Many desert sand dunes emit a loud and harmonious sound as they avalanche, with large amounts of sand sliding down the dune. An avalanche spontaneously occurs when the surface angle is locally larger than a threshold called the static angle (usually 32 to 35°). The flow freezes when the slope is relaxed below a second angle called the dynamical angle or the angle of repose (30 to 32°). The phenomenon was first documented in a Chinese manuscript dating back to the ninth century. In 1298, Marco Polo described it as the sounds of all kinds of musical instruments—and more ordinary, drums—filling the air. This loud sound, which can be heard up to 10 km (6 mi) away, resembles the sound of a foghorn or of a low-flying twin-engined jet.
 Hear the sounds of the singing dune as a person slides down the slope.
Bruno Andreotti
Université Denis Diderot (Paris 7)
Laboratoire de Physique et Mécanique des Milieux
Hétérogènes
Paris, France
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