A NEW OCCURRENCE OF SAILING STONES

Numerous geologic phenomena have been observed over the years, perhaps none more so than the phenomena of sliding or sailing stones reported from the surfaces of playas. In the United States, two occurrences of sailing stones have been reported: Racetrack Playa in Death Valley National Park, California, and Bonnie Claire Playa in Nevada.

To the above can be added: Alkali Flat Playa in Nevada. Located southwest of Tonopah, Nevada, Alkali Flat Playa is oriented roughly SW-NE, and is approximately 125 km² in area. While travelling over the playa in January 2015, we noted six small rocks near its northwestern edge, with long, curved grooves or trails behind them in the surface silts of the playa. All six rocks are less than 15 cm in diameter; trails vary in length from 6 m to 10 m, and possibly in one case, up to 22 m. Most trails bear a north to northwesterly orientation from the rocks, but two of the rocks also exhibit short, northeasterly components.

The trailed rocks appear to have been derived from a N-S trending rocky ridge 4-5 km away, bordering the playa to the northwest. Peak elevation of the ridge is 300 m higher than the adjacent playa and is composed of Paleozoic sedimentary and meta-sedimentary rock units, as are the trailed rocks.

The trailed rocks were deposited onto the playa by downslope erosional processes, aided perhaps by high rainfall events. The tracks left on the playa surface indicate that the rocks moved to their positions during periods of northwesterly to northerly winds, with two of the rocks indicating slightly northeasterly winds as well. As shown by work at Racetrack Playa (Norris, et al., 2014), GPS-instrumented rocks were seen to move as ice that had formed on the playa during winter began to break up under the action of morning sun and steady, light winds. Likewise, we suggest that the trailed rocks of Alkali Flat Playa moved to their locations on the playa surface during the winter months, as ice that had formed on the playa during the winter began to break up under morning sunshine and steady winds. Winter winds in the area generally come from the north to northwest, with sustained winds up to 32-48 km/hr at times. Thus, Alkali Flat Playa joins Racetrack Playa, and Bonnie Claire Playa (Clements, 1952) as the third playa in the western United States exhibiting the phenomenon of sailing stones.