In a few places around the world sand dunes make a sound like a sad tuba when you walk on them.
In the Saharan sand dunes of eastern Morocco, walking along the crest of a certain type of sand dune produces a cry like that of a lost elephant, or an orchestra’s forlorn horn section. This phenomenon occurs in many different crescent dunes around the world: in California, Namibia, Qatar, Kazakhstan, Chile, Dunhuang, and others. Hear it here:
The so-called song of the dunes, or the singing sand, is not a well understood phenomenon. We know a little about the conditions under which it occurs – the sand has to be a specific size and humidity, and it has to be a particular type of sand – but the mechanism that produces such an eerie sound is still a mystery.
A 2012 study found that the size of the sand grains affects the pitch of the sound, and hypothesised that it is actually millions of little sand collisions, too small to hear individually but collectively producing that deep hum. Others have suggested that the sound reverberates off a damp layer of sand underneath the surface.
Similar sound effects can also be produced by beach sand, but they tend to be at a much higher pitch – more like a scream than a hum. Like the singing sand dunes, this phenomenon is not well understood, but the most reasonable and logical conclusion is clear: the sand is haunted.