Sailing stones

A big boulder sticks out of the dried mud. This rock is too heavy to pick up. Yet, it has mysteriously moved. A few days ago, it was 250 meters (820 feet) away. 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 glide in straight lines, then stop and settle into the dry mud. Some rocks 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. 

Boulders mysteriously zig and zag in Death Valley, California, U.S.A.



A man takes a photograph of boulders and their trails.

for a Cause

Over the years, people have come up with wild ways to explain how the rocks move. Some people say the rocks are magical and move on their own. Others say aliens from space are moving them. Still others think pranksters are playing tricks, moving the rocks when no one is looking. Scientists have looked for evidence in nature to find answers.

An early theory was that gravity moves the rocks. This force could tug on the rocks and pull them downhill. Even though this area looks flat, it actually slopes a little.

So, scientists looked for patterns in which direction the rocks moved. That’s when the gravity theory fell apart. Most of the rocks had moved uphill. Gravity pulls things down, not up.

Another theory was that winds pushed the rocks. The winds here are strong. The scientists did experiments to test the wind theory. One even used the wind from a plane propeller to try to move the rocks. The tests showed that winds aren’t strong enough to move the biggest boulders.

This video follows the trail made by a heavy stone.

Cold Clue

Finally, scientists noticed that the rocks seem to move only in the winter. That’s when this area sometimes floods. A thin layer of water surrounds the rocks.

Studying the water led scientists to new theories. Geologist Paula Messina observed a thin layer of slimy bacteria growing in the water. The slime makes the ground really slippery, so the rocks can slide easily. Even a small wind may be able to push the rocks.

An Experiment

The water gave scientist Ralph Lorenz a different idea. Could rings of ice form around the rocks? Since ice floats on water, the ice might lift even the biggest rocks a little. Then a light wind could push them.

Lorenz did an experiment to see if his theory worked. He tested it on a model, and the rock moved! Its bottom scraped along the sand, leaving a trail. So, it seems that ice and wind could help the rocks move. So could bacteria and wind. Both theories are possible. No one’s ever seen the rocks move, so this mystery remains unsolved.

Scientist Ralph Lorenz stands near a flooded area of Death Valley.