Monday, August 14, 2006

Singing Sand Dunes

We have all grown up hearing about the wierd singing noises sand dunes make. Science never offerred very convincing answers for this phenomena. But now recent research promises to solve this mystery.
Interest in them is bound to rise when u get to know how good these dunes are at singing: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 atleast the time of Marco Polo, desert travellers have heard the songs of the dunes, a loud upto 115 decibels-deep hum that can last several minutes. While the somgs are steady in frequency,the dunes donot have a perfect pitch. Scientists already knew that the sounds were caused by avalanches, but they were not sure how.
Now after 5 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 synchronised. The outer cone of the dunes vibrate 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 Morrocan desert to a Paris lab and reproduced the singing by pushing the sand around with a metal blade. "Its not at all like any other instrument we know", said one of the scientists, Stephane Douady of the National Centre for Scientific Research in Paris. The most beautiful dune tune comes from the sands of Oman. "Very pure sound," Douady said, "this one is really singing." The least musical bits of silicon were from China. They hardly sang at all.

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