March 28, 2008

Singing Sand

Stupid Question ™
Feb. 27, 2003
By John Ruch
© 2003

Q: What is “singing sand” and does it actually make music?

A: “Singing sands” are a really neat natural mystery: relatively easy to experience first-hand and with a basic mechanism that is obvious, yet still baffling.

Singing sands make strange noises when disturbed. “Singing” is romantic; really they can be divided into squeakers and boomers.

Squeakers emit a short, sharp, single-frequency sound when stepped on or poked, with some sounding like a dog bark or frog ribbit. I experienced this first-hand on a Cape Cod beach that emitted a mild squeak as though walking in icy snow.

Boomers create a truly astonishing, and at times deafening, roar when they avalanche down the sides of sand dunes (whether blown down by wind or pushed by a human hand). It’s a complex, multiple-frequency sound that can be heard for miles.

Boomer recordings have a resonant bass sound with clear harmonics and a steady underlying beat. The most accurate comparisons are to a propeller airplane or a gigantic didgeridoo, the Australian aboriginal wind instrument.

Squeakers are apparently much more common than boomers, though this may be a matter of geography: squeakers are exclusively a beach phenomenon, while boomers are almost exclusively a desert phenomenon. Obviously, beaches get more visitors than deserts.

Dozens of squeaker sites are known around the world, with the most famous being Singing Beach near Manchester, Massachusetts and the shores of Lake Michigan and of the Scottish Isle of Eigg (all the subjects of the earliest scientific reports). In all cases, squeaking sand is visually indiscernible from regular, silent sand.

Boomer dunes are known in nearly every sandy desert area of the world. The most famous are Sand Mountain near Fallon, Nevada; “Jebel Nakus,” a large dune in the Sinai desert; and the Hill of Sounding Sand in Dunhuang, China.

“Singing sands” are almost always silica-based, but the “Barking Dunes” of the Hawaiian island of Kauai are calcium carbonate and are the only boomers known outside of deserts. (They’re now overgrown and no longer boom.)

Nobody knows what’s behind the sounds, or if booms and squeaks are even related. Most boomers will emit squeaks if rapidly compressed in lab experiments, but at multiple frequencies.

Clearly, friction between sand grains is key, but the sound seems out of all proportion to the rubbing. Squeakers tend to have highly spherical, very uniform grains that probably compress in a unique way. Boomers, on the other hand, are often bumpy and irregular, but extremely smooth. The mechanics of sand avalanches are poorly understood, compounding the mystery.

Moisture is also key. Even slight atmospheric humidity will utterly kill a boomer’s boom. Squeakers must also be dry, but are best if they have recently been wetted and dried out. They are rarely found farther than 100 feet from a shoreline.

Another oddity is that if you take a bag of singing sand home, it will delight you with sounds for only a few weeks before going silent. But it can usually be revived: boomers by baking in an oven, and squeakers by washing and drying.

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