Collaborative Research: Characterizing Small-scale Lightning Discharges Associated with Explosive Volcanic Activity at Sakurajima Volcano

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Volcanic lightning discharges have length scales ranging from tens of meters to tens of kilometers. Most small discharges occur proximally to a volcanic vent concurrent or within a few minutes of an explosive volcanic eruption. Large scale discharges typically occur throughout a mature plume formed 5 or more minutes subsequent to an explosive eruption. This research work focuses on studying the small, proximal discharges that occur concurrent with explosive volcanic eruptions. The main goal is to better characterize the proximal electrical activity within the context of the eruptive activity to gain a better understanding of the eruptive conditions that are required to produce different types of small-scale discharges. This characterization will be accomplished by making high-resolution 3-D lightning mapping observations of lighting discharges during small explosive eruptions of Sakurajima Volcano located in the Kyushu region of southwestern Japan. Other instrumentation (infrasound, video cameras, and electric field change sensors) will be used to monitor the explosive activity, plume development, and changes in electric field caused by lightning. The data will be used to determine when different types of electrical discharges occur relative to the onset of an explosive eruption and in relation to the ascent of volcanic ejecta. Electrical discharges will be characterized by determining the length scales, speeds, and polarities of the discharges, as well as by locating where the discharges initiate.Intellectual Merit: The research would be the most detailed study of volcanic lightning to date, combining measurements of volcano infrasound, electric field changes, and plume development with high-resolution Lightning Mapping Array (LMA) data and high-speed video observations of volcanic lighting. The inclusion of electric field change measurements, high-speed video, and visual plume observations distinguishes this project from previous research. The research will increase knowledge of electrical activity that occurs as a direct result of an explosive volcanic eruption. This will contribute to our understanding of the eruption processes that are responsible for producing electrical activity proximally to a volcanic vent.Broader Impacts: Because small-scale discharges frequently accompany volcanic eruptions of a large range of sizes, the results of the research will be applicable to developing an eruption monitoring system that utilizes VHF observations of lightning and electrical activity. In addition, the results of the research will be used to determine if one can predict eruption magnitudes or ash plume heights based on observations of electrical activity. The research will also provide training for an early career researcher from an underrepresented group and three graduate students. They will participate in gathering, organizing, archiving, and analyzing the data.