Picture a waste land of sand dunes and a big, empty sky.

If you were venturing alone through this vast desert landscape, would you think you'd gone crazy if you began hearing sounds like organs and bells, cannon fire and thunder? In fact, noises like these can actually arise from ordinary sand dunes.

Singing sand dunes have been described in the myths of desert cultures for thousands of years. Their booming or harmonic noises have been recorded by scientists in such places as China, Saudi Arabia, Nevada, and California. While this phenomenon is not yet completely understood, there are a few things scientists are pretty sure about.

Singing or thundering noises are produced by moving sand, generated as the sand grains rub against each other. If you've ever walked on a beach and noticed that the sand seemed to squeak underfoot, then you've heard a miniature version of this same phenomenon.

In the desert, singing sand is caused by a certain type of avalanche, in which a flat area of sand near the top of a dune shears away, then slides down the face of the dune more or less intact, kind of like a plate sliding off an uneven table. At the interface between the moving bulk of sand and the rest of the dune there's likely to be a lot of activity. Individual sand grains jump back and forth between the two masses of sand, creating a noisy vibration. The size and consistency of the grains, and how smooth or rough they are, all help determine the type of sound a sand dune will make, or whether it will sing at all.