十万个为什么·科学阅读30篇（2）

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是什么导致某些沙丘发出‘吠叫’般的声音？

Singing or booming dunes produce loud, low-frequency sounds that resemble distant thunder or foghorns.
This phenomenon occurs only when sand grains are nearly identical in size, roundness, and silica content.
As layers of sand avalanche down a slope, synchronized grain vibrations generate standing sound waves.
The dune itself acts like a natural amplifier, resonating at frequencies between 70 and 105 Hz.
Scientists confirmed this by measuring vibrations with geophones buried beneath active slip faces.
Dryness is essential: even slight humidity dampens grain motion and silences the effect instantly.
Only about 30 locations worldwide host reliably singing dunes, mostly in deserts of Morocco, China, and the USA.
Wind alone doesn’t trigger it — human footsteps or small slides often initiate the acoustic cascade.
Laboratory experiments show that grain coatings of clay or salt prevent synchronization and stop the sound.
Understanding this helps geophysicists model granular flow in landslides and planetary surfaces like Mars.