Racetrack Playa
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Racetrack Playa is a seasonally dry lake (a playa) located in the northern part of the Panamint Mountains in Death Valley National Park, California, U.S.A.. It is famous for 'sailing stones', rocks that mysteriously move across its surface.
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[edit] Geography
The playa is nestled between the Cottonwood Mountains to the east and the Last Chance Range to the west. During periods of heavy rain, water washes down from nearby mountain slopes onto the playa, forming a shallow, short-lived lake. Under the hot Death Valley sun, the thin veneer of water quickly evaporates, leaving behind a layer of soft mud. As the mud dries, it shrinks and cracks into a mosaic of interlocking polygons.
The playa is 3708 feet (1130 m) above sea level, 2.8 miles (4.5 km) long north-south, and 1.3 miles (2 km) wide east-west. It is also exceptionally flat and level with the north end being only 1.5 inches (4 cm) higher than the south. Two islands of bedrock poke above the playa's surface at its north end:
- The Grandstand, a 73 feet (22 m) high outcrop;
- A small carbonate outcrop.
Racetrack is dry for almost the entire year and has no vegetation on it. When dry, its surface is covered with small but firm hexagonal mud crack saucers that are typically 3 to 4 inches (7.5 to 10 cm) in diameter and about an inch (2.5 cm) thick. During the bimodal rainy season (summer and especially winter) a shallow cover of water deposits a thin layer of fine mud on and between the saucers of Racetrack. Heavier winter precipitation temporarily erases them until spring when the dry conditions cause new mud cracks to form where the old ones had been. Sandblasting wind continually helps to round the edges of exposed saucers. Annual precipitation is 3 to 4 inches (75 to 100 mm) and ice cover can be 1 to 2.5 inches (2.5 to 6.5 cm) thick. Typically only part of the playa during any given year will flood.
The highest point in the immediate area is Ubehebe Peak, itself 5,678 feet (1731 m) above sea level, a full 1970 feet (571 m) above the lakebed, and 0.85 mile (1.37 km) to its west.
[edit] Sailing stones
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Main article: Sailing stones
The sailing stones are a geological phenomenon found in the Racetrack. The stones slowly move across the surface of the playa, leaving a track as they go, without human or animal intervention. They have never been seen or filmed in motion and are not unique to The Racetrack. Similar rock travel patterns have been recorded in several other playas in the region but the number and length of travel grooves on The Racetrack are notable.
Racetrack stones only move once every two or three years and most tracks last for just three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different-sized track in the stone's wake.
The sailing stones are most likely moved by strong winter winds (up to 90 mph), once it has rained enough to fill the playa with just enough water to make the clay slippery. The prevailing winds across Racetrack Playa travel blow from southwest to northeast. Most of the rock trails are parallel to this direction, lending support to this hypothesis.
[edit] References
- Messina, P.; Stoffer, P., and Clarke, K.C. (1997). "Mapping Death Valley's Wandering Rocks". GPS World (April, 1997): 34-44.
- Reid, J.B.; Bucklin E.P., Copenagle L., Kidder J., Pack S.M., Polissar P.J., Williams M.L. (1995). "Sliding rocks at the Racetrack, Death Valley: What makes them move". Geology 23 (9): 819-822. doi:.
- Sharp, R.P.; Carey D.L. (1976). "Sliding stones, Racetrack Playa, California". Bulletin of the Geological Society of America 87 (12): 1704-1717. doi:.
- Sharp, R.P.; Carey, D.L., Reid, J.B., Jr., Polissar, P.J., and Williams, M.L. (1996). "Sliding rocks at the Racetrack, Death Valley: What makes them move? Discussion and Reply". Geology 25: 766-767.
- Sharp, R.P.; Glazier, A.F. (1997). Geology Underfoot in Death Valley and Owens Valley. Missoula: Mountain Press Publishing Company. ISBN 0-87842-362-1.
- Shelton, J.S. (1953). Can Wind Move Rocks on Racetrack Playa 117. The American Association for the Advancement of Science, 438-439.
- Stanley, G.M. (1955). "Origin of playa stone tracks, Racetrack Playa, Inyo County, California". Bulletin of the Geological Society of America 66 (11): 1329-1350. doi:.
[edit] External links
- USGS: Racetrack Playa
- The Sliding Rocks of Racetrack Playa
- The Mystery of the Rocks on the Racetrack at Death Valley
- Differential GPS/GIS analysis of the sliding rock phenomenon of Racetrack Playa, Death Valley National Park
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