347 The Stromboli Volcano: An Integrated Study of the 2002–2003 Eruption Geophysical Monograph Series 182 Copyright 2008 by the American Geophysical Union. 10.1029/182GM28 The 5 April 2003 Paroxysm at Stromboli: A Review of Geochemical Observations A. Rizzo, A. Aiuppa, G. Capasso, F. Grassa, S. Inguaggiato, and M. Longo Istituto Nazionale di Geoisica e Vulcanologia—Sezione di Palermo, Palermo, Italy M. L. Carapezza Istituto Nazionale di Geoisica e Vulcanologia—Sezione di Roma 1, Rome, Italy This paper reviews the published geochemical variations observed during the 2002–2003 eruption at Stromboli volcano. At the end of 2002, a new eruption began at Stromboli with a lava low that lasted until the end of July 2003. In 5 April 2003, an explosive paroxysm occurred with the ejection of bombs that reached the village of Ginostra, about 4 km from the craters. During the eruption, speciic variations in chemical composition of groundwaters and summit fumaroles were recorded before the explosion, most of them for the irst time. The water pH decreased signiicantly (0.5 units), and the dissolved CO 2 increased in two thermal wells (Cusolito and Zurro) located near Stromboli harbor from March until 5 April. Peaks in the dissolved He were also observed at all the sampling sites. All of these changes in the thermal aquifer suggested a pressurization of the system due to the degassing of a volatile-rich magma at depth. In the summit area, the SO 2 /HCl and SO 2 /HF ratios in the plume increased suddenly between 1 and 3 April due to the degassing of an S-rich magma that was approaching the shallow levels of the plumbing system, and this was involved in the explosion that occurred a few days later. This eruption was the irst at Stromboli to be analyzed using geochemical models. The variations observed in the basal aquifer and in the summit area occurred on very different timescales: a few weeks and a few days, respectively. of the volcano [Landi et al., 2006]. This magma is continu- ously crossed by gas bubbles coming from a crystal-poor, volatile-rich magma located in the deep portion of the feed- ing system, whose ascent and bursting is probably responsi- ble for the Strombolian activity at the surface [Ripepe et al., 2002; Chouet et al., 2003; Metrich et al., 2005]. Sometimes, this persistent activity is interrupted by lava effusion onto the Sciara del Fuoco (SdF) lank and/or by more violent and dangerous paroxysmal explosions. The latter result in the ejection of bombs that often reach a few kilometers from the crater area and comprise golden pumice and mingled blocks due to the coexistence of dark-colored, crystal-rich scoria, and crystal-poor pumice [Landi et al., 2006]. 1. InTROdUCTIOn The Italian volcano Stromboli is internationally famous because to its persistent activity characterized by mild explo- sions every 15–20 min fed by three vents located in the cra- ter area, at an elevation of 700 m above sea level (asl). The present-day activity is sustained by a degassed, crystal-rich shoshonitic magma residing in the shallow plumbing system