Racetrack Playa
Páginas: 5 (1080 palabras)
Publicado: 8 de febrero de 2013
The Sliding Rocks of Racetrack Playa
One of the most interesting mysteries of the world is the sliding rocks at Racetrack Playa (a playa is a dry lake bed). One of the strangest occurrences that Dr. Bob has been the mysterious sliding boulders of Death Valley National Park, California. There are trails showing that boulders up to 705 pounds (320 kg) have moved large distances over flatterrain. Some of these rocks weigh several hundred pounds. That makes the question, How do they move? No one has actually seen these boulders move. 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.
About Racetrack Playa
Racetrack playa is lake bed that is almost perfectlyflat much so, that on a calm day only 2 inches ( 5 cm) of water will entirely cover the playa, but its always dry. It is about 4 kilometers long (2.5 miles - north to south) and about 2 kilometers wide (1.25 miles - east to west). The surface is covered with mudcracks and the sediment is made up mainly of silt and clay.
The climate in this area is arid. It rains just a couple of inches per year.However, when it rains, the steep mountains which surround Racetrack Playa produce a large amount of runoff that converts the playa floor into a broad shallow lake. When wet, the surface of the playa is transformed into a very soft and very slippery mud.
Are They Moved by People or Animals?
The shape of trails behind the rocks suggest that they move during times when the floor ofRacetrack 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?
Recent research by NASA on Racetrack Playa
"This is the favorite explanation. The prevailing winds that blow across Racetrack Playa travel from southwest to northeast. Most of the rocktrails 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." 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 irregularlyshaped rock.
Are They Moved by Ice?
A few people have reported seeing Racetrack Playa covered by a thin layer of ice. There must first be enough rain to form a shallow lake on the playa, followed by freezing temperatures to form a sheet of ice. When there is wind, all the trapped boulders and the ice sheet are pushed around the shallow lake. The wind blowing over the ice causes "frictionaldrag". As the air blowing over the ice is slowed down by this friction, it exerts a pushing force on the ice which helps to move it. This is how the wind pushes the ice sheet . The bottoms of the boulders leave the tracks that we see in the pictures. When the ice melts, the boulders assume their new resting places.
Some researchers have found highly congruent trails on multiple rocks thatstrongly support this movement theory. However, the transport of a large ice sheet might be expected to mark the playa surface in other ways - these marks have not been found.
Other researchers experimented with stakes that would be disturbed by ice sheets. The rocks moved without disturbing the stakes. The evidence for ice-sheet transport is not consistent.
All of the best explanationsinvolve wind as the energy source behind the movement of the rocks. The question remains is do they slide while encased in an ice sheet or do they simply side over the surface of the mud? Perhaps each of these methods is responsible for some rock movement?
Perhaps this story will remain more interesting if the real answer is never discovered!
One of the unusual things about the sliding...
One of the most interesting mysteries of the world is the sliding rocks at Racetrack Playa (a playa is a dry lake bed). One of the strangest occurrences that Dr. Bob has been the mysterious sliding boulders of Death Valley National Park, California. There are trails showing that boulders up to 705 pounds (320 kg) have moved large distances over flatterrain. Some of these rocks weigh several hundred pounds. That makes the question, How do they move? No one has actually seen these boulders move. 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.
About Racetrack Playa
Racetrack playa is lake bed that is almost perfectlyflat much so, that on a calm day only 2 inches ( 5 cm) of water will entirely cover the playa, but its always dry. It is about 4 kilometers long (2.5 miles - north to south) and about 2 kilometers wide (1.25 miles - east to west). The surface is covered with mudcracks and the sediment is made up mainly of silt and clay.
The climate in this area is arid. It rains just a couple of inches per year.However, when it rains, the steep mountains which surround Racetrack Playa produce a large amount of runoff that converts the playa floor into a broad shallow lake. When wet, the surface of the playa is transformed into a very soft and very slippery mud.
Are They Moved by People or Animals?
The shape of trails behind the rocks suggest that they move during times when the floor ofRacetrack 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?
Recent research by NASA on Racetrack Playa
"This is the favorite explanation. The prevailing winds that blow across Racetrack Playa travel from southwest to northeast. Most of the rocktrails 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." 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 irregularlyshaped rock.
Are They Moved by Ice?
A few people have reported seeing Racetrack Playa covered by a thin layer of ice. There must first be enough rain to form a shallow lake on the playa, followed by freezing temperatures to form a sheet of ice. When there is wind, all the trapped boulders and the ice sheet are pushed around the shallow lake. The wind blowing over the ice causes "frictionaldrag". As the air blowing over the ice is slowed down by this friction, it exerts a pushing force on the ice which helps to move it. This is how the wind pushes the ice sheet . The bottoms of the boulders leave the tracks that we see in the pictures. When the ice melts, the boulders assume their new resting places.
Some researchers have found highly congruent trails on multiple rocks thatstrongly support this movement theory. However, the transport of a large ice sheet might be expected to mark the playa surface in other ways - these marks have not been found.
Other researchers experimented with stakes that would be disturbed by ice sheets. The rocks moved without disturbing the stakes. The evidence for ice-sheet transport is not consistent.
All of the best explanationsinvolve wind as the energy source behind the movement of the rocks. The question remains is do they slide while encased in an ice sheet or do they simply side over the surface of the mud? Perhaps each of these methods is responsible for some rock movement?
Perhaps this story will remain more interesting if the real answer is never discovered!
One of the unusual things about the sliding...
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