Booming Sand Dunes

Citation

Vriend, Nathalie Maria (2010) Booming Sand Dunes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BFHE-0969. https://resolver.caltech.edu/CaltechTHESIS:05312010-051551703

Abstract

"Booming" sand dunes are able to produce low-frequency sound that resembles a pure note from a music instrument. The sound has a dominant audible frequency (70-105 Hz) and several higher harmonics and may be heard from far distances away. A natural or induced avalanche from a slip face of the booming dune triggers the emission that may last for several minutes. There are various references in travel literature to the phenomenon, but to date no scientific explanation covered all field observations.

This thesis introduces a new physical model that describes the phenomenon of booming dunes. 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. The frequency of the booming is a direct function of the dimensions and velocities in the waveguide. The higher harmonics are related to the higher modes of propagation in the waveguide.

The experimental validation includes quantitative field research at the booming dunes of the Mojave Desert and Death Valley National Park. Microphone and geophone recordings of the acoustic and seismic emission show a variation of booming frequency in space and time. The analysis of the sensor data quantifies wave propagation characteristics such as speed, dispersion, and nonlinear effects and allows the distinction between the source mechanism of the booming and the booming itself.

The migration of sand dunes results from a complicated interplay between dune building, wind regime, and precipitation. The morphological and morphodynamical characteristics of two field locations are analyzed with various geophysical techniques. Ground-penetrating radar images the subsurface structure of the dunes and reveal a natural, internal layering that is directly related to the history of dune migration. The seismic velocity increases abruptly with depth and gradually increases with downhill position due to compaction. Sand sampling shows local cementation of sand grains within the discrete layers that explains the increase in velocity and decrease in porosity. The subsurface layering may influence the speed of dune migration and therefore have important consequences on desertification.

The positive qualitative and quantitative correlation between the subsurface layering in the dune and the manifestation of the booming sound implies a close relation between environmental factors and the booming emission. In this thesis, the frequency of booming is correlated with the depth of the waveguide and the seismic velocities. The variability on location and season suggests that the waveguide theory successfully unravels the phenomenon of booming sand dunes.

Thesis Files