Some volcanoes ‘scream’ at ever-higher pitches until they blow their tops

Swarms of small earthquakes often precede a volcanic eruption. They can reach such rapid succession that they create a «harmonic tremor» that resembles sound made by some musical instruments. A new analysis of an eruption sequence at Alaska’s Redoubt Volcano in March 2009 shows the harmonic tremor glided to substantially higher frequencies and then stopped abruptly just before six of the eruptions.

Fuente : http://www.eurekalert.org/pub_releases/2013-07/uow…