Caltech Team

The mystery of singing sands debated, but not yet solved, by Goldsack, Douday or Andreotti, currently has several other research teams searching for an explanation to the phenomenon. Knowing that they were entering controversial ground, Nathalie M. Vriend and Melany Hunt, from the California Institute of Technology (Caltech), proposed the research question as to why only certain dunes sing while other dunes do not. Vriend and Hunt believe that neither Douday’s nor Andreotti’s analysis provides an answer. By using radar, Vriend and Hunt have not observed any dependence of the frequency on grain diameter and have actually been able to feel the sound over a large area of a dune, proposing that sound depends on the dune itself, not on individual grains. Vriend and Hunt think that the frequency is set by the width of the waveguide layer of sand. Their research explains that dunes that lack this layered structure, like smaller dunes do, won’t sing at all. Smaller dunes do not sing because the vibrations get lost within the sliding sands. Vriend and Hunt also have found that more moisture condensed between the sand grains during the winter smears out the boundaries between the layers of singing dunes and silences them. The equation featured in the Prince Edward Island SuperGraphic is Vriend’s General Wave Equation, which is used to measure singing and booming sands.

With pressure P, time t, special coordinates x and y and speed of sound c.

The speed of sound is how fast a sound wave travels through time and space. Imagine that you see the flash of lightning before you hear the thunder. This is because light travels faster (300,000,000m/s) than sound (300m/s). The speed of sound depends on the medium (air, water, soil) that a wave is traveling in.

The pressure P is the measure of how loud a sound is, usually it is measured in decibels dB. The threshold of pain for the human ear is around 125dB, sound beyond that power can produce permanent hearing loss.

The tone of the sound, just like the tone of a musical instrument, is measured in frequency. The human ear is able to hear frequencies between 20 and 20,000 Hz, with speech to be between 100 to 300Hz as a fundamental frequency. Booming dunes produces the same tones as a cello, around 80 Hz. Squeaking sand on a beach however has a higher pitch, in the 500-1000 Hz range.