[meteorite-list] OT (Sorta...) Why Are Death Valley's Rocks Moving Themselves?

From: Todd Smith <lubbinv_at_meteoritecentral.com>
Date: Fri, 18 Feb 2011 20:25:46 -0600
Message-ID: <18B8C322-EA16-4F81-B8B2-1DECB153A3E5_at_gmail.com>

On Feb 18, 2011, at 7:24 PM, Michael Groetz <mpg4444 at gmail.com> wrote:

> Interesting photo- wish I could crawl out of my chair in Ohio and
> go check those rocks out.
> I know this has been discussed on the list before.
> Have a good night.
> Mike
>
> http://www.foxnews.com/scitech/2011/02/18/death-valleys-rocks-moving-racetrack-playa/
>
> Why Are Death Valley's Rocks Moving Themselves?
>
> By Philip Schewe
>
> Published February 18, 2011 | Inside Science News Service
>
> Death Valley National Park contains many mysteries, including one of
> nature's strangest phenomena: rocks that seem to move around all on
> their own.
>
> In the remote, almost totally dry lakebed called Racetrack Playa, some
> of the rocks move themselves across the desert floor when people
> aren't watching.
>
> Scientists know the rocks move because they leave narrow tracks
> trailing behind them, but they haven't actually seen it happen. And
> although one can't entirely rule out the possibility of some prank
> being played, at least some of the rocks appear to be moving under
> natural circumstances.
>
> It doesn't rain often in Racetrack Playa, and when it does the lakebed
> can flood. The rocks don't float exactly, but the main explanation for
> their movement is that moisture can make the mud on which the rocks
> sit more slick, making it easier for high winds to push the rocks
> along. Another explanation offered is that the temporary deposit of
> water, chilled to form extensive sheets of ice, might help to reflect
> and focus the winds, making it easier for the rocks to move.
>
> The winds required to move rocks in this way would seem to be at the
> level of 100 mph or more. That's why the rocks are sometimes referred
> to as "sailing stones." They are rare but they have been noticed in
> Racetrack Playa and a few other arid places around the world subject
> to occasional floods
>
> Ralph Lorenz, a scientist at Johns Hopkins University, offers a new
> explanation. The rocks are actually lifted up by the ice, or at least
> made more buoyant by the ice, making it easier for the rocks to
> migrate. If the rocks are moving about on ice rafts, the ground below
> cannot offer as much resistance against their motion and the winds
> needed for movement wouldn't have to be as great, he argued.
>
> So why hasn't the motion been observed?
>
> "Movement happens for only tens of seconds, at intervals spaced
> typically by several years," said Lorenz. "This would demand
> exceptional patience as well as luck."
>
> So, the rocks are probably traveling on the coldest and windiest days
> that occur over a period of several years. The most likely time would
> be in the very early dawn. Little wonder no one is around to witness
> the event.
>
> Lorenz and his colleagues would like to install inexpensive time-lapse
> monitoring of the Playa area, using digital cameras. The lakebed is
> about 2.5 miles long and 1.25 miles wide. They have also performed
> some laboratory tests by blowing on ice-assisted rocks. These simple
> tests support the ice-raft hypothesis. The results appear in the
> January 2011 issue of the American Journal of Physics.
>
> An additional reason for studying the rocks of Racetrack Playa is that
> its qualities resemble those at a drying-up lake on Saturn's moon
> Titan. Pictures taken by the Cassini-Huygens mission reveal what look
> like river channels, cobblestones, and lake beds or mud flats. Only at
> Titan's "Ontario Lacus," as one interesting site is called, the runoff
> consists of liquid hydrocarbons, not water. Some pictures even seem to
> be showing a "bathtub ring" left by what is probably a drying lake.
>
> One of Lorenz's colleagues, Brian K. Jackson, who works at NASA's
> Goddard Space Flight Center, also likes the idea that their research
> at Racetrack Playa has a dual purpose.
>
> "It's been exciting trying to solve a mystery that has resisted
> solution for sixty years," Jackson said. "Scientific accounts of the
> Racetrack Playa rocks go back to at least 1948, and there were
> certainly stories about the playa long before that.
>
> And Jackson also believes discoveries in Death Valley, here on Earth,
> will help us to better understand similar real estate on Titan or
> Mars.
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Received on Fri 18 Feb 2011 09:25:46 PM PST