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Philosophically, we may still be arguing over whether a tree makes a sound when it falls if no one is there to hear it, but scientists at the University of Washington have confirmed that volcanoes emit a scream of sorts before erupting, called a “harmonic tremor.”

Though poets may attribute the sound to the labor pains of Gaia, researchers are more cautious in assigning a cause.

Some volcanoes emit sound when magma – a mixture of molten rock, suspended solids and gas bubbles – resonates as it pushes up through thin cracks in the Earth’s crust.

But [University of Washington doctoral student Alicia] Hotovec-Ellis believes in this case the earthquakes and harmonic tremor happen as magma is forced through a narrow conduit under great pressure into the heart of the mountain. The thick magma sticks to the rock surface inside the conduit until the pressure is enough to move it higher, where it sticks until the pressure moves it again.

The first recording is of ten minutes of sound from Alaska’s Redoubt volcano condensed into a ten second “scream,” the second, and hour’s worth of small earthquakes condensed into what sounds like a one-minute drum solo.

Full story at Smithsonian Magazine via Kottke.

Explosive science.

Photo credit: Wikimedia Commons