Tunes from dunes
For years researchers have marvelled at the phenomenon of singing sands. Marcel Leach and Douglas Goldsack at Laurentian University in Sudbury, Canada have discovered that for sands to sing, they need to be coated with a layer of silica gel. After examining various types of sands they found that the booming sand had an unusually high silica content. While most sands typically consist of about 50 per cent silica and a mixture of other minerals, booming sands were 95 per cent silica and also tended to be slightly moist from night air.
Researchers found that singing sands, unlike normal sand, contained water mixed with silica, forming a silica gel. The gel is used as a drying agent, often seen in packaging for electronic equipment, and commonly used in chemistry labs. When Goldsack shook some pure silica gel in a glass jar, the gel made a thrumming sound. Goldsack and Leach think silica gels make dunes sing. The gel loosely glues sand particles together. While air blows through the gel, the grains shake in unison, transforming ordinary air patterns into coherent vibrations, like those produced with a tuning fork ( Discover , Vol 18, No 8).