For thousands of years people have known that certain sand dunes make a low humming sound, the musical note of G, E or F. It occurs when the sand is moving but you can force the sound if you slide downhill. Why does it hum?
A decade ago scientists at CalTech studied two humming sand dunes in California to answer that question. They found that for the sand to sing, the grains have to be all the same size, the dune must have a slope greater than 30 degrees and be over 120 feet tall, and the sand must be dried under the desert’s summer sun. It was very hot work.
The humming sound occurs naturally when the sand moves but that doesn’t happen on a predictable schedule so the CalTech team forced the sound. Dr. Melany Hunt explained,
Usually we would trigger it by having a number of people slide down the dune in unison. We always called it ‘Science by the seat of our pants.’
(screenshot from CalTech video: The Science of Booming Sands – 2015)