Sailing Stones of Death Valley - 1900

Sailing Stones of Death Valley

Sailing stones, sliding rocks, and moving rocks all refer to a geological phenomenon where rocks move and inscribe long tracks along a smooth valley floor without human or animal intervention. Tracks from these sliding rocks have been observed and studied in various locations, including Little Bonnie Claire Playa in Nevada, and most notably Racetrack Playa, Death Valley National Park, California, where the number and length of tracks are notable. At Racetrack Playa, these tracks have been studied since the early 1900s, yet the origins of stone movement are not confirmed and remain the subject of research for which several hypotheses exist.

The stones move only every two or three years and most tracks develop over three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms tend to wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different track in the stone's wake.

Trails differ in both direction and length. Rocks that start next to each other may travel parallel for a time, before one abruptly changes direction to the left, right, or even back to the direction from which it came. Trail length also varies – two similarly sized and shaped rocks may travel uniformly, then one could move ahead or stop in its track.

The first documented account of the sliding rock phenomenon dates to 1915, when a prospector named Joseph Crook from Fallon, Nevada visited the Racetrack Playa site. In the following years, the Racetrack sparked interest from geologists Jim McAllister and Allen Agnew, who mapped the bedrock of the area in 1948 and published the earliest report about the sliding rocks in a Geologic Society of America Bulletin. Their publication gave a brief description of the playa furrows and scrapers, stating that no exact measurements had been taken and suggesting that furrows were the remnants of scrapers propelled by strong gusts of wind – such as the variable winds that produce dust-devils – over a muddy playa floor.Controversy over the origin of the furrows prompted the search for the occurrence of similar phenomena at other locations. Such a location was found at Little Bonnie Claire Playa in Nye County, Nevada, and the phenomenon was studied there as well.

Naturalists from the National Park Service later wrote more detailed descriptions and Life magazine featured a set of photographs from the Racetrack. In 1952, a National Park Service Ranger named Louis G. Kirk recorded detailed observations of furrow length, width, and general course. He sought simply to investigate and record evidence of the moving rock phenomenon, not to hypothesize or create an extensive scientific report. Speculation about how the stones move started at this time. Various and sometimes idiosyncratic possible explanations have been put forward over the years that have ranged from the supernatural to the very complex. Most hypotheses favored by interested geologists posit that strong winds when the mud is wet are at least in part responsible. Some stones weigh as much as a human, which some researchers, such as geologist George M. Stanley, who published a paper on the topic in 1955, feel is too heavy for the area's wind to move. After extensive track mapping and research on rotation of the tracks in relation to ice floe rotation, Stanley maintained that ice sheets around the stones either help to catch the wind or that ice floes initiate rock movement.

Progress in the 1970s

Bob Sharp and Dwight Carey started a Racetrack stone movement monitoring program in May 1972. Eventually thirty stones with fresh tracks were labeled and stakes were used to mark their locations. Each stone was given a name and changes in the stones' position were recorded over a seven-year period. Sharp and Carey also tested the ice floe hypothesis by corralling selected stones. A corral 5.5 feet (1.7 m) in diameter was made around a 3 inches (7.6 cm) wide, 1 pound (0.45 kg) track-making stone with seven rebar segments placed 25 to 30 inches (64 to 76 cm) apart. If a sheet of ice around the stones either increased wind-catching surface area or helped move the stones by dragging them along in ice floes, then the rebar should at least slow down and deflect the movement. Neither appeared to occur; the stone barely missed a rebar as it moved 28 feet (8.5 m) to the northwest out of the corral in the first winter. Two heavier stones were placed in the corral at the same time; one moved five years later in the same direction as the first but its companion did not move during the study period. This indicated that if ice played a part in stone movement, then ice collars around stones must be small.

A panorama of the Milky Way with the tracks of sailing stones below. Notice the stone on the right side.

Ten of the initial twenty-five stones moved in the first winter with Mary Ann (stone A) covering the longest distance at 212 feet (65 m). Two of the next six monitored winters also saw multiple stones move. No stones were confirmed to have moved in the summer and some winters none or only a few stones moved. In the end all but two of the thirty monitored stones moved during the seven-year study. At 2.5 inches (6.4 cm) in diameter, Nancy (stone H) was the smallest monitored stone. It also moved the longest cumulative distance, 860 feet (260 m), and the greatest single winter movement, 659 feet (201 m). The largest stone to move was 80 pounds (36 kg).

Karen (stone J) is a 29 by 19 by 20 inches (74 by 48 by 51 cm) block of dolomite and weighs an estimated 700 pounds (318 kg). Karen did not move during the monitoring period. The stone may have created its 570 feet (170 m) long straight and old track from momentum gained from its initial fall onto the wet playa. However, Karen disappeared sometime before May 1994, possibly during the unusually wet winter of 1992 to 1993. Removal by artificial means is considered unlikely due to the lack of associated damage to the playa that a truck and winch would have caused. A possible sighting of Karen was made in 1994 a half mile (800 m) from the playa. Karen was rediscovered by San Jose geologist Paula Messina in 1996.

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