What Causes the Rocks to Slide on Death Valley's Racetrack Playa?

[runner_one]

What would you estimate to be the depth of the tracks left behind? Does this tend to vary according to the size [weight] of the rock?

There seems to be no rhyme or reason to the depth of the tracks. for example this rock http://runner.coleskingdom.com/pics/racetrack/large/100_4132.jpg"
which was one of the largest, has the most shallow track while this much smaller rock http://runner.coleskingdom.com/pics/racetrack/large/100_4093.jpg" has a much deeper track. the differences in depth could however be attributed to weathering, (I.E. the larger rock moved much longer ago.) However I did notice that one consistency, the smaller rocks in general seem to always have the deeper tracks. However I did not spend enough time there to verify this observation scientifically

 

[Ivan Seeking]

Did you feel compelled to check and be sure that they did not move overnight?

Sorry, but as I was thinking about it, I decided that the impulse would have struck me.

What would you say was the deepest track that you saw? They look to be about a quarter of an inch?

 

[PRDan4th]

It seems to me that wind must play a role in this phenomenon as the tracks cross in your picture "4132.jpg". The dry lake bed must freeze in the winter with a thin layer of ice. The strong wind moves the rocks slightly downwind compressing the ice layer leaving a slight indentation in the soft sand base of the dry lake. Gravity may also play a role if the surface is not perfectly flat. It is a very curious mystery.

 

[runner_one]

and I found one rock that appeared to be following the track left by another. ( I will have to find that photo and upload it later.)

I am now back home in Tennessee after the road trip of a lifetime, I have uploaded all 229 images of our Racetrack Playa trip to http://www.coleskingdom.com/photos/album.php?dir_name=racetrack&thumbnails=large"
There are photos there taken by more than one person so forgive the different styles.
They also include photos of the trip out and back.
But as I stated before I found more than one rock that "appeared to" be following the trail left by another. Whether this is a fact, coincidence, or maybe just a trick of the light, or even some practical joke played by a previous visitor I don't know, but as I promised I would link to those when I found them.
http://runner.coleskingdom.com/pics/racetrack/large/DSC02474.JPG"
http://runner.coleskingdom.com/pics/racetrack/large/DSC02485.JPG"
http://runner.coleskingdom.com/pics/racetrack/large/100_4118.JPG"

 

[Mk]

Add self-rolling snowballs to the list...
http://www.telegraph.co.uk/topics/weather/6950788/Snow-stories-rare-self-rolling-snow-balls-found-in-UK.html

 

[dhundsness]

I suspect the daily thermal expansion and contraction of the rocks may cause them to creep a small increment everyday, like an inchworm. This would work only on rocks which happen to have ratchet-like grooves on the bottom in roughly the same direction, so the edges slide in one direction, but grab traction in the other direction. This would explain why different rocks move in different directions, but some don't move at all. And as the bottom surface deteriorates, that would explain why some rocks suddenly change direction.

Winter probably has more effect, with greater temperature extremes, plus ice and rain. Also the ice sheets may help steer the rocks to move more or less in the same directions. The angle of the sun would cause the ice to melt on the sunny side, but remain frozen on the shaded side, causing differential friction. Weather patterns may also influence different rocks to move and change directions in parallel. For example, if there is cloud cover every morning for a month, the sun wouldn't break till it's in the south, while otherwise it would break in the east, changing which side melts first over time.

I imagine you could demonstrate this motion by putting a heavy metal plate with ratcheted grooves on an even wooden(?) surface in a sunny location -- most likely an indoor terrarium to rule out wind and human interference.

 

[DaveC426913]

I suspect the daily thermal expansion and contraction of the rocks may cause them to creep a small increment everyday, like an inchworm. This would work only on rocks which happen to have ratchet-like grooves on the bottom in roughly the same direction, so the edges slide in one direction, but grab traction in the other direction. This would explain why different rocks move in different directions, but some don't move at all. And as the bottom surface deteriorates, that would explain why some rocks suddenly change direction.

Winter probably has more effect, with greater temperature extremes, plus ice and rain. Also the ice sheets may help steer the rocks to move more or less in the same directions. The angle of the sun would cause the ice to melt on the sunny side, but remain frozen on the shaded side, causing differential friction. Weather patterns may also influence different rocks to move and change directions in parallel. For example, if there is cloud cover every morning for a month, the sun wouldn't break till it's in the south, while otherwise it would break in the east, changing which side melts first over time.g

I imagine you could demonstrate this motion by putting a heavy metal plate with ratcheted grooves on an even wooden(?) surface in a sunny location -- most likely an indoor terrarium to rule out wind and human interference.

It has to happen muuuuuch faster than that to leave the lengths of trails they leave before the trails are eroded by weather.

 

[zoobyshoe]

There have recently been two separate programs about this on the History Channel. In one a hapless team of Mythbusters-type characters did a poor debunking of the wind + rain theory. They had a 70mph fan set up but clearly failed to saturate the clay to the point of slipperiness required.

For the rocks to be blown, the clay would have to be dried to "leather hardness" as potters say, which it is out in Death Valley, and then suddenly flooded with a surfeit of water, which it is when it rains. This would create a thickish layer of "slip" (as potters call very watery clay-water mixture), over a very hard bed of dried clay. The debunkers merely sprayed the clay with spray bottles, dampening the surface. No where near enough "slip" was created. That there is plenty of "slip" out in the desert is in evidence from the dried banks of it on either side of the tracks behind the rocks.

 

[dhundsness]

What's the measured speed of these things? Surely someone has bothered to do some daily/weekly surveys.

 

[Ivan Seeking]

What's the measured speed of these things? Surely someone has bothered to do some daily/weekly surveys.

No one has ever witnessed the underlying process in action.

 

[Ivan Seeking]

I suspect that the reason the process has never been witnessed, may be that it only happens at times when conditions are so unfavorable that no one would be there.

 

[pallidin]

No one has ever witnessed the underlying process in action.

Exactly. Why is it that no-one has used our current technology to see this in action?
I find it unimaginable that a university grad has not tackled this.

 

[Ivan Seeking]

Exactly. Why is it that no-one has used our current technology to see this in action?
I find it unimaginable that a university grad has not tackled this.

It could easily be an undergrad project, for that matter.

Arguably, a UT Dallas chapter of the SPS solved the "Marfa Lights Mystery" in one evening.
http://www.spsnational.org/wormhole/utd_sps_report.pdf

 

[dhundsness]

Wind would cause objects to rotate or even tumble. These tracks are so remarkably linear, where the rock has clearly held a constant orientation. Some rocks appear to move sideways rather than lengh-wise, without rotating, which is not how wind would push something. Small lightweight rocks with high profiles don't appear to tumble. And rocks with low, flat profiles appear to move just as much as the bulkier rocks.

I cannot tell if these trails have a *starting* point, at least not from the photos. An event like a wind storm would create a trail from a starting point to an ending point. But if there are no starting points, that suggest a slow gradual process happening continuously, right under everyone's noses.

A few hundred bucks for a solar-powered gps tracker and weather station tacked to one of these things would get some real data.

 

[DaveC426913]

A few hundred bucks for a solar-powered gps tracker and weather station tacked to one of these things would get some real data.

Yeah, it's not quite as easy as you might think. Like other unexplained phenom, the targets don't tend to cooperate so much. When, where, etc. How many rocks can you afford to tag? Which on'es next most likely to go?" How many days, weeks, months do you trudge out to them to replace their batteries on the off-chance that one will cooperate?

 

[Ivan Seeking]

Yeah, it's not quite as easy as you might think. Like other unexplained phenom, the targets don't tend to cooperate so much. When, where, etc. How many rocks can you afford to tag? Which on'es next most likely to go?" How many days, weeks, months do you trudge out to them to replace their batteries on the off-chance that one will cooperate?

An interesting argument in defense of many unsupported claims, here we have a bunch of rocks sitting on a lake bed, and we know that they move, but after a century, no one has been able to catch them moving! Too funny!

A+, Dave, jolly good. I had never quite connected those dots before.

 

[DaveC426913]

A+, Dave, jolly good. I had never quite connected those dots before.

Oh dear, I just defended UFO sightings, didn't I? :blush:

 

[Ivan Seeking]

Oh dear, I just defended UFO sightings, didn't I? :blush:

Not pointing to anything in particular, but not knowing when something might happen, is sufficient to make verification difficult, even if we know where it will happen. I find that to be a highly salient point.

 

[susa]

Might there not be salts in the topsoil working as an agent for providing a sliding ground when hydrated through seasonal humidity fluctuations or even on a daily basis through night and early morning cooling? Such an environmental setting suggests at least some salt accumulation in the toplayer of the basin soils. Also many images show a clear prismatic structure with rounded tops that remind me to a tipical swelling and shrinking feature of Solonetz soils – although these latter are alkaline soils… May be spatially varying salt contents then even could explain (partly) track length and direction changes: where friction gets too strong, rocks might stop and eventually slightly rotate, and under different exposure to the winds move in a different direction.

I can’t imagine how the ice sheet mechanism should work. ?According to this idea where would this sheet form? Right on top of the surface? Wouldn’t the surface then still be too rough to provide for sliding? Also many images show that heavy rocks apparently sunk a little into a soft enough surface layer, leveling the surface in the track by beheading the rounded tops of prisms and creating small dikes on each track side.

 

[Pythagorean]

So... how do the tile domains form as the mud dries?

 

[Pythagorean]

Seems windish to me:

The prevailing winds that blow across Racetrack Playa travel from southwest to northeast. Most of the rock trails are parallel to this direction.

Nasa took some interns there this year:

They confirmed earlier observations that some of the big rocks have moved farther than the small ones.

And look!

Rilee later fed this information into a model that can be used to determine where on the playa a photo was taken even if no GPS coordinates were documented. Soon, any visitor to Racetrack Playa will be able to upload photos for analysis at www.racetrackplaya.org.

http://geology.com/articles/racetrack-playa-sliding-rocks.shtml
http://geology.com/nasa/racetrack-playa/

 

[pallidin]

So... how do the tile domains form as the mud dries?

Contraction perhaps?
I once owned some property that had a high clay content, and when it rained and then dried in hot weather, it developed numerous fissure cracks.
Not sure if that type of scenario is going on there though.

 

[susa]

Sorry, I´m not a native English speaker: ?what does tile domain mean? The more level or bowl shaped type of soil surface features?

1) What most Racetrack pictures show varies from a pronounced to a slightly domed surface of soil peds. This is a columnar structure mostly associated with sodic, very fine textured clay soils in arid to semiarid regions. It is not prismatic in soil science terms (as prismatic peds show a flat top) and usually they are subsurface features (but in the Racetrack case obviously there is no humus accumulation nor biological activity to form a topsoil). Yes, drying causes soil contraction and thereby cracking - but it needs many cycles of swelling and drying for a pronounced columnar structure to form. With each wetting, the soil doesn´t swell completely, so aggregates formed from former drying don´t get destroyed by wetting. On some tracks the surface seems quite homogenized by the sliding, and on some others the columnar structure seems to have reformed. May be these features could help in a rough relative dating of tracks?

I found a his English page that explains the formation of a columnar structure.
http://soils.missouri.edu/tutorial/page9.asp

2) I`ve also found another hint on a possible cause of direction changes. I´ll send the link later, but there´s a photo that shows well that the floor is not flat on a microrelief scale, because old tracks may act as barriers that force the moving rocks into another direction (if not forcing them to stop moving).

3) Large rocks may travel for larger distances than small ones because they offer more surface for the wind.

 

[susa]

This is the link to the microrelief image I referred to: see Photo 54 http://www.coleskingdom.com/photos/a...name=racetrack

 

[susa]

Sorry, have to correct or specify my words:
when I said "Might there not be salts in the topsoil working as an agent for providing a sliding ground when hydrated..." I did not mean something like a pure salt crust or concentration at the very surface, but salt in the clayely surface layer, so hidration might explain the very smearyness of the surface.

 

[nesp]

Sorry if this has been mentioned, but I thought this phenomenon was pretty well addressed by John Reid and a group of Hampshire College students in the mid 90s. They peformed on-site studies and experiments and concluded that the rocks were moved by wind-driven sheets of ice, confirming previous conjectures by Stanley. I read through their original paper, but can't locate it now, nor can I find the full text on the internet. Here is the reference:

Sliding rocks at the Racetrack, Death Valley: What makes them move?
Geology; September 1995; v. 23; no. 9; p. 819-822;
http://geology.geoscienceworld.org/cgi/content/abstract/23/9/819

A portion of the abstract:

As proposed by Stanley (1955), it seems that the rocks, resting on mud, were locked into a single floating ice sheet, in this case at least 850 X 500 m. Final resting places of these rocks are much more widely scattered than their starting points, suggesting that the sheet broke into smaller plates. Large ice sheets can move rocks even with light winds and may explain the gentle curvature of tracks hundreds of metres long, a pattern very unlikely with gusty high winds and no ice."

Again, sorry if this was previously brought up.

 

[susa]

Hi,
the ice sheet hypothesis (yes, as far as I remember, it has been mentioned on this forum several times and I think also a link to the authors) as I understand has been cuestioned as a mechanism, that´s also mentioned in the new article at
http://geology.com/articles/racetrac...ng-rocks.shtml
http://geology.com/nasa/racetrack-playa/

I didn´t understand, looking at the tracks, how this ice sheet explanation should work in practice, in relation to what can be seen on the surface of the playa. Anyway, ice is still part of other hypothesis as you may read in the article mentioned above, but I wonder : ? why is ice formation at all necessary to explain the whole thing, especially if in the same hypothesis mud also acts as a sliding ground? What function has the ice then? Is it necessary to get the rock started and then it slides on soft, may be very water saturated mud? Why wouldn´t the whole thing work, from the beginning to the end, through a watersaturated ground as a surface for sliding?

 

[susa]

As to the "regelation hypothesis" - another ice oriented one - mentioned in the article on
http://geology.com/articles/racetrac...ng-rocks.shtml
http://geology.com/nasa/racetrack-playa/

I´m not a physician to tell if this is possible, but I think of very high pressures (like happens under a glacier) to get ice molten by pressure. And then also, what gets and holds the movement of the rocks according to this hypothesis?
The suggested "bubble indicators" taken for this hypothesis may have an explanation that seems more straightforward to me : on sodic soils (like the external Solonchaks, that are sodic at the surface) bubbles may form at the surface through degassing of the mud, when a crust forms through drying of the peptised surface layer after a wetting event. The bowlshaped prints of these gas bubbles remain visible when this fine crust is detached through wind erosion. See also "vesicular crusts" or "vesicular horizons" (another mechanism of bubble formation in desert soils) on google.

 

[nesp]

why is ice formation at all necessary to explain the whole thing, especially if in the same hypothesis mud also acts as a sliding ground? What function has the ice then? Is it necessary to get the rock started and then it slides on soft, may be very water saturated mud? Why wouldn´t the whole thing work, from the beginning to the end, through a watersaturated ground as a surface for sliding?

Thanks for those more recent links. I had pretty much forgotten about this phenomenon after reading Reid's work but I see that it's still of interest, and is useful in teaching geophysical processes.

As far as the need for the ice, as the NASA study states, they performed water-absorption experiments and found that the clay got slippery, but concluded that most rocks needed other help. The problem with wet clay by itself is that, even though the coefficient of friction would be reduced, a heavy rock with compress it and the rock would likely settle into the mud, offsetting the reduction in friction. An ice layer would make a clay/water/ice mixture that would reduce friction while maintaining sufficient solidity. As you probably know, the slipperiest surface is not ice, but wet ice.

The hypothesis of semi-frozen wet clay and high winds seems to me to be testable. Place such a mixture in a wind tunnel, put a heavy Dolomite boulders on top, and crank up the wind speed until something moves. Try different mixtures and boulder size/shape/weight and compare the results with the Playa. Would be a good term project for a geophysics class.

 

[susa]

"As far as the need for the ice, as the NASA study states, they performed water-absorption experiments and found that the clay got slippery, but concluded that most rocks needed other help. The problem with wet clay by itself is that, even though the coefficient of friction would be reduced, a heavy rock with compress it and the rock would likely settle into the mud, offsetting the reduction in friction. An ice layer would make a clay/water/ice mixture that would reduce friction while maintaining sufficient solidity. As you probably know, the slipperiest surface is not ice, but wet ice.

The hypothesis of semi-frozen wet clay and high winds seems to me to be testable."

I don´t know what was the "water-absorption experiment" that tested if the soil "gets slippery": checking the soil material? Putting 100 l of water on a spot and looking what happens? It´s quite a common sense result that the soil material gets slippery. But you can´t test in the field (or at least not in that "field") what happens in a flashflood. `With " watersaturated ground" I don`t just mean that the soil material is somehow saturated, but that there is also nearly no infiltration of floodwater in the soil: a water film forms and gives the rock buoyant pressure from below (it does not sink a lot because it can´t), while at the same time the soil particles on top of the aggregates peptize and get slippery. Just because there are cracks seen from the top, it does not mean that these are profound. On some spots infillings of the cracks are even recognizable.

As far as I understand you suggest the possibility of a situation where a) the soil is very wet b) so that the top cm of the soil profile can become a semifrozen ice-soil mixture when it`s cold enough to freeze (semifrozen because then soil is still soft enough to get the furrows formed) and c) winds are present. ?What prevents the rock from sinking in this scenario? a) Compressed ice that gets fluid at the bottom of the rock (regelation-hypothesis?) ?What prevents the water then from infiltration? b) ?Permafrost? (yes, this is just a joke).

I hope somebody soon will take students for several two-week investigation camps out there when the combination of the specific conditions of all the hypothesis are potentially expected (not to forget snow melt peaks). Somewhere I read, that the same fenomenon is observable at some other playas near (?outside?) the Death Valley Park (hope to find that link...).

 

[nesp]

As far as I understand you suggest the possibility of a situation where a) the soil is very wet b) so that the top cm of the soil profile can become a semifrozen ice-soil mixture when it`s cold enough to freeze (semifrozen because then soil is still soft enough to get the furrows formed) and c) winds are present. ?What prevents the rock from sinking in this scenario? a) Compressed ice that gets fluid at the bottom of the rock (regelation-hypothesis?) ?What prevents the water then from infiltration? b) ?Permafrost? (yes, this is just a joke).

I'm not suggesting anything, just interpreting what the NASA students reported. According to their study, "...it's thought that collars of ice can form around the lower parts of the stones, probably because the mass of a rock retains the cold. When more water moves in, the collar helps the rock partially float, so even a heavy rock might slide when the wind blows. The presence of ice collars could explain why some trails start narrow and get wider: the rock gradually sinks into the wet clay as its icy lifejacket melts away."

However, I went back to some of Reid's observations, and he believes there are at least two mechanisms involved, and ice is only one of the possibilities. He also believed that thin mud on a firm substrate allowed some of the smoother rocks to skim with a much lower coefficient of friction.

I hope somebody soon will take students for several two-week investigation camps out there when the combination of the specific conditions of all the hypothesis are potentially expected (not to forget snow melt peaks). Somewhere I read, that the same fenomenon is observable at some other playas near (?outside?) the Death Valley Park (hope to find that link...).

Well, there's been at least two student expeditions out there, Reid's and NASA's. Not that other expeditions wouldn't be worthwile but the problem, as I understand it, is that this is a pretty rare phenomenon and no one has actually observed the rocks moving. That's why I suggested a test in a wind tunnel, doesn't have to be a full scale, expensive one. Could be a scaled down version, as is found in many aero labs. Even if that doesn't find the answer, it could put boundaries on what is or is not likely with wet clays, partially frozen wet clays, etc.

As far as other playas with similar phenomena, Reid refers to this paper in discussing rock trails in South Africa
Eriksson, P. G., Fortsch, E. B., Snyman, C. P., Lingenfelder, J. H., Beukes, B. E., and
Cloete, W., 1996, Wind-blown rocks and trails on a dry lake bed, an alternative
hypothesis: Journal of Sedimentary Research, v. 66, p. 36–38.

 

[susa]

http://www.ldeo.columbia.edu/~polissar/publications/Sharp_et_al_2006_Geology_sliding_rocks_of_death_valley_discussion_and_reply.pdf

 

[FlexGunship]

http://www.ldeo.columbia.edu/~polissar/publications/Sharp_et_al_2006_Geology_sliding_rocks_of_death_valley_discussion_and_reply.pdf

Interesting reading. This was one of my favorite mysteries for a long time. Glad to know it's been solved.

 

[WernerML]

..when I stumbled over this phenomen 2 days ago I wondered that obviously the impact of "clay swelling" is totally neglected.

It can be assumed that the clay/salt layers in the areas where the rock travel occurs have no consistent thickness; it looks plan on the surface, but can reach different meters into the ground. When it rains the water will generate a slippery surface, but most of the water will run into the crevices and cracks and will accumulate in deeper areas/layers creating inconsistent moisture pattern / gradients. Likely that the clay/salt texture at the surface stays firm enough to carry the weight of stones without letting them sink into the mud. Now, when the water is absorbed by this clay/salt mixture in deeper layers, these layers will expand lifting anything what is on the surface. A small slope caused by such a local lift of only a few centimetres will let the rocks slide on the slippery, but still firm surface. Due to dynamic processes (rain patterns, crevices / cracks close and open, different thickness of layers, impacts of the lifts .… etc.) the “local lifts” can happen anywhere at any time facilitating any directions the rock can travel.

“Swelling clay” can cause severe issues for tunnels (there are cases where tunnels collapsed due to the pressure local areas with the right clay blend generated) and tailings / tailing dams (for tailing dams the impacts could be positive, e.g. dewatering effects, and negative, e.g. wasting of storage volume).

The right clay/salt mixture can facilitate a volume variation (dry vs. saturated) by factor 1.3! that can result in enormous high temporarily pressures definitely strong enough to lift big rocks. This can also be linked to osmotic pressures that can build up if the clay/salt blend has the right texture (think about ceramic membranes for RO plants where a relative high osmotic pressure is utilized for desalination). It is also likely that the clay/salt ratio or the clay composition varies locally which even would increase local lifting effects in combination with variations in the moisture gradients and the different thickness of layers.

The surface (with small variations in heights) that can be seen on sites where the rock movements occur is only a snapshot: over a longer period with rain and dry seasons it will likely looks more like “rolling waves” of an ocean due to temporarily local expansions and shrinking (….an expansion factor 1.3 can achieve a distinct local lifting!). The pictures I could study so far in the internet also indicate that the movements only happen when the surface is wet (hence slippery): the tracks (from the “bow wave” ) behind the rocks seemed to be generated when the surface was wet and then dried out. If the rock would have been traveled on a dry surface it can be assumed that the wind would have destroyed a track made from lose dry clay dust. So the major driver behind the movement will be rain water which will accumulate temporarily in particular areas (due to cracks) of layers and will cause local swelling and lifting.

http://en.wikipedia.org/wiki/Sailing_stones : while the wikipedia article also focuses more on wind and icy surface layers as the culprits, in a way it also gives hints (like the other sources) that winter rains and the clay composition (feldspar rich syenite?) will play a major part. Local, temporarily lifting generating slopes due to local clay swelling in winter month in combination with an icy, slippery surface layer and strong winds seems to be a reasonable explanation…..strong winds will be supportive, but I don’t think that the wind could be strong enough to move the stones without the impact of gravity / slopes.

 

[runner_one]

I posted the photos here last year of my trip to the racetrack. I am staying in Las Vegas now, and plan to make another trip to the racetrack at some point in the near future.
I was wondering if anyone who has posted here was going to be in this area in the next couple of months and would like to make the trip out to there with me? I have no set date or time for the trip, so I have a open schedule. In lieu of actually going out there with me does anyone have any suggestions or requests of specific data or photos I should concentrate on?
At some point I must return to Tennessee but hopefully I can make it back out to the racetrack before I do.

 

[godscountry]

http://geomaps.wr.usgs.gov/parks/deva/racetrack.pdf

[link updated] 6/20/09

I say a little moisture,freezing temps,a little ice forms,the rocks slide,maybe ?I haven't studied the area,just a good guess.

 

[pumila]

Anyone looked at dreikanters / ventifacts? These are wind-blown stone which can look similar to the pic in the wiki article. They are four sided, with surfaces etched into them and polished by windblown sand. If the mass of the stone is changed enough by the etching they will turn over and present a new face to the wind. If this was happening with sailing stones that would explain why they can suddenly change direction or stop.

Also, if motion occurs only during sandstorms (inevitable on windy days in desert) then a) most likely observers would be in shelter, and b) large movements would occur as a single event rather than be built up over a period, since it takes more energy to start the slide than to continue it.

 

[woco]

Is there any seismic activity in the area? If you take a hard bound book and place a pebble on it, shake it back and forth, the pebble will migrate across the surface. If the ground was semi frozen at the time, I would imagine that these boulders could move quite easily.

 

[CGOLDING]

This has already been tested as I have seen a documentary on it. The conclusion was that the mountains caused a temperature difference between the surface where the rocks are and the surrounding area, this created a strong wind that was channeled into the rocks. Moisture from rainfall makes it possible for the rocks to be pushed by the wind. If you look at the path each rock takes they are all in a similar direction which indicates a force acting on each rock from the same direction which is what a wind would do.

 

[billiards]

A new paper claims to have finally solved this one:

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0105948See also, blog: http://blogs.discovermagazine.com/d...valleys-sailing-stones-revealed/#.U_8GeShhraq

and university press release: https://scripps.ucsd.edu/news/myste...st-time?hash=3f42fa4a60340630b1fde436c4f177fe

https://www.youtube.com/watch?v=watch?feature=player_detailpage&v=uyHcs7B27Zk

 

[Evo]

Very cool! Thanks billiards!

 

[davenn]

^^ what Evo said ^^

 

[AlephZero]

The video is wrong about this being "the most boring experiment ever". Two years wait is nothing compared with http://www.bbc.co.uk/news/science-environment-28402709

Prof Mainstone, however, never saw the pitch in motion. In 1979, the sixth drop went on a weekend. In 1988,
with the experiment proudly displayed at Brisbane's World Expo, Prof Mainstone was fetching a drink when the seventh drop fell. By 2000, a video camera had been set up to capture drop number eight, but it malfunctioned at the crucial moment.

When the ninth drop fell in April this year it was watched by three webcams and thousands of online enthusiasts - but not by Prof Mainstone, who died eight months earlier at the age of 78.

 

[Ivan Seeking]

A new paper claims to have finally solved this one:

Finally! It only took about 100 years. :) Until now the explanations involved far too much arm waving. But this one seems to be definitive. Thanks for the post.

 

[Astronuc]

The story was covered on NPR.

http://www.npr.org/2014/08/28/343681708/an-icy-solution-to-the-mystery-of-the-slithering-stones