The Physics of a Dune's Song
In about 35 desert locations worldwide, certain sand dunes produce a loud, low-pitched rumble when sand avalanches down their face. The Kyzylkum Desert holds some of these rare "singing dunes." The sound, which can reach 105 decibels and be heard up to 10 kilometers away, is not a trick of the wind but a product of physics. For a dune to sing, a specific set of conditions must be met. The sand grains need to be spherical, contain silica, and measure between 0.1 and 0.5 millimeters in diameter. Most importantly, the sand must be extremely dry; any significant moisture will silence the effect.
The sound begins when sand on a steep slope—typically the crescent-shaped dunes known as barchans—begins to slide. As a layer of sand shears and moves over the stationary sand beneath it, the billions of uniform grains collide and vibrate in unison. This synchronized motion creates pressure waves. The entire face of the dune is the diaphragm of a loudspeaker, amplifying these waves into the powerful hum that reverberates across the desert. The exact frequency of the sound, often between 75 and 105 Hertz, appears to be controlled by the size of the sand grains.