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From: Dan Richter (1:317/3)
To: All
Date: Sun, 20.09.20 13:00
ES Picture of the Day 20 2020
EPOD - a service of USRA

The Earth Science Picture of the Day (EPOD) highlights the diverse processes
and phenomena which shape our planet and our lives. EPOD will collect and
archive photos, imagery, graphics, and artwork with short explanatory
captions and links exemplifying features within the Earth system. The
community is invited to contribute digital imagery, short captions and
relevant links.

EPOD 20th - The Mysterious Moving Rocks

September 20, 2020

We’re celebrating 20 years of Earth Science Picture of the Day during
the month of September! Today’s photo features a popular EPOD from the
past. Thanks to all of our followers (on the blog, Facebook, Instagram
and Twitter) for supporting us. Thanks also to all of you who’ve
submitted your photos. We’re most appreciative. This EPOD was
originally published March 5, 2002.

Provided by: Joe Orman
Summary author: Joe Orman

In a remote corner of California's Death Valley National Park, on the
floor of a dry lakebed called Racetrack Playa, can be seen the
geological oddity of the sliding stones. While the force of gravity
easily explains how dozens of rocks -- weighing up to 700 pounds --
could have fallen from the adjacent hillsides onto the margins of this
long-vanished ancient lake, it cannot explain how the rocks have moved
far out onto the perfectly flat surface.

No one has ever seen the rocks actually move, but the evidence is
indisputable: distinct tracks in the hard clay surface, some extending
for hundreds of feet. Some of the grooves are arrow-straight, while
others curve, take sharp turns, or even make complete loops.

For decades scientists have plotted the tracks, analyzed the soil, and
charted the weather in an attempt to solve the mystery. All of the
theories involve extremely strong winds, but they differ on the exact
physical process that allows the rocks to overcome friction. Is the
answer mud, water, ice -- or some combination of these? What is clear
is that the Racetrack is a unique opportunity for science to explain
what at first appearance seems to be completely inexplicable.

Earth Science Picture of the Day is a service of the Universities
Space Research Association.

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