Tuesday, February 12, 2008
Landing Strip for Flying Rocks?
The Sliding Rocks of the Racetrack Playa Mystery, Death Valley, California
One of the most interesting mysteries of Death Valley National Park is the sliding rocks at Racetrack Playa (a playa is a dry lake bed). These rocks can be found on the floor of the playa with long trails behind them. Somehow these rocks slide across the playa, cutting a furrow in the sediment as they move. Some of these rocks weigh several hundred pounds. That makes the question: "How do they move?" a very challenging one. The truth: No one knows for sure exactly how these rocks move - although a few people have come up with some pretty good explanations. The reason why their movement remains a mystery: No one has ever seen them in motion!
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.
Via Chelsea. More info here: http://geology.com/articles/racetrack-playa-sliding-rocks.shtml