Insight on recent Stromboli eruption inferred from terrestrial and satellite ground deformation measurements

The multi-parametric permanent system (tilt and GPS networks, robotized geodetic station) for monitoring ground deformation at Stromboli volcano was set up in the 1990s and later greatly improved during the effusive event of 2002–2003. Unlike other volcanoes, e.g. Mt. Etna, the magnitude of ground deformation signals of Stromboli is very small and through the entire period of operation of the monitoring system, only two major episodes of deformation, in 1994–1995 and 2000, which did not lead to an eruption but rather pure intrusion, were measured. Similarly to the 2002–2003 eruption, no important deformations were detected in the months before the 2007 eruption. However, unlike the 2002–2003 eruption, GPS and tilt stations recorded a continuous deflation during the entire 2007 eruption, which allowed us to infer a vertical elongated prolate ellipsoidal source, centered below the summit craters at depth of about 2.8 km b.s.l. Due to its geometry and position, this source simulates an elongated plumbing system connecting the deeper LP magma storage (depth from 5 to 10 km) with the HP shallower storage (0.8–3 km), both previously identified by petrologic and geochemical studies. This result represents the first contribution of geophysics to the definition of the plumbing system of Stromboli at intermediate depth. Finally, no deformation due to the plumbing system was measured for a long time after the end of the eruption. Meanwhile, the new terrestrial geodetic monitoring system installed within the Sciara del Fuoco, on the lava fan formed during the eruption, indicated that during the first months after the end of the eruption the ground velocity progressively decreased in time, suggesting that part of the deformation was due to the thermal contraction of the lava flow.