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  Geotimes - November 2007 - The sounds of the sands
NEWS NOTES

Geomorphology
The sounds of the sands

Sand dunes
Copyright Marli Miller, University of Oregon; courtesy of ESW Image Bank
Sand dunes such as these in California are known to produce occasional booming noises. Researchers now say they know why.

Walking around in a desert, especially near sand dunes, one occasionally hears audible prolonged thuds or booms. Now, researchers have an explanation for these booming sand dunes: Natural slumping events or sand avalanches caused by animals or humans cause booms that reach frequencies audible to the human ear based on compressional wave velocities and depths of the surficial sand layers. Previously, researchers had thought that whether or not the booms were audible was based on the size of the sand grains. But Nathalie Vriend of Caltech in Pasadena, Calif., and colleagues created a mathematical model that suggests that the sound frequency results from natural sound waves reacting to the surficial layer of loose sand interacting with the air above it, which acts as a loudspeaker, as they reported in Geophysical Research Letters on Aug. 23.

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