Journal de géologie et géophysique
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Abstrait

A Miniscule System of a ‘Sailing Rock’

Brigitte Schoenemann

The ‘Sailing Rocks’ of Death Valley, California are known worldwide, and the enigma of how they move over a desert ground without intervention of animal or human forces, still remains one of the great natural mysteries. There exist different theories about how these movements happen, the most recent was that ice-rafts build up below and around the rocks, which are then pushed forward by moving ice floes. Earlier theories regarding this phenomenon describe the influence of wind, and flows of melting water on fine soil material (Hypothesis of ‘Sailing Rocks’). We describe here the same phenomenon, observed not in a large rock weighing several hundreds of kilograms, but in a small pebble of about 2 cm in size. A clear analysis of the conditions under which its movement took place has allowed the formulation of the minimum conditions under which a rock starts moving. Ice rafts may be sufficient but are not necessary. Here we show that pebbles sail driven by the wind over a watery surface that covers an icy but water saturated substrate, similar to an aquaplaning car. The same physical rules apply whatever the scale, to this small system as well as to the large sailing rocks of Death Valley.