GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.3 191 been several phases of potential reactivation since the last eruption, as testified by geochemical anomalies measured in fumarolic gases emitted at the La Fossa cone in some periods. Various authors have attributed these unrests to an increasing contribution of fluids coming from deep magmas (Diliberto 2013, 2017; Tamburello et al., 2010; Alparone et al., 2018; Chiodini, 1995). In this work, a review of geophysical data regarding the deformation sources integrated with those coming from the geochemical surveillance network is proposed, with the aim of evidencing the role of the deeper magmatic source in the feeding mechanism of fluid release and deformation processes. Results and discussion. This work is principally focused on the 1988 unrest occurred at Vulcano island, when the volcano showed specific chemical and physical signals for almost 2 years that caused apprehension among the population and the volcanological community. During this unrest, all the recorded parameters displayed the most significant variations since the last critical episode occurred in 1924. Temperatures at the fumarolic field located on the crater rim reached the highest value of 700°C, with normal temperatures during quiescence generally clustered between 100° and 300°C. Also the amount of gases discharged from fumaroles largely increased. The seismic monitoring network recorded an exponential increase in low-magnitude earthquakes. The increase in events at depths between 300 m and 1.5 km below the crater and magnitudes between 1.5 and 2.8 increased of an order of magnitude, being from an average of 3 events per day to a maximum of 20. The low-magnitude events increased exponentially due the resonance and small-cracks within the fumarolic ducts, but no digital data are available. Regional seismicity between Lipari and Vulcano is controlled by the ATLFS, mostly related to a dextral transform fault movement. Beneath La Fossa crater (0.5-1.1 km), seismicity is controlled by hydrothermal activity not connected with regional tectonics. The geophysical surveillance has been carried out using an EDM network located between Lipari andVulcano islands. In theperiod1975-1998, thenetwork recordedgeodeticmeasurements which have been used to determine the state of unrest of the volcano. Two different networks were used to carry out measurements, the LIPVUL network between Vulcano and Lipari islands and the VULNORD network located in the norther part of Vulcano island (Fig. 1). The LIPVUL network recorded an expansion of the area until the earthquake of April 1978, then a period of deflation that sharply increased during the unrest phase. Data from the VULNORD network show inflation between the years 1987-88 and then a deflation after 1989. Inflation recorded by the VULNORD network was probably consequence of the thermal expansion of pressurized aquifers, a phenomenon that led to the landslide of the summer of 1988. Fig. 1 - Areal dilatation recorded by VULNORD and LIPVUL from 1975 to 1996 (source: INGV).