Combined discrete and continuous gravity measurements at Vulcano Island (Aeolian Archipelago, Italy)

We present the preliminary results of combined discrete and continuous gravity measurements, carried out at Vulcano Island (Aeolian Archipelago, Sicily, southern Italy), in the period October 2021 - January 2022. The gravity observations have been aimed at investigating the dynamics of the volcanic-hydrothermal system, during an interval when significant changes in chemical properties, temperatures and emission rates of La Fossa crater fumaroles were observed.

Campaigns of gravity measurements were carried out at Vulcano on an annual basis, between 1982 and 2014. The gravity network initially included 11 benchmarks and grew through time. For the period considered here, the discrete gravity measurements were repeated twice (October and November 2021) on a network consisting of 19 benchmarks. The network is linked to an external reference station, situated in Milazzo (Sicily north coast), that has been a site of absolute measurement since 1990. In order to obtain information on the time scales of the volcanic and hydrothermal processes able to induce bulk mass changes, three stations for continuous gravity measurements were installed in October 2021.

Comparison between campaign data collected in 2014 and in October 2021 reveals a gravity decrease affecting the whole volcano, with a maximum amplitude of about -100 microGal in the area of La Fossa. No significant gravity changes were observed between October and November 2021. On the other hand, continuous gravity observations showed high frequency variations affecting only one of the three stations, thus indicating that they are due to fast-evolving and local processes, occurring within shallow sources. Transient signals also appear in the time series from the three stations during Very Long Period (VLP) events.

Our findings indicate that the combined use of discrete and continuous gravity measurements is a promising tool for studying the volcano-hydrothermal system of Vulcano and mitigating potential hazards.