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SAILING STONES


A big boulder sticks up out of the dried mud. This rock is too heavy to pick up. Yet it has mysteriously moved. A trail shows where it moved across the dirt.





This isn’t the only rock on the move here. Many of the rocks in this part of Death Valley don’t stay in one place. Their trails crisscross the cracked mud of a dried lake.


Some rocks move in straight lines. Some move in pairs. Others zigzag this way and that, leaving a jagged trail. How did they move? No one has ever seen it. It’s a mystery.


Searching for a Cause Over the years, people have wondered what makes the rocks move. T ey have come up with some wild ideas. Some people think the rocks are magical. Others say pranksters secretly move the rocks. Scientists wanted a better theory. So they looked for some evidence.


Looking to Nature An early theory was that gravity moves the rocks. Gravity is a force in nature. It pulls things down. Yet many rocks moved uphill, not downhill. So gravity wasn’t the answer. Another theory was that strong


winds pushed the rocks. Scientists tested this theory. T e tests showed that even the strongest winds in the area weren’t strong enough. T ey couldn’t move big boulders.


22 NATIONAL GEOGRAPHIC EXPLORER


Cold Clue T en scientists realized an important fact. T e rocks move only in winter, when this area fl oods. One scientist decided to study the water. She found a slimy bacteria grew in


the water. T e slime made the ground slippery. On a windy day, a small wind could make the rocks slide.


An Experiment T e water gave another scientist a diff erent idea. He knew that ice floats. So maybe ice helped the rocks move To test his theory, he froze a wet


rock. He set it in a tray of water and sand. T e ice liſt ed the rock a little bit. When he blew on the rock, it moved! It leſt a trail in the sand. T e bacteria and ice theories might


be true. Yet no one has seen the rocks move. T is mystery remains unsolved.


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