The singing earth
The earth sings in many ways. I wrote previously about the drum-like sounds produced by earthquakes and the flute-like sounds produced by volcanoes (see The earth is a musical instrument). But the earth sings in other ways, too. Sand dunes sing under certain conditions, producing a low-pitched rumble that has variously been described as a kettle drum, bass violin, zither or foghorn. Marco Polo, in his 13th century travels, said the singing sands “at times fill the air with the sounds of all kinds of musical instruments, and also of drums and the clash of arms.”
The sand grains must be within certain diameters, contain silica, and be a particular humidity. These conditions exist in about 35 locations around the world, including Kelso Dunes and Eureka Dunes in California’s Mojave Desert. The sound is usually triggered by wind passing over the crest of a dune or by walking on the sand. Scientists have not been able to definitively determine how the sand produces the sound, but the face of the dune apparently acts like a huge loudspeaker, amplifying the volume of the grains of sand as they collide.
Sound of singing dunes (recorded by Dr. Franco Nori and Dr. Nick Lancaster at Sand Mountain, near Reno, Nevada}
Another unusual phenomenon is the system of blowholes at Wupatki National Monument in the lava fields of northern Arizona. Water seeping into fractures in the limestone layers of the Colorado plateau dissolved limestone and created fissures and cavities. Small openings in the earth — blowholes and wells — tap into the cavities. When the atmosphere above the blowhole changes pressure, the air inside responds, “exhaling” or “inhaling” with a moaning, singing sound.
Japanese seismologists in 1998 discovered that the earth emits a low humming noise well below the limits of human hearing, but weren’t able to deduce the source. A study in 2004 by geologists Barbara Romanowicz and Junkee Rhie determined that the sound shifted between the northern and southern hemispheres according to the onset of winter in each hemisphere, which suggests that stormy seas might be causing the hum.
High above our planet, charged particles from the solar wind collide with the earth’s magnetic field, creating chirps and whistles — a kind of musical accompaniment to the aurora borealis and aurora australis. The radio waves are blocked by the ionosphere, a charged layer of atmosphere, so they do not reach the earth.
Sounds of earth in space, recorded by European Space Agency’s Cluster mission
These are a few of the sounds emitted by the earth in an ongoing symphony that takes place all around us.
Photo: Dune of Altynemel (“The Singing Dune”) in the valley of Ili River, Kazakhstan — copyright Jonas Satkauskas
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