Elementary Processes of Magmatic Eruption --Mechanisms of Instability and Bubbling in a Partially molten material--

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The purpose of this project is to clarify some important clues in the elementary processes and dynamics of magmatic eruption. Among them, we focused two instability mechanisms likely to occur in the partial melting zone in the upper mantle and in the magma chamber --conduit during magma ascent in the near surface condition. The former includes (1) the separa-tion of meltphase from solid material, which is controlled by the critical melt fraction and connectivity of the melt network, (2) the Rayleigh-Taylor type instability occuring in a partial melting zone under island arcs which may be reflected the non-uniform spatial distribution of polygenetic volcanoes, and (3) non-linear coupling in rising magma dynamics which may result in the fractal structure of eruption interval from hot spot activity to the eruptive activity of active volcanoes. The latter includes some physico-chemical rate processes and fragmentation-bubbling kinetics in the magma chamber and the conduit. It is suggested that the volatile elements content, degree of super saturation, and the size distri-bution of magmatic fragments are important factors in the eruption column dynamics.