Geochemical precursors of the activity of an open‐conduit volcano: The Stromboli 2002–2003 eruptive events

Abstract

[1] Marked increases of CO 2 , H 2 and He dissolved in thermal waters and changes in the dissolved carbon isotopic composition, were observed at Stromboli before the 28 December 2002 eruption and before a violent explosive paroxysm occurred on 5 April 2003. High anomalous CO 2 flux values were recorded at the crater rim since a week before the eruption onset. The first anomalies in the thermal waters (dissolved CO 2 amount) appeared some months before the eruption, when magma column rose at a very high level in the conduit. High peaks of dissolved H 2 and He were recorded a few days before the paroxysm. Carbon isotopic composition indicates a magmatic origin of the dissolved CO 2 whose increase, together with those of H 2 and He, is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas-rich magma, whose fragments have been emitted during the explosion.

Crystal recycling in the steady-state system of the active Stromboli volcano: a 2.5-ka story inferred from in situ Sr-isotope and trace element data

“…This suggests that: i) the arrival of LP-magmas at shallow levels and their mixing with HP-magmas seem to be also occurred before the 5-April paroxysm; ii) the rapid ascent of LP-magmas to the surface during the paroxysm does not immediately affect the composition of the shallow HP-magmas, although the two magmas use the same conduit to the surface (Pistolesi et al, 2008 and reference therein), but it possibly affects the composition of lavas erupted one month after the paroxysm. The evidence at point (i) is also corroborated by the occurrence of few LP glassy shards in ashes erupted on 8-March-2003 (Schiavi et al, 2010), together with changes in fluid geochemistry (Aiuppa and Federico 2004;Carapezza, 2004) and lowering of Sr isotope ratios in scoria groundmasses during October-November 2002. As for the considerations at point (ii), it is also worthy noting that the mineral bulk compositions and zoning patterns of post-paroxysm lavas do not change, maintaining the typical crystal outer-rim compositions in equilibrium with the HP-magmas Landi et al, 2006Landi et al, , 2008; furthermore, no variations in the crystal size distribution of lavas are found immediately after the paroxysm, and the decrease in nucleation density observed in the 20--July lavas can be considered to be the only petrographic effect of the arrival of LP magmas in the shallow system (Fornaciai et al, 2009).…”

H<sub>2</sub>S interference on CO<sub>2</sub> isotopic measurements using a Picarro G1101-i cavity ring-down spectrometer

“…Carbon isotopes are powerful tracers of volcanic gases and degassing processes (Gerlach and Taylor, 1990;Taylor, 1986) and are currently analyzed along with a suite of other geochemical tracers to monitor activity at active volcanoes (Carapezza et al, 2004). CRDS has a promising future monitoring activity at volcanic centers and tracking real-time changes in the isotopic composition of volcanic gases.…”

Radon mapping, automatic measurements and extremely high 222Rn emissions during the 2002–2007 eruptive scenarios at Stromboli volcano

“…Refilling of volatile-rich magma is invoked to explain periods of increasing Strombolian activity with high tremor levels and high explosive regimes (Falsaperla et al, 1998), generally coupled with increasing degassing (Carapezza et al, 2004;Cigolini et al, 2005). The March-May 2006 and January-February 2007 phases, characterized by high radon concentrations, infrasonic and seismic tremor amplitude (cf.…”

“…The hydrothermal system of Stromboli volcano is essentially concentrated in the surrounding of the summit area (Finizola et al, 2002;. However, the presence of thermal waters and vapors in the surrounding of the Stromboli village together with radon anomalies and low resistivity layers suggests the extension of the hydrothermal shell at lower altitudes (Carapezza et al, 2004;Cigolini et al, 2005;Revil et al, 2011).…”

“…The geochemical data that preceded the onset of both lava effusion and the paroxysmal explosion were discussed by Carapezza et al (2004) and Cigolini et al (2005). The evolution of VLP (very long period) signals, thermal anomalies and SO 2 plume concentrations were analyzed by Ripepe et al (2005).…”