Pruiti, Lucia

At the end of the summer 2021, an increase in CO2 emissions at Vulcano brought an increase in the alert level and, consequently, to the upgrade of the monitoring activities by increasing the number of instruments deployed and the rate of the surveys. One of the new devices installed was a geodetic GNSS mobile network for a real-time and high-frequency monitoring of ground deformation, to increase the detail with respect to the existing permanent network. The mobile stations were initially installed at the northern base of the La Fossa crater, where the highest values of soil degassing were recorded. Two stations were co-located with gravimeters, in order to compare and integrate the data. After this very first period of testing, the mobile GNSS array has been reconfigured, to investigate the mud pool area. Thus, four stations were installed around the degassing area, one of them being in the same site of the gravimeter. Data has been acquired at 1 Hz rate and is used for the weekly reporting to Civil Protection. It was the first experience of a light and quick-to-install geodetic real-time and high-rate GNSS mobile network in this area, and it was the occasion for testing its performance, as well as different approaches for the real-time kinematic (RTK) differential positioning in order to find the most suitable for the ongoing phenomena. Furthermore, direct data communication and archiving in the institutional database have been implemented for immediate querying from the control room tools. We report the experiences collected during the installation phase, site selection, RTK approaches, and ground motion and provide the daily raw data in RINEX format for any future precise postprocessing for the mid- to long-term analyses.

In September 2021, the La Fossa crater at Vulcano, in Italy, entered a new phase of unrest. We discuss a set of monitoring parameters included in the INGV surveillance network, which closely tracked the sequence of effects related to the crisis. The low-frequency local seismicity sharply increased, while the GPS and tiltmeter networks recorded the inflation of the cone, as an effect of fluid expansion in the hydrothermal system. Gravity variations were probably the effects of fast processes within shallow sources. The anomalies in soil CO2 flux, fumarole temperature, and in plume SO2 flux marked the strong increase in the vapor output from crater fumaroles. The signs of the impending crisis had been evident in the chemical and isotopic composition of fumarole gases since July 2021. These geochemical anomalies were clearly indicative of the enhanced input of gases from a magmatic source. In October, the massive degassing also influenced the areas at the base of the cone. In some areas, soil CO2 degassing and the thermal aquifer recorded strong anomalies. By early November, the crisis reached its acme. Afterward, the monitored parameters started a slow and discontinuous decreasing trend although remaining, some of them, sensibly above the background for several months. The multidisciplinary approach proved decisive for the interpretation of the underlying processes acting in the different phases of the unrest, thus allowing a consistent evaluation of the multiple hazards.

Descrizione degli effetti di avvertibilità e risentimento del terremoto del 04/12/2022, ML 4.6

Vulcano and Stromboli are the most active volcanoes of the Aeolian Islands. Vulcano is in a quiescent stage since the eruption of 1888-90, but in the last decades it underwent several crises with huge increase in the gas output and temperature of crater fumaroles, and in the magmatic gas components. Stromboli is characterized by a permanent mild explosive activity, episodically interrupted by major explosions, lava effusions, or paroxystic explosive events (October 2001: a tourist killed; December 2002: lava effusion, tsunami generated by flank collapse; April 2003: explosive paroxysm, block fallout on Ginostra village; February-March 2007: lava effusion and paroxysm). Both island are renowned tourist sites and during summer risk increases as there are 10,000-15,000 persons per island (only a few hundreds in winter). In order to reduce the risk by educational activity, a Volcanological Information Centre has been established on each island (since 1990 at Vulcano and 1997 at Stromboli), by Istituto Nazionale di Geofisica e Vulcanologia (INGV) in cooperation with National Civil Protection and local authorities. Visitors receive informations on volcanic hazards, volcano monitoring systems and preparedness plans. Past and current volcanic activity is illustrated in the exhibition rooms, where real-time images of the active craters of Stromboli, Vulcano and Etna can be observed, together with seismic and geochemical signals, on dedicated monitors. A special attention is given to provide instructions minimizing the risk for those willing to climb the summit crater area. Booklets and posters are distributed freely. During summer, volcanology students of several Italian universities, coordinated by senior researchers, are involved in the tourist educational/information activity in the visitor centres.