Volcanic lightning is a common phenomenon observed during explosive eruptions of high magnitude and intensity. Lightning observations in milder explosive eruptions, generally of basaltic composition, are less frequent, arising the question of whether electrification may be a common feature over the whole spectrum of explosive styles and magma compositions.

The 2021 eruption of Cumbre Vieja on the island of La Palma (Canary Islands, Spain) started on 19 September 2021, continuously producing lava flows and tephra of average basanite to tephrite composition during 85 consecutive days, eventually generating a >200 m tall scoria cone (about 1220 m asl) and a vast compound lava flow field. Lightning was frequently observed in the plume during different phases of the explosive activity. This eruption provided the rare opportunity to monitor variations in the electrical potential on various time scales continuously over several weeks. We measured such electrical activity using a lightning detector operating in the extremely low frequency range with a sample rate of 100 Hz (Vossen et al., 2021), installed about 2 km away from the active vents. The detector was deployed on 11 October 2021 and recorded continuously until the end of the eruption on 13 December 2021, thus providing a unique dataset of its kind. Stable fair-weather conditions over La Palma recorded by climatological stations during the entire monitoring period (exception made for a thunderstorm episode on 26 November 2021), allow a confident attribution of the changeable lightning activity to the explosive activity of the scoria cone. Here we present volcanic lightning and electrification timeseries as a function of the varying explosive activity as observed through thermal videography and acoustic recordings (Cigala et al., 2022). Variations in lightning activity were apparent during the eruption. Scaled lab experiments have allowed for constraining empirical relationships between “explosion intensity” and lightning discharges. These findings will allow to unravel the dynamical evolution of the explosive component of the Cumbre Vieja eruption thanks to the close-range, direct monitoring of the ongoing eruption.