Exploring the conditions for occurrence of volcanic lightning

• Applicants: Privatdozent Dr. Corrado Cimarelli; Professor Dr. Matthias Hort
• Subject Area: Atmospheric Science ; Geophysics
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 386434708

Volcanic eruptions have fascinated people for as long as mankind exists especially if lightning occurs during eruptions, making them even more enigmatic. First reported during the 79 AD eruption of Mt. Vesuvius by Pliny the younger, volcanic lightning has caught significant attention during the last decade through increasingly detailed photographs documenting the recurrence of lightning in numerous eruptions. The increasing interest in volcanic lightning resides in the fact that flashes can be detected using remotely deployed antennas making this a potential hazard mitigation tool to detect eruptions and constraining their size. Furthermore, volcanic lightning is widely thought to have kick-started life on our early Planet by promoting the transformation of the volcanic gases composing the primordial atmosphere into complex organic compounds as proposed by Miller-Ureys pioneering experiments.Comprehensive models for volcanic lightning, however, have been quite sparse due to lacking of systematic observation of the phenomenon. Several fundamental electrostatic processes like triboelectrification versus fracture-induced charging of the ash have been looked at in quite some detail but still most models of plume electrification invoke mechanisms recognized in thundercloud lightning. However, the phenomenology of thunderclouds is far from being similar to that of volcanic plumes, relegating this comparison to a very general level. In this proposal we will shed new light onto the occurrence of volcanic lightning during volcanic eruptions by combining novel multiparameter field measurements, lab experiments and numerical simulations to help unravel the nature of volcanic lightning. Field measurements using Doppler radar, high speed video, electric field measurements and seismic and acoustic recordings will constrain the dynamic conditions that lead to volcanic lightning. These measurements will be carried out at Sakurajima volcano, Japan, which is well known for his very frequent, mostly vulcanian, eruptions as well as the frequent occurrence of volcanic lightning. The field data will document pre eruptive conditions, eruption velocities associated with lightning, the location of lightning flashes and associated electric fields, and in situ measurements of ash size distributions. Those data will be complemented by detailed laboratory experiments, carried out in a shock tube, determination of electrical properties of ash either generated in the lab under controlled conditions or measured on natural ash collected in the field. Finally, numerical modeling will combine our results on charge generation and eruption dynamics with a state of the art eruption column model to explore why some eruptions generate lightning while others not. Our data and modeling effort will lead to a significantly improved and self-consistent model for the occurrence of volcanic lightning which can be further used to tightly constrain dynamic conditions in volcanic plumes.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Co-Investigator: Dr. Keri Nicoll