Geochemical evaluation of observed changes in volcanic activity during the 2007 eruption at Stromboli (Italy)

Abstract

On February 27, 2007 a new eruption started at Stromboli that lasted until April 2 and included a paroxysmal 12 explosion on March 15. Geochemical monitoring carried out over several years revealed some appreciable 13 variations that preceded both the eruption onset and the explosion. The carbon dioxide (CO2) flux from the 14 soil at Pizzo Sopra La Fossa increased markedly a few days before the eruption onset, and continued during 15 lava effusion to reach its maximum value (at 90,000 g m−2 day−1) a few days before the paroxysm. Almost 16 contemporarily, the δ13CCO2 of the SC5 fumarole located in the summit area increased markedly, peaking just 17 before the explosion (δ13CCO2~−1.8‰). Following the paroxysm, helium (He) isotopes measured in the gases 18 dissolved in the basal thermal aquifer sharply increased. Almost contemporarily, the automatic station of CO2 19 flux recorded an anomalous degassing rate. Also temperatures and the vertical thermal gradient, which had 20 been measured since November 2006 in the soil at Pizzo Sopra La Fossa, showed appreciable variabilities that 21 lasted until the end of the eruption. The geochemical variations indicated the degassing of a new batch of 22 volatile-rich magma that preceded and probably fed the paroxysm. The anomalous 3He/4He ratio suggested 23 that the ascent of a second batch of volatile-rich magma toward the surface was probably responsible of the 24 resumption of the ordinary activity. A comparison with the geochemical variations observed during the 25 2002–2003 eruption indicated that the 2007 eruption was less energetic.