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

[Hunter]

On rare occasions this area is flooded with a few inches of water. Also at times the temperature falls below freezing. When this is combined with wind a sheet of ice gripping the rock will break loose and drag the rock with it. Ice melts water evaporates and the word is puzzled! Walla! I Love it.

[Guest]

I think this is the correct version of that USGS link:

http://geomaps.wr.usgs.gov/parks/deva/ftrac1.html

[bystander]

I think this is the correct version of that USGS link:

http://geomaps.wr.usgs.gov/parks/deva/ftrac1.html

Thanks

[Boomer12k]

Why don't they just post someone out there for more than a day, and do the observations?

[BMAONE23]

Sounds like a job for the MythBusters.
Take a Sound Stage wind generator out to the Playa and some water.
Set several stones similar to the moving stones in a test area. wet the area and turn on the giant fan. See if the combo works

[Beyond]

I like that racetrack video. It reminds me of the Gumby cartoons.

[neptunium]

I wonder why so many peole get hyped whenever an APOD is not about astronomy. Just give it a rest-we need a break once in a while!

But this big rock being pushed by the wind is quite a mystery to me. That's something you don't hear about every day! A rock like this that slides in the mud.

This is also the first time I've seen Death Valley. Looks interesting.

[ken8paul]

Look to the right of the rock, I see foot prints. Looks like the work of big-foot or the crop circle people.

[Walter Clark]

There's a bigger mystery nobody has addressed. After millions of years of this, why aren't all the rocks blown over to one side or the other. It's similar to the mystery of sand dunes. Why in geological time don't they all blow to one side trapped against a mountain.

[Bob-O-Rama]

I was under the impression that this has been explained recently by observing that the lake bed floods, then freezes. The next day as additional melt / rain water arrives, this lifts the ice, with the rocks frozen in them. These floes move around under the influence of the winds or the water, dragging the rocks with them. Once the ice melts, nobody is the wiser.

[neufer]

There's a bigger mystery nobody has addressed. After millions of years of this, why aren't all the rocks blown over to one side or the other. It's similar to the mystery of sand dunes. Why in geological time don't they all blow to one side trapped against a mountain.

Strong winds are not always in the same direction.

[abellg]

"Not scientifically puzzling..." "a mundane solution..."

Your descriptions seem to be getting a bit loose. I'm surprised to hear that offering a hypothesis without confirming data is sufficient to answer a scientific question. To quote the last line of Paul Messina's 1998 dissertation: "However, until researchers actually observe the rocks in action, the cause still remains controversial."

[Mactavish]

Leprechauns!

[stowaway]

I like the Bigfoot playing shuffleboard hypothesis.

[TXGunGeek]

Look up Weird or What TV show on Discovery. We had them in the wind tunnel at work and ran different sized rocks on playa like base material under normal dry wet and freezing conditions and got trails behind the large rocks as they moved under wind power across recently frozen and now thawing ground. Nothing really new here as past research has pretty much shown what causes this.

[Scabulus]

Everybody, go to Google Maps, select the satellite view, enter "racetrack playa," and hit return. You'll see that the racetrack is about 2 miles N-S and roughly 1 mile E-W. At the southern end, there is a little point in the shape of the playa. The eastern edge of that point has a half-circle scribed out by a hillside. It looks dark in the satellite image. It is dark. The northernmost point of that half circle hillside is the primary source of the rocks. Take a careful look too at the south eastern portion of the playa, it looks like a bay. Well come back to that.

Water is 784 times more dense than air. Aerodynamic/fluid-dynamic force is proportional to the density times the velocity of the fluid squared, so water moving at 3 mph will exert the same force as air moving at 84 mph. But our rocks are on a surface, so the water displaced by the rock provides buoyancy. Having handled the rocks on the hillside (and set them back), I can tell you they are not especially dense. They are denser than water, but not by much. Having surfed on a rocky shoreline in big waves, my feet can attest to how well water can thrown around good sized dense rocks.

I've worked beside the Muroc and Rosamond dry lake beds for over a decade. They're not always dry. Water can get blown from one side to the other and stay concentrated there for as long as the wind keeps blowing that direction. That can be weeks or more. In 2005, Rosamond lakebed had a few inches of water, and the wind kept blowing it against Rosamond Blvd. Little 2-3" high waves kept pummeling the shoreline. It eroded the shoreline up to the road over the course of several weeks. I also saw easterly winds blow water completely across Muroc Dry lakebed. Westerly winds had blown the water to the eastern shore. I didn't even know it was there. A strong easterly wind came up and was blowing dust everywhere off the lakebed when I came to work. A little later, the dust stopped, but not the wind. I looked out and water had come completely across the lakebed and dampened everything that had been producing dust.

Pacific storms that come out of the west drop their rain on the western slopes of the mountain ranges, and are dry over the California High Deserts. Storms that slowly come out of the SSW will drop the most rain in the deserts because they miss most of the mountain ranges. Those southerly winds will also blow the water dropped on the playa to the northern portion of the lake. If you get a few storms in a row that follow that pattern, as we did in 2005, a lot of water falls in the desert and on the playa. Then, when a storm with strong winds comes through, even if it doesn't have rain, it will further concentrate the water at the northern portion of the playa. When the front passes through, the winds will turn to the northwest. What may only be an inch or few deep of water will get concentrated against the south eastern shoreline when the high winds blows it there. It will have velocity. It will have depth. It will get turned by the topography to where it will come across the northern tip of that half-circle hillside. The velocity of the water combined with the buoyancy provide by the depth will easily move the rocks to the west. Remember, it will start out only an inch or so deep, but it covers a square mile or more. When it gets pushed across to the eastern edge of the lakebed, it will get much deeper. The topography will likely turn the surface winds some too further accelerate the water.

Once at the southern end of the playa, the waves from the wind blowing on the water will push the smaller rocks around because they have a greater percentage of their volume submerged than the bigger rocks. The waves may only be an inch high in two or three inches of water, but a couple will hit a rock every second. That'll be about 170,000 waves hitting a rock in a day. The buoyancy component is why the smaller rocks will cross the paths of the bigger rocks. As the winds change direction, so does the movement of the rocks. Rock can even loop across their own paths as the winds change direction around the compass headings. Throw in some wind blown ice on top of the water, and it is even easier to move the rocks. That explains how that big rock got moved at the northern part of the playa - go there and you'll know what I'm talking about.

IF IT WAS ONLY WIND MOVING THE ROCKS, THEY WOULD ALL MOVE IN UNISON ALL THE TIME.

I have a great panoramic picture taken from the hillside looking across the playa. It shows a whole bunch of rocks with parallel tracks to the west that start not far from the bottom of the hillside, and you can see the south eastern bay in the distance too. I either don't have the knack of how to use this forum or I don't have privilege yet to attach it to this discussion. I wish you could see it. It was taken in the spring of 2005 after a very wet year. We went to Death Valley to see and take pictures of the wildflowers, and we also drove the the Racetrack Playa. I laughed my backside off when I saw what was going on. However, I hadn't though about the ice.

[attachment=0]Screen shot 2012-02-23 at 6.43.03 PM.jpg[/attachment]

[rstevenson]

That's a convincing explanation. However, my own experience with both lake and ocean beaches strongly suggests that waves in shallow water inevitably produce ripples in the sand. So I have to ask, where are the ripples? Also, such wave movement should mostly obliterate the tracks themselves, yet the tracks are sharp and obvious, and there are no ripples. Is there something peculiar about the sand and mud of that area which prevents the creation of ripples while ensuring the tracks remain clearly visible? (Obviously there is, but what?)

Rob

[lakeside]

Hi All:

How is it that the obvious is overlooked. Death valley is a wet place some of the time. Those rocks are moved by water in sheet flow mode during flash floods. This explains the smooth curved paths. Water in sheet flow moves in long curves as for example waves traveling slowly across flat beaches. This also explains parallel paths. Wind blown material would produce irregular paths. Furthermore immersion in water unweights the rocks so that a rock with a density of 2.7 has an effective density of 1.7 immersed in water. In addition deeper water flows faster and faster at the surface too than at depth, explaining how larger rocks can move farther because they are acted on by faster moving water near the surface. The reason some paths have no associated stones is that someone picked them up for souvenirs or class specimens. The reason no one has seen this happen is that it happens underwater during flash floods when people are busy trying not to get drowned. Come on all, why the mystery and mythologies, why spend public funds on something so obvious.


d.

[BMAONE23]

Hi All:

How is it that the obvious is overlooked. Death valley is a wet place some of the time. Those rocks are moved by water in sheet flow mode during flash floods. This explains the smooth curved paths. Water in sheet flow moves in long curves as for example waves traveling slowly across flat beaches. This also explains parallel paths. Wind blown material would produce irregular paths. Furthermore immersion in water unweights the rocks so that a rock with a density of 2.7 has an effective density of 1.7 immersed in water. In addition deeper water flows faster and faster at the surface too than at depth, explaining how larger rocks can move farther because they are acted on by faster moving water near the surface. The reason some paths have no associated stones is that someone picked them up for souvenirs or class specimens. The reason no one has seen this happen is that it happens underwater during flash floods when people are busy trying not to get drowned. Come on all, why the mystery and mythologies, why spend public funds on something so obvious.


d.

How is it that the "Flood waters" can move the much heavier rocks causing them to leave tracks and not obliterate the tracks themselves which are made up of what would then be easier to move disturbed silty mud. It is my experience that material with the viscosity of silty Mud tends to flatten out when submerged and not leave ridged trails.

[lakeside]

Hi All:

Well, I do like the windblown water or windblown ice-floating-on-water explanation too. There is more than one way to move those rocks. I had no first hand experience with wind blown water! I am sure we now have the question answered.

As to erasing the clay ridges, the floating ice explanation helps solve that, however,there may be more to it. The clay may be swelling bentonite that has unexpectedly slippery but tough properties when wetted this way.

[astro_buff]

lolz they had this same apod in 2002 search death valley in the archive

[bystander]

If you had read the previous posts, you might not have even needed to do the search.