カルデラ生成噴火の準備過程解明に向けた研究の展望 [in Japanese] Future view to understanding the preparation process of caldera forming eruptions [in Japanese]
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Caldera-forming eruptions are characterized by their large scale and low frequency. The question of how to prepare for such a rare, large-scale eruption poses a serious problem for the general public, administrative agencies, and volcanologists. The most commonly employed method is to investigate the past. Volcanologists seek to understand past events and to predict future developments by examining the history of eruptions. However, we face a high hurdle in preparing for such large eruptions. Using current prediction techniques, it is possible to detect the anomalous signals that immediately precede an eruption, by carefully monitoring volcanic activity. It is difficult, however, to judge whether such signals will lead to a caldera-forming eruption. In addition, it may be necessary to continue monitoring for thousands of years, until such an eruption occurs. From this reason, caldera-forming eruptions are not considered as part of the prediction program in Japan. Rather than waiting for such an eruption, it would be better to identify the processes that precede caldera-forming eruptions. This paper presents a hypothesis regarding the diversity of volcanic activity, as a basis for considering caldera-forming eruptions. The hypothesis holds that volcanic activity occurs as two end-member patterns: eruption dominant (ED) volcanism, in which magma is readily transported to the surface; and geothermal activity dominant (GD) volcanism, in which magma stagnates in the subsurface and induces geothermal activity. A spectrum of activity patterns exists between these two end members, related to the tendency of magma to ascend or to stagnate in the crust. Basic magma is stored repeatedly after intrusive events at GD volcanoes, eventually evolving to silicic magma. After repeated events, basic magma from deeper levels interacts with pre-existing magma in the chamber, causing heating, bubble formation and a huge eruption. According to this hypothesis, large amounts of magma will be found beneath volcanoes at which a caldera-forming eruption will occur in the future. It is also important to know where and why magma stops rising in the crust. The first step in understanding the preparation process of a caldera-forming eruption is to examine the hypothesis proposed in this study.
- The Journal of the Geological Society of Japan
The Journal of the Geological Society of Japan 116(9), 463-472, 2010
The Geological Society of Japan