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.

The NEWTON-g Gravity Imager: Toward New Paradigms for Terrain Gravimetry

“…Instead of a mechanical spring, SGs exploit the magnetic levitation of a superconducting sphere in a field of superconducting persistent coils. SGs provide much better quality data than spring instruments (Carbone et al, 2019), but they have high power requirements and occupy a large physical footprint; therefore, they are not well suited for field deployments.…”

“…Furthermore, the 30-year history of conventional gravity measurements at Mt. Etna (Carbone et al, 2017 and references therein) and the existing multi-parameter monitoring system of the volcano, including a mini-array of three SGs (Carbone et al, 2019), will provide context for the NEWTON-g deployment and will aid in the interpretation of the observed gravity signals. Nevertheless, harsh environmental conditions at the summit of Mt.…”

“…Etna (∼6.5 km), hence only minor gravity changes are expected to develop in response to most volcanic processes. Furthermore, a SG has acquired continuous data at this site since 2014 (iGrav#16; Carbone et al, 2019), implying that having the quantum gravimeter operating at this site would provide partially redundant information.…”

Long‐Term Stability of Tilt‐Controlled gPhoneX Gravimeters

“…Only relative gravimeters can provide long-term time series. Traditionally, one considers that the relative gravimeters which use a spring to counteract the Earth's gravity force are not suited for continuous observations over long periods (Carbone et al, 2019;Torge, 1989). Some of the reasons for that include long-term thermal instabilities, a large instrumental drift, and tilt variations.…”

“…They can be more easily installed in places such as caves (Tanaka et al, 2013;Watlet, 2017). Their lower price and maintenance cost could increase the density of stations networks, as for instance on volcanoes (Carbone et al, 2019) or the development of methodologies based on multiple instruments (e.g., Kennedy et al, 2014).…”