Researchers at Yale University, along with colleagues at the University of British Columbia, said no matter their size or shape, explosive volcanoes produce tremors at similar frequencies, a Yale release said Wednesday.

Prior to most explosive eruptions the volcanoes shake slightly but measurably, and the shaking becomes more dramatic during the eruption itself and is a primary precursor used by vulcanologists for forecasting an eruption.

"Tremor is very mysterious, most notably because it shakes at pretty much the same frequency in almost every explosive volcano, whether it's in Alaska, the Caribbean, New Zealand or Central America," Yale geology professor David Bercovici said.

"That it's so universal is very weird because volcanoes are so different in size and character," he said. "It would be like blowing on five different musical wind instruments and having them all sound the same."

Tremors in nearly all volcanoes stay in a narrow band of frequencies from about 0.5 to 2 hertz, then just before and during the eruption the frequency climbs to a higher pitch, between 0.5 and 7 hertz, researchers say.

Bercovici and colleague Mark Jellinek at UBC suggest these similarities can be explained by "magma wagging," or the rattling that occurs from the interaction of rising magma and the foamy jacket of gas that surrounds it.

The factors that control this rattling or wagging vary little between volcanoes, which explains why the same tremors occur in very different volcanoes, they said.

"This model will provide a much-needed framework for understanding the physics of tremors, and this can only help with the prediction and forecasting of destructive eruptions," Bercovici said.

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