Dune avalanches create their own music with burping and booming sounds, which correspond to separate classes of waves, the researchers found.
For the new research – published Tuesday October 27 in the journal Physics of Fluid – the researchers went to the Dumont Dunes in the Mojave Desert and the Eureka Dunes in Death Valley and stayed there for 25 days during the summer.
Nathalie Vriend was a doctoral student at the California Institute of Technology in Pasadena when she completed the research, and she is now a research fellow in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge in England.
Vriend said that dunes produce low-frequency sounds that are similar to pure notes coming from a music instrument.
“The sound has a frequency between a D and G sharp, and several higher harmonics that may be heard from distances far away and may last for minutes,” Vriend added.
The team of researchers measured the energy and frequency of the sounds that were emitted by the dunes, as well as the motion of the sand grains that moved individually.
They found that the Rayleigh waves – surface acoustic waves – resulted in short-pulsed burps which then travelled through the dunes (the upper part) at a slower pace, compared with the P waves (primary waves) – which are seismic body waves – that resulted in booming noises.
To record the seismic vibrations, the researchers used geophones – device that converts ground movement into voltage. The geophone perceives the force exerted by each grain of sand that moves as the waves travel through the dunes, Vriend said.
Researchers also found that the booming sounds had a higher frequency of approximately 85 hertz, compared with the burping sounds which had a lower frequency of 76 hertz. The avalanching dunes usually emit sounds that have frequencies from 70 to 105 hertz.
According to Vriend, the ‘songs’ of the dunes are without a doubt out of this world. It is very impressive how a thin and quite small avalanche is able to create loud booming sounds that resonate over the desert floor, Vriend added.
Image Source: strangesounds