Have you ever heard a sand dune burp? If you were in the Gobi Desert at the time, did you feel relieved that the Mongolian death worm had eaten something other than you? If you also heard some booms before the burps, did you think “thumpers” and reach for your maker hooks for a ride? Here’s some good news (or bad if you were really looking forward to seeing a sandworm or death worm) – those burps and booms coming from sand dunes have a perfectly natural cause.
According to a new report in the latest edition of Physics of Fluids, a group of researchers from California Institute of Technology and the University of Cambridge investigated loud burping and booming sounds in the Mojave Desert and Death Valley National Park in California. They spent 25 days probing the dunes with geophones that pick up seismic vibrations in the sand.
The researchers found that the seismic activity created waves of sand and different waves created the two distinct sounds. The short bursts that sounded like burps were from Rayleigh waves that travel on the surface of a dune in a nonlinear manner. The louder booms were caused by linear P-waves traveling inside the dunes.
They also found that it didn’t take a seismic event to create the burps and booms. The researchers were able to create “natural dune resonance” inside a dune simply by striking a hammer on a plate. Whoever came up with the idea of hitting a plate rather than the ground was probably worried about the thumping attracting sandworms.
While most people describe the sounds as burps and booms, some of the scientists noted that the burp frequencies ranged from 70 to 105 Hertz and referred to it as “singing.” This was a good indication that they’d been in the desert too long.
Is there any benefit to studying the burps, belches and booms of sand dunes? Of course there is. Team member Nathalie Vriend, a Ph.D. student at Caltech, said their research will help others explore …
… the granular dynamics during avalanching and its influence on the origin of structure in sand dunes in greater detail. Our recent work involves using field and laboratory techniques to probe natural avalanching and sorting on large desert dunes in Qatar.
Meanwhile, the guys on the team were drinking beer and doing sand dune impressions.