Tuesday, July 16, 2013

Vocal volcanoes

Popocatepetl (Puebla, Mexico), Tungurahua (Tungurahua, Ecuador), and Pavlof (Alaska, U.S.) are among the volcanoes currently erupting in the world. But it is Alaska's Mount Redoubt that has been studied to determine that some volcanoes "scream." Alicia Hotovec-Ellis, a doctoral student in Earth and Space Sciences at the University of Washington, has reexamined an eruption sequence from March 2009 for clues to the volcano's pressurization right before it explodes. Some volcanoes emit sound when magma (comprised of molten rock, suspended solids, and gas bubbles) resonates as it is pushed up through cracks in the Earth's crust. The pressure often causes a series of small earthquakes that occur in such quick succession that they create a low-frequency signal called harmonic tremor, that resembles the sound of a musical instrument – if only we could hear it. Happily, Hotovec-Ellis - who theorizes that the magma in Mount Redoubt is moving through a single conduit inside the mountain because of its "ridiculously high frequencies" - allows us to do just that. In the first 10-second recording, she speeds up 10 minutes of seismic sound 60 times for our ears. In a second recording she condenses an hour of activity, which includes more than 1,600 small earthquakes, into a single minute. Listen to Mount Redoubt scream here.

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