Geochemical variations of air-free crater fumaroles at Mt Etna: new inferences for forecasting shallow volcanic activity

We investigated the gas geochemistry of fumaroles close to the Voragine crater of Mt Etna that have a temperature of 90-95°C, are CO2-dominated, and have an air content as low as <1%. This is the first report of the monitoring of such air-free fumaroles at the Etnean crater area - previous studies indicated an air contribution of 70% or more. The helium and carbon isotopes (Rc/Ra = 6.5 ± 0.4, δ13CCO2 = -1.7 ± 0.5‰) suggest that the released gas is directly related to the magmatic degassing. The fumaroles were sampled 12 times between June 2007 and June 2008, which revealed an increase in Rc/Ra from 6.1 to 6.9 that can be related to the increasing volcanic activity at the summit area of Mt Etna. These famaroles offer a new tool for detecting magmatic processes (magma ascent, refilling, degassing, etc.), and will be useful for volcano surveillance.