Sailing stones

Sailing stones, also known as sliding rocks, rolling stones, and moving rocks, are a geological phenomenon where rocks move and inscribe long tracks along a smooth valley floor without human or animal intervention. Instead, rocks move when large ice sheets a few millimeters thick floating in an ephemeral winter pond start to break up during sunny days. These thin floating ice panels, frozen during cold winter nights, are driven by wind and shove rocks at up to 5 m/min.

Trails of sliding rocks have been observed and studied in various locations, including Little Bonnie Claire Playa in Nevada, and most famously at Racetrack Playa, Death Valley National Park, California, where the number and length of tracks are notable.

The Racetrack’s stones speckle the playa floor, predominantly in the southern portion. Historical accounts identify some stones around 100 m (300 ft) from shore, yet most of the stones are found relatively close to their respective originating outcrops. Three lithologic types are identified: (1) syenite, found most abundant on the west side of the playa; (2) dolomite, subrounded blue-gray stones with white bands; and (3) black dolomite, the most common type, found almost always in angular joint blocks or slivers. This dolomite composes nearly all stones found in the southern half of the playa, and originates at a steep promontory, 260 m (850 ft) high, paralleling the east shore at the south end of the playa. Intrusive igneous rock originates from adjacent slopes (most of those being tan-colored feldspar-rich syenite). Tracks are often up to 100 m (330 ft) long, about 8 to 30 cm (3 to 12 in) wide, and typically much less than 2.5 cm (1 in) deep. Most moving stones range from about 6 to 18 in (15 to 46 cm) in diameter.

Stones with rough bottoms leave straight 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.

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Wikipedia