User:Py175yp/Racetrack Playa

Strong winds, water that flows, and ice have all been connected to the movement of rocks. Despite these correlations, this phenomenon has never been directly observed. The study, which makes use of GPS-equipped rocks, photography, a weather station, and time-lapse cameras, is the first to capture rock motions scientifically.

Numerous rocks were propelled along courses that were influenced by the movement of both the wind and the water beneath the ice by enormous ice panels that were several meters long and reached speeds of up to 80 mm/s. However, the roughness is substantially increased by the presence of boulders poking through the surface and the overlap of shattered ice slabs that have since been refrozen.

According to the consensus of all researchers, wind is a key factor, and rocks are more likely to shift when the playa surface is moist, generating a smooth/slick surface. The early scientific investigation of the Racetrack suggested that dust devils were what caused the mobility of the rocks. Additional water on the playa may lift the rock and sediment assembly to a point where the wind can mobilize the ice sheet and the caught boulders and debris if the ice sheet thickens to a sufficient depth.

A boulder can then be removed from a sediment pile and moved away, leaving a rock imprint on the top of the pile, as the rock base melts and possibly more water is added.

A thorough system was put up for the investigation of Racetrack Playa's rock movement, including a weather station near the playa, time-lapse cameras centered on the southeast corner, and 15 GPS-equipped boulders on the surface. The researchers went to the location for maintenance and data retrieval 5-8 times per year. From November to March each year, the time-lapse camera recorded hourly conditions.

Interwoof GPS loggers were installed in limestone blocks northeast of natural stones and captured GPS and temperature data every 60 minutes. They began recording constantly at one-second intervals after being triggered.

Rock mobility was associated with clear days following sub-freezing nights, which were caused by light breezes and the morning sun breaking up floating ice. Rocks were moved by ice disintegration, with over 60 moving in a single occurrence. Ice frequently fractured near rocks, causing wakes downstream.

Some rocks went ahead of others, covering varied lengths. Ice fractures altered neighboring rocks, even those that were close together. The presence of a playa pool with precise depth parameters was a critical requirement for rock motion.

Other elements included floating ice, appropriate temperatures, sunlight, and mild winds, which were most common around midday when the ice melted. Because of their origin beneath the ice, the formation of rock trails was difficult to detect.

The rocks moved slowly, lasting up to 16 minutes at speeds ranging from 2 to 5 meters per minute. During the coldest weeks, weather station data revealed freezing temperatures and winds of up to 3-5 m/s. Episodic rock motion, which can last for years or decades, has been related to occasional rain or snow episodes that build winter ponds.

RACETRACK PLAYA AND THE ENVIRONMENT

Racetrack playa is approximately 3 miles long and 114 miles wide and is located at a height of 3708 feet in a north-south valley east of the Panamint Range within Death Valley Monument. It receives only 3 inches of annual precipitation and is bounded on all sides by north-south ranges rising 1500 to 2000 feet. The overall drainage area is around 70 square miles, with most of it flowing onto the playa from eastern mountain rivers.

The surface of the playa, which is mainly dried clay, provides a hard, smooth, and level pavement. The distribution of stones varies, with some regions a few hundred feet from the shore having 5-10 tiny stones per square yard. There is evidence of downgrade transit in a few places.

Method of Mapping:

Detailed plots were made by nailing numbered tabs of tracing fabric to the clay along specific paths. Baselines, aligned by alidade beside paths, marked stations at 25 or 50-foot intervals. Distances were measured to the closest 0.005 feet using a 100-foot tape. Trigonometric computations were used to precisely connect the basis lines.

A portion of the playa's shoreline indicates ice activity, notably on the east side of the southernmost arm. A pavement of angular rock fragments and periodic alignments of bigger stones reveal little ice ramparts. Stone traces and ridges near the shore suggest ice thrusting and shearing.

Despite its thin grain, the pavement has closely matched parts that provide a mosaic-like effect. The pavement is lined with faint stone footprints, mostly to the northeast. Although modest, ice ramparts rise a few inches above the chip pavement. Ice along the beach seemed to be thrusting and shearing, with stones periodically scouring windows in the pavement.

Racetrack Playa's distinctive traits, including its low precipitation, large clay surface, and indications of ice action along the shore, add to its remarkable natural landscape.

Rocks weighing up to 320 kg travel across Racetrack Playa in northern Death Valley National Park, California, leaving tracks. This phenomenon, which has been documented since 1948, is not unique and has been observed in various playas in southern California, the Tunisian Sahara, and South Africa.

Traditionally, these rocks were considered to be pushed by wind over a wet and slippery playa surface. Recent observations from 2014 called this assumption into question. Norris et al. observed pebbles being transported as thin sheets of ice melted in 4-5 m/s winds. The ice panels moved several rocks at speeds of 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.

Surprisingly, an observation from the early 1970s calls the current thinking into question. During April or May 1972 or 1973, rocks up to 0.25 m in length were spotted moving purely owing to high winds on the wet playa surface. This calls into question the notion that strong winds and a water-slickened playa surface were both required for boulder movement on Racetrack Playa.

While recent observations have indicated movement by wind alone and by wind operating on small sheets of ice, many features of the phenomena, particularly those involving bigger ice sheets, still require additional investigation.