Dune Tunes
Kelly Garcia '07

Kelly playing in the sand

Abstract:

   This study reviews literature on the topic of booming sand which investigates the unusual and unexplained acoustical properties of sand known as booming. The sounds (as loud as 110 dB) have been compared to low-flying propeller airplanes. Typical frequencies range from 60 – 100 Hz depending on the sand grain size. The booming contains only the fundamental frequency and the first overtone. It occurs in special types of dunes all over the world: the Sahara, deserts in Morocco, Chile and China. There have been many attempts to replicate the booming dunes in the laboratory. Some researchers have collected sand from these different parts of the world and have had success, while others have instead used glass spheres. These latter studies were neither unsuccessful nor successful: the experiments produced sounds, but these sounds were unlike those found in nature. In the lab, we were unable to make galss spheres boom. This is most likely a result of imuriteis within the glass spheres. The exact cause for the booming is still undetermined. The most recent notable study in this area has been that of Douady et al¹, which suggests that the booming of sand is not due to resonance within the dune as with wind instruments, nor is it due to “stick-slip motion of grain” as with stringed instruments. That paper claims the sound frequency depends on the shear gradient in the avalanche and that a standing wave resonance is somehow created in the air located within the shear layer. An alternate model is includeded in which the sand grains themselves act like gas molecules confined in a closed pipe. Computer simulations show that the “sand gas” model may explain the mechanics of this longstanding puzzle.

   For more information, contact Dr. Brian Watson:

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