Re: Semi-OT: Secrets of the Singing Sand Dunes

WadeInChugiak@xxxxxxx wrote:

On the video that accompanies this article on the NY Times website, the
sand dunes make a sound not unlike a musical saw...

whm



Secrets of the Singing Sand Dunes

By KENNETH CHANG


The dunes at Sand Mountain in Nevada sing a note of low C, two octaves
below middle C. In the desert of Mar de Dunas in Chile, the dunes sing
slightly higher, an F, while the sands of Ghord Lahmar in Morocco are
higher yet, a G sharp.

Since at least the time of Marco Polo, desert travelers have heard the
songs of the dunes, a loud - up to 115 decibels - deep hum that can
last several minutes. (You can listen to them here.) While the songs
are steady in frequency, the dunes do not have perfect pitch. At Sand
Mountain, for example, dunes can sing slightly different notes at
different times, from B to C sharp.

Scientists already knew that the sounds were generated by avalanches,
but were not sure how. One thought had been that the force of an
avalanche could cause an entire dune to resonate like a flute or a
violin. But if that were true, dunes of different sizes and shapes
should produce a cacophony of notes instead of one characteristic tone.


Now, after five years of research, visiting sand dunes in Morocco,
Chile, China and Oman, a team of scientists from the United States,
France and Morocco say they have the answer.

In a paper that will appear in Physical Review Letters, the scientists
say that collisions between sand grains cause the motions of the grains
to become synchronized. The outer layer of the dune vibrates like the
cone of a loudspeaker. The particular note depends primarily on the
size of the grains.

Indeed, no dune was required at all. The scientists shipped sand from a
Moroccan desert to a Paris laboratory and reproduced the singing by
pushing the sand around with a metal blade.

"It's not at all like any other instrument we know," said one of
the scientists, Stéphane Douady of the National Center for Scientific
Research in Paris.

The most beautiful dune tune comes from the sands of Oman. "Very pure
sound," Dr. Douady said. "This one is really singing." The least
musical bits of silicon were those from China, which hardly sang at
all.


Years ago on a trip to Nova Scotia we were advised to look for a beach with "moaning" sands. I don't remember just where, but I'm sure it could be googled.
Anyhow, we finally and after not a small amount of trouble located this mystical beach. Slowly we climbed down onto the beach sand.
The guidebook stated quite clearly that the sand would "oohh and ahhh" as we walked along. Pretty soon I was stomping around, feeling like the biggest idiot in creation.
From high above on a rock ledge, I saw a couple of teenagers looking down on us, convulsed with laughter.

Steve

--
Mark & Steven Bornfeld DDS
http://www.dentaltwins.com
Brooklyn, NY
718-258-5001
.

Relevant Pages

  • This Weeks Finds in Mathematical Physics (Week 228)
    ... Last week I showed you some pretty pictures of dunes on Mars. ... This week I'll talk about dunes called "barchans" and their relation ... Wind-blown sand accumulates on the front of the barchan, ... for this I need to explain "self-organized criticality". ...
    (sci.math.research)
  • This Weeks Finds in Mathematical Physics (Week 228)
    ... Last week I showed you some pretty pictures of dunes on Mars. ... This week I'll talk about dunes called "barchans" and their relation ... Wind-blown sand accumulates on the front of the barchan, ... for this I need to explain "self-organized criticality". ...
    (sci.physics.research)
  • Re: Sean Pitman and the Coconino Sandstone
    ... >> leeward dune fracture faces and cracks in the sand, ... >> characteristics that match the dunes in the Coconino Sandstone.71 Heavy ... >> You seem in part to acknowledge a desert environment recognized in the ... seen as a result of current hurricanes and tsunamies, that sediments are ...
    (talk.origins)
  • Semi-OT: Secrets of the Singing Sand Dunes
    ... Secrets of the Singing Sand Dunes ... Scientists already knew that the sounds were generated by avalanches, ... Now, after five years of research, visiting sand dunes in Morocco, ...
    (rec.music.makers.guitar.acoustic)
  • Re: Sean Pitman and the Coconino Sandstone
    ... > Ocean currents can and do make very pure quartz sand dunes with specific ... > characteristics that match the dunes in the Coconino Sandstone.71 Heavy ... The sand dune angle found in the Coconino Sandstone layers would ... If such prints were left in a desert environment, ...
    (talk.origins)