Three scientists believe they've determined why some sand dunes produce a strange humming sound.
The mystery of the 'singing sand dunes' has baffled for centuries. When sand grains shuffle down dunes under certain circumstances they produce a deep groaning sound - something that Marco Polo once attributed to evil spirits. But how exactly are these sounds produced and how do some dunes produce more than one note at a time ?
Three scientists from Paris set out to find the answers to these questions. Deliberately triggering avalanches at sand dunes in Morocco and Oman, the trio noted that each dune seemed to create a sound in a different note. What they discovered is that the sound is caused by a constant stream of collisions between sand particles and that the size of the particles dictate which sound is made.
"When Marco Polo heard it in China, he suspected evil spirits."
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Source: National Geographic
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