Link #21: Rocks Can Move By Themselves!

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Chain of Facts - A Connection of Facts

Link #21: Rocks Can Move By Themselves!

Racing Rock at at Racetrack Playa, Death Valley National Park, CA.
Racing Rock by Scott Beckner cc2.0

If the moving countries and land masses we explained in our last post freaked you out, then the mystery of the Racetrack Playa will really bake your noodle. Racetrack Playa is a region of dry lake with exposed bedrock located in the Death Valley National Park of California, United States of America. What is the great and shocking mystery about Racetrack Playa? Here, rocks seem to move all by themselves!

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The Sailing Stones of Racetrack Playa

A view of a rock sliding in Racetrack Playa.
A view of a rock sliding in Racetrack Playa. Tracks are sometimes non-linear. Image credit: Jon Sullivan

In Racetrack Playa, rocks have long tracks behind them in the mud as proof of their movement. A casual examination of the rocks reveals that there are no other tracks around them and that they seemed to have moved by themselves.

What’s even more confounding about these sailing stones is that they move on a whim. They move in a general direction for a period of time and then completely change their direction. The tracks behind them run straight for a while and then bend in another direction.

Racetrack-Playa-Death-Valley
Picture of two rocks on Racetrack Playa in Death Valley. Notice the mysterious groves leading away from the stones. By Daniel Mayer GFDL

Even more confusing is the fact that some rocks seem to move together for a while and change directions at the same time. The effect is multiple tracks running parallel to each other even when directions change.

Many people in the last century have mulled over the problem but couldn’t find any logical reason for the movements of these sailing stones. However, a few clever scientists did manage to solve the mystery at the end of the last century.


How Was The Mystery Of Sailing Stones Solved?

Racing Rock Mystery
Racing Rock by Scott Beckner cc2.0

It wasn’t easy to discover how these stones moved by themselves. Before the actual truth was discovered, people came up with a wide variety of theories. These ranged from hurricane level winds to ice build-up. One of the reasons why finding the truth was so difficult was that the stones sometimes wouldn’t move for decades.

However, finally Dr Brian Jackson leading a group of scientists discovered the truth. He went about the whole process in the most scientific way possible. He set up a highly advanced and sensitive weather station in the valley and fitted 15 stones with specialized GPS systems. The strategy worked.


How Do Sailing Stones Move?

The sailing stones need a number of things to be just right to move. The precision required can be explained by the first step. When it rains in the valley, it needs to rain enough for it to be filled with water but without completely submerging the stones.

However, at the same time, the water can’t be too shallow because it needs to be deep enough for ice to form on its surface. If these conditions are met then the temperature at night needs to plummet enough for the ice sheets to form. These sheets need to be thin enough to move freely when they break later and thick enough not to shatter when they move.

Once all these conditions are met, there needs to be a few sunny days for the ice sheets to melt. Then there needs to be light winds to move the stones on the sheets of ice below. It is these ice sheets which move the stones between them. As the mud at the bottom is already wet because of the rain, it gives against the stone and they move.




Can you Guess the Next Link in the Chain?

What will be the next link in our Chain of Facts? Think you might know? Scroll down to add a comment below with your best guess.

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You can view the full list of links in the chain here.


Sources:

http://en.wikipedia.org/wiki/Sailing_stones
http://en.wikipedia.org/wiki/Racetrack_Playa
http://www.sci-news.com/physics/science-death-valley-sailing-stones-02148.html
http://www.slate.com/blogs/bad_astronomy/2014/09/02/mystery_solved_the_sliding_stones_of_death_valley.html

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