Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why 'singing' sand dunes hum certain notes

25.10.2012
What does Elvis Presley have in common with a sand dune?

No, it's not that people sometimes spot both in the vicinity of Las Vegas. Instead, some sand dunes, like The King, can sing. And new research looking for clues to how streams of sand can sing may explain why some dunes croon in more than one pitch at the same time.

Sand dunes only sing in a few areas across the globe, and their songs - always a low, droning sound -- have been an object of curiosity for centuries. Marco Polo encountered their haunting drone during his travels and Charles Darwin, in his book "The Voyage of the Beagle," wrote of testimonials from Chileans about the sound of a sandy hill they called the "bellower."

The song of the sands is a low hum at a frequency within the bottom half of a cello's musical range. These dunes only sing when the sand is sliding down their sides. People can set the sand in motion themselves or, more eerily, the wind can create sand avalanches, creating a sudden, booming chorus.

(To hear the dunes, go to: http://youtu.be/EzbGQXUL9vg)

Scientists previously thought the sound arose because avalanching sand created vibrations in the more stable underlayers of the dunes. But evidence that the avalanche of sand itself sings, not the dunes, emerged from experiments in 2009 by researchers who got a shallow pile of sand to sing while spilling down a laboratory incline. Now, the same research team has investigated a deeper mystery of the dunes -- how multiple notes can sound simultaneously from one dune.

To study this question, physicist Simon Dagois-Bohy and his fellow researchers at Paris Diderot University in France recorded two different dunes: one near Tarfaya, a port town in southwestern Morocco, and one near Al-Askharah, a coastal town in southeastern Oman. No matter where recordings were made near the Moroccan dune, the sands sang consistently at about 105 hertz, in the neighborhood of G-sharp two octaves below middle C. The Omani sands also sang powerfully, but sometimes unleashed a cacophony of almost every possible frequency from 90 to150 hertz, or about F-sharp to D, a range of nine notes.

The research will be published this Friday in the American Geophysical Union journal Geophysical Research Letters.

Even though the Omani dunes are somewhat sloppy singers, the researchers identified some tones that were slightly stronger than others. But with all the sand avalanching at once, those prominent frequencies were often buried in sea of notes. The scientists also observed that sand grains from the Omani dune came in a much wider range of sizes than their Moroccan counterparts. The Omani dune's grains were 150 to 310 microns, while the Moroccan dune's grains were only 150 to 170 microns.

So Dagois-Bohy and his colleagues brought grains from the Omani dune back to the lab. First, they ran the mix of the Omani sands down a constructed incline, recording its sound with microphones and measuring the sand's vibrations with sensors that floated on the surface. Then, they used a sieve to isolate the sand grains that were between 200 and 250 microns, and ran those sands down the same slope.

(To see a video of sand running down the slope in a lab, go to: http://youtu.be/_Rj6oSd3B0s)

The researchers then compared the sound of the isolated sands with the sound of the mixed-size control. They found that while the grains of a broad size range sang noisily, the sands of a narrow size range sang a clear note at about 90 hertz, much like the Moroccan sands do naturally. This suggested that grain size is an important factor in what tone the dunes sing, Dagois-Bohy said.

"The sound we hear is correlated to the size of the grains," he said. "So we can start to say that the size of the grains is important."

The research team suggests the grain size affects the purity of tones generated by the dunes. When grain size varies, the streams of sand flow at varied speeds, producing a wider range of notes. When the grains of sand are all about the same size, the streams of sand within the avalanche move at more consistent speeds, causing the sound to narrow in on specific tones. But scientists still don't know how the erratic motion of flowing grains translates into sounds

coherent enough to resemble musical notes, Dagois-Bohy said.

His team's hypothesis is that the vibrations of flowing sand grains synchronize, causing stretches of the sand grains to vibrate in unison. Their thousands of meager vibrations combine to push the air together, like the diaphragm of a loud speaker, Dagois-Bohy said. "But why do they synchronize with each other?" he noted. "That's still not resolved."

"The study attempts, and I think succeeds in many ways, to solve the problem of what's the mechanism" that translates tumbling sand into a song, said Tom Patitsas, a theoretical physicist at Laurentian University in Sudbury, Ontario, who did not participate in the study.

Patitsas said the theory behind the sound still requires more elaboration to explain why, for example, the flowing sand still needs a thin layer of stationary sand underneath it to make a sound. He suggests the sliding sands resonate with similar-sized grains beneath the avalanche. Those buried grains may lie in chain-like patterns that intensify the resonance. "Once you have this resonance, the amplitude of the vibration will be large," Patitsas said.

Notes for Journalists
Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this paper in press by clicking on this link:

http://www.agu.org/journals/pip/gl/2012GL052540-pip.pdf

After the paper publishes on Friday, 26 October, it will be accessible at:
http://dx.doi.org/10.1029/2012GL052540
Or, you may order a copy of the paper by emailing your request to Sean Treacy at streacy@agu.org. Please provide your name, the name of your publication, and your phone

number.

Neither the paper nor this press release is under embargo.

Title:
"Singing-sand avalanches without dunes"
Authors:
S. Dagois-Bohy, S. Courrech du Pont, and S. Douady: Laboratoire Matiere et Systemes Complexes, UMR 7057, CNRS, Universite Paris Diderot, Paris, France.
Contact information for the authors:
Simon Dagois-Bohy, +31 071 527 5517,
Email: dagois-bohy@lorentz.leidenuniv.nl

Sean Treacy | American Geophysical Union
Further information:
http://www.agu.org

More articles from Earth Sciences:

nachricht Ice cave in Transylvania yields window into region's past
28.04.2017 | National Science Foundation

nachricht Citizen science campaign to aid disaster response
28.04.2017 | International Institute for Applied Systems Analysis (IIASA)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>