Sliding Rocks Bemuse Scientists

An anonymous reader writes "Scientists can't figure out why these rocks — weighing up to several hundred pounds each — slide across a dry lake bed. The leading theory proposes that wind moves the rocks after a rain when the lake bed consists of soft and very slippery mud.

Comments

Mark Newman Poster

[stoolpigeon]

Mark Newman has a very nice sliding rock poster with a good shot of rock and trail in a variety of sizes.

Re:Mark Newman Poster

[An ominous Cow art]

I was there in August this year, and it was quite windy. It's very easy to imagine that if the ground had been muddy, the wind could slide the rocks around.

Re:Mark Newman Poster

[Linux_Bastard]

What is happening there is that the cohesive water is acting as a flexible seal around the bottom of your glass, and it is resting on a cushion of trapped air.

When the glass is put down, if the water seal forms before the glass has fully contacted the surface, the air pressure will lift the glass as it evens out the pressure on the air cushion. This will cause it to be riding on an air bearing, and slide very easily.

Usually it will only go until the water seal is broken, releasing the air pressure that forms the cushion. If the surface is moist enough, the cohesive water can renew the seal as it glides.

If you try this with a very flat, nearly level surface and a glass with a concave bottom you can get good results.
Hot liquids can actually expand the air under them and suddenly lift up and slide.

Re:Amazing how no-one bothers to actually CHECK.

[DigitalCrackPipe]

In true /. form, you either failed to RTFA or to WTFV, as the video clearly does not show the rocks moving. It shows water and miscelaneous floating scum moving, and posits the same theories as in the article (just claiming them to have been proven).

And as to the foolishly simple explanation, H.L. Mekcken is quoted to have said, "Every complex problem has a solution that is simple, direct, plausible, and wrong".

Re:It's a Horta!

[vought]

Given the hottest temperature ever recorded in the United States is 56.7 degrees celsius (134.1 degrees fahrenheit) I find it impossible to believe this small part of America regularly gets temperatures of above 65.6 degrees celsius (150F). A friendly nitpick: surface temperatures on the desert floor - even on light-colored surfaces like the Racetrack - can often rise above 200 degrees F. Note that the ambient temperature may be far cooler than the ground surface.

From a dependable source:

In the heat of summer, Death Valley roasts in temperatures greater than 120 degrees, cool when compared with the surface temperature of the salt pan. "The ground temperature gets to over 200 degrees [f] at some points here," says Dr. Douglas. I'd wager that the surface temperatures at the Racetrack in early afternoon during high summer range above the boiling point of water at sea level*, since the racetrack's playa is lower and darker than the salt pan at Badwater. In other words, don't fall; you'll skin and burn your knees.

If you've never been to Death Valley in the summer, you should give it a try. If you're from a mild climate, I suggest March instead; the regular 90 degree temperatures before April has shown it's face will give you a little idea of the radical heat that this region experiences.

*The Racetrack and Badwater are both below sea level, so you'd need to get up to at least 240f to boil water.