What is the mystery behind Sailing Stones Of Death Valley?

LOCATION : Racetrack Playa, Death Valley National Park, California, U.S.A.The Racetrack Playa, or The Racetrack is a dry lake located in northwestern side of Death valley in Death Valley National park.
Racetrack is dry for almost the entire year and has no vegetation. When dry, its surface is covered with small but firm hexagonal mud crack polygons that are typically 3 to 4 inches (7.5 to 10 cm) in diameter and about an inch (2.5 cm) thick.

SAILING STONES

Sailing stones are one of the mystical geographical phenomenon found in the Racetrack Playa. The sliding rocks can be found on the floor of the playa with long trails behind them.
The heavy stones appear to move across the dried lake bed without any human or animal force, leaving a trail behind them in the cracked mud. These rocks weigh from few pounds to 700 pounds. Historical accounts identify some stones around 100 m (300 ft) from shore, yet most of the stones are found relatively close to their respective originating outcrops.
Stones with rough bottoms leave straight tracks while those with smooth bottoms wander. But sometimes stones move in a zig-zag pattern.

Theories and suggestions :

As nobody had ever witnessed the actual movement of rocks, countless theories were associated for this phenomenon.

• One earlier theory suggested that the rocks were driven by gravity down the slope. But the theory was discounted when it was revealed that the northern end of the playa is actually higher than the southern end and that most of the rocks were in fact traveling uphill. (Northern end is 1.5 inches (3.8 cm) higher than the Southern end.)
• Researchers believed strong winds that frequently whip across the vast lake bed could cause the rocks to slide across the ground. But soon the theory was discarded.
• Some researchers thought that dust devils might move the rocks, some of which weigh as much as 318 kilograms.

Explanation

The mystery was finally solved in 2013, when researchers observed rock movements using GPS and time-lapse photography. They were the first people in the world to see the stones in motion.
The research team witnessed and documented rock movement on December 20, 2013, that involved more than 60 rocks, with some rocks moving up to 224 m between December 2013 and January 2014 in multiple movement events.

Sailing stone tracks, via PLOS ONE.
Watching the stones move enabled them to see the cause:

In contrast with previous hypotheses of powerful winds or thick ice floating rocks off the playa surface, the process of rock movement that we have observed occurs when the thin, 3- to 6-millimeter “windowpane” ice sheet covering the playa pool begins to melt in late morning sun and breaks up under light winds of ~4–5 meters/second.

Floating ice panels tens of meters in size push multiple rocks at low speeds of 2–5 meters/minute along trajectories determined by the direction and velocity of the wind as well as that of the water flowing under the ice.

Thus the mystery of sailing stones of death valley is finally solved..

Originally published at mybookofmysteries.blogspot.com.