Some desert dunes can 'sing' or whistle as loud as a low-flying plane.

The phenomenon of singing sands has been documented for centuries, with Marco Polo mentioning the 'spirits of the desert' during his 13th-century travels through the Gobi Desert. Modern research by institutions like the California Institute of Technology and the University of Paris has identified that the sound is produced by a specific type of sand grain. These grains must be round, contain silica, and possess a specific moisture content to vibrate effectively. When an avalanche occurs, the sliding layers of sand act like a massive speaker membrane. The grains move in a synchronized fashion, creating a fundamental frequency that typically ranges between 60 and 150 Hertz. This frequency is determined by the size of the grains and the speed at which they shear against one another. A study published in 'Physics of Fluids' in 2012 revealed that the thickness of the moving sand layer also influences the pitch. In the Al-Askharah desert of Oman, dunes produce a drone-like hum, while the 'Singing Mountain' in Nevada produces a whistle. This acoustic effect is rare, occurring in fewer than 40 locations worldwide because it requires perfectly dry conditions and uniform grain sizes. The volume of these sounds is truly remarkable, often peaking at 105 decibels, which is comparable to the noise of a lawnmower or a power drill. Scientists use seismic sensors to track these vibrations, which can travel through the ground for several kilometers. This natural musical instrument remains one of the most striking examples of self-organization in granular physics.