Terminal Strombolian activity at Etna's central craters during summer 2012: The most CO2-rich volcanic gas ever recorded at Mount Etna

By using a permanent network of multi-component gas analyzer systems (Multi-GAS), we report for the first time the H2O-CO2-SO2 composition of the volcanic gases emitted prior to, during, and after terminal Strombolian activity at Mount Etna's central craters (CCs). We show that the summer 2012 Strombolian episodes of the Bocca Nuova crater (BNC), the largest of Etna's CCs, are associated with the emission of the most CO2-rich gas measured at the volcano thus far. The BNC plume was particularly CO2-rich with CO2/SO2 up to 100, H2O/CO2 < 1 in the quiescent periods between Strombolian episodes. However, more CO2-poor gas with CO2/SO2 < 27, H2O/CO2 > 1 prevailed at the BNC and at other degassing vents such as Voragine and Northeast craters during Strombolian eruptions. Based on the results of numerical simulations of volcanic degassing, conclude that the shallow Etna plumbing system was invaded in summer 2012 by a CO2-rich gas front likely supplied by the deep (> 100 MPa pressure) volcano's magmatic storage zone. This deep gas-bubble supply eventually caused a general rejuvenation of the resident magma in the upper conduits/shallow reservoirs, thereby triggering the first Strombolian episodes on the volcano's summit after years of quiescence.