MULTIPHASE FLOWS IN MAGMATISM

Diversity of volcanic activities reflects various styles of magma flow s. One of the most important characters of the magma flows is that the y are composed of gas, liquid and solid phases (multiphase flow). Macr oscopic behaviours of multiphase flows are affected by their internal microstructures including the distribution of each phase and the shape of the boundaries between the two phases. Magma segregation from part ially molten rock occurs by porous flow being accompanied with compact ion of the matrix rock, the macroscopic behaviours of which are govern ed by microscopic flows of the melt at grain boundaries and deformatio n of each crystal. The fluctuation of magma effusion at volcanic erupt ions is explained by instability of gas-liquid two-phase flow, which d epends on motion of each bubble and the ability of bubbles to coalesce . Complex features of pyroclastic flow result from a wide range of gra in-size, and hence, variable settling velocities of volcanic fragments within the flow. Physical processes of these multiphase flows in magm atism are reviewed.