Racetrack Playa

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Racetrack Playa
File:Racetrack Playa from space.jpg
Location Death Valley National Park
Inyo County, California
Coordinates Lua error in package.lua at line 80: module 'strict' not found.
Lake type Endorheic basin
Primary outflows Terminal (evaporation)
Basin countries United States
Max. length 4.5 km (2.8 mi)
Max. width 2 km (1.2 mi)
Surface area 7 km2 (2.7 sq mi)
Shore length1 12 km (7.5 mi)
Surface elevation 1,132 m (3,714 ft)
References U.S. Geological Survey Geographic Names Information System: The Racetrack
1 Shore length is not a well-defined measure.

The Racetrack Playa, or The Racetrack, is a scenic dry lake feature with "sailing stones" that inscribe linear "racetrack" imprints. It is located above the northwestern side of Death Valley, in Death Valley National Park, Inyo County, California, U.S..

Geography

The Racetrack Playa is 3608 feet (1130 m) above sea level, and 2.8 mi (4.5 km) long (north-south) by 1.3 mi (2.1 km) wide (east-west). The playa is exceptionally flat and level with the northern end being only 1.5 inches (4 cm) higher than the southern. This occurrence is due to major influx of fine-grained sediment that accumulates at the north end. The highest point surrounding the Racetrack is the 5,678 feet (1731 m) high Ubehebe Peak, rising 1970 feet (571 m) above the lakebed 0.85 mile (1.37 km) to the west.

The playa is in the small Racetrack Valley endorheic basin between the Cottonwood Mountains on the east and Nelson Range to the west. During periods of heavy rain, water washes down from the Racetrack mountain area[1] draining into the playa, forming a shallow, short-lived endorheic lake. Under the hot desert sun, the thin veneer of water quickly evaporates leaving behind a surface layer of soft slick mud. As the mud dries, it shrinks and cracks into a mosaic pattern of interlocking polygons.

The shape of the shallow hydrocarbon lake Ontario Lacus on Saturn's moon Titan has been compared to that of Racetrack Playa.[2]

360° night-time panorama of the Racetrack Playa. The Milky Way is the visible arc in the center above a sailing stone and tracks from others.

Features

The Racetrack

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. The polygons form in sets of three mud cracks at 120° to each other.[3] A few days after a precipitation event, small mud curls, otherwise known as “corn flakes” form on the playa surface. Absence of these indicates that wind or another object has scraped away the tiny mud curls.

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 polygons of Racetrack. Heavier winter precipitation temporarily erases them until spring when the dry conditions cause new mud cracks to form in the place of the old cracks. Sandblasting wind continually helps to round the edges of exposed polygons. 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 will flood in any given year.

Sailing stones

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Main article: Sailing stones
File:Runningrock2.jpg
File:Runningrock.jpg
Sailing stone in Racetrack Playa

The sailing stones are a geological phenomenon found in the Racetrack. Slabs of dolomite and syenite ranging from a few hundred grams to hundreds of kilograms inscribe visible tracks as they slide across the playa surface, without human or animal intervention. The tracks have been observed and studied since the early 1900s, yet until 2014 no one had ever seen the stones in motion. Racetrack stones only move once every two or three years and most tracks last for three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander.

The sailing stones were originally thought to be moved by strong winter winds, in the upwards of 90 mph, once it had rained enough to fill the playa with just enough water to make the clay slippery. The prevailing southwest winds across Racetrack playa blow to northeast. Most of the rock trails are parallel to this direction, lending support to this hypothesis.[4][5]

An alternate theory suggests that as rain water accumulates, strong winds blow thin sheets of water quickly over the relatively flat surface of the playa. Sheets of ice form on the surface as night temperatures fall below freezing. Wind then drives these floating ice floes, their aggregate inertia and large area providing the necessary force required to move both small and large stones. Rock trails would again remain parallel to the southwest winds. According to investigator Brian Dunning, "Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor."[6]

Another hypothesis[1] focused on observations and measurements of narrowing trails, heat conductivity of the playa's rocks, water, ice and sediments, missing rocks from ends of the trails, and an intermittent spring system in the playa. Kletetschka with his team identified three groups of Racetrack playa spring lineaments, Spinal Springs, Edge Springs, and Gindarja Springs, through which additional water flows into the playa once the ice forms on the water inside the playa. This mechanism, in addition to the raft hypothesis,[7] allows lifting the rocks by adding additional amount of water via these springs.[1]

The most recent research[7] and observations of moving stones[8] indicates that ice collars form around rocks and the rocks along with ice are buoyantly floated off the soft bed. The minimal friction allows the rocks to be moved by arbitrarily light winds.[9]

In a study released in August, 2014, researchers observed rock movements using GPS and time-lapse photography. They documented a rock movement on December 20, 2013 that involved more than 60 rocks, with some rocks moving up to 224 meters between December 2013 and January 2014 in multiple move events. This study contradicted earlier hypotheses of winds or thick ice floating rocks off the surface. Instead, rocks move when ice sheets just a few millimeters thick start to melt during periods of light wind. These thin floating ice panels ice shove the rocks at up to five meters per minute.[8]

Islands

Two islands of bedrock outcrops rise dramatically above the playa's surface at its northern end. The larger landmark is The Grandstand, a 73 feet (22 m) high dark dolomite outcrop, rising in dramatic contrast from the bright white surface of the Racetrack. The second 'island' feature is a smaller carbonate outcrop.

Visiting

Access is via Racetrack Road, reached at the Grapevine Junction near Scotty's Castle. The 28 mile rough gravel road heading south-west from Ubehebe Crater is passable with non-4WD vehicles but requires high ground clearance. It rounds the western side of the playa to a parking area with descriptive signs by the National Park Service. A bench here, placed by the Mano Seca Group, has scenic views of The Racetrack, The Grandstand, and mountain scenery. Another access to Racetrack Playa is Lippincott pass road that enters the Racetrack valley from the south west, climbing up from Saline Valley. Lippincott Pass and the roads in Saline Valley are extremely rough and negotiable for high clearance 4WD vehicles with all-terrain tires only.

Camping, while not allowed on the playa, is available in "primitive campsite" areas to the north and south. Visiting remote areas of Death Valley bears considerable risk. Summer temperatures can surpass 120 °F (49 °C), large areas are without cellphone reception, roads are treacherous and the closest gas station is in Panamint Springs.

File:Death Valley NP - Racetrack Playa - Grandstand.JPG
The Grandstand in the northwest area of the playa

See also

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See also the categories Death Valley and Protected areas of the Mojave Desert

References

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  1. ↑ 1.0 1.1 1.2 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lorenz, R. D., B. Jackson and A. Hayes, Racetrack and Bonnie Claire : Southwestern US Playa Lakes as Analogs for Ontario Lacus, Titan, Planetary and Space Science, 58, 723-731, 2010
  3. ↑ Sharp, Robert P. and Allen F. Glazner, Geology Underfoot In Death Valley and Owens Valley, 161-173, 1997
  4. ↑ http://geosun.sjsu.edu/paula/rtp/images/map.gif
  5. ↑ Messina, P.; Stoffer, P., and Clarke, K.C. (1997). "Mapping Death Valley's Wandering Rocks". GPS World (April, 1997): 34–44.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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External links

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