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Abstract:
Explosive eruptions of large magnitude generate strong electrical activity, as shown by several recent eruptions, including the record-breaking 2022 Hunga Tonga-Tonga Ha’apai event. However, it remains undetermined if electrification phenomena are ubiquitous over the whole spectrum of explosive activity. Therefore, our recent research efforts have focused on mafic explosive eruptions, as they occupy the lower end of volcanic explosivity. Furthermore, we extend our investigations to geyser which, together with their associated geophysical signals, can be considered as analogues to low-viscosity magmatic systems. We use an ELF (1-45 Hz) electrostatic lightning detector (100 Hz sampling rate) to detect electrical activity associated with mafic explosive eruptions spanning a wide range of eruptive styles at Stromboli and Etna (Italy) and Cumbre Vieja (Spain) volcanoes, as well as Strokkur (Iceland) and Pōhutu (New Zealand) geysers.We show that single jet bursts and prolonged fountaining of both magma and water produce detectable ELF signals associated with the movement of space charge. Electrical signals mark the inception of the eruptions and correlate in time and duration with both audible and infrasound measurements. Variations in the electrical signature reflect the eruption styles displayed and are modulated by velocity, volume and nature of ejected materials, as well as duration of the eruptions.Notably, volcanic eruptions generate electrical signals of larger amplitude compared to geysers, due to the average larger magnitude of the explosions. Furthermore, the lack of electrical discharges in water fountains suggests that electrical and rheological properties strongly influence charging mechanism of the ejected material.
