Sailing stones

Wandering Rocks (English wandering rocks or sailing stones ) are a phenomenon on the Racetrack Playa (Eng. "racetrack - level " ) in Death Valley.

On a dry lake in the northwest of Death Valley National Park travel up to 350 -pound boulders sporadically over the almost perfectly flat plane and leave this mark on the terrain surface. The movements could not be observed directly from people so far, but typically take place in winter. Most common are movements with a tendency from south to north and northwest. The grooves are between a few centimeters and about 1000 meters long, some straight, some often tortuous. After no longer than a few years, the grooves disappear by erosion, which complicates the tracking of the sliding of the stones over time.

Was the cause of the phenomenon and there are various theories, according to recent studies, the formation of ice is discussed as a key factor.

Location and description

The Racetrack Playa is a community on about 1120 m above the sea level of around 5 to 3 km Size in a remote part of the park. It is accessible from undeveloped part of the park via a 40 km long gravel road, which is to drive in most seasons only with four-wheel drive and high ground clearance. This part of the national park is a designated wilderness area, so only the marked trails may be driven on.

The plane originated from a now- dry lake between two mountain chains Cottonwood Range and Last Chance Range. The surface consists of a high proportion of clay, which breaks in regularly published, small blocks on drying out in summer. Rainfall is in the Desert National Park in winter only, the clay takes this up quickly and precipitate is moist after around 10 mm and develops a smooth surface with reduced friction.

Investigations

It is certain that the actual movement can be explained by the wind. Especially during the fierce winter storms hurricane strength is often achieved in the area. But this alone is not enough, because in order to move up to 350 -pound rock, theoretically wind speeds of over 800 kilometers per hour would be required.

Since the area is a nature reserve and is reported as " pristine wilderness ", permanent installations such as fixed mounted cameras to monitor are not allowed. Especially in the time of the strongest movements during rainy periods the access is completely prohibited, since each footprint permanently changed in the soft ground then the surface.

In recent studies, all were mapped "wandering rocks " with GPS support and monitor their position regularly. It turned out that neither the size or the weight nor the shape of the individual rocks have a verifiable impact on speed or linearity of the hike.

Rather, the migration appears to be strongly dependent on the position of each rock. For example, there are the longest and straightest tracks in places that act as a natural wind tunnel and so channel and amplify the movement of air. The most " twisted " Traces, however, are located in a region where two such air currents meet and form vortices. Nevertheless, the question remains how the wind up to 350 kg can move heavy rocks so easily.

Theories, hypotheses, explanations

• One current hypothesis constituting the bacteria present in the soil in rainy seasons on the surface of a " lubricating film ", which greatly reduces the friction between the stone and soil.

• Another theory states that forms in the night temperatures during the winter months ice that could move like ice floes on the rocks listed on the Racetrack Playa level. This would also explain why the larger rocks migrate further than small, as they slow down more slowly when they are first going. Especially during the ice melt, decreasing the rock in the sand where those ominous traces would arise.

• 2011, a study was published, after the stones freeze in ice floes, so that the common specific gravity is greatly reduced. The wind moves these clods then. Traces are formed when stones are only raised incomplete and still drag on the ground.

• At the annual fall meeting of the American Geophysical Union ( AGU) from 13 to 17 December 2010 in San Francisco presented the NASA geologist Gunther Kletetschka before his gained in the laboratory experiment theory that the rocks in the course of winter storms from a layer of ice on floats subsequently flowing water can be lifted and moved with the constraints deriving currents and turbulence. This theory also explains edge phenomena such as the emergence of tracks without stones or with dimensions that differ from those of the stones. In nature Kletetschka had marked some of the stones with GPS receivers in March 2010 and found no movement to a certain time of reporting, which would be explained by its results so far by the lack of summer weather conditions. More clues and ultimately the eventual proof of the correctness of the theory is to provide a more extensive instrumentation of the stones.

• Researchers admit not every movement of the stones could be attributed to the ice. Rather, if it were a complex mechanism between wind, ice, rain, clayey soil and algae, which can be explained not unique to this day.