatever. I generally blame topo maps for dragging me into geology. I was a scout, and I was fascinated by the maps we used while hiking. I collected them, I practiced my orienteering/compass skills constantly, and eventually became the "go-to" guy when we were out in the wilds. They called me Captain Eagle-Eye Wrong-Way, because it was just about impossible to get me lost if I could see any two mountains and had a compass and map (even today students ask "How far?" and when I answer, they say "Garry-miles or real miles"?).

A couple of years back I was going through the department map collections, and I found a map that I realized would defeat my efforts at orienteering. I saluted the map-makers, and posted the map on the wall in the department to be a shrine to the pratfalls of topographical arrogance. It is pictured below, and people familiar with contour lines will notice a near complete lack of them. The red lines form a grid made of square miles, so this map is about 6 1/2 by 8 miles, or about 52 square miles. The contour interval is 5 feet, which means that elevations across this entire quadrangle vary by only a few feet, primarily because of some 8 foot high dunes on the lower left-hand corner.

The map is part of the Carson Sink, a place in western Nevada where a number of rivers come to die. This was part of the ghastly last 40 miles where settlers in the 1840-50s came to grief as they tried to reach the California gold fields. Even today, a notation on the map mentions "no roads or trails". Well played, topographers, well played!

Strangers in a Strange Land: Even the stones have minds of their own...

Death Valley is the very epitome of (easily visited) remoteness and loneliness. There are outposts of civilization at Furnace Creek, Stovepipe Wells, and Scotty's Castle, but the rest of the park is a vast wilderness with only a few roads, paved or otherwise. I've called this blog series "Strangers in a Strange Land" because most humans are strangers here, and it seems like almost everything about this landscape is truly strange. One of those strange landscapes are playa surfaces. I previously talked about the Death Valley salt pan, one aspect of an interior drainage desert, but there are many other "lakes" in the park which never collected much in the way of salt. They have smaller drainage basins, and no river systems fed into them, so the most common mineral on the floor of these playas is fine-grained clay. They will occasionally have water following flash flood events, but most of the time they are dry, and the clay breaks up into millions of small, mostly hexagonal mudcracks.

Pure clay makes for poor soils, and plants do not grow on the playas. So...no plants, few animals or insects, no particularly interesting minerals. Why are these students so fascinated with the surface of the playa? Well, there is one thing on this playa that seems "alive"...it's the rocks. They've been moving around...

It's strange for large pebbles and small boulders to be on the playa in the first place if you think about it. Playas are the tail end of a flash flood sequence. There might be a mudflow careening down a desert drainage, tearing at the cliffs and carrying large rock fragments. But then the flood reaches the alluvial fans on the flanks of the mountains, and with the gentler slopes, the flood slows and the larger fragments drop out. The only sediment that usually reaches the playa surface is a brown slush containing only suspended clay particles. Sometimes there are rock outcrops found within the playa or along the margins, so the rocks can be easily explained. But how are they leaving behind trails?

By now, readers familiar with Death Valley are thinking that we are visiting Racetrack Playa in Death Valley National Park, but we aren't. Although the Racetrack is justly famous for the number and size of its moving stones, it turns out that moving stones can be found in at least eight other places across the Basin and Range Province in Nevada and California. I haven't been to the Racetrack yet (it is at the end of a 25 mile long gravel road), but I have seen the phenomenon at two other places: along Highway 50 on the Carson Sink in Nevada, and on this playa that we visited in February, Bonnie Claire, just outside of Death Valley National Park.

So, how is it that they move? If you are looking for a definitive answer, I am sorry, I don't actually know. No one truly does, because no one has ever seen it happen. I think we can safely dismiss stories of aliens playing jokes, elves, and pixies, and of strange magnetic forces. The stones lie on exceedingly flat surfaces, so gravity sliding is probably not involved. It seems that only one force exists in the Death Valley region that can account for the movement of these rocks: the wind.

Wind seems a real stretch. Even first-time geology students know that wind normally can only move sand and dust particles. It would take extraordinary conditions for wind to be able to push rocks that weigh many pounds. Yet it happens. Extremely high winds are not unusual in the Death Valley region, especially during and after winter storms. Studies are ongoing as to whether wet saturated clay is slick enough to allow for the movement of stones in such winds.

There may be another important factor. The playas where the rocks move are at higher elevations where freezing temperatures are common. If enough rain has fallen, water may cover the playas and freeze around stones sitting on the playa surface. It is suggested that broken sheets of ice around the stones can act as sails, helping push the rocks along. This idea is supported by rock trails that move in tandem, as if the rocks were physically connected. This explanation works for me, but additional testing of some of the rocks shows that ice cannot completely explain the movement (researchers put stakes around some stones, and they moved out, passing through spaces barely bigger than the stones themselves).

So the moving stones are still a bit of a mystery. One of these times, someone is going to brave a horrific windstorm and will be standing there with a camera when the stones are moving about. At that time we will be able to see the elves themselves pushing the rocks along!

Ron Schott has allowed me to post some of his photographs taken at Racetrack Playa in Death Valley National Park. The first is a gigapan 360 degree view of the playa (click on the image below to see how gigapans work; it's pretty amazing). More gigapans of Racetrack and other parts of Death Valley can be found here: http://www.gigapan.com/gigapans?gallery_id=7940&order=most_popular&page=2&per_page=10

More of his shots can be found on his Flicker page at http://www.flickr.com/photos/rschott/tags/racetrackvalley/

A final note: if you visit Racetrack or any of the other moving stone sites, please leave the stones alone. They are mysterious, but not mystical. They are normal run-of-the-mill rocks with no unusual properties other than being on a playa, and the position of each stone is recorded with GPS. Stealing the rocks (and that is what you would be doing) will screw up years of research. You will also take from the enjoyment from other visitors.