Author: Carolyn Gramling / Source: Science News for Students
The South American volcano Cotopaxi sometimes sings. But people will never hear it deep and distinct voice.
It’s frequency is too low for the human ear to hear. But microphones can listen in. And between late 2015 and early 2016, they heard this peak in Ecuador sign out an unusual pattern of sound. Researchers now say that pattern is due in part to the unique shape of the volcano’s crater.Other volcanoes might have a similarly distinct “voiceprint.” Identifying it could help scientists listen for changes within a crater. Such changes might even warn of an upcoming eruption.
Scientists from Ecuador installed a network of microphones on Cotopaxi’s flanks. They could record the very low frequency infrasound. Two weeks after the volcano’s August 2015 eruption, the network recorded the unusual acoustic pattern. It showed a strong, clear oscillation. The sound curve resembles a screw — or “tornillo,” in Spanish — that tapered off with time.
Scientists described the volcano’s distinctive call in the June 16 Geophysical Research Letters.
Cotopaxi repeated this tornillo pattern 37 times between September 2015 and April 2016. Each time, the signal lasted through a dozen or more oscillations. It resonated much like a musical instrument, before dying away.
Indeed, notes study leader Jeffrey Johnson, the volcano “rang like a bell for more than a minute.
” A geophysicist, he works at Boise State University in Idaho.Too low to hear
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