Nature – Singing Sand

Marco Polo thought it was evil spirits when he heard it in China. Residents of Copiapo, Chile, heard it emanating from a sandy hill and called it El Bramador because of its roar and bellow. Scientists today call it “singing sand,” but they all refer to the same thing: sand grains shuffling down the slopes of certain sand dunes producing a deep, groaning hum known as the “Song of Dunes.”

There is a lot of uncertainty surrounding what causes the sands to “sing,” but scientists have determined certain conditions and actions that must exist and/or occur in order for the desert sands to produce their song.

So exactly how does it happen? The sound you hear typically is more of a roar or boom than an actual song and can reach from 105 to 150 decibels of sound. That’s the equivalent of the sound you would experience at a sporting event or from a fighter jet engine. To put that in perspective of noise, a human continuously exposed to these levels of sound could experience ear damage within 15 minutes.

It is known that most of the time, sand produces sound at a frequency near 450 Hz (hertz equals the number of cycles per second). Some scholars have suggested that the thickness of the dry sand layer determines the frequency while others suggest it is the shear rate, the flow of the top dry sand layer moving at a constant speed over the stationary layer of moist sand below, each grain colliding with and rolling around its neighbors, creating a constant stream of collisions.

The difference in moisture content between the sand layers causes sound waves to bounce between the layers, increasing the resonance and volume of sound. What actually generates the noise is unclear, but one theory is that it is produced by friction between the sand particles. Another is that air is compressed between the particles and yet another suggests it is electrostatics.

Other contributing factors are believed to be the size of the grains of sand, typically 0.1 – 0.5 mm in diameter, which controls the actual sound and determines the pitch of the note, though the “why” is still unknown.

Humidity levels can also have an effect.

Crescent-shaped dunes (barchans) are the main source of sound, such as the singing dunes of the Badain Jaran Desert, which has some of the tallest sand dunes in the world at a height of 1,600 feet, whose song can be deafeningly loud.

Since this singing occurs in areas with little to no human presence, it is believed that the singing is triggered by powerful winds blowing over the sand rather than by any human influence. The wind shears off the thicker top layer of dry sand from the dunes, like an avalanche. The energy produced between the dry sand layer as it slides down the dune and the wet layer beneath causes this “booming” sound that continues for a time even after the dry sand avalanche has stopped and can reverberate for miles.

Each boom can be a single musical note on the musical scale. The thicker the layer of dry sand, the lower the musical note. A low G-sharp note on the musical scale was found in dunes in Morocco, however Dunes in Oman have produced a nine-note blare.

There are about 35 deserts around the world with dunes that produce the “Song of Dunes.” These include deserts found in the United States, China, Japan, Africa, Qatar and Egypt.

You can also find singing sand on the beach.

“For ye shall go out with joy, and be led forth with peace: the mountains and the hills shall break forth before you into singing, and all the trees of the field shall clap their hands” (Isaiah 55:12).

Sources: National Geographic – Singing Sand Dunes Explained by Shannon Fischer, October 13, 2012; World Atlas – What are Singing Sands? By Ferdinand Bada, June 29, 2018, in World Facts; and Wikipedia – Singing Sands