Friday, October 26, 2012

Singing sand

Dunes make a strange noise when they are at least 140' tall, have a slope of 30° or more, and are hot. The wind (or walkers) trigger a small avalanche at the crest and what you hear are the reverberations of that - at up to 105 decibels - through the sand. The sand granules must be round and .1-.5mm in diameter, the sand has to contain silica, and it needs to be at a certain humidity. These conditions are met in about 35 locations around the world (video clips here, audio clips and links here), including Death Valley, California, and the eastern shore of Lake Michigan in the U.S.A. "It's a very special tune played by the sand," says park ranger Elizabeth Brockwell. A forthcoming paper in Geophysical Research Letters ties the notes - most often E, G, or F - to the size of the sand grains and an earlier article in the New York Times quotes scientists as saying that the most beautiful dune tune comes from the sands of Oman. “Very pure sound. This one is really singing.” Others claim the haunting sounds from the dunes of Morocco are more consistent.

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