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Sliding rocks at the Racetrack, Death Valley; what makes them move?

John B. Reid, Edward P. Bucklin, Lily Copenagle, Jon Kidder, Sean M. Pack, Pratigya J. Polissar and Michael L. Williams
Sliding rocks at the Racetrack, Death Valley; what makes them move?
Geology (Boulder) (September 1995) 23 (9): 819-822


Sharply angular boulders as large as 320 kg sit on the Racetrack Playa, Death Valley, California; trails leading to them indicate that the rocks have moved large distances. The process has never been witnessed. Although high winds and a wetted surface seem necessary, controversy persists about the need for other conditions, especially ice sheets. On the basis of experiments with a wetted Racetrack surface (soft mud approximately 3 cm deep), we find the effective coefficient of friction to be surprisingly high, approximately 0.8. Movement by wind alone of moderate-sized (20 kg) rocks with cubic shape requires sustained winds close to the ground of approximately 80 m/s ( approximately 180 mph). Larger flat-lying rocks require much higher winds. To assess the ice-sheet hypothesis, we mapped a large number of tracks into a precise coordinate system with an electronic theodolite. Certain tracks, separated by <1 to approximately 830 m, have nearly identical curving patterns near their starts. The distance between a distinctive bend on one such track and its mate on another matches the distance for another mated pair of bends on these same tracks within several centimetres, even for tracks 830 m apart. As proposed by Stanley (1955), it seems that the rocks, resting on mud, were locked into a single floating ice sheet, in this case at least 850 X 500 m. Final resting places of these rocks are much more widely scattered than their starting points, suggesting that the sheet broke into smaller plates. Large ice sheets can move rocks even with light winds and may explain the gentle curvature of tracks hundreds of metres long, a pattern very unlikely with gusty high winds and no ice.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 23
Serial Issue: 9
Title: Sliding rocks at the Racetrack, Death Valley; what makes them move?
Affiliation: Hampshire College, School of Natural Science, Amherst, MA, United States
Pages: 819-822
Published: 199509
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 9
Accession Number: 1995-059777
Categories: GeomorphologySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N35°45'00" - N37°30'00", W118°45'00" - W115°40'00"
Secondary Affiliation: University of Massachusetts, Amherst, MA, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199521
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