Continuous soil radon monitoring during the July 2006 Etna eruption

Continuous soil radon monitoring was carried out near
the Southeast Crater (SEC) of Mt. Etna during the 10-day
July 2006 Strombolian-effusive eruption. This signal was
compared with simultaneously acquired volcanic tremor
and thermal radiance data. The onset of explosive activity
and a lava fountaining episode were preceded by some
hours with increases in radon soil emission by 4–5 orders of
magnitude, which we interpret as precursors. Minor changes
in eruptive behavior did not produce significant variations
in the monitored parameters. The remarkably high radon
concentrations we observed are unprecedented in the
literature. We interpret peaks in radon activity as due
primarily to microfracturing of uranium-bearing rock. These
observations suggest that radon measurements in the
summit area of Etna are strongly controlled by the state of
stress within the volcano and demonstrate the usefulness of
radon data acquisition before and during eruptions.

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