The Sliding Rock Phenomenon

Ivan Seeking

Two random photos selected

Phrak

I'll bet we're not going to get better close-ups than those. #1 is the best of the two. I'd like to get in real close and look evidence of water softening on the edges of the cracked clay.

Either way it could be inconclusive, unless one could tell the difference between water softening and wind errosion without experimentation. Who wants to grab and test some samples?

OAQfirst

It's 1,600 × 1,067 pixels at Wikipedia.
http://upload.wikimedia.org/wikipedi...ate_Scott).jpg

Phrak

Thanks, OAQ. But still not enough to reveal the shapes of the pieces of the ridges of earth left behind --though the visible ridge is certainly not a monolithic trail of solidified mud.

Ivan Seeking

Here is a paper from the folks at Cal Tech
http://www.jstor.org/pss/30068068

pallidin

This is just a thought, but I think I might know what's happening here.

First, lets examine this statement from http://geology.com/articles/racetrac...ng-rocks.shtml
----------------------------

The climate in this area is arid. It rains just a couple of inches per year. However, when it rains, the steep mountains which surround Racetrack Playa produce a large amount of runoff that converts the playa floor into a broad shallow lake. When wet, the surface of the playa is transformed into a very soft and very slippery mud.

----------------------------

Now, and here is what I believe might be the key: The surface prior to water saturation is cracked. Relatively deep cracks and many of them.

When water falls on top, air is trapped in the cracks. During contraction of those cracks by virtue of the water, this scenario would likely cause the formation of massive amounts of tiny, practically imperceivable bubbles rising to the surface and underneath any large rock.

Then, with this bubbling "cushion", other external forces moves the rock.

Anyway, that's my hypothesis.

Phrak

But what is the coefficient of friction of a rock on tiled clay surface, lubricated by a layer of mud?

pallidin

Phrak, I understand what you are saying. Which is why it's so puzzling.
However, let's consider the following(these are my presumptions, not saying that they are correct):

1) There is a presumption that this phenomenon is not a "prank"

2) There is a further presumption that this phenomenon is specific to that location, specific to the geology and topology of that location, and specific to the unique, sometimes transient extreme environmental conditions at that location.

So, my summary presumption is that the phenomenon is real, but that the natural mechanism behind it is based on complex factors which must come together in some unique way to achieve this.

As such, when addressing issues such as the coefficient of friction, I am looking at what complex natural forces might play a role.
Thus my hypothesis that trapped air/rising bubbles from the cracked surface during a rainstorm might be a key contributing factor mitigating friction.

Even still, it's just my thoughts.

Ivan Seeking

I think the notion of a prank was ruled out about fifty years ago. IIRC, the phenomenon has been noted for about a century now. Also, we are talking about death valley, which is remote, desolate, and where it was about 120 degrees yesterday, as is usually the case.

Back when this was first discovered, which is cited as being around the turn of the century, Death Valley was about as remote of a place as one could find.

pallidin

OK, that was my presumption. What about my hypothesis??

Ivan Seeking

The bubbles? It sounds to me like a reasonable idea, but I'm not a geologist. I can certainly imagine that something like you suggest might be possible at least in principle.

Ever played air hockey?

pallidin

Exactly, that's what I'm getting at.


Edit: Sorry for all the edits... late night.

runner_one

Hello all, I'm new here and thought I might jump in here and let you all know I visited the racetrack this week and have some good photos of the stones and trails. If anyone is interested here is a link to them (no ads) http://www.coleskingdom.com/photos/a...name=racetrack I will upload more later.

Ivan Seeking

Cool! Was this trip motivated by casual or professional interests?

Were you left with any particular impressions wrt the mechanism?

runner_one

More Casual, although I have been fascinated by the racetrack ever since I first learned of it years ago. This was my fist visit there and we spent the night. The road there seems designed to destroy any vehicle short of a ATV, I suspect the park service keeps it that way to deter more visitors who might damage or move the rocks. as for the rocks themselves, I came away more perplexed than ever, although the wind is thought by most to be the prime mover I found some problems with this theory first look at this rock http://runner.coleskingdom.com/pics/...e/Dsci0123.jpg It appears to have dug up the dirt in front of it as it moved. 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.) an how do you explain these that move in perfect formation, http://runner.coleskingdom.com/pics/...e/100_4086.jpg All in all it was a fascinating trip.

Ivan Seeking

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?

runner_one

There seems to be no rhyme or reason to the depth of the tracks. for example this rock http://runner.coleskingdom.com/pics/...e/100_4132.jpg
which was one of the largest, has the most shallow track while this much smaller rock http://runner.coleskingdom.com/pics/...e/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