In deserts through out the world many people have heard a bizarre low pitch droning coming from the sand dunes.
In Central Asia these sounds were attributed to malignant spirits, evil demons and goblins. Today this phenomenon is known as “singing sand,” and it’s eerie!
Italian explorer Marco Polo heard it in the Gobi Desert in the 13th century and described the strange noises as sounding like “all kinds of musical instruments, and also of drums and the clash of arms”. In Central Asia these sounds were attributed to malignant spirits, evil demons and goblins.
Today this phenomenon is known as “singing sand” (sand booming and sand barking as well). It occurs when grains cascade down the sides of the dunes either by the wind or people walking and sliding down.
Around 40 locations worldwide are known to produce this phenomenon, though it doesn’t occur through the whole year or across the entire dune.
Scientists have even found that Sand Mountain in Nevada gives a low C, Mar de Dunas in Chile gives an F, and the sands of Ghord Lahmar in Morocco give a G sharp.
Certain sand dunes are known to emit these noises for up to 15 minutes and can be heard around 10 kilometers away on a daily basis.
Sound frequency tends to range from 65 to 120 Hertz and its volume can reach 110 decibels, with researchers noting that its tone can change according to season. People have likened it’s low frequency droning to that of an airplane.
For centuries scientists have remained mystified as to how sand makes these noises, how separate dunes can “sing” different tunes and even produce a range of notes simultaneously. A few of the many differing theories surrounding singing sand are that:
- waves are produced in the surface of the avalanche and amplified via friction of the grains rubbing together;
- vibrations from flowing sand grains synchronize and combine to push air together, like a loud speaker diaphragm;
- the size of grains determine which notes are heard;
- the singing is produced by the contrast in acoustic properties between the sand and a concrete-hard layer of grains cemented together by calcium carbonate located up to two meters below the surface.
However there is still no consensus as to how the sand is able create sounds what resemble musical notes.
A similar phenomenon is squeaking sand beaches.