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.

Since at least the time of Marco Polo, desert travelers have heard the songs of the dunes, a loud — up to 115 decibels — deep hum that can last several minutes. (You can listen to them here.) While the songs are steady in frequency, the dunes do not have perfect pitch. At Sand Mountain, for example, dunes can sing slightly different notes at different times, from B to C 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.

Image A sand dune. Credit... Stéphane Douady

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.