Meteorological Conditions at Racetrack Playa, Death Valley National Park: Implications for Rock Production and Transport

Abstract

Three decades of weather records at meteorological stations near Death Valley National Park are analyzed in an attempt to gauge the frequency of conditions that might form and erase the famous trails of wind-blown rocks in the mud of Racetrack Playa. Trail formation requires the playa to be wet, followed by strong winds and/or freezing conditions. Weather records are compared with a limited set of meteorological data that were acquired in situ at the playa over three winters and that indicate freezing on 50, 29, and 15 nights during the winters of 2007/08-09/10, respectively, as well as with the hydrological condition of the playa as determined by time-lapse cameras that observed flooding over ;1, ;5, and ;40 days, respectively, during those winters. Measurements at the nearby Panamint and Hunter Mountain stations are found to be a useful, if imperfect (;50%), indicator of Racetrack Playa conditions and give some features of Racetrack Playa's micrometeorological behavior. Wind speed probability distributions suggest that winds that are fast enough to cause unassisted rock motion are rare and therefore that freezing of water on the playa has a role in a significant fraction of movement events.

A Miniscule System of a ‘Sailing Rock’

“…It becomes obvious that the outer ridge of mud is closed backwards, forming a ring. The closeness of this ring emphasises that there was no ice-collar around the small quartzite, and no rafting [17,19]. The otherwise homogenously flat ground of the hollow form displays a small dark stone (Ø ~0.4 cm) which may well have stopped the movement of the pebble ( Figure 2E, arrow) and a larger one in the front.…”

“…Also movements of small ice rafts have never been observed during the melting processes along these field track margins. Even more, physical properties of these systems conflict with the building of 'ice collars' around the blocks later forming 'ice-rafts' , which have been observed several times at Racetrack Playa [14,19,20]. The thermal conductivity λ of rocks of dolomite, granite (Racetrack Playa) or quartzite (Vorgebirge) is some multitudes higher than that of water or loess [ rocks and surrounding ice, the rock will warm up and melt the substrate around, as is documented by examples in Figures 4A-4G.…”

“…Because λ is a material property and not depending on the mass, small rocks as pebbles behave as big ones. This, however, means that the 'ice rafts' [19,20] must have been formed in a different way. One hypothesis could be that water which comes from mountains far away ( Figure 1B) rushes downwards, flows under the ice, pushing the whole system upwards, while the iced surface breaks to ice floes, which still includes the big blocks.…”

“…Furthermore it was postulated that ice rafts form around the blocks [10], reducing the specific weight of the entire system, and providing buoyancy lifting the rocks off the lake bed, acting as 'rafts' rather than as 'sailors' , which were then driven by the winds over the plane surface [19,20]. This model was further developed by Kletetschka et al in a laboratory experiment [21].…”

Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion

“…2 ), including apparently synchronous high angle turns and sometimes reversals in travel direction [1] , [2] , [3] , [4] . The phenomenon of rock motion has excited considerable interest, and there is a scientific and popular literature extending back to the first report in 1948 [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] . Since then, theodolite mapping surveys, repeat photography and, most recently, the use of high resolution submeter GPS to map the rocks and their trackways have shown that the rocks move very episodically, often with no motion for several years to a decade or more [1] , [2] , [3] , [4] .…”