by Scabulus » Fri Feb 24, 2012 4:25 am
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.
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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.
[size=85][attachment=0]Screen shot 2012-02-23 at 6.43.03 PM.jpg[/attachment][/size]