Singing Sand Dunes: The Spontaneous Acoustic Emission from Granular Shear Flow

One of the highly striking yet poorly understood natural phenomena is the song of dunes. Some sand dunes in deserts have a peculiar ability to emit a loud persistent sound with a characteristic audible low-frequency (75-105 Hz), sometimes can be heard up to 10 km away. Scientific investigations suggest that the sustained low- frequency sound of sand dunes that resembles a pure note from a musical instrument, is due to the synchronized motion of well-sorted dry sand grains when they spontaneously avalanche under gravity. This article describes the underlying mechanism for sustained sound emission in singing sand dunes in light of the recent physical experiments.