Geochemical Prediction of the 2002–2003 Stromboli Eruption From Variations in CO2 and Rn Emissions and in Helium and Carbon Isotopes

Significant changes in both the chemistry of coastal thermal waters and the soil
CO2 and Rn emissions in the crater area were recorded at Stromboli prior to the
eruption that began on 28 December 2002. The dissolved CO2 contents and the
d13C and 3He/4He values were elevated in the thermal aquifer from July 2002.
Synchronous variations in the same isotope ratios were recorded in the summit
fumarolic gases, with both 3He/4He and d13C values of gases released from a
fumarole in the summit area increasing between May and November 2002. These
variations are indicative of early degassing of a new gas-rich magma batch with
a 13C- and 3He-rich signature. This magma recharge probably fed the intense
Strombolian activity recorded during that period. The eruption began with a major
explosion that produced a glowing avalanche, immediately followed by a fluid lava
overflow from the NE crater and subsequent lava effusion from vents opened in the
Sciara del Fuoco depression. Sharp increases in CO2 soil flux and Rn emissions—
to values never observed previously—were recorded in the summit crater area
10 d before the eruption onset. These CO2 and Rn anomalies are indicative of a
high gas-driven magma supply rate and gas overpressure within the conduit. The
sudden depressurization of the magma filling the upper conduit probably caused
the major explosion that occurred on 28 December, which heralded the effusive
phase. These data demonstrate the importance of collecting a wide spectrum of
geochemical data from different geological sites when monitoring a volcano.