Re: singing sand dunes


Subject: Re: singing sand dunes
From: Morgan Sutherland (skiptracer@gmail.com)
Date: Wed Sep 21 2005 - 21:12:17 EDT


Wow. I live in a world of many sand dunes and i've never heard of or
heard that. Of course there is much grass on my dunes.

On 9/21/05, Innes A. Park <oceanicverse@postmaster.co.uk> 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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