Magma migration beneath the active craters of Sakurajima volcano before the 2023 eruption of Showa crater inferred from ground deformation and muon monitoring

Abstract Ground deformation source modeling and muographic mass density monitoring were applied for studying the plumbing system of Sakurajima volcano, Kyusu Japan using data collected by Interferometric Synthetic Aperture Radar and Sakurajima Muography Observatory. Lateral movement of ground deformation source was observed to east beneath the active craters around sea level that resulted in the shift of eruption frequency between the Minamidake craters. During the same period, muography showed opposite trends in mass changes for adjacent craters: mass decreased beneath the Minamidake A and B craters and mass increased beneath the Showa crater that also suggests the lateral movements of materials towards east. Thereafter, the ground deformation source started to rise and the eruption sequence of Showa crater started when the deformation source reached a depth of about 350–450 m beneath the craters. The muographically measured mass increased beneath Showa crater before the start of the eruption sequence. During eruption episodes of Minamidake A and B craters, the mass did not change beneath these craters and decreased beneath Showa crater, suggesting a connection between the adjacent craters. These observations suggest the presence of a deep magma channel around sea level which feeds Minamidake A and B craters and the existence of a shallow magma chamber about 350–450 m beneath the active craters which feeds all craters. Joint measurement of ground surface deformations and cosmic-ray muons allows simultaneous monitoring of shallow volcanic processes that may allow more reliable assessment of impending eruption sequences of Showa crater of Sakurajima volcano. Graphical Abstract