Sand Dunes Sounds



What is singing or musical sand dunes?

Musical sand dunes is a reference to the natural sounds made by sand dunes from various deserts from around the world, including the Sahara desert. The sounds have mystified the imagination for over one thousand years, and were known to both Marco Polo and Charles Darwin. According to the inhabitants of the great Sahara the sounds were attributed to God as he was speaking to them through the sand. But according to science the mystery is a natural phenomenon still under investigation. There are various theories put forward to explain the phenomena, ranging from acoustic reverberation to piezoelectric aggregation, but a satisfactory explanation is still unavailable.

The sound types include deep roaring, whistling, squeaking, and humming, which in a way is very similar to the reported deep humming sounds of the big bang. The acoustic sounds produced by large-scale slumping events on dry booming sand dunes, which can be heard up to 10 kilometres away, sound like African drums, thunder, or the drone of low-flying propeller planes (see the pdf link below for more on this). Many of these sites have become a tourist destination and are often listed under Sound Tourism.






Watch the following NewScientist video at YouTube to hear some of these deep humming sounds.

Humming or roaring sand dunes.

Is it an Aboriginal orchestra or a German V-2 ?





What is the cause of these sand dunes sounds?

Scientist have previously thought that the sounds were produced by the friction of the sand grains during a sand avalanche, where the size of the sand grains, the amount of silica present in the sand, stress, and humidity have all played their part in the [Aboriginal] orchestra.

But according to professor Melany Hunt, of California Institute of Technology, the sounds continue after the sand has stopped moving, and that the frequency of the vibration changes with the time of the year. After radar analysis this has suggested to her that the wet layer of sand (located about 2 meters below the dry sand) is involved in the sound production in that the sound is actually a reverberation reflected by the wetter layer back to the top dry layer.

Paul Sholtz, Michael Bretz and Franco Nori (in their Sound-producing Sand Avalanches [see below for link]) have also examined the grain-size parameters, the morphology of sound-producing grains, and the role that exceptional granular polishing might play in both types of sounding mechanisms - that is in both booming and squeaking sand dunes.

While according to Bagnold, R. A. (1954b, Physics of Blown Sand and Desert Dunes), the stress applied to sheared booming grains may lead to tiny piezoelectric dipoles to accumulate in a way as to produce acoustic sounds.






The following video illustrates the squeaking nature of some of the sand dunes. The sounds are very similar to rubbing one's hands over a tightly-inflated balloon or clean glass and hence the say: "squeaky-clean".

Squeaking sand dunes.





The frequencies of the sand dunes sounds

The high-frequency of 500 ± 2500 Hz of  squeaking sand is produced when the sand dunes are  sheared or compressed, mostly at beaches and riverbeds.  The low-frequency of 50± 300 Hz of booming sand dunes is produced during avalanches, mainly of large desert sand dunes.





References & Further Resources

  1. Marco Polo, 1295, edited by T. Wright, 1968, The Travels of Marco Polo, The Venetian (AMS Press, New York), p. 101.
  2. Charles Darwin, 1889, Voyage of H.M.S. Beagle Around the World (London: Murray).
  3. Sound-producing Sand Avalanches (http://www-personal.umich.edu/~nori/boom/Review-Booming-Sand.pdf)
  4. Singing Sand (https://en.wikipedia.org/wiki/Singing_sand)
  5. Carus-Wilson, C., Nature, 1915, 95, 90.
  6. Takahara, H., 1973, Sounding Mechanism of Singing Sand, J. Acoust. Soc. Amer., 53 (2), 634.
  7. Ridgway, K., and Scotton, J. B., 1973, Whistling Sand Beaches in the British Isles, Sedimentology, 20, 263.
  8. Why Sand Dunes Go Boom: (http://news.nationalgeographic.com/)
  9. Clarke, J. A. R. C., 1973, Singing Sands, New Sci., 59, 222.
  10. Richardson, W. D., 1919, The Singing Sands of Lake Michigan, Science, 50, 493.