High-Resolution Continuous Helium Measurement: A New Frontier in Volcanic and Seismic Monitoring Technology.

The measurement of geochemical parameters such as He and CO₂ concentrations are important and useful for the study of characterization of volcanic systems and seismically active areas. Furthermore, the He/CO₂ ratio gives useful information on the depth of the outgassing origin. Finally, extensive parameters such as He and CO₂ flux are even more binding in the interpretation and modeling of these systems in question.

In an ambitious move to volcanic risk mitigation, INFICON GmbH—a global leader in measurement and sensor technology—has partnered with premier scientific institutions (INGV_Italy) to monitor active volcanic centers on Italy’s Vulcano and Stromboli islands.

The research focuses on the characterization of natural volcanic emissions at Stromboli and Vulcano (Aeolian Archipelago, Italy), where an advanced geochemical monitoring network for deep-seated fluids is currently operational. A key development in this study involves the deployment of a high-resolution instrument for the continuous measurement of helium (He) concentrations. This device was strategically located with an existing station monitoring soil CO₂ flux to investigate the temporal correlation between different volatile species. The 'He-Man' sensor is a cutting-edge helium detector designed for field deployment. It employs a selective helium-permeable membrane to isolate the analyte from the atmospheric matrix, followed by a Penning ionization process to quantify the gas. This setup allows for the detection of trace levels of helium, providing a high-fidelity proxy for the arrival of primitive, mantle-derived fluids within the volcanic plumbing system.

Two 'He-Man' instruments were successfully deployed across the Aeolian Archipelago to monitor high-frequency helium variations. The first unit was installed at Vulcano Island, positioned in a target area characterized by anomalous diffuse soil degassing. The second unit was deployed on Stromboli Island, integrated within a thermal well monitoring system. In the latter configuration, the sensor is coupled with a specialized sampling interface designed for the real-time analysis of dissolved gases in the hydrothermal aquifer. These dual installations enable a comparative study of helium behavior in both sub-aerial and sub-aqueous volcanic environments.

Soils anomalous degassing:

By coupling the 'He-Man' instrument with a high-precision infrared CO₂ detector, we are able to determine the He/CO₂ concentration ratio within a sub-surface probe (sampling pipe) installed at the Palizzi site. This monitoring point is strategically located adjacent to the Palizzi station, which provides continuous measurements of diffuse CO₂ soil fluxes. Utilizing this integrated setup, the helium soil flux (J_He) is indirectly quantified by scaling the measured He/CO₂ ratio against the absolute CO₂ flux (J_CO2) according to the relation: J_He = ([He]/[CO₂])*J(CO₂)

 

Dissolved CO₂ in natural waters:

By integrating this helium concentration sensor with an automated system for monitoring dissolved CO₂ in a thermal well at Stromboli, we have successfully characterized the He/CO₂ ratio within the hydrothermal environment. This setup targets the specific aquifer situated between the degassing magma body and the anomalous diffuse degassing areas of Scari. This integrated monitoring approach provides critical insights into the geochemical evolution of fluids as they migrate from the magmatic source through the island's groundwater system toward the surface.