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

From: Michael Groetz <mpg4444_at_meteoritecentral.com>
Date: Fri, 18 Feb 2011 17:24:20 -0800
Message-ID: <AANLkTimR1q_x8_xegrn2Eeyy7FwAGu_H5QApSoAvffRH_at_mail.gmail.com>

   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.
Received on Fri 18 Feb 2011 08:24:20 PM PST