Investigation of magmatic processes and reconstruction of magma feeding system of active volcano based on precise eruption history

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Based on precise eruption history and sequence, we investigated temporal evolution of magma plumbing systems of several active volcanoes. Main results are as following. 1)Although mixed magmas erupted in 1663 and 1769 eruptions of Usu volcano, end-member magmas of each mixed magma were distinct. Thus previous petrologic model of the volcano must be revised. In addition, we revealed petrological features of juvenile materials of the 2000 eruption. 2) Magma system of deeper basaltic and shallower andesitic magma chambers had evolved since 1469 eruption beneath Miyake-zima volcano. However, the system has been destroyed during the 2000 eruption. This suggests that the volcano might not erupt every 20-30 years as in 20^<th> century, because magma system would be reconstructed after the 2000 eruption. 3)Shallower mush chamber had been injected frequently by deeper basaltic magma during several months before 1995 eruption sequence of Ruapehu volcano, resulting to form several small mixed magma pockets. The pockets had erupted sequentially during eruptive activity for two months. 4) We reveal eruption history during the last 1000 years of Tyatya volcano by using wide-spread tephras. We also investigate detail eruption sequence of the unique 1973 eruption, which occurred northern and southern flanks of the volcanic edfice. In addition to the above, we also reveal petrological features of historical eruptive products of Hokkaido-Komagatake and Tarumai volcanoes. In these volcanoes, zoned magma chamber has been formed during the initial eruptions after long dormancy.