The Benefits of Using a Network of Superconducting Gravimeters to Monitor and Study Active Volcanoes

Abstract

We present results from a mini-array of three iGrav superconducting gravimeters (SGs) at Mount Etna. This is the first network of SGs ever installed on an active volcano. Continuous gravity measurements at active volcanoes are mostly accomplished with spring gravimeters that can be operated even under harsh field conditions. Nevertheless, these instruments do not provide reliable continuous measurements over periods longer than a few days due to the instrumental drift and artifacts driven by ambient parameters. SGs are free from these instrumental effects and thus allow to track even small gravity changes (1–2 μGal) over a wide range of time scales (minutes to months). However, SGs need host facilities with main electricity and a large installation surface, implying that they cannot be deployed in close proximity to the active structures of tall volcanoes. At Mount Etna the three iGrav SGs were installed at distances from the summit active craters ranging between 3.5 and 15 km. Despite the relatively unfavorable position of the installation sites, we show that these instruments can detect meaningful (i.e., volcano-related) changes that would otherwise remain hidden, like, for example, the weak gravity signature (within a few μGal) of gas buildup at intermediate depth in the plumbing system of Etna, during noneruptive intervals. Our results prove that iGrav SGs are powerful tools to monitor and study active volcanoes and can provide unique information on the bulk processes driving volcanic activity.