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Science Frontiers ONLINE No. 103: Jan-Feb 1996 |
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A Subterranean Trombone
In 1992, while making seismic recordings near Java's Mount Semeru, a German scientific team noticed that the seismic waves were much more regular than one would expect from deep volcanic activity. Their recordings revealed a series of evenly spaced harmonic frequencies. They likened it to a musical instrument emitting a fundamental note accompanied by overtones. Sometimes, the fundamental tone would rise and fall, as if the mountain were playing a tune for them. The Germans, V. Schlindwein et al, postulated that the vibrations originated in a gas-filled cavity, presumably cylindrical -- something like an organ pipe -- capped at the top, with a pool of molten magma at the bottom. Volcanic vibrations resonated in this chamber and, as the magma pool rose and fell, so did the fundamental tone. Rather than a fixed organ pipe, it was a natural trombone! Unfortunately, the "earth music" was always in the infrasound range, 8 Hertz and less, and could not be heard by the researchers directly -- only their instruments could "listen."
(Schneider, David; "Country Music," Scientific American, 273:28, November 1995.)
Comments. There is no physical reason why such a subterranean trombone cannot play in the audible range. Such a mechanism might explain some of the mysterious hums heard in various localities, such as the Taos hum. (SF#88)
Many unusual natural sounds are cataloged in Chapter GS in our catalog: Earthquakes, Tides, Unidentified Sounds. Ordering information here.
Some animals can hear infrasound. Pigeons, for example, have special organs on their legs (of all places!) that respond to infrasound. Could pigeons and other birds use "musical mountains" for homing and other navigation feats?