There is a picturesque dry lake feature called The Racetrack Playa, or The Racetrack, where “sailing stones” leave linear “racetrack” impressions. It is situated in Death Valley National Park in Inyo County, California, United States, above the northwest portion of Death Valley.
Geography
Racetrack Playa is in a north-south valley east of the Panamint Range in Death Valley National Park. It is around 3 miles long and 1.2 miles broad, with an elevation gain of 3708 feet. Its yearly precipitation is a mere 3 inches, and north-south mountains rising to elevations of 1500–2000 feet surround it on all sides. The majority of the 70 square mile drainage region flows onto the playa from eastern mountain rivers.
The playa’s surface, which is mostly made of dried clay, makes for a flat, sturdy, and smooth pavement. The distribution of stones varies; five to ten small stones per square yard can be found in certain areas several hundred feet out from the coast. In a few locations, downward transit is evident.
There are tracks left by rocks up to 320 kg that roll across Racetrack Playa in northern Death Valley National Park, California. Documented since 1948, this phenomena is not unique; it has also been seen in other playas in South Africa, the Tunisian Sahara, and southern California.
These pebbles were traditionally thought to have been moved over a slick and wet playa surface by wind. This premise was questioned in 2014 by recent observations. Pebbles were seen being moved by Norris et al. when 4-5 m/s winds dissolved thin sheets of ice. Several rocks were pushed by the ice panels at up to 80 mm/s.
While these discoveries give information on the physics, several aspects of the tracks remain a mystery. Kletetschka et al. proposed that when an ice sheet arises, rocks with better thermal conductivity than water or ice could become frozen to the rock’s base. This permits the ice sheet to be moved together with the rock and silt by the wind.
A comprehensive system of 15 GPS-equipped boulders on the surface, a weather station close to the playa, and time-lapse cameras aimed at the southeast corner were installed to study the movement of stones on Racetrack Playa. 5-8 times a year, the researchers visited the site to do upkeep and retrieve data. Hourly circumstances were recorded by the time-lapse camera every year from November to March.
Every 60 minutes, Interwoof GPS loggers were placed in limestone blocks northeast of naturally occurring stones to record temperature and GPS information. After being activated, they started recording continuously at intervals of one second.
The Racetrack Playa is 2.8 mi (4.5 km) long (north-south) and 1.3 mi (2.1 km) broad (east-west), at an elevation of 3,714 feet (1,132 m) above sea level. The playa is remarkably level and flat, with barely 1.5 inches (3.8 cm) between the northern and southern ends.
The main cause of this phenomenon is the accumulation of fine-grained silt near the north end. Rising 1,964 feet (599 m) above the lakebed 0.85 miles (1.37 km) to the west, Ubehebe Peak, at 5,678 feet (1,731 m) high, is the highest peak encircling the Racetrack.
Situated between the Nelson Range to the west and the Cottonwood Mountains to the east, the playa is part of the tiny Racetrack Valley endorheic basin. A small, transient endorheic lake is created when heavy rains cause water from the nearby mountains to spill into the playa.
The tiny coating of water rapidly evaporates in the scorching desert heat, leaving behind a soft, slippery layer of mud on the top. The mud shrinks and fractures into a mosaic of interconnecting polygons as it dries.
Racetrack Playa and the shallow hydrocarbon lake Ontario Lacus on Saturn’s moon Titan have similar shapes.
Features
Racetracks have little vegetation and are dry for virtually the whole year. Small, hard hexagonal mud crack polygons, approximately an inch (2.5 cm) thick and ranging in diameter from 3 to 4 inches (7.5 to 10 cm), cover its surface after it dries.
Sets of three mud cracks at a 120° angle to one another are how the polygons develop. On the playa surface, tiny mud curls, sometimes referred to as “corn flakes,” appear a few days following a rainfall event. If these are absent, the little mud curls have likely been scraped away by the wind or another item.
A thin coating of fine mud is deposited on and between the Racetrack polygons by a shallow body of water during the bimodal rainy season (summer and especially winter). When winter precipitation is heavier, the fissures are momentarily covered up until spring, when the dry weather leads to the formation of new cracks in the mud.
The constant sandblasting wind aids in rounding the edges of polygons that are exposed. There is one to two inches (2.5 to 6.5 cm) of ice cover and three to four inches (75 to 100 mm) of precipitation every year. Usually, each year, just a portion of the playa floods.
Late in 2016, there was vandalism at the Racetrack.
There is evidence of ice activity along a section of the playa’s shoreline, particularly on the eastern side of the southernmost arm. Little ice ramparts are visible through a pavement of sharp rock shards and sporadic alignments of larger stones. Shearing and pushing of ice is suggested by ridges and stone marks close to the coast.
The pavement features closely matched pieces that give it a mosaic-like appearance despite its fine grain. Faint stone footprints are scattered around the pavement, especially to the northeast.
Ice ramparts are little, just rising a few inches above the chip pavement. Stones shattered windows in the pavement from time to time, and the ice on the shore appeared to be pushing and shearing.
Raceway Playa’s magnificent natural beauty is enhanced by its unique characteristics, which include its huge clay surface, limited precipitation, and signs of ice activity along the beach.
Mapping
Plots were created in detail by affixing numbered tabs of tracing cloth to the clay along designated routes. Baselines indicated stations at intervals of 25 or 50 feet and were aligned by alidade beside routes. Using a 100-foot tape, distances were measured to the nearest 0.005 feet. Precise trigonometric calculations were utilized to join the basis lines.
Clear days after sub-freezing nights, brought on by mild winds and the breaking up of floating ice by the early sun, were linked to rock mobility. Ice broke up and shifted rocks; in one instance, more than sixty relocated. Wakes were created downstream when ice often cracked close to rocks.
Rocks varied in length, some moving ahead of others. Rocks in close proximity to one another were transformed by ice cracks. For rock motion, the existence of a playa pool with exact depth characteristics was essential.
Other necessary conditions were sunlight, gentle breezes, floating ice, and suitable temperatures, which were most prevalent around noon when the ice melted. It was hard to find the creation of rock paths since they started beneath the ice. For a maximum of sixteen minutes, the rocks traveled slowly at a pace of two to five meters per minute.
Weather station data during the coldest periods showed freezing temperatures and winds as high as 3-5 m/s. Periodic snow or rain events that create winter ponds have been linked to episodic rock motion, which can persist for years or decades.
Sailing stones
The Racetrack’s floating stones are a geological phenomena. Without the assistance of humans or animals, slabs of dolomite and syenite weighing anywhere from a few hundred grams (a few ounces) to hundreds of kilograms (pounds) leave noticeable traces as they move over the playa surface. Rather, during times of light wind, ice sheets that are only a few millimeters thick begin to melt, which causes the rocks to shift. The rocks may move up to five meters (16′) every minute because to the ice shove produced by these thin, floating ice panels.
The topic of how the movement of the sailing stones was formerly mysterious but was eventually explained via the use of critical thinking and the scientific method is the main focus of the 2017 documentary Principles of Curiosity.
Islands
At the northern edge of the playa, two islands of bedrock outcrops rise sharply above the surface. The Grandstand, a black quartz monzonite outcrop rising to a height of 73 feet (22 meters) and standing in stark contrast to the pure white surface of the Racetrack, is the most notable feature. Another ‘island’ characteristic is a tiny outcrop of carbonate.
Springs
The playa is divided into three halves by aligned depressions, or intermittent springs.
In the middle of the Racetrack playa is Spinal Springs. It begins at its northern end, where conical depressions barely a few millimeters (inches) deep are located, and is 550 meters (600 yards) long. As one moves south, the depressions widen to around five meters (16 feet) and are dotted with creosote bushes. After then, they start to get smaller, shallower once more, and eventually vanish. There were also more depressions along this linear formation, to the north and south, which could represent a continuation of the Spinal Springs alignment.
The depressions that line the southeast portion of the Racetrack playa are aligned to form Edge Springs. Along the base of the steep mountain range, the alignment runs parallel to the toes of alluvial fans.
Within the Racetrack playa, Gindarja Springs is a sequence of depressions made up of three sizable indentations oriented northwesterly. Three is on the edge, while two are entirely inside the playa. Each of the three is connected to substantial vegetation.
