Singing sand

Singing sand, also called whistling sand, barking sand, booming sand, or a singing dune, is sand that produces sound either when wind passes over a dune or when a person walks across it. The effect requires fairly specific conditions: the grains must be rounded, generally between 0.1 and 0.5 millimeters across, contain silica, and sit at a particular level of humidity, with the sound most often measured around 450 hertz. Proposed explanations for how the sound is generated include friction between grains, compression of air between them, and resonance created as sound waves bounce between a dry surface layer and a moister layer beneath it. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/