Electrification of Geysers: Insights from the Andernach Geyser and Comparative Sites

Abstract

Electrification in volcanic systems has been widely studied, especially in relation to volcanic lightning, offering valuable insights for eruption monitoring and plume characterization. However, directly linking electrical signals to eruptive processes remains challenging due to the complexity and inaccessibility of volcanic environments. Geysers, which exhibit similar explosive two-phase flow dynamics as low-viscosity volcanic eruptions, offer a safer and more accessible analogue. Their frequent activity, coupled with generally well-constrained plumbing systems, allows for high-resolution observations and isolation of water-related electrification processes. Motivated by these advantages, this study presents the first investigation of short-term atmospheric electric field variations during geyser eruptions. The main focus is on the cold-water geyser of Andernach (Germany), with comparative observations at the hot-water geyser of Strokkur (Iceland) and the Jet d’Eau fountain of Geneva (Switzerland). A Biral Thunderstorm Detector (BTD) was used to record electric field variations, with an electric field mill additionally deployed at the Jet d’Eau site to measure field magnitude and polarity. Two hypotheses were initially proposed to explain signal generation: (1) space charge production via interfacial processes such as bubble bursting and droplet breakup, and (2) shielding, where erupting jets distort the local electric field. It is shown that each field site exhibits its own characteristic electrical signal patterns, reflecting differences in eruption style and jet morphology. The rhythmic, pulsating eruptions of the Andernach geyser consistently produce a positive–negative (P–N) sawtooth pattern, while the Strokkur geyser produces single bipolar waveforms of which polarity is dependent on local weather conditions. Lastly, the Jet d’Eau produces high-amplitude peaks related to water impact at the base and is accompanied by a local field reversal. Combined, these observations support a dominant role for space charge production, likely governed by two mechanisms: (a) Electric Double Layer (EDL) disruption, generating both small negatively charged aerosols and larger positively charged droplets; and (b) Field-driven charging, whereby the erupting jet conducts ground potential, generating dominantly negatively or positively charged droplets, depending on ambient electric field polarity. The relative contribution of these mechanisms is suggested to depend on eruption style. While direct application to volcanic systems remains complex, the conceptual models developed here offer new insights into charge generation in explosive two-phase eruptions and may inform future monitoring of electrical activity in both geyser and volcanic environments.