Wandering rocks

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Wandering rocks on Racetrack Playa

Wandering rocks ( engl. Wandering rocks or sailing stones ) are a phenomenon on the Racetrack Playa ( Eng. "Racetrack level") in California's Death Valley National Park .

On a dry lake in the northwest of the Death Valley National Park, boulders weighing up to 350 kg wander sporadically over the almost completely flat plain, leaving traces on the surface of the terrain. The movements, which humans could only directly observe in 2014, mostly take place in winter. The most common are movements with a tendency from south to north and northwest. The grooves are between a few centimeters and about 1000 meters long, sometimes dead straight, sometimes twisted many times. After a few years at the latest, the grooves disappear again due to erosion, which makes it difficult to follow the sliding of the stones over long periods of time.

There were and still are various theories about the cause of the phenomenon, at the end of August 2014 it was announced that researchers and geologists at the Scripps Institution of Oceanography in La Jolla had clarified the mystery of the Wandering Rocks .

Location and description

The Racetrack Playa is a plateau about 5 by 2 km in size at about 1120 m above sea level in a remote part of the national park. It can be reached from the developed part of the park via an approximately 40 km long gravel road, which in most seasons can only be driven with four-wheel drive and high ground clearance. This part of the national park is designated as a wilderness area, so only the designated slopes may be used.

The plain emerged from a now dry lake between the two mountain ranges Cottonwood Range and Last Chance Range . The surface consists to a large extent of clay, which breaks up into regularly appearing, small blocks when it dries out in summer. Precipitation occurs in the desert national park only in winter, the clay soil absorbs it quickly and becomes damp after around 10 mm of precipitation and develops a smooth surface with reduced friction.

Investigations

Two wandering rocks
Wandering rock

It is considered certain that the actual movement can be explained by the wind. Especially during the fierce winter storms is often in the area hurricane strength achieved. But this alone is not enough to move the rocks weighing up to 350 kg. This would theoretically require wind speeds of over 800 kilometers per hour.

Since the area is under nature protection and has been designated as “untouched wilderness”, permanent installations such as fixed cameras for surveillance are not permitted. Access is completely forbidden, especially during the periods of strong movement during rainy periods, as every footprint in the soft ground changes the surface permanently.

In more recent investigations, all “moving rocks” were mapped with GPS support and their position was regularly monitored. It turned out that neither the size or weight nor the shape of the individual rocks have a comprehensible influence on the speed or straightness of the hike.

Rather, the hike seems to be strongly dependent on the position of the respective rock. For example, the longest and straightest tracks are in places that act like a natural wind tunnel, channeling and increasing air movement. The most “twisted” tracks, on the other hand, are located in an area where two such air currents meet and form eddies. Still, the question remains how the wind can move rocks weighing up to 350 kg so easily.

Theories, hypotheses, attempts to explain

bacteria
  • According to a current hypothesis , the bacteria present in the soil form a "lubricating film" on the surface during rainy seasons, which greatly reduces the friction between stone and soil.
ice
  • Another thesis says that ice forms at night temperatures during the winter months, which can move the rocks on the level called Racetrack Playa like on ice floes. This would also explain why the larger rocks migrate further than small ones, as they brake more slowly once they are in motion. Especially as the ice melts, the rock sinks into the sand, where those ominous traces would arise.
  • In 2011 a study was published, according to which the stones freeze in ice floes, which greatly reduces the joint specific weight. The wind then moves these clods. Traces arise when stones are not lifted completely and still grind on the ground.
  • At the annual autumn meeting of the American Geophysical Union (AGU) from December 13th to 17th, 2010 in San Francisco, NASA geologist Gunther Kletetschka presented his theory, which was obtained in a laboratory experiment, according to which the rocks in the course of winter storms from a layer of ice Following water floats, lifts and moves according to the resulting currents and turbulence. This theory also explains peripheral phenomena such as the formation of tracks without stones or with dimensions that differ from those of the stones. In March 2010, Kletetschka had marked some of the stones in nature with GPS receivers and had not detected any movement up to a certain reporting time, which, according to his previous results, would be explained by the lack of weather conditions in summer. A more extensive instrumentation of the stones should provide further information and ultimately the possible evidence for the correctness of the theory.
Algae in interaction with other factors
  • Researchers admit that not every movement of the stones can be attributed to the ice. Rather, it is a complex mechanism between wind, ice, rain, clayey soil and algae, which has not yet been clearly explained.
The traces of the stones on December 20, 2013. Also noticeable are the few immobile stones

Explanation

In August 2014, a study was published that explains the secret of the wandering rocks. Researchers observed the rocks over an extended period of time using GPS and time-lapse photography. On December 20, 2013, the movement of over 60 stones was documented and proven. Some of them moved up to 224 meters at speeds of up to 5 meters per minute.

The prerequisite for movement are thin, only a few millimeters thick ice sheets. When these begin to melt, even low winds of three Beaufort or more are enough to set the stones in motion. The actual movement is brought about by the pressure of the ice sheets, which are heavy over a large area, despite their small thickness. While the necessary temperature and wind conditions are typical for the coldest periods of the local climate, they must coincide with previous precipitation in the form of rain or already melted snow. These conditions are so rare that it can often take years or even decades. If the basic conditions are given, around noon, after the ice surface has thawed, the movement of ice sheets on open water can begin and move the stones.

The wandering rocks in the film

The Oscar- winning film The Desert Is Alive mentions the phenomenon of the Wandering Rocks.

literature

  • Paula Messina: The Sliding Rocks of Racetrack Playa, Death Valley National Park, California: Physical and Spatial Influences on Surface Processes . Dissertation, City University of New York, Department of Earth and Environmental Sciences, New York 1998 (unpublished).
  • Paula Messina, Phil Stoffer, Keith C. Clarke: Mapping Death Valley's Wandering Rocks. In: GPS World . The business and technology of GNSS , Vol. 8 (1997), No. 4, pp. 34-44, ISSN  1048-5104 .
  • Robert P. Sharp, Allen F. Glazier: Geology Underfoot in Death Valley and Owens Valley . Mountain Press Publ., Missoula 1997, ISBN 0-87842-362-1 .
  • George M. Stanley: Origin of playa stone tracks. Racetrack Playa, Inyo County, California . In: Geological Society of America Bulletin , 66 : 1329-1350 (1955), ISSN  0016-7606 .
  • John B. Reid Jr., Edward P. Bucklin, Lily Copenagle, Jon Kidder, Sean M. Pack, Pratigya J. Polissar, Michael L. Williams: Sliding rocks at the Racetrack, Death Valley. What makes them move? In: Geology , Vol. 23 (1995), Issue 9, pp. 819-822, ISSN  0091-7613 .
  • Robert P. Sharp, Dwight L. Carey, John B. Reid Jr., Pratigya J. Polissar, Michael L. Williams: Sliding rocks at the Racetrack, Death Valley. What makes them move? Discussion and Reply . In: Geology , 25 : 766-767 (1996), ISSN  0091-7613 .

Web links

Commons : Sliding rocks of Racetrack Playa  - Collection of images, videos and audio files

Individual evidence

  1. ↑ 'Wandering stones' of Death Valley explained , accessed August 28, 2014; Jan Dönges: Death Valley - the mystery of the "Wandering Stones" finally solved . In: Spektrum.de from August 28, 2014.
  2. ↑ The Racetrack in the Geographic Names Information System of the United States Geological Survey
  3. ↑ wilderness.net: Death Valley Wilderness
  4. ↑ Motorist ruins natural wonders in the valley of death in Der Spiegel , on September 25, 2016
  5. ^ On the research history: Joseph Stromberg: How Do Death Valley's “Sailing Stones” Move Themselves Across the Desert? , Smithsonian.com, June 10, 2013
  6. ↑ Ralph D. Lorenz, Brian K. Jackson, et al .: Ice rafts not sails: Floating the rocks at Racetrack Playa  ( page no longer available , search in web archives )  Info: The link was automatically marked as broken. Please check the link according to the instructions and then remove this notice. . In: American Journal of Physics , Volume 79, Issue 1 (January 2011), page 37 ff. Doi: 10.1119 / 1.3490645@1@ 2Template: Dead Link / ajp.aapt.org  
  7. ↑ Axel Bojanowski : Researcher explains the mystery of the stray rocks . In: Der Spiegel from December 16, 2010 (popular science report)
  8. ↑ RD Norris, JM Norris, RD Lorenz, J Ray, B Jackson: Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion. . In: Public Library of Science (Ed.): PLoS ONE . 9, No. 8, August 27, 2014. doi : 10.1371 / journal.pone.0105948 .

Coordinates: 36 ° 40 ′ 52.7 "  N , 117 ° 33 ′ 45.7"  W.