What Are Singing Sand Dunes?
In about 35 deserts on every inhabited continent there are dunes that “sing.” When sand avalanches down their leeward faces the slope gives off a low-pitched, single-note boom that can last up to two minutes and be heard ten kilometers away. Bedouins have called the phenomenon “the voice of the desert” for at least a thousand years; Marco Polo wrote of evil spirits that “beat great drums” in the Gobi. Today geophysicists simply call them booming or singing sand dunes.
Sound, Not Mirage
The noise is real, measurable, and repeatable. Recordings made by the French research group CEA show sound-pressure levels of 105 dB at one meter—about the volume of a passing subway train. The pitch hovers between 70 and 110 Hz, the bottom two octaves of a piano. What is strange is that the dune acts like a gigantic loudspeaker: the sand itself vibrates, yet the surrounding air carries the note away with almost no loss.
The Physics Behind the Boom
Four conditions must come together. First, the grains must be almost perfectly spherical, 0.1–0.5 mm in diameter, and coated with a thin film of silica gel. Second, they must contain 1–3 % silt-size dust that separates the grains just enough for them to jostle. Third, the dune must be at least 30 m tall so gravity can create a rapid avalanche. Fourth, the humidity must be below 2 %; any more and capillary bridges glue the grains together.
When a person slides down the slope or when wind triggers an avalanche, grains move in sheets. Each grain bounces roughly once every millisecond, creating a shear layer roughly 2 cm thick. The impacts act like stick-slip friction on a violin string: they generate elastic waves that synchronize into a single frequency. Because the dune is layered—an outer dry crust and an inner moist core—it behaves like the sounding board of a cello; the internal waves bounce back and forth, amplify, and the whole dune becomes a resonator.
Where to Hear the Concert
- Dunhuang Mingsha Shan, Gobi Desert, China – 200 m star-shaped dune that sang as early as the Han dynasty (208 BCE).
- Badain Jaran, Inner Mongolia – the tallest stationary dunes on Earth at 500 m, producing notes closer to 65 Hz.
- Kelso Dunes, Mojave National Preserve, USA – accessible by foot; visitors trigger avalanches on a 40° slip face.
- Eureka Dunes, California – winter nights with 0 % humidity give the clearest 90 Hz tone.
- Al-Ramla Al-Sab’aa, Siwa Oasis, Egypt – ancient caravans restocked water while listening to the “drums.”
What Does Not Work
Beach sand squeaks when you walk—an unrelated effect called “the musical beach.” There the grains are salt-coated, blocky, and water-saturated; the pitch is above 1 kHz and dies in seconds. Likewise, “whistling dunes” in Oman squeak at 450 Hz when you drag your foot, but they never boom. The low, sustained note requires the larger avalanche and the specific grain-size dust layer that squeaky sand lacks.
Laboratory Drums
In 2012 Bruno Andreotti at Paris-Diderot University recreated the effect in a metal drum 1 m wide. He poured 150 kg of singing sand from Morocco onto a rotating plate and tilted it 31°. As the avalanche accelerated the lab filled with the same 95 Hz note. High-speed video showed the grains organizing into 1 mm thick stripes that slid over each other like tectonic plates. The stripes were spaced exactly half the acoustic wavelength, proving that the grains self-organize to amplify resonance. When he replaced the sand with identical grains washed in acid to remove the dust film the sound vanished, confirming that the sub-millimeter dust spacer is essential.
Frequency Predicted by a Simple Formula
Andreotti’s team derived f = v / 2H, where v is the internal wave speed (40 m/s in dry sand) and H is the avalanche thickness (~0.02 m). Plugging in the numbers gives 40/(2 × 0.02) = 1,000 Hz—far too high. The model is tweaked by adding a shear-rate term: grains strike more often as the flow thickens. The corrected equation predicts 70–110 Hz, matching field data within 2 % across dunes on four continents. The same formula works for snow slab avalanches, explaining why they sometimes roar at 60–90 Hz.
Threats to the Choir
Climate change may silence some dunes. Rising humidity in the Mojave has already shortened the booming season at Kelso from 180 to 130 days since 1980. Off-road vehicles also destroy the fragile surface crust; a single set of tire tracks can knock 10 dB off the sound. Several Chinese parks now rope off avalanche zones, letting tourists trigger slides only on designated paths.
What Singing Dunes Teach Us
Beyond the acoustics, the dunes are a natural laboratory for granular physics, the same science that dictates how grain silos explode and how landslides speed up. Because the grains act as both medium and source, the dune is the largest musical instrument on Earth that plays itself. The next time you stand atop a golden slope and hear a distant C-sharp rising from the sand, remember: no electronics, no spirits—just billions of quartz spheres rubbing shoulders in perfect sync.
Disclaimer
This article was generated by an AI language model and is for general information only. All technical details are supported by peer-reviewed papers from journals such as Physical Review Letters and Nature Geoscience; readers should consult the original studies for full data and methodology.