Death Valley's sliding rocks may actually hitch a ride on ice rafts

June 16, 2011 5:23 PM

The sliding rocks of Racetrack Playa in Death Valley, California have mystified and delighted visitors for decades (previously). Now planetary scientist Ralph Lorenz and colleagues think they've figured out how the rocks get around: ice rafts float the rocks out of the mud, reducing friction enough that modest winds can push them along (PDF of Lorenz et al., American Journal of Physics, Vol. 79, 1 January 2011).

Ralph Lorenz spends most of his time studying Saturn's moon Titan and often looks to Earth's geology for clues. Racetrack Playa's surface resembles a dry lakebed on Titan, so it's easy to see how Lorenz and his colleagues got interested in the mysterious sliding rocks. (To date nobody has actually seen the rocks in motion, since they only move every few years for a few seconds at a time.)

Don't miss the low-tech experiment in the AJP article - in addition to theoretical calculations the authors provide experimental evidence in support of their theory using a small rock, a Tupperware container of water, a baking sheet filled with sand, and a home freezer (p 39 - 40). High school science fair project, anyone?

posted by Quietgal (25 comments total)

That is not as cool as my explanation. My explanation involved faeries.
posted by TwelveTwo at 5:29 PM on June 16, 2011 [2 favorites]

Or at least wizards.
posted by thsmchnekllsfascists at 5:30 PM on June 16, 2011

My explanation involved faeries.

The Faeries are all pretty busy keeping their lives going at Short Mountain, Zuni Mountain, Wolf Creek, Blue Heron Farm, and other sanctuaries around the country. I seriously doubt they are going to leave behind their gardens and such just to go to Death Valley and push around some rocks.

Still, they might. They're into that kind of trickery when it fucks with the straights.
posted by hippybear at 5:34 PM on June 16, 2011 [5 favorites]

"Racetrack Playa" is the name of my new hip-hop gambler's oh never mind.
posted by Decani at 5:36 PM on June 16, 2011 [3 favorites]

I really, really love the little home-brew experiment. So cute!
posted by poe at 6:35 PM on June 16, 2011 [1 favorite]

sitzmark!
posted by toodleydoodley at 6:40 PM on June 16, 2011 [1 favorite]

That is not as cool as my explanation.

Don't hate the Playa
posted by East Manitoba Regional Junior Kabaddi Champion '94 at 6:47 PM on June 16, 2011 [1 favorite]

Previously, where I totally made the playa hater joke already.
posted by Horace Rumpole at 6:51 PM on June 16, 2011

To date nobody has actually seen the rocks in motion, since they only move every few years for a few seconds at a time.

What they could do to confirm this if they had a great grant writer to write an amazing proposal for many thousands of dollars:

1) Train a set of (fancy, heat-resistant, camouflaged or theft-resistant) cameras on the rocks and hook them up to a remote computer. Hit record.

2) Get someone to write a program to break up each day's video into 5-minute segments and upload them to a robust server.

3) Have someone write another program that uses the Amazon Mechanical Turk API to post each segment of video automatically as a templated HIT, 288 times a day.

4) Pay the good people of Amazon Mechanical Turk cents on the dollar to watch each 5-minute segment and note whether they see rock movement, so as to narrow down which time periods have potential rock movement. (And it has to be cents, or you're going to be paying upwards of $300 per day or $100,000 per year for this; a good figure might be between 10 cents and 20 cents per segment, depending on how much grant money you have. Obviously you'll get more interest from Turkers by offering higher figures, so it's a tradeoff.)

5) Depending on how many segments with potential movement this yields, determine next steps to further narrow the video range, whether that involves rinse/repeat on MTurk with smaller segments or getting student volunteers or what have you.

6) Probably other things I haven't considered.
posted by limeonaire at 6:55 PM on June 16, 2011 [1 favorite]

I was wondering whether, if the wind suddenly and sharply blew hard enough, the Bernoulli effect reduction in pressure at the surface could cause enough air to come up out of the soil to make the playa very briefly like an air hockey table, and the rocks like pucks that would then move almost frictionlessly in the wind.
posted by jamjam at 7:04 PM on June 16, 2011 [1 favorite]

4) Pay the good people of Amazon Mechanical Turk cents on the dollar to watch each 5-minute segment and note whether they see rock movement, so as to narrow down which time periods have potential rock movement.

You wouldn't actually have to do this. There are many commercially available webcam applications that automatically detect movement in the frame. You can even define the exact area or size of movement for use in stuff like home security cameras so the cat won't trigger it, but a human will.

Beyond vandalism or theft the hardest part would be getting a camera and a computer to survive an entire year in the middle of Death Valley, which wouldn't be that difficult, really. It would just be expensive.
posted by loquacious at 7:27 PM on June 16, 2011 [2 favorites]

The Racetrack rocks are pretty cool (for lack of a more esoteric description). There's this "What the fuck?"ness about them. The ground is like a piece of marble with a very thing veneer of velvet- it gives the *tiniest* bit at first, and then no more. Looking at the rocks, and the tracks they leave, you wonder how long they've been at this schtick.

(of course, the smoothness of the ground might be an illusion - perhaps it's just smooth when compared to the tooth-loosening washboards of the 30 mile road out there...)
posted by notsnot at 7:52 PM on June 16, 2011 [3 favorites]

Is anyone else a little sad when mysteries get solved?
posted by doublehappy at 8:30 PM on June 16, 2011 [2 favorites]

Also, I'm always excited by low-tech $5 experiments proving potentially complicated theories. But when you consider that nature can do it without spending a cent it's not all that impressive.
posted by doublehappy at 8:36 PM on June 16, 2011

Is anyone else a little sad when mysteries get solved?

Nopes. Mysteries are not an endangered species. The more we know, the more we know what we don't know.
posted by b1tr0t at 8:44 PM on June 16, 2011 [3 favorites]

Beyond vandalism or theft the hardest part would be getting a camera and a computer to survive an entire year in the middle of Death Valley, which wouldn't be that difficult, really. It would just be expensive.

Well, and you could probably lower your costs even more (and make the data more readily/easily/quickly available) by getting a camera and a satellite uplink to survive an entire year in the middle of Death Valley, rather than a camera and a computer.
posted by limeonaire at 9:08 PM on June 16, 2011

Mysteries are not an endangered species. The more we know, the more we know what we don't know.

So, they are like Shmoo?
posted by TwelveTwo at 9:20 PM on June 16, 2011

The sailing stones on the racetrack are great. The ice raft theory has been "floated" before (har HAR!), neat to see some new thoughts about it. Thanks for posting this article!
posted by LobsterMitten at 10:55 PM on June 16, 2011

ROCKS GOT ICE SKATES!
posted by KingEdRa at 11:23 PM on June 16, 2011 [1 favorite]

Wouldn't it be cheaperto just pay an old hermit to sit out there and watch the rocks? Out even more cheaply, grad students- that's what they're for, after all.
posted by happyroach at 12:23 AM on June 17, 2011 [1 favorite]

When Mother Nature plays curling...
posted by Skeptic at 1:25 AM on June 17, 2011

Mysteries are not an endangered species. The more we know, the more we know what we don't know.

So, they are like Shmoo?

Schmoo? Man, that's *gasp!* (shudder) reaching back a long ways, innit?
posted by Herodios at 5:31 AM on June 17, 2011

a camera and a satellite uplink

Nah. You need a camera and some bright lights pointing at a nearby rock. Put a box over the camera to keep it clean until needed. Use a thin wire to tether the rock to a nearby stake. When the rock pulls the wire taut, the camera pops out of the box, turns on the lights, and takes some pictures. Besides triggering the camera, the wire also keeps the rock from zipping out of the frame.

This is just your basic Santa Claus trap. Digital camera, some solar cells, rechargeable batteries, some bright LEDs, etc. You could probably assemble a dozen units for a few thousand dollars.
posted by ryanrs at 7:05 AM on June 17, 2011 [3 favorites]

Add a winch if you want to see what's under the rock.
posted by ryanrs at 7:06 AM on June 17, 2011

Metafilter: Just your basic Santa Claus trap
posted by toodleydoodley at 7:54 AM on June 17, 2011 [1 favorite]