Have you heard of strange musical notes struck by blowing winds over sand dunes? The Singing Sand Dunes in Dunhuang, northwest China's Gansu Province, sing and play music for their visitors. These natural wonders were formed at least 3,000 years ago.

Under certain conditions, sand in any part of the world can create various sounds like barking or thunder. There are multiple explanations for the mechanism of singing sound. One theory says the sound may be generated by friction between the sand grains or the compression of air between them.

(All images via VCG)

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