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Booming Sand Dunes: An Example of Wave Propagation Through a Granular Material

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Booming sand dunes are known for the persistent, low-frequency sound they emit during avalanches on the leeward face of the dune. The sound can last for several minutes and be audible from miles away. A dominant audible frequency (70 – 105 Hz) and several higher harmonics characterize the acoustic emission. Travel literature has described the phenomenon for centuries, but to date no scientific explanation covers all field observations.

Quantitative field research at the booming dunes of the Mojave Desert and Death Valley National Park has been combined with modeling to unravel the booming phenomenon. The waveguide model explains the selection of the booming frequency and the amplification of the sound in terms of constructive interference in a confined geometry. Microphone and geophone recordings of the acoustic and seismic emissions show a variation of booming frequency in space and time. Geophysical techniques image the subsurface structure of the dune and reveal a natural internal layering. This layering is crucial for the existence of a natural waveguide that guides and amplifies the waves to a magnificent sound. The variation in booming with location and season indicate that the waveguide theory successfully unravels the phenomenon of booming sand dunes.

This talk is part of the Fluid Mechanics (DAMTP) series.

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