Mega Basso Profundo â€“ Listening to Volcanoes - Attractiontix Tickets
Hereâ€™s a new take on the â€œif a tree falls in a forest and no one is around to hear itâ€ riddle: if you canâ€™t hear a volcano, does that mean that itâ€™s not making a sound â€“ in fact, a very loud sound?
Milton Garces emerges from the lava.
Fire field captured with infrared and conventional photography.
Tree ferns and ground cover surround one of ISLA's isolated instrument vaults, which houses microphones and equipment.
Take, for example, Hawaiiâ€™s Kilauea Volcano. â€œItâ€™s one of the loudest things in this whole island,â€ says Milton Garces, director of the University of Hawaiiâ€™s Infrasound Laboratory (ISLA). â€œThis thing is louder than the ocean, this thing is louder than anything else around it. In terms of human perception, you can stand right by it, and you don't hear a thing.â€
Thatâ€™s because the sounds emerging from the volcano fall well below the range of human hearing. Such frequencies are known as infrasounds. Sound is measured in hertz (cycles per second), and humans can hear frequencies in the range of 20 to 20,000 hertz. The frequencies emanating from Kilaueaâ€™s Halemaumau crater are in the vicinity of 0.5 hertz â€“ under the radar of our aural perceptions. By using arrays of supersensitive microphones that can detect these low frequencies, Garcesâ€™ team records the signal, then speeds up and processes the sound file until it can be heard with our own ears.
A March 2008 explosion exposed a new vent within Kilaueaâ€™s Halemaumau crater. As gasses ascend from deep within, this vent acts like a kind of wind instrument and produces a low-frequency resonance, which has been referred to as Peleâ€™s Chant. Pele is the volcano goddess of ancient Hawaiian legend. â€œWe picked up this explosion really loud and clear,â€ says Garces. â€œAnd that is producing a very unique, very loud infrasonic signal that weâ€™re going to be studying in great detail over the next few months.â€
Infrasound arrays are used not only to detect volcanic activity, but can also be employed to hear meteors, asteroids or comets that collide explosively with the earthâ€™s atmosphere (these are collectively known as bolides). The arrays can also detect an ongoing chorus of infrasonic activity in our oceans. ISLAâ€™s primary role, however, is listening for the infrasonic activity associated with nuclear weapons testing. Infrasound is one of four technologies used in the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty, and Garcesâ€™ lab is an important link in that chain.
Infrasounds produced by things like meteors and nuclear weapons tests are brief and unpredictable, though. Peleâ€™s Chant, in contrast, is providing a persistent source of sound, enabling Garces and his crew to better understand the capabilities of infrasonic monitoring itself. Theyâ€™re assessing things like range limitations, andâ€“â€“thanks to Kilaueaâ€™s locationâ€“â€“the effects of wind on acoustic wave propagation. Infrasounds can also help in predicting volcanic eruptions, and these data are made available to government and civil defense organizations.
As you might imagine, volcanic craters are not the best locations for placing microphones, which are very sensitive to wind noise. In addition to the wind, thereâ€™s always the possibility that a volcano will bury your instruments in molten rock or ash. This is why Garces places his arrays in remote locations sheltered from wind, at a distance of several kilometers to several hundred kilometers from the volcano. This precaution not only removes the microphones from harmâ€™s way, itâ€™s also a safety measure for human researchers. After all, someone has to maintain all that equipment.
â€œEvery time you go deal with an instrument close to a volcano, you put yourself at substantial risk,â€ Garces warns. â€œYou have flying fragments of hot rock, you have the shockwaves that can actually produce a lot of internal damage. Glowing avalanches of rocks. Gas that comes out of an open vent can flow down mountains, a little bit like a river, without you even seeing it coming. The only way to perceive it is through a shimmer in the light. By then, it might be too late.â€
Interact with Milton Garces and read about his latest research
You can hear some of Garcesâ€™ sped up infrasonic recordings in the following stories :
Science Diary: Volcano - Array
Science Diary: Volcano - Silence
Science Diary: Volcano - Pele
Links to other related stories:
Science Diary: Volcano - Climb
Science Diary: Volcano â€“ Eruption
Science Diary: Volcano - Death
Science Diary: Volcano - Analyze