Development of the very long-range cosmic-ray muon radiographic imaging technique to explore the internal structure of an erupting volcano, Shinmoe-dake, Japan

摘要

Muography offers us a tool to observe hazardous erupting volcanoes remotely.However, practical muographic observations of volcanoes from a distance aredifficu therefore, various observations have been performed in thevicinity (< 1.5 km) of volcano peaks to suppress background noiseand enhance images. In this study, we created a muographic image directlybeneath the caldera floor of the erupting Shinmoe-dake volcano in Japan bylocating our muography telescope 5 km from the peak. The Shinmoe-dakevolcano began to erupt on 19 January 2011 and, in less than 1 month, theejected lava almost completely filled the caldera and completely changed thetopography of the caldera floor. The resultant image shows a low-densityregion underneath the western part of the newly created caldera floor, whichindicates the existence of a void there. After the volcano became less activein February 2011, infrequent eruptions might have left a void beneath thecaldera floor, which may trigger a collapse in the future. We anticipate thatour novel muography will be a practical tool for monitoring and predictingeruption sequences in the near future.