Music in Nature: Singing Sand-Dunes

For hundreds of years now, there has been documented records of those who have heard the monotone eerie sound phenomenon of the singing sand-dunes. Different tribes in the Sahara have attributed it to God's voice, and Marco Polo called it the sounds of evil spirits.

In an article entitled "Sound-Producing Sand Avalanches", physicists from The University of Michigan give a short history of the phenomenon:

"...[The]rarer type of sound-producing sand occurs principally in large, isolated dunes deep in the desert (Nori et al.,1996; Criswell et al., 1975). The loud, low-frequency (typically 50-300 Hz) acoustic output of this "booming" sand, resultant upon avalanching, has been the subject of desert folklore and legend for centuries."

"Marco Polo (1295) wrote of evil desert spirits which "at times fill the air with the sounds of all kinds of musical instruments, and also of drums and the clash of arms." References can be found dating as far back as the Arabian Nights (Carus-Wilson, 1915), and as recently as the science fiction classic Dune (Herbert, 1984). Charles Darwin (1889) also makes mention of it in his classic Voyages of the Beagle . At least 31 desert and back-beach booming dunes have been located in North and South America, Africa, Asia, the Arabian Peninsula and the Hawaiian Islands (Lindsay et al., 1976; Miwa and Okazaki, 1995).

That's right. Sands that produce a resonant sound, one that can be heard audibly a kilometer away! It can easily be created by causing a sand-avalanche artificially at these deserts, and it can last several minutes after the avalanche itself. However, it only works in about 30 locations around the world. So there has to be something about the sands, the dunes etc, that enables this phenomenon to occur. Yet scientists have yet to come to a conclusive explanation for it. With 3,4 competing theories, the debate is still going on (I won't get into the science, because that's not what this blog is about).

I find this interesting for two reasons. One, it's just plain neat. Anything that produces sound in a musical sort of way makes me giddy. Two, the more research they have done, the more they are realizing that the method of sound production is incredibly different from any instrument humans have designed, or any other sound producing phenomenon on earth. What does this mean? It means that if and when they figure out how this works, it could lead to a whole new category/sound instrument!

Because right now, you can roughly categorize all sound production into four categories: Chordophones (sound produced by vibrating strings, like a guitar), Aerophones (vibrating columns of air, like a pipe organ), Idiophones (vibrating objects, like xylophones), and Membranophones (Vibrating membranes, like drums).

But the sand-dunes are supposedly producing sound in a way that does not fit ANY of those categories. How cool is that? What kind of instruments could we design when we figure out how this phenomenon works?

To find out more, here are some links:

From Physics World - The troubled song of the sand dunes
From National Geographic - Why Sand Dunes Go Boom
From U of Michigan - Sound-Producing Sand Avalanches

And finally... to hear it yourself, check the video below. Turn up the volume way way up though, because the recording is not very loud.