カルデラ形成噴火と大規模火砕噴火の研究の展望

抄録

The study of large-scale explosive eruptions that form collapse calderas has progressed dramatically in the last decade. Several caldera systems have been studied using geological and petrological approaches to investigate the development of long-term magma reservoirs as a preparatory process for large-scale eruptions. The concept of caldera cycle is useful for understanding the long-term activity of caldera volcanoes with repetition of large-scale caldera-forming eruptions. Several calderas have been studied for their eruptive phenomena that immediately preceded a major caldera-forming eruption. However, the development of the magmatic system and its relationship with precursory eruptive activities is still poorly understood. The eruptive processes of several caldera systems in Japan, such as those at Kutcharo, Shikotsu, Toya, Aso, Aira and Kikai, have been intensely studied, using geological and petrological approaches. These studies reveal the detailed sequence of caldera-forming, large-scale, explosive eruptions. In addition, the eruption history of smaller calderas, such as Ikeda and Nigorigawa, has also been studied, highlighting the similarity and contrast against the larger calderas. Theoretical studies on the collapse mechanisms of calderas that cause these large-scale eruptions have also made significant progress in the past decade. Furthermore, geophysical surveys have been conducted to gather information on the deep structures and activity of caldera volcanoes such as Aira, Aso and Kutcaharo. However, due to the lack of real-world observations of large-scale explosive eruptions, our knowledge of such eruptions relies primarily on the geological and petrological analysis of past eruptions. In the next decade, we should aim to integrate these geological and petrological data with geophysical and geochemical observations to improve our understanding of the current activity of caldera volcanoes and evaluate their future activity.