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posted by n1 on Thursday August 28 2014, @05:13PM   Printer-friendly
from the patents-for-procedurally-generated-asset-movement dept.

An article published in plosone.org finally solves the mystery of sailing stones. Rocks from the size of pebbles to boulders that move and inscribe long tracks along a smooth valley floor without human or animal intervention, most notable on Racetrack Playa. TFA has some nice pictures documenting the movements.

Essentially, this happens when there's enough water to cover the playa, but not enough to submerge the rocks. At night time, the water freezes and the next day it may melt sufficiently to create ice sheets floating on a shallow pool. Even light wind are able to move these ice-sheets which, even when they break around large rocks, exercise enough pressure to move them.

Related Stories

Death Valley's Moving Stones Caught on Camera 10 comments

A few days back we reported the phenomenon of the Moving Stones found in several locations around the world including, most famously, Death Valley. Community member evilviper and an Anonymous Coward update us with reports that they have now been filmed:

Remember those stones in death valley which leaves mysterious tracks across the desert floor? Turns out they've been caught in the act and the process responsible for it is liquid water and thin sheets of ice.

Geologists have been studying the moving rocks since 1948, when the first scientific study suggested they were driven by dust devils. Theories over the decades have included sporadic hurricane-force winds when the surface is covered with rain water, or rocks carried across the mud by small rafts of ice, or UFOs. But until the Norrises had an incredible stroke of luck that day last December, no one had scientifically verified the phenomenon.

http://www.thestar.com.my/Lifestyle/Features/2014/09/03/Solved-The-riddle-of-the-rolling-rocks/

https://en.wikipedia.org/wiki/Sailing_stones

http://arstechnica.com/science/2014/09/death-valleys-famous-moving-stones-caught-in-the-act/

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  • (Score: 3, Funny) by Anonymous Coward on Thursday August 28 2014, @05:56PM

    by Anonymous Coward on Thursday August 28 2014, @05:56PM (#86839)

    What's behind the secret of moving rocks in a place named after its murderous heat? Ice!

    • (Score: 2) by TK on Thursday August 28 2014, @06:04PM

      by TK (2760) on Thursday August 28 2014, @06:04PM (#86843)

      I guess it makes sense that no one had thought of it before.

      --
      The fleas have smaller fleas, upon their backs to bite them, and those fleas have lesser fleas, and so ad infinitum
      • (Score: 2, Informative) by aclarke on Thursday August 28 2014, @06:07PM

        by aclarke (2049) on Thursday August 28 2014, @06:07PM (#86846) Homepage

        Actually the theory has involved ice since the '50s if not earlier. Most of the theories involved thicker sheets of ice. This discovery is interesting as I believe it's the first time that the rocks have been documented actually moving, and it involved 3-5mm ice sheets, much thinner than most people had conjectured.

        • (Score: 2) by edIII on Thursday August 28 2014, @07:03PM

          by edIII (791) on Thursday August 28 2014, @07:03PM (#86864)

          I can't believe it myself. Something else is going on too. Probably fairies.

          5mm?

          These are *large* rocks. Some sources say up to 18 inches, but other sources say up to 700lbs (Karen) [smithsonianmag.com].

          Just how big does this 5mm sheet of ice need to be to move 700lbs? Even with very significant drops in friction, the rock itself has no reduction in friction (my reading of the article) initially. At 700lbs just how much ice could have formed a small layer under the rock to help? I have to believe that most of the rock is contact with the dirt and clay underneath. That, and it does leave trails. If they moved *and* left no trails we could be really talking about something.

          I think there is a pretty rough start with 700lbs. Once going the friction would be reduced. Even assuming that they are equal, a 5mm ice sheet equal to 700lbs would be 24ftx1ft (if my math is right - 57.41lbs per cubic foot of ice, convert cubic foot to cubic mm, reduce height).

          It needs to be larger than that to get over inertia (correct me if I am wrong), but I don't know how to calculate what that is. Not sure that a 5mm sheet of ice has the structural integrity to allow 100% of its momentum to be transferred into the rock either. Only way I know of to increase structural integrity is the height.

          So it doesn't sound like an adequate explanation to deserve the word "solved", as it explains much smaller rocks and not the largest ones. I want to see timelapse on Karen moving with 5mm sheets hitting her. Reading TFA it doesn't look like they studied the mammoth rocks, but only the small ones.

          P.S - If anyone out there really well versed in physics could tell me if I'm wrong or not, I would appreciate it. I'll admit I'm puzzled :)

          --
          Technically, lunchtime is at any moment. It's just a wave function.
          • (Score: 0) by Anonymous Coward on Thursday August 28 2014, @07:28PM

            by Anonymous Coward on Thursday August 28 2014, @07:28PM (#86884)

            Hmm it is an interesting theory. With testable items.

            I think it would depend heavily on how flat the bottom of the rock is and what is the viscosity of the clay/salt/sand when it is wet and almost frozen and under pressure from the rock.

            Also it could break up the ice as it moves and a new bit of ice is pushing on it and then it refreezes on the other side as it melts on top of the rock.

            To really test it you should see grooves even if tiny on the sides of the rocks from where the ice is grinding against it.

            A good test would be to create artificial rocks of various shapes sizes and weight and texture. Then put a high res time lapse camera aimed at it.

            5mm is a decent thickness too. About 2 quarters stacked on top of each other. Also the rock is not perfectly smooth so it could have a decent amount of surface area to 'grip' onto the ice as it would be frozen in place if the ice didnt break up. If that were the case it may be enough for the ice sheet to actually lift the rock a mm or two and let water under it?

            All conjecture but very testable.

          • (Score: 3, Informative) by c0lo on Thursday August 28 2014, @09:36PM

            by c0lo (156) on Thursday August 28 2014, @09:36PM (#86925) Journal
            From FTA:

            Additional calculations for rocks of various sizes and sail heights showed that most rocks would move across a wetted playa surface where the coefficient of static friction is about 0.15 ...

            --
            https://www.youtube.com/watch?v=aoFiw2jMy-0
          • (Score: 2) by FatPhil on Thursday August 28 2014, @11:02PM

            by FatPhil (863) <{pc-soylent} {at} {asdf.fi}> on Thursday August 28 2014, @11:02PM (#86964) Homepage
            If the sheet of ice has got enough grip on the rock, then, when the water is melting and flowing, the conditions where the rocks are presumed to be moving, then perhaps the underswell of water could lift the rocks, thus decreasing the frictional reaction to their weight. I agree that this does not scale well with size. I wonder what is the largest boulder is that can sail this way?

            Vids or it didn't happen.
            --
            Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
          • (Score: 1) by Joe Desertrat on Friday August 29 2014, @05:00PM

            by Joe Desertrat (2454) on Friday August 29 2014, @05:00PM (#87283)

            I don't know about the physics of it but the Racetrack Valley can be subject to some ferocious hurricane force winds, particularly in winter storms. I was there on a fairly mild day and the wind was strong enough to allow me to scramble up a nearly vertical rock face (had it stopped while I was on the way up it would have been interesting). The lake bed, when wet, becomes a slick gumbo that would cause very little friction. My belief was always that when conditions were right for the rocks to move it wasn't very safe or comfortable conditions for observation.

    • (Score: 3, Funny) by ngarrang on Thursday August 28 2014, @06:17PM

      by ngarrang (896) on Thursday August 28 2014, @06:17PM (#86849) Journal

      Despite the video evidence to the contrary, I still think the are moved by small winged faeries that are engaging in a game of curling. Badly.

    • (Score: 1) by dpp on Thursday August 28 2014, @11:01PM

      by dpp (3579) on Thursday August 28 2014, @11:01PM (#86962)

      Sure, but some had already theorized that the aliens were using ice to move the rocks.

  • (Score: 4, Funny) by E_NOENT on Thursday August 28 2014, @06:22PM

    by E_NOENT (630) on Thursday August 28 2014, @06:22PM (#86851) Journal

    ...don't hate the playa, hate the game.

    --
    I'm not in the business... I *am* the business.
  • (Score: 2) by Dunbal on Thursday August 28 2014, @08:38PM

    by Dunbal (3515) on Thursday August 28 2014, @08:38PM (#86907)

    Glaciation, in a desert. Who'da thunk it.