Infrasonic evidences for branched conduit dynamics at Mt. Etna volcano, Italy.

On multi-vents volcanoes changes in activity between different vents reflect a complex fluid-dynamics of the shallow feeding systems and are often explained numerically and experimentally in terms of conduit branches and bifurcations. We present new geophysical constraints on the shallow feeding system of Etna volcano derived from array analysis of infrasound radiated from two distinct sources, one located in the SE crater and one in the Voragine or NE crater (VNE). These two sources alternated in their behavior, with the VNE crater system radiating low amplitude background infrasound interrupted by episodes of increased infrasound radiation from the SE crater. This switching behavior suggested a branched shallow feeding system strongly controlled by the gas/magma-flux. Here, the VNE craters represented the preferential and most stable branch of degassing during stationary flux regime, while the SE crater branch activated in response to an increase in the magma/gas supply rate.