Textual analysis of the pyroclastic rocks: Insights to degassing in the volcanic conduit (Keiichi OHTAKI) * This paper reviews recent studies on textural analysis of pyroclasts, especially those on degassing in the volcanic conduit. Potential importance of geophysical observations on eruption events inspired by progresses in magma rheology is suggested, and links between quantitative textural analysis and forward approaches from both theory and experiments are discussed. Permeability of the

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... mented materials may provide useful information to consider permeable flow degassing in the volcanic conduit. Permeability data of pyroclasts reported so far, however, show somewhat dispersed values which can not be fitted by a simple relation with porosity based on a percolation theory. This indicates that geometrical diversities originated form bubble coalescence, deformation and collapse are important to control degassing efficiency. Geological observations of fossil conduit have been made, in which brittle behavior of viscous magmas under high shear stresses near the volcanic conduit has been underscored.