Several years ago I hiked up the Kelso Dunes in the Mohave Desert in California, then sat and slid down them to the bottom. If you’ve ever tried this, or heard a similar avalanche of sand, you know that the sand emits a distinctive and mysterious low whining sound, which some people call “singing” and some call “booming.” According to physicist Bruno Andreotti, who’s been studying the phenomenon, the noise can be as 105 decibels and, being low-frequency, can be heard up to 10 kilometers away.
Studying actual dunes, Andreotti found that vibrations in the sand act like slow-moving elastic sound waves that run across the surface of the dunes. The vibration of the sand bed tends to synchronize the collisions, and the surface of the sand bed acts like the membrane in a loudspeaker, accounting for the sound.
Try it next time you’re out in the desert.