Linking Fountain Dynamics to Electric Field Variations: A Study of Strokkur Geyser

Geysers provide natural laboratories for studying eruptive dynamics, analogous to those observed at volcanoes, offering a safe and accessible setting in which processes can be observed at high spatial and temporal resolution. However, despite their easy accessibility and reliable activity, there is a lack of research regarding the electrical signals they generate. In this study, we investigate the source of electrical signals recorded by a Biral Thunderstorm Detector (BTD) in close proximity to Strokkur Geyser in Iceland. We focus on the effect known as shielding, where a moving conductive object connected to the ground distorts the electric field lines, inducing a current in a conductor, in our case, the BTD antenna. To test whether this effect is the source of the recorded signals, Finite Element Method Magnetics (FEMM) models are used to model the rising fountain. The results show that the induced charge and current are dependent on the fountain height, radius, and atmospheric potential gradient. We determine the atmospheric potential gradient using an electric field mill, colocated with the BTD, and measure the fountain height using video recordings. After deriving an empirical equation from the FEMM results, we can reproduce the measured BTD signal with the model by inverting for the fountain radius. Due to the high coherence between the signals and the good agreement between observed and calculated fountain radius, we conclude that the shielding effect is mostly responsible for the electric signals measured close to a geyser. This result is a significant contribution to understanding electric signals from various natural phenomena, including lava fountain activity and discharge generation in volcanic plumes.