APOD: A Sailing Stone in Death Valley (2012 Feb 22)

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APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by APOD Robot » Wed Feb 22, 2012 5:06 am

Image A Sailing Stone in Death Valley

Explanation: How did this big rock end up on this strange terrain? One of the more unusual places here on Earth occurs inside Death Valley, California, USA. There a dried lakebed named Racetrack Playa exists that is almost perfectly flat, with the odd exception of some very large stones, one of which is pictured above. Now the flatness and texture of large playa like Racetrack are fascinating but not scientifically puzzling -- they are caused by mud flowing, drying, and cracking after a heavy rain. Only recently, however, has a viable scientific hypothesis been given to explain how 300-kilogram sailing stones ended up near the middle of such a large flat surface. Unfortunately, as frequently happens in science, a seemingly surreal problem ends up having a relatively mundane solution. It turns out that high winds after a rain can push even heavy rocks across a temporarily slick lakebed.

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Barry

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by Barry » Wed Feb 22, 2012 5:38 am

That don't look like a 'very large rock' to me. Looks more like a Mayan stela or something else along that line.

dennis93555

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by dennis93555 » Wed Feb 22, 2012 7:11 am

I don't agree with the mud flowing part of the description. I live near Death Valley and to playas similar to the Race Track. The playa gets covered with water when it rains and then wets the lake bed silt and makes it slick and sort of muddy. Then as it dries out the geometric shapes form on the surface as shown.

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by MSP1 » Wed Feb 22, 2012 7:57 am

We seem to be moving towards TPOD (Terrestrial Picture of the Day) again. What exactly does this picture have to do with Astronomy?

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by nstahl » Wed Feb 22, 2012 8:36 am

Imagine the uproar if this phenomenon had been seen first, say, on Mars. Rocks that move from one month to the next! Must be critters moving them! Now the excitement would be that it had been wet enough for it to happen (or some other means of slickness).

romanian marsrock

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by romanian marsrock » Wed Feb 22, 2012 8:55 am

the difference between a theory and a hypothesis is that the theory has been verified/proven experimentally, whereas the hypothesis is not verified, it is more like an idea or opinion; it is of course significant that the "viable" "scientific" hypothesis leads us to error 404;
now, if winds are strong enough to push around 300kg rocks, they should have pushed smaller pebbles around as well, right? but only large rocks seem to be pushed around there, isn't that funny;
about what would be the friction resistance for a 300kg rock on wet and on dry flat ground as in the image, and what would be the required windspeed, at which atmospheric pressure, to push it around? are such winds present in that area? would the winds from Neptune suffice?
note that trying to push something around on mud may cause it to dig into the mud;
keep in mind that on mars, the atmospheric pressure is 6 millibars (compared to 1000 millibars at sealevel on earth) so it would take far more wind to push a rock around there, even at the lower .38G gravity;
there is a similar viable scientific hypothesis saying how egyptians poured water on the sand, to get the 2.5 ton rocks to slide easier, but no one has actually tried to see if that works, and no one explains how they lifted the 80 ton granite slabs 50 meters above ground in the center of the pyramid...

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by bystander » Wed Feb 22, 2012 8:57 am

The Mysterious Roving Rocks of Racetrack Playa
http://asterisk.apod.com/viewtopic.php?t=20631
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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by 500pesos » Wed Feb 22, 2012 9:49 am

When I first saw the photo, I thought the large stone would turn out to be a meteorite or something, but no.
Ok, it's a regular stone on a muddy field. Has anyone actually seen it slide when it rains?

Browndog

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by Browndog » Wed Feb 22, 2012 11:13 am

If it is caused by wind over time. How come the track is so neatly curved. Surely with the wind blowing in different directions over the many rain events the path would be varied.

-Browndog

Plant Biology

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by Plant Biology » Wed Feb 22, 2012 11:39 am

It seems that the "viable scientific hypothesis" leads to a 404. Oh well, can happen to even the best hypotheses =)

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by Indigo_Sunrise » Wed Feb 22, 2012 12:07 pm

So I watched the link that is supposed to show the rocks actually moving in the playa, but all it shows is the water slowly moving across the valley floor. There is one part at about 41 sec's, that shows a decent sized rock, and I thought, 'good, now we'll see something exciting!', but the camera operator continues to pan to the left, and no rocks are shown actually moving..... :(

And is the image for today one of those 600+ lb rocks? It looks a bit small without something to show the scale.

Interesting, but I wish there was a bit more.

:-|


ETA:
I did find this link, that states:
Not only [do] the stones move, but they move in completely different directions. Two stones could start next to one another, and start moving at approximately the same speed, but one will suddenly stop or change directions. Sometimes the sailing stones will turn around completely, moving back towards their point of origin. The tracks left behind are generally no wider that 30 cm, and less than 2.5cm deep. The longest tracks have been forming for numerous years, though to date, nobody has ever witnessed the event.


I'd really like to see one of those BIG rocks and the 'racetrack' it might create.......

:shock:
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Strangerbarry

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by Strangerbarry » Wed Feb 22, 2012 1:21 pm

This would have been a great picture for Geography Picture of the Day

Guest

Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by Guest » Wed Feb 22, 2012 1:46 pm

note that trying to push something around on mud may cause it to dig into the mud;
I agree with that, more so, the object will tend to roll and not slide.

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by orin stepanek » Wed Feb 22, 2012 2:12 pm

What will they think of next: a racetrack for rocks! Of all things. :idea: :D :mrgreen: :wink:
Orin

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by solserenade » Wed Feb 22, 2012 3:46 pm

:P
in small print: Cropped from photo - a 3 wheeled forklift with a flat tire.

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by TNT » Wed Feb 22, 2012 4:07 pm

It's amazing how strong winds must blow to move a big rock like that, even if the ground is muddy!
The following statement is true.
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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by neufer » Wed Feb 22, 2012 4:16 pm

Indigo_Sunrise wrote:
I'd really like to see one of those BIG rocks and the 'racetrack' it might create.......
bystander wrote: The Mysterious Roving Rocks of Racetrack Playa
NASA GFSC LPSA | 11 Aug 2010
In a particularly parched region of an extraordinary planet, rocks big and small glide across a mirror-flat landscape, leaving behind a tangle of trails. Some rocks travel in pairs, their two tracks so perfectly in synch along straight stretches and around curves that they seem to be made by a car. Others go freewheeling, wandering back and forth alone and sometimes traveling the length of several football fields. In many cases, the trails lead right to resting rocks, but in others, the joyriders have vanished.

This may sound like an alien world, but it's actually Racetrack Playa in Death Valley, Calif. Since the 1940s, researchers have documented trails here and on several other playas in California and Nevada. Seventeen undergraduate and graduate students from the Lunar and Planetary Sciences Academy (LPSA) at NASA's Goddard Space Flight Center in Greenbelt, Md., traveled to the Racetrack and nearby Bonnie Claire playas this summer to investigate how these rocks move across the nearly empty flats.

Some rocks are thought to have moved nearly as fast as a person walks. But nobody has actually seen a rock in motion, and scientists haven't deduced exactly how it happens. The easy explanations—assistance from animals, gravity, or earthquakes—were quickly ruled out, leaving room for plenty of study and irresistible speculation over the years.
...
Sporting sunhats and carrying lots of water, the students arrived around 7 a.m. for their day of data collecting. They broke into five teams, each led by a Goddard scientist, and took out their maps. Then they packed their equipment and headed in different directions in search of rocks and trails. ...

For each rock and trail, the students recorded GPS coordinates and snapped photos. They dug up small sensors called Hygrochrons that had been buried (with the required permission of the National Park Service) three months earlier by Gunther Kletetschka, one of the trip leaders. The interns captured the electronically stored temperature and humidity data. They marked the trail boundaries by slipping colored pushpins into cracks in the clay and measured each track's length, depth, and width. They confirmed earlier observations that some of the big rocks have moved farther than the small ones.

The interns also found small mounds at the ends of some trails. People speculate these were formed when the rocks ploughed into the clay and came to rest. Quite puzzling were the mounds at the ends of trails that had no rocks.

The students checked for unusual or changing magnetic fields. (Nope, no evidence of that.) One student conducted radiation measurements. (Nothing strange there, either.) They pulled out small levels to determine if the rocks might be moving along trails tilted ever-so-slightly downhill. Instead, "the general trend is that they move uphill," as reported by Andrew Ryan of Slippery Rock University in Slippery Rock, Penn., in a talk that the LPSA group gave later at Goddard. "But the slope is so insignificant that we don't think it would influence this movement."

Two interns, Kynan Rilee from Princeton University in Princeton, N.J, and Gregory Romine, a graduate student at San Francisco State University, got the special assignment of photographing the playa's skyline and correlating these pictures with GPS coordinates. Rilee later fed this information into a model that can be used to determine where on the playa a photo was taken even if no GPS coordinates were documented. Soon, any visitor to Racetrack Playa will be able to upload photos for analysis at http://www.racetrackplaya.org.
...
For a while, speculation was that the Racetrack Playa rocks have properties that help them move. But the rocks are just dark dolomite boulders that tumbled down from the mountain highlands. (That's not how the trails were made; those came after the rocks found a home on the playa.) "Dolomite is relatively common, and the rocks themselves are not unusual," explains Jackson. "It's where the rocks are located that makes them special."

Some of the rocks that have moved weigh less than a pound, but many are 25–30 pounds. One of the largest sliders, named Karen, has been estimated at 700 pounds. A powerful force is required to move rocks that big, and the obvious candidate is the fierce playa wind. "It's surprising when you see how big some of these boulders are," says Ryan. "You think, 'How can something that big get blown around?'"

Wind speeds of 150 miles per hour or more would probably be necessary to move most of the rocks. The wind speeds that graze the playa's surface are very fast, but not that fast, so the newer studies tend to ask how the friction between the rocks and the clay might be reduced.

The interns evaluated several hypotheses that have been offered over the years. ...

Investigators have thought for years that the friction is somewhat reduced when the playa's surface gets wet and the top layer of clay transforms into a slick film of mud. Algae may lie dormant in the dry clay and bloom when the surface wets, further reducing the amount of friction. The students performed water-absorption experiments at Bonnie Claire Playa and found that the clay does get slippery. Even so, the students concluded that most rocks could not move without other help.

The aid probably comes in the form of ice—in this high desert, winter brings snow to the mountains. The meltwater washes downhill and collects in huge, shallow pools that spread across the playa and freeze at night. Decades ago, researchers proposed that big sheets of ice might envelop clusters of rocks, then catch the wind and drag the rocks around together. This might explain the cases in which two tracks run perfectly alongside each other.

When an experiment ruled out the possibility that this happens in all cases, the concept was refined. Now it's thought that collars of ice can form around the lower parts of the stones, probably because the mass of a rock retains the cold. When more water moves in, the collar helps the rock partially float, so even a heavy rock might slide when the wind blows. The presence of ice collars could explain why some trails start narrow and get wider: the rock gradually sinks into the wet clay as its icy lifejacket melts away.
...
Kletetschka is coordinating a research paper by the group that will present Hygrochron and other data and will suggest a slightly different mechanism for the rock movement. The rocks are still thought to be collared by ice, but the group has identified a new parameter that is critical in explaining why it is so easy to move the rocks and create trails. The paper will give the details, but the finding means that the wind speed doesn't have to be as great to move the rocks. "This idea would also explain the trails that don't have rocks," Kletetschka says. "The trails were made by rocks whose larger parts were made from ice."
APOD: A Dark Sky Over Death Valley (2008 Jul 13) | http://asterisk.apod.com/viewtopic.php?t=14297
APOD: A Dark Sky Over Death Valley (2007 May 08) | http://asterisk.apod.com/viewtopic.php?t=11432
APOD: Unusual Rocks in Death Valley (2002 Apr 10)
Art Neuendorffer

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by BMAONE23 » Wed Feb 22, 2012 6:04 pm

It would seem to me that Rain "Soaking" the area sufficient to cause a surface slick enough to allow the rocks to "Sail" would obliterate the prior trails and leave the surface as cracked as and looking similar to the trackless areas.

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by kroosing 37 to 42 » Wed Feb 22, 2012 6:19 pm

nstahl wrote:Imagine the uproar if this phenomenon had been seen first, say, on Mars. Rocks that move from one month to the next! Must be critters moving them! Now the excitement would be that it had been wet enough for it to happen (or some other means of slickness).
I was thinking the same - but about the form. You'd never convince these guys that this was not some kind of engine if it was on a Moon or Mars photo! So funny...

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by stowaway » Wed Feb 22, 2012 6:55 pm

My first question was; What does this have to do with Astronomy? Then I remembered that Human Speculation is greater than the known universe.

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by alphachapmtl » Wed Feb 22, 2012 8:06 pm

Strangerbarry wrote:This would have been a great picture for Geography Picture of the Day
http://photography.nationalgeographic.c ... f-the-day/

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Earth is a planet. (Re: APOD: A Sailing Stone in Death Valle

Post by Anthony Barreiro » Wed Feb 22, 2012 8:08 pm

Thanks Neufer for the article about the ice collar hypothesis. As to the question "what does this have to do with astronomy?", well, Earth is a planet, orbiting a star, in a galaxy ... . And if it's so hard to figure out some things here on Earth, where we can walk up to rocks and poke them with sticks and more sophisticated tools, how much more impressive is it to be able to figure out the geology (areology?) of Mars, or to deduce the composition of planets orbiting stars hundreds of light years away, or the composition of stars in other galaxies ... . But don't listen to me. I'm mostly here for the pretty pictures and the sense of wonder.
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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by alphachapmtl » Wed Feb 22, 2012 8:12 pm

kind of a crop circle with no crop

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by alphachapmtl » Wed Feb 22, 2012 8:16 pm

Interesting reference here:
The Sliding Rocks of Racetrack Playa, Death Valley National Park, California: Physical and Spatial Influences on Surface Processes
A dissertation submitted to the Graduate Faculty in Earth and Environmental Sciences
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy, the City University of New York
by PAULA MESSINA ©1998 All Rights Reserved
http://geosun.sjsu.edu/paula/rtp/disser ... title.html

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Re: APOD: A Sailing Stone in Death Valley (2012 Feb 22)

Post by ChumbleSpuzz » Wed Feb 22, 2012 8:19 pm

Never really liked the high winds explanation. Brian Dunning, of Skeptoid, suggests it may be caused by a flowing layer of moving ice patches. The water from a rain freezes and high winds push the ice around, taking the stones for a ride. This sounds much more plausible.
http://skeptoid.com/episodes/4021