So your audiometer decides to call it quits all of a sudden and you have a full schedule of patients to see. What do you do? Well, if you happen to be in Death Valley or a few select other sandy places in the world you have your back up right outside the door. Just walk out to the nearest sand dune, climb to the top, and start a mini avalanche by pushing some sand down. Soon you will have the entire dune humming a low frequency tone around 500 Hz.
Indeed, sand dunes in several places around the world have the right combination of sand particle size (between 0.1 and 0.5 mm in diameter), the right amount of silica, and the perfect moisture content to create resonant sound waves between the dry and wet sand layers. Some of this energy leaks out and can be heard. These emissions may not be calibrated well enough for measuring hearing thresholds, but they certainly are a scientific curiosity and pleasant reminder of the many mysterious ways of nature.