A review of volcanic electrification of the atmosphere and volcanic lightning
Corrado Cimarelli, Kimberly Genareau, 2021
Examples of volcanic lightning at different volcanoes of theworld. Fromupper left: Surtsey, Iceland, December 1963 (photo Sigurgeir Jónasson); Eyjafjallajökull, Iceland,March 2010 (photo Marco Fulle); Taal, Philippines, January 2020 (photo Domcar C. Lagto); Sakurajima, Japan, March 2015 (photo Martin Rietze); Cumbre Vieja at La Palma, Canary Islands, October 2021 (photo INVOLCAN), Etna, Italy, November 2013 (photo Simona Scollo).
The electrification of volcanic ash plumes and the occurrence of volcanic lightning are now known to be common phenomena during explosive volcanic eruptions. This knowledge stems from centuries of anecdotal observations, and in recent decades, from improved instrumentation and media attention. Following a summary of previous reviews, this contribution will detail the most recent findings concerning electrification mechanisms of eruption columns/plumes (triboelectrification, fracto-electrification) and how hydrometeor charging contributes to this electrification depending upon the eruption style and abundance of external H2O. Field measurements to determine the charge structure of volcanic ash and gas plumes reveal wide variability both spatially and temporally, indicating the influence of these different charging mechanisms. The charge structure and resulting lightning characteristics have been provided by a suite of both ground-based and satellite-based light- ning detection methods and the various characteristics of each are summarized. As these detection methods have revealed, the electrical properties of ash plumes can provide insight into their physical dynamics throughout the course of an eruption. Lightning may therefore provide a means to track changing eruption conditions and the associated hazards, providing another tool for monitoring efforts. Volcanic lightning also leaves physical evidence in associated ashfall deposits. These lightning-induced textures have been documented and are summarized here, in addition to the different experiments that have reproduced such textures. Lightning simulation experi- ments provide information on changes to ash grain size, size distribution, chemical, and magnetic properties of ash. Lightning discharge and the lightning-induced changes to ash grains potentially impact not only the hazards induced by ashfall, but also changes in atmospheric chemistry relevant to biologic activity, the fluid dynamics of eruption columns/plumes, and ash dispersion. Additionally, shock-tube experiments provide insight on the mi- crophysical dynamics and environmental variables that influence electrification of dusty gas mixtures. Finally, this review summarizes the challenges to volcanic lightning research and the future efforts that can aid in addressing the unanswered questions regarding this phenomenon.
(a) High-speed (HS) video frame (10 kHz) of emerging ash jet with shockwave (note lofting of ash at the crater rim; white arrows) and vent lightning (~30m; red arrows in a and b). (b) multiparametric signals of explosion in (a), showing CRF coinciding with thermal anomaly and highest jet velocities. Grey lines are flashes detected by HS-video. (c) Discharge (6 cm) in particle-laden jet in shock tube experiment (50 kHz; from Cimarelli et al., 2014, 2016). (d) Electrical and pressure signals recorded during a shock tube experiment. In analogy to the CRF signals, the electrical discharges (blue spikes) occur during conditions of overpressure (hump in in the orange line) of the jet at the nozzle (after Gaudin and Cimarelli, 2019). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Although volcanic lightning has been reported for centuries (e.g., Pliny the Younger; Volta, 1782; Fouqué, 1879; Symons, 1888; Mercalli and Silvestri, 1891; Friedlaender, 1898; Fischer, 1893; Anderson, 1903; Table 1 in Supplementary Material), an increasing number of volcanic lightning reports and instrumental detections (e.g., Stromboli 2003, 2007 and 2019, Eyjafjallajökull 2010, Puyehue 2011, Kirishima 2011, Etna 2013, 2015 and 2021, Sinabung 2014, Villarrica 2015, Calbuco 2015, Colima 2015, 2016 and 2017, Pavlov 2016, Sakurajima 2009–2021, Bogoslof 2016–17, Ambae 2018, Fuego 2018, Anak Krakatau 2018–19, Taal 2020, St. Vincent 2021, Cumbre Vieja of La Palma 2021) demonstrate that electrification is observed over a wide range of explosive styles and extends to the lower end of the volcanic explosivity index scale (VEI ~0) so that it can be considered an intrinsic property of volcanic ash plumes (Fig. 1). Interest in this phe- nomenon has been fostered by the opportunity to use detection of vol- canic lightning as a viable real-time monitoring method for hazardous volcanic activity. Besides advances in remote sensing methods, insight gained from laboratory experiments and microanalyses of ashfall de- posits has revealed that volcanic plume electrification has the potential to impact both the hazards induced by volcanic ash and the fluid dy- namics of the eruption column/plume. Consequently, there is much still to be discovered. This contribution will summarize the current state of knowledge on volcanic lightning and gaps that remain to be filled.