Sunday Science: Sailing Stones Solved?

I love mysteries. I also love wild landscapes. Rocks? Not so much.

I may have just offended a small part of my audience; sorry to all the geologists out there. Let me cut to the chase: out in the barren expanse of California’s Death Valley, there exists a decades-old mystery. It’s the mystery of the sailing stones. How can rocks move across a featureless, flat landscape, leaving distinct furrows in their wake? What, or who, is pushing them along?

A sizeable sailing stone, with a characteristic track. Image: JMP, Flickr.

The rocks range in size from small to several kilos. The tracks are sometimes dead straight, other times curved or zig-zagged. A trail may weave past other nearby rocks which have apparently remained stationary.

The unique conditions of Death Valley are incredible in themselves. It almost never rains, so the barren flatland (called Racetrack Playa, after the ‘racing’ stones) is only disturbed by wind and occasional snowmelt from the surrounding mountains.

When the stones were discovered, they were a baffling phenomenon. Efforts were made to work out how the trails were made. No-one ever witnessed a rock moving, but a tagging program confirmed that the rocks were indeed shifting about the place. Some rocks shifted regularly; others with trails never budged again.

A number of possible explanations have been advanced. The Playa is so flat that the strong winds are felt even very close to ground level. It’s possible that a massive gust of wind could get a stone moving. Once the stone is moving, it could be dragged along by the wind for a distance before it comes to rest again.

Another explanation is that of ice sheets on the Playa. When snow melts in the surrounding mountains, water flows over the flat Playa in a thin sheet. The temperature drops sharply overnight, forming a sheet of ice. When the ice starts to melt the next day, it breaks up into thin, flat ice floes, which may be driven across the surface by the howling wind.

That makes sense, but how does this move the rocks? The idea is that they become embedded in the ice sheets. It’s quite easy for a whole ice sheet, with just the base of a rock sticking down into the dirt, to move around in a high wind or if the water underneath it is moving. The rock, trapped in the sheet, digs a furrow which remains after the water evaporates.

One of the most perplexing things about the sailing stones is their ability to move in different directions. The ice-sheet hypothesis can explain that quite easily; if there is an ice sheet breaking up into bits, and the bits move around, it’s simple to picture them bumping into each other or otherwise changing direction before they melt. This also helps to explain why some stones will move and others nearby may not.

Despite reasonable evidence that this takes place, it still hasn’t been directly observed. There’s something romantic about the Sailing Stones, that in one of the most barren and inhospitable places on the Earth’s surface, natural conditions bring inanimate rocks to life and give them stories, history and trails of their own.

 

The Milky Way Galaxy, captured beyond a natural mystery. Click to see it large; it’s amazing! Image: Wikimedia Commons.
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Categories: Puzzles, Science | Tags: , | 24 Comments

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24 thoughts on “Sunday Science: Sailing Stones Solved?

  1. Oh dave. You and your crazy rocks. It was the Giant Spag. Monster with his noodely appendage that moved them. Its simple really.

  2. M@

    Groovy baby

  3. That is awesome. My family travels all through the California desert . . I wonder if they have heard of these Sailing Stones. Cool. :)

  4. sailing stones … how many stories can you write about them, don´t you think? I found them poetical …

  5. Amazing – and a great explanation. You couldn’t make it up.

  6. Henk

    Despite the fact that “it never rains in California” water is the main agent in sculpting the landscape. The trails can only be caused when the lake is soft and muddy. At Lake Frome, a normally dry salt lake , in South Australia I have seen the water move from one sie of the lake to the other over a 24 hour period( ~30 km).Actually I didn’t see it I came back the next day and there it was!

    • That must have been quite a sight. I’ve not had the chance to see any of the salt lakes with water – even the lakes I’ve visited in Queensland were bone dry! I guess they’re not at the moment.

  7. Chris

    Where do you find those little gems? That was really interesting. Has anyone considered human intervention for prank purposes for the rock movement?

  8. Chris

    On second thoughts, that would leave way too much evidence, wouldn’t it? I wish I had second thoughts before posting my first ones!

    • I think it was considered, yes. Death Valley’s so inhospitable that there wasn’t much incentive for year-round on site monitoring! However you’re right, it would probably leave too much evidence.

  9. This is such an interesting mystery! I’d heard about them on a National Geographic podcast a couple of years back. Thanks for the update.

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  11. Solved? That’s a stretch. But I too think that rocks embedded in ice makes the most sense. When I was last there – late October, 2010, it certainly was cold enough to freeze. The clay soil also doesn’t absorb water very fast so it’s not unreasonable to have snowmelt or rain pool and freeze.

    Prank: yes, it’s also possible. But a lot of trouble to go through in such a remote place. Giant Spag is possible :-)

    • Yes, solved is a big word to use, but that’s why I did the cover-my-ass trick of putting a question mark on it. I think as a prank it’s too difficult, pointless and spans over a very long time – I wonder how long they were doing it before it got noticed!

      I think your last hypothesis is the most plausible. The trails are left by His Noodly Appendage!

      • Oklahoma J. Hill

        And that there track looks like it’s perhaps slidding “through” mudd. I have yet to see frozen mud that was wet “soft” enough to leave a trail through or on Ice.
        Ya’ll are very gullable out there. No hone has shown me anything indicating these rocks or anyother rocks can trail frozen… and the basin is as level as anything. across 2 mi span only off by 1.7″ (inches). The forse of ice pushing it would also bog it down and force gravety to take over. Like when your car gets stuck in the yard in the middle of the winters freezes. Come On Ya’ll, Think for yourselves and not let Big Brother your freedom to think outside the Box…

    • Jordan

      No, it doesnt make any sense at all. Didn’t you know that some of the stones had actually turned around and kept moving after that. This fact makes your hypothesis impossible. If the base of the rock is stuck in the ice layer and the rock turns around it shouldnt be possible for the rock to keep moving.

      • Oklahoma J. Hill

        The ice would not allow the rocks to slide nor move unless the rock was aplied to the surface only after the ice had developed, Other wise it would be the ground and rock frozen together, thus as if aplying a disc brake.
        Other wise these rocks would be more common in other places that may have a simular basin, Like 2 miles further up the ridge. and why are there no scientist exploring. Hell, We are on mars and everywhere else. and the data is so sparse on the subject. You may get a knock on the door from the “Men In Black”.

  12. That would be crime to have them removed! In any case, the waters have strange ways to have their work done, but that makes it all even better,

  13. Smith

    Likely uneven heating. Ice forms on one side of the stone, (in the shadow?) and expands applying pressure and pushes the stone a bit at the base. If this happens every day, the stone could move bit by bit with the right weather conditions. Frost heave is a powerful force that can lift cement posts so by not stones?

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  15. Anonymous

    That is not the reason at all and it’s too easy to explain if that were the case and it would have never been amaizing or a wonder. If that were the case it would happen all over. Keep guessing. I will tell you later.

    EWR

  16. Interesting hypothesis, but how would a large thin sheet of ice flat on the ground get pushed along by the wind? I could understand it if there was a sail attached…
    Back to the drawing board.

  17. Anthony Solberg

    I have a theory that might explain this, I am working on proving it but I would need an overhead map of the stones movement paths to know if I am right. I have been looking for one but so far have found nothing. any help would be appreciated.

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