Stromboli volcanic activity variations inferred from observations of fluid geochemistry: 16 years of continuous monitoring of soil CO2 fluxes (2000-2015)

Stromboli volcano is characterized by a persistent strombolian activity that was interrupted by effusive eruptions in 1985, 2002-2003, 2007, and 2014. The considerable amount of soil CO2 flux data acquired by the continuous geochemical network installed in the summit and peripheral areas of Stromboli Island have allowed us to thoroughly investigate and to model the plumbing system. This study analyzed 16 years of soil CO2 fluxes from the summit area, which showed a wide range of values (from 2000 to 85,000 g m(-2) day(-1)). A set of discontinuous pCO(2) data (ranging from 0.1 to 0.35 atm) from a dedicated thermal well (COA) drilled in the Stromboli village has been taken into account for the peripheral degassing evaluation. One of the major accomplishments of this study is the confirmation of the previous formulated geochemical model based on of the soil CO2 fluxes database and the recent effusive eruptions. The analysis of soil summit degassing data recorded at the summit STR02 station throughout the monitoring period (2000-2015) revealed that the log(CO2 flux) values conformed to a polimodal distribution with different mean values of CO2 fluxes being recorded for each sub-period during the different effusive eruptions. The three selected periods (2000-2004, 2005-2010, and 2011-2015) were characterized by considerable increases in soil CO2 degassing coinciding with the periods of effusive eruptions, indicating volatiles overpressure and disequilibrium of the volcanic system. Moreover, the CO2 output evaluations based on soil CO2 fluxes and pCO(2) values of thermal waters (COA), have showed a long increasing trend both in the summit and peripheral areas. From 2007 to 2014, culminating in the last effusive eruption (August-November 2014). (C) 2017 Elsevier B. V. All rights reserved.