Changes in CO2 Soil Degassing Style as a Possible Precursor to Volcanic Activity: The 2019 Case of Stromboli Paroxysmal Eruptions

Abstract

Paroxysmal explosions are some of the most spectacular evidence of volcanism on Earth andare triggered by the rapid ascent of volatile-rich magma. These explosions often occur in persistentlyerupting basaltic volcanoes located in subduction zones and represent a major hazard due to thesudden occurrence and wide impact on the neighboring populations. However, the recognition ofsignals that forecast these blasts remains challenging even in the best-monitored volcanoes. Here, wepresent the results of the regular monitoring of soil CO2flux from a fumarole field at the summit ofStromboli (Italy), highlighting that the 2016–2019 period was characterized by two important phasesof strong increases of volatile output rate degassing (24 g m2d−2and 32 g m2d−2, respectively)and moreover by significant changes in the degassing style few months before the last paroxysmalexplosions occurred in the summer 2019 (3 July and 28 August). Establish that the deep portionsof a volcano plumbing system are refilled by new volatiles-rich magma intruding from the mantleis therefore a key factor for forecasting eruptions and helping in recognizing possible precursors ofparoxysmal explosions and could be highlighted by the monitoring of soil CO2flux. The abruptincrease of degassing rate coupled with the strong increase of fluctuating signal (daily naturaldeviation) recorded during 2019 at Stromboli could be the key to predicting the occurrence ofparoxysmal events.