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Abstract

Recent clusters of deep, low-frequency earthquakes southeast of Laacher See in the East Eifel region of Germany suggest the presence of an active magmatic system in the lower crust and upper mantle. Measuring fluid data at the Earth's surface could help identify processes in the deep magma system. Dense and continuous monitoring is required to distinguish between environmental and deep processes, but this is rarely carried out. Here, we present a pilot study of an intracontinental, distributed volcanic field in the Eifel, where twelve measuring stations have been installed since 2020 in decommissioned CO₂ wells, mofettes, CO₂-rich springs, CO₂-rich soil, and a cold-water geyser. For the first time, fluid data is being recorded continuously with a high temporal resolution of up to 1 Hz. Interestingly, seasonal variations in fluid parameters are relatively small, and baseline data was determined within two to three years. Short-term transients were observed at individual network stations and were related to events such as heavy rainfall, atmospheric pressure waves, or local and distant earthquakes. However, over longer periods, we also observed trend changes in important magmatic indicators, such as helium isotope ratios, radon concentration, and water temperature. For instance, one location exhibited notable shifts in helium isotopes from 2021 to 2025, seemingly correlating with earthquake swarms at depth. These examples underscore the importance of establishing a network of fluid measuring stations, conducting continuous monitoring, and jointly evaluating meteorological, hydrogeological, geophysical, and geodetic data.