
Scientist Figures Out How 'Sailing Stones' Move Themselves Across Death Valley - sethbannon
http://www.core77.com/blog/transportation/scientist_figures_out_how_those_big-ass_sailing_stones_move_themselves_across_death_valley_25038.asp
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ghshephard
It's a good theory, and not the first time that ice has been proposed as
playing the major role at the Racetrack Playa. I have a friend who is obsessed
with taking photographs of these, and it was about five years ago that I first
heard the ice theory (and about these wacky furrows in the Playa) - I'm sure
people have had ideas like this for even longer.

I think it's a stretch to say that this has been "Figured Out" \- I'll give
that credit to the first person who records an observation of them moving.

Until then - just more theories.

[Edit - I like this 10+ year old theory, which suggests it's actually a case
of moving ice sheets, with rocks embedded in them, that actually causes the
furrows.
[http://skeptoid.com/episodes/4021](http://skeptoid.com/episodes/4021)]

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Luyt
There exist a Skeptoid episode about this:
[http://skeptoid.com/episodes/4021](http://skeptoid.com/episodes/4021) , the
'Living Stones of Death Valley':

 _" When we reached the lake, we found to our great surprise that the entire
lake was moving with the wind, at a speed we estimated at about one half of a
mile per hour. The sun was on the lake by now and we could see a few very thin
ice sheets that were now dissolving back into water. This whole procession was
washing past many of the famous rocks. It's easy to imagine that if it were
only few degrees colder when we were there — as it probably had been a couple
of hours earlier — the whole surface would be great sheets of thin ice. Solid
ice, moving with the surface of the lake and with the inertia of a whole
surrounding ice sheet, would have no trouble pushing a rock along the slick
muddy floor. Certainly a lot more horsepower than wind alone, as has been
proposed. The wind was gusty and moved around some, and since the surface is
not perfectly flat and with rocks and various obstructions, the water didn't
flow straight; rather it swapped around as it moved generally forward. Ice
sheets driven by the water would move in the same way, accounting for the
turns and curves found in many of the rock trails."_

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6d0debc071
> And if you're wondering why they don't just strap a GoPro camera onto a rock
> to see what's going on, scientists returning to the site over the years have
> calculated that the rocks move for short periods of time, just once every
> three years. That's a bit longer than your battery's likely to last.

Stick a solar panel on it to charge it up then. Christ >_<

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charonn0
It is, after all, rather sunny in Death Valley.

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thufry
Cameras are so cheap these days. Why doesn't he set up a camera continuously
recording for the next 5 years until he catches a glimpse of it moving?

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jlgreco
Hell, can't they just get some grad students to camp out there for a few
months with a motion detector and a siren? It would hardly be the _most_
boring job ever given to grad students.. This really doesn't seem like the
sort of thing that should go unobserved for so long.

I suppose I should be glad that this isn't as bad as the pitch drop.

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kbenson
Because during part of the year it's actually a shallow lake, and the rocks
only move one year in three, which is a fairly low chance of it happening.

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asynchronous13
Like gp said, perfect for a grad student!

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dougk16
The small-scale proof-of-concept mentioned seems a little flawed to me...the
surface area => volume ratio of a small rock can't be compared to a boulder.
The ice collar formed inside a tupperware container is also very idealized
compared to the ice layer that would form in nature. I guess if the ice collar
were thick enough, maybe it's possible, but that's quite an ice build-up you
would need. It doesn't seem too hard to get a large-scale experiment going to
confirm some of this...Myth Busters needs to get on this.

Until then, my theory is that this phenomenon is brought to you by the same
kind of people that make crop circles :P

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Pherdnut
If they only move a little bit in just the right conditions during the winter,
why do they maintain course for so long before making sharp turn and then
maintaining that course for a long period of time? Wouldn't the wind have to
be mostly blowing in the right direction for years during the winters and then
suddenly start mostly blowing in another direction for years? Or is it maybe
some subtlety in terrain variation that determines where they'll move?

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Buttons840
> Lorenz realized that as moisture levels changed with the seasons, a collar
> of ice could form around the rock. With the rest of the lakebed covered in a
> thin, cold-but-not-frozen sheet of water, this ice collar would enable the
> rock it encased to float—slightly.

So "ice collars" are responsible for moving 700 pound rocks on a "thin sheet
of water"; and all this in the hottest and driest place in America? I must be
missing something....

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dredmorbius
The Racetrack is a dry lake bed. Which is to say, it's a lake but the water
level is (usually) below ground level. Often only just. Along some parts of
the road running along the edge of The Racetrack is a trench and there's often
water visible in this, 6-12" below the lakebed level.

Moreover, the playa is at 3700 feet. The desert floor itself gets cold enough
in the winter time, and the extra elevation only excacerbates this: adibiatic
lapse accounts for about 3.5F cooling per 1000 feet, so Racetrack Playa would
be 13F cooler than sea level.

Deserts, despite their reputation as hot places (and yes, Death Valley and the
Racetrack can be quite hot in the summer months) are largely characterized by
their _exposure_. Which means they can get quite cold in wintertime.

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Turing_Machine
Many deserts can get quite cold at night, even in the summer time.

No cloud cover, low humidity -> the heat just radiates off into space.

The Romans supposedly used to make ice in the Middle East and North Africa by
digging a deep pit and insulating it with straw. They'd open it up at night
and cover it back up during the day.

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teeja
Maybe. 700-pound rocks 'floated' by ice, though? I'm inclined to think about
ice build-up on the ground on the windward side. Note the pancake-sized
hillocks with valleys between that can fill with water. When it freezes, the
rock lifts. Hmmm. Anyhow, the interaction with that 'special' surface is more
complex than just 'sand'.

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morpher
Interesting. The original Am. J. Phys. paper[1] is from 2011.

[1]
[http://ajp.aapt.org.offcampus.lib.washington.edu/resource/1/...](http://ajp.aapt.org.offcampus.lib.washington.edu/resource/1/ajpias/v79/i1/p37_s1)

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ghshephard
"The resource you requested requires you to log in with your UW NetID and
password"

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mdturnerphys
[http://ajp.aapt.org/resource/1/ajpias/v79/i1/p37_s1](http://ajp.aapt.org/resource/1/ajpias/v79/i1/p37_s1)

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Zarathust
So you create a doughnut of ice around the base of a rock. The base of the
rock has friction reduced by the area of the doughnut while slightly scraping
the bottom sand. How high does this layer of frost get?

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Jabbles
Ice blown by wind can be dangerous:

[https://www.youtube.com/watch?v=rjWq-
bwhgZA&noredirect=1](https://www.youtube.com/watch?v=rjWq-bwhgZA&noredirect=1)

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thehme
Nice summary of theory. I hope we can get this on video soon.

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monsterix
And I am thinking can this table top experiment be used in _Earth Moving_
tech? There is a lot of rock to be moved both in construction and road-
building industry.

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reeses
Or aliens.

