Re: singing sand dunes


Subject: Re: singing sand dunes
From: steve bradley (sbradley@umbc.edu)
Date: Wed Sep 21 2005 - 21:25:02 EDT


This reminded me of an experience I had around 9 years old barefoot
late one summer night, almost full moon in White Sands, New Mexico;
http://www.nps.gov/whsa/

I would run as fast as I could, ski-like fashion dragging the bottoms
of my feet on the crusty surface of the dunes creating these slightly
grayish sinewave-like whisky vibrating sounds.

  Steve

On Sep 21, 2005, at 8:59 PM, Innes A. Park wrote:

>
>
> .. two messages from the World Forum for Acoustic Ecology list
>
> Singing Croissandwich
> For centuries, explorers have reported that crescent-shaped sand dunes
> can emit low sounds like that of a turbo-prop airplane (giving rise to
> a legend involving the ghost of a buried dinosaur). Apparently the
> best way to experience the effect is to climb to the top of a dune and
> then slide down the steep slip face (causing a small avalanche). A
> news item in the 4 April issue of Science (page 47), describes how a
> team headed by Stephane Douady was able to replicate this sound by
> slowly turning 72 kg of Moroccan sand in a 2 meter doughnut shaped
> container. Douady believes that this phenomenon can be explained by
> something called the Reynolds dilatency—a vibration created by the
> dilation and compression of air as grains separate and come together.
> (http://www.lorentz.leidenuniv.nl/~mvhecke/Workshop/
> granular_workshop.html).
>
> For more links and sound recordings of "singing sand" see
> http://www-personal.engin.umich.edu/~nori/booming_sand.html
> http://www.desertusa.com/magjan98/dunes/jan_dune1.html
> http://www.bigai.ne.jp/~miwa/sand/index.html
> http://www.schweich.com/sbdA.html
>
> *Sound dunes: Desert resonance / Sonic harddrive*
>
> "Sand dunes in certain parts of the world are notorious for the noises
> they make," the New Scientist <1>
> reports, "as sand avalanches down their sides. Some [dunes] emit low
> powerful booms, others sound like
> drum rolls or galloping horses, and some are even tuneful. These dune
> songs have been reported to last for
> up to 15 minutes and can sound as loud as a low-flying aeroplane."
>
> To test for the causes, properties, and other effects of these sand
> dune
> booms, "Stéphane Douady of the
> French national research agency CNRS <2> and his colleagues shipped
> sand
> from Moroccan singing dunes back
> to his lab to investigate." There, Douady's team "found that they could
> play notes by pushing the sand by
> hand, or with a metal handle."
>
> They performed, in other words, the transformation of a sand dune –
> and,
> by extension, the entire Sahara
> desert, indeed any desert – even, by extension, the rust deserts of
> Mars
> – into a musical instrument.
>
> Music of the spheres, indeed.
>
> "When the sand avalanches, the grains jostle each other at different
> frequencies, setting up standing
> waves in the cascading layer, says Douady. These waves reinforce one
> another, making the layer vibrate
> like the surface of a loud speaker. 'What's funny is that in these
> massive dunes, only a thin layer of 2
> or 3 centimetres is needed to set up the resonance,' says Douady. 'Soon
> all grains begin to vibrate in
> step.'"
>
> Douady has so perfected his technique of dune resonance that he has now
> "successfully predicted the notes
> emitted by dunes in Morocco, Chile and the US simply by measuring the
> size of the grains they contain."
> The music of the dunes, in other words, was determined entirely by the
> size, shape, and roughness of the
> sand grains involved, where excessive smoothness dampened the dunes'
> sound.
>
> I'm reminded of the coast of Inishowen, a peninsula south of Malin Head
> in the north of Ireland, where the
> rocks endlessly grind across one another in the backwash of heaving,
> metallic, grey Atlantic waves. Under
> this constant pressure of the oceanic, the rocks carve into themselves
> and each other, chipping down over
> decades into perfectly polished and rounded spheres, columns, and eggs
> –
> as if ideal, Archimedean solids
> <3> or the nested orbits of Kepler could be discovered on the Irish
> ocean foreshore – all glittering. The
> rocks, I later learned, were actually semi-precious stones, and I had a
> kind of weird epiphany, standing
> there above the hush and clatter of bejewelled rocks, rubbing and
> rubbed
> one to the other in the
> depopulated void of a coastal November. It was not a sound easy to
> forget.
>
> Because the earth itself is already a musical instrument: there is "a
> deep, low-frequency rumble that is
> present in the ground even when there are no earthquakes happening.
> Dubbed the 'Earth's hum', the signal
> had gone unnoticed in previous studies because it looked like noise in
> the data." <4>
>
> "Competing with the natural emissions from stars and other celestial
> objects, our Earth sings like a
> canary – it drones on in a constant hum of a gazillion notes. If it
> were
> several octaves higher, and
> hence, audible to the human ear," <5> it could probably get recorded by
> the unpredictably omnidirectional
> antennas of ShortWaveMusic <6> and... you could download the sound of
> the earth.
>
> *Free Radio Interterrestrial*.
>
> Which, finally, brings us to Ernst Chladni and his Chladni figures <7>,
> or: architectonic structures
> appearing in sand due to patterns of acoustic resonance.
>
> Architecture through sound, involving sand. Silicon assuming structure.
> Desert harddrive, humming.
>
> The gist of Ernst Chladni's experiments involved spreading a thin layer
> of sand across a vibrating plate,
> changing the frequency at which the plate vibrated, and then watching
> the sand as it shivered round,
> forming regular, highly geometric patterns. Those patterns depended
> upon, and were formed in response to,
> whatever vibration frequency it was that Chladni chose.
>
> So you've got sand, dune music, terrestrial vibration, some Chladni
> figures – one could be excused for
> wondering whether the earth, apparently a kind of carbon-ironic bell
> made of continental plates and
> oceanic resonators, is really a vast Chladni plate, vibrating every
> little mineral, every pebble, every
> grain of sand, perhaps every organic molecule, into complex,
> three-dimensional, time-persistent patterns
> for which we have no standard or even technique of measurement. Or
> maybe
> William Blake knew how to do it,
> or Pythagoras, or perhaps even Nicola Tesla, but...
>
> The sound dunes continue to boom and shiver. The deserts roar. The
> continents hum. <8>
>
> (Geoff Manaugh)
>
> + + + + + + + + + +
>
> <1> http://www.newscientist.com/article.ns?id=dn8014
> <2> http://www.cnrs.fr/index.html
> <3> For an illustration of the 13 Archimedean solids see
> http://www.math.dartmouth.edu/~matc/math5.geometry/unit6/unit6.html,
> and
> scroll down.
> <4> http://www.newscientist.com/article.ns?id=dn6464; see also
> http://news.bbc.co.uk/2/hi/science/nature/3701944.stm
> <5>
> http://www.space.com/scienceastronomy/planetearth/
> space_symphony_000323.html
> [Note:
> this link offers a contrary, but no less interesting, theory (published
> in 2000) about
> the origins of these planetary soundwaves]
> <6> Here I’m referring to the excellent transglobal sonic resource,
> ShortWaveMusic,
> found at http://shortwavemusic.blogspot.com/
> <7> For more on Ernst Chladni, click through his Wikipedia entry:
> http://en.wikipedia.org/wiki/Ernst_Chladni; and for more on Chladni
> figures themselves
> see http://www.phy.davidson.edu/StuHome/jimn/Java/modes.html
> <8> An illustrated version of this post appears on BLDGBLOG:
> http://bldgblog.blogspot.com/2005/09/sound-dunes.html
>
>
>
>
>
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>
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