Sommaire:

Many desert sand dunes emit a loud sound with a characteristic tremolo around a well defined frequency whenever sand is avalanching on their slip face. This phenomenon, called the "song of dunes", has been successfully reproduced in the lab, at a smaller scale. In all cases, the spontaneous acoustic emission in the air is due to a vibration of the sand, itself excited by a granular shear flow. I will present a complete characterisation of the phenomenon : frequency, amplitude, source shape, vibration modes, instability threshold. I will then review the most prominent characteristics of acoustic propagation in weakly compressed granular media. Finally, I will describe the different mechanisms proposed to explain booming avalanches. I will show how measurements performed to test these theories against data allow one to contrast explanations that must be rejected (sound resonating in a surface layer of the dune, for instance) with those that still need to be confirmed to reach a scientific consensus, amplification of guided elastic waves by friction, in particular.

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