Achievements in Volcano Research in the Earthquake and Volcano Hazards Observation and Research Program from 2019 to 2023: Towards Prediction of Volcanic Eruptions by Building Volcanic Activity Transition Models

The prediction of volcanic eruptions and eruption hazards is important to mitigate volcanic hazards. The purpose of the Volcano Program Promotion Panel in the Research Program on Earthquake and Volcanic Observations is to elucidate the conditions and logic of the event branch of volcanic activities, construct a transition model of volcanic activity, and promote research for the prediction of volcanic eruptions. During 2019–2023, submarine and remote-island volcanic eruptions were prominent. Additionally, terrestrial volcanic eruptions highlighted issues in volcanic disaster prevention. Significant progress was realized in material science research. The effects of water content, conduit size, and magma ascent rate on the magma supply systems and eruption explosiveness were evaluated. The relationship between the increase in phenocryst and decrease in eruption size was also elucidated, and the time evolution of the silicic magma system leading up to the caldera-forming eruption was elucidated using a new analytical method based on isotopes. The isotopic ratios of volcanic gases revealed the effects of magma foaming on shallow hydrothermal systems. The importance of rapid analysis of eruptions was highlighted, and magma supply systems and volcanic activity transitions were modeled. Remarkable progress was also made in geophysical observation research. An increase in the amplitude of volcanic tremors and a change in the epicenter location were detected, which were presumed to be caused by the rising of magma before the eruption. New observation techniques were actively introduced, and detailed magnetization structures and temporal changes were detected from aeromagnetic observations using uncrewed aerial vehicles. Distributed acoustic sensing observations were used to determine the epicenter of volcanic earthquakes and estimate the ground structure. Furthermore, seismic survey and ejecta analyses indicated the volume of deposits and magma production process in caldera-forming eruptions. Standardization of the volcanic activity index was promoted through applications of the index for multiple volcanoes as an objective method of volcanic activity evaluation. The addition of highly accurate information on the subsurface structure of volcanoes has advanced our understanding of the eruptive activity and processes. Through these results, the trial and verification of predictions based on the transition model of volcanic activity will be conducted in the following research plan.