The Mysterious Sliding Rocks of Racetrack Playa

If you ever visit the Death Valley National Park in California, you may notice large rocks with long trails behind them at Racetrack Playa (a dry lake bed). It looks like someone pushed the rocks along the surface. Only, it wasn’t ‘someone’. The rocks appear to slide across the playa all by themselves, but how they do it is a mystery, and no one has ever actually seen them move. There are a few theories, though.

Racetrack Playa is totally flat and almost always completely dry, with a surface covered in mudcracks and sediment made up of silt and clay. When it does rain, runoff from the mountains surrounding Racetrack Playa turn it into a shallow lake, transforming the surface into very soft and slippery mud.

From Geology.com:

Are They Moved by People or Animals?

The shape of trails behind the rocks suggest that they move during times when the floor of Racetrack Playa is covered with a very soft mud. A lack of disturbed mud around the rock trails eliminates the possibility of a human or animal pushing or assisting the motion of the rocks.

Are They Moved by Wind?

This is the favorite explanation. The prevailing winds that blow across Racetrack Playa travel from southwest to northeast. Most of the rock trails are parallel to this direction. This is strong evidence that wind is the prime mover or at least involved with the motion of the rocks.

Strong wind gusts are thought to nudge the rocks into motion. Once the rock begins to move a wind of much lower velocity can keep the rock in motion as it slides across the soft and very slippery mud. Curves in the rock trails are explained by shifts in wind direction or in how the wind interacts with an irregularly shaped rock.

There are a couple other theories, but most people agree that wind is the most likely culprit.  It may happen too slowly for anyone to see it happening, though, so we may never know for sure. It’s one of those strange mysteries of nature.

Link [Geology.com]

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