SAILING STONES

Sailing stones, sliding rocks, and moving rocks all refer to a geological phenomenon where rocks move in long tracks along a smooth valley floor without human or animal intervention. They have been recorded and studied in a number of places around Racetrack Playa, Death Valley, California ,where the number and length of travel grooves are notable. The force behind their movement is not confirmed and is the subject of research.

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 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 the direction it came from. Trail length also varies – two similarly sized and shaped rocks may travel uniformly, then one could move ahead or stop in its track.

Most of the so-called sailing stones originate from an 850 ft-high (260 m) hillside made of dark dolomite on the south end of the playa, but some are intrusive igneous rock from adjacent slopes (most of those being tan-colored feldspar-rich syenite). Tracks are often tens to hundreds of feet long, about 3 to 12 inches (8 to 30 cm) wide, and typically much less than an inch (2.54 cm) deep.

A balance of specific conditions are thought to be needed for stones to move:
1.A saturated yet non-flooded surface,
2. A thin layer of clay,
3.Very strong gusts as initiating force, and
4.Strong sustained wind to keep stones going

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, feel is too heavy for the area's wind to move. They maintain that ice sheets around the stones either help to catch the wind or move in ice floes.

Wind and ice both are the favoured hypothesis for these mysterious sliding rocks. Noted in Don J. Easterbrook's "Surface Processes and Landforms", he mentioned that because of the lack of parallel paths between some rock paths, this could be caused by the breaking up of ice resulting in alternate routes. Even though the ice breaks up into smaller blocks, it is still necessary for the rocks to slide.

A study published in 2011 postulated that small rafts of ice form around the rocks and when the local water level rises, the rocks are buoyantly floated off the soft bed thus reducing the reaction and friction forces at the bed. Since this effect depends on reducing friction, and not by increasing the wind drag, these ice cakes need not have a particularly large surface area if the ice is adequately thick, as the minimal friction allows the rocks to be moved by arbitrarily light winds.