During his travels near the Gobi Desert in the 1200s, legendary explorer Marco Polo wrote about the haunting sounds of the sands. The dunes seemed to “fill the air with the sounds of all kinds of musical instruments” by day and with voices of demons and spirits by night.
His descriptions were difficult for many Europeans to believe. But Chinese writings from as far back as the ninth century confirm his experiences in the region.
In the 1800s, Chilean residents of a prosperous mining town named the area El Bramador (the belltower) after hearing the booming musical notes from the sandy hills. Charles Darwin also heard and commented on these singing sand hills when he visited the area.
In the 1940s, the British explorer of the Arabian and Gobi Deserts, R. A. Bagnold, was fascinated by the “weird chorus” emanating from the dunes, describing it as “the song of sirens who lure travelers to a waterless doom, the tolling of underground bells in sand-engulfed monasteries.
It’s only been in the last century that scientists have begun to understand the source of some of the various singing, booming, burping, roaring, and barking of sandy dunes and beaches. Research is ongoing, shedding new light each year as investigators combine old and new methods of applying the physics of sound to well-known noisy locations worldwide.
Listen For Yourself To The Sounds The Dunes Make
Singing Dunes in Morocco
The Singing Sands at Great Sand Dunes National Park & Preserve
The Science of Sound
Simply put, most dunes create sound the same way our voices are produced–by air moving through and creating friction in our vocal cords. Different frequencies are produced depending on speed and depth of movement.
The most common dune frequency is around 450 Hz, an E note. G and F are also recurrent in some dunes.
Frequencies from as low as 50 Hz to as high as 2500 Hz have been recorded. Some are at the very edges or out of the range of human hearing. Some of the higher frequencies are created on beach sand by simply walking along, causing a high-pitched squeak. But to have actual singing and booming requires giant dunes and a number of consistent factors.
Ingredients for a Singing Dune
The deserts best known for their sandy arias have specific characteristics in common. Scientists have so far identified the following requirements for singing, booming musical notes.
- Rounded, polished sand grains between 0.1-0.5 millimeters in diameter. The grains must have a high silica content. The size of the sand grains affects the tone.
- Very low humidity
- A slope of over 30 degrees
- Heat. Death Valley dunes may be as hot as 118 degrees in the summer.
- Height. Dunes over 120 feet high produce a more resonant, long-lasting sound.
- Gusting winds
Irregular grain shapes, vegetation, or increased moisture content can all prevent sands from booming or singing. Cooler weather slows the movement of the sound waves, preventing them from amplification.
Most research on the source and quality of dune songs is conducted during the hottest part of the summer months. Teams often prefer conducting experiments in the early morning or late evening, when they are less likely to be injured by the sun’s oppressive rays, but that’s not always possible. So gathering sufficient data for accurate conclusions can be slow and tedious.
Stirring Up a Song
The face of a dune is forever changing. Lighter winds may move sand slowly from one location to another. Then, higher gusts of wind cause piled dry sand to suddenly shear, creating a sand avalanche.
The avalanching sands trap air in the upper, drier layers, causing vibrations. The vibrations move between the top surface and the wetter, more compact layer beneath.
The dune itself amplifies the moving sand as trapped air is propelled through the rounded grains, causing a cacophony of musical notes or a booming sound as waves collide. The mass of tiny grains falling together flows like a liquid, increasing resonance and volume.
The thicker the sound layer, the lower the audible tone. The dune’s music may be heard as a humming sound or as a booming vocal call.
Seismic Waves and Thresholds
By definition, seismic activity is related to vibrations in the earth’s surface and is synonymous with earthquake activity. However, the shearing movement on the surface of dunes is also an earth-moving phenomenon and has been categorized as seismic in nature.
The seismic waves produced by dune avalanching are divided into two types:
- Primary (P-waves)–produce booming sounds and can travel through an entire dune
- Rayleigh waves–spread only across a dune’s surface, causing burping sounds
A massive, low-frequency wave can cause the whole body of anyone nearby to vibrate. Sands may continue to boom after an intense sand storm when the shearing (avalanching) has not yet stabilized. Bystanders can experience the effects of the sand’s movements through more than just their ears.
Both acoustic and seismic factors contribute to the length of each dune’s song. When there are many dunes, an entire choir or percussive orchestra may seem to be playing among the moving hills.
Sudden changes in the wind, such as starting or stopping, contribute to the booming noises. Minor collisions cause burping and barking noises. And prolonged avalanching generates musical notes.
The tone and volume of a dune also depend on passing two crucial thresholds. The first is the volume of sand that is pushed by the wind. The greater the weight of sand, the more amplified the sound.
The second threshold is the speed needed to generate sufficient friction to create sound. Together, volume and speed make a sustained musical tone–up to fifteen minutes long.
Where Do the Sands Sing?
There are about thirty identified sites for singing and other noise-making sands worldwide. Not all are deserts. Some beaches with well-developed shore dunes, or particularly rounded sand grains may produce high-pitched squeals or whistles when walking or if a stick or other object is pulled through the surface.
Some well-known sites include