Science

Secrets of the Singing Sand Dunes

The dunes at Sand Mountain in Nevada sing a note of low C, two octaves below middle C. In the desert of Mar de Dunas in Chile, the dunes sing slightly higher, an F, while the sands of Ghord Lahmar in Morocco are higher yet, a G sharp. Scientists already knew that the sounds were generated by avalanches, but were not sure how. One thought had been that the force of an avalanche could cause an entire dune to resonate like a flute or a violin. But if that were true, dunes of different sizes and shapes should produce a cacophony of notes instead of one characteristic tone.

Now, after five years of research, visiting sand dunes in Morocco, Chile, China and Oman, a team of scientists from the United States, France and Morocco say they have the answer.

In a paper that will appear in Physical Review Letters, the scientists say that collisions between sand grains cause the motions of the grains to become synchronized. The outer layer of the dune vibrates like the cone of a loudspeaker. The particular note depends primarily on the size of the grains.

 Indeed, no dune was required at all. The scientists shipped sand from a Moroccan desert to a Paris laboratory and reproduced the singing by pushing the sand around with a metal blade. The most beautiful dune tune comes from the sands of Oman.