Branched Conduit Structure Beneath the Active Craters of Sakurajima Volcano Inferred From Muography.

Observing in‐conduit physical mechanism underlying the switching of eruptive activity between the craters of multi‐vent volcanoes could contribute to hazard assessment at these complex volcanic edifices. We performed monitoring of mass density changes beneath two active craters of Sakurajima volcano in Kyushu, Japan between September 2018 and July 2023 with cosmic‐ray muography. From December 2022, the mass density decreased beneath Minamidake crater and increased beneath Showa crater in accordance with a switch of eruptive activity from Minamidake crater to Showa crater. Plug formation and convective magma degassing processes have been observed with muography in accordance with the deformation of the surface of volcanic edifice measured by Interferometric Synthetic Aperture Radar. We found a moderate inverse correlation with a Pearson's coefficient of −0.52 between the mass densities observed beneath the two active craters throughout the entire period. The inverse correlation of mass densities indicates a magmatic gas flux dynamics which characterizes a branched conduit structure. Muography thus reveals the shallow magmatic processes during switching of eruptive activity between the craters of multi‐vent volcanoes and allows to infer to the conduit structure. Plain Language Summary: Observing the changing of structure and amount of materials in the upper plumbing systems of active volcanoes can contribute to the visualization the ongoing volcanic phenomena and assessing of related hazards. For instance, the increase in mass density indicates the uprise of deep volcanic materials in the conduit that may result in the onset of eruption. We measured the directional dependent yield of naturally occurring cosmic‐ray muon particles across the active Sakurajima volcano in Kyushu, Japan. We utilized muography to visualize the changes in mass density structure beneath the erupting craters over time. The captured muon images revealed that the mass densities varied inversely underneath the Minamidake and Showa craters throughout the measurement period. The observed inverse correlation between the mass densities indicates a branched linkage between the conduits of the two active craters. Key Points: Muography is utilized for visualizing and monitoring the mass density changes beneath the active craters of Sakurajima volcano, Kyushu, JapanInverse correlation is found between the mass densities observed beneath the two active cratersA branched linkage between the conduits of active craters inferred from the changes of eruptive activity and mass densities [ABSTRACT FROM AUTHOR]