A Numerical Program for Steady-State Flow of Magma-Gas Mixtures Through Vertical Eruptive Conduits
DEPARTMENT OF THE INTERIOR WASHINGTON DC
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In many volcanic studies, estimates must be made of the changes that magma and its associated gases experience when traveling through an eruptive conduit to the surface. Exsolution of magmatic gas, acceleration, changes in pressure and temperature, depth of fragmentation, and final exit velocities affect such features as lava fountain heights, the ability of a volcanic column to convect or collapse, and the degree to which water can enter the conduit during eruptive activity. Most of these quantities cannot be easily estimated without some sort of numerical model. This report presents a model that calculates flow properties pressure, vesicularity, and some 35 other parameters as a function of vertical position within a volcanic conduit during a steady-state eruption. The model idealizes the magma-gas mixture as a single homogeneous fluid and calculates gas exsolution under the assumption of equilibrium conditions. These are the same assumptions on which classic conduit models e.g., Wilson and Head, 1981 have been based. They are most appropriate when applied to eruptions of rapidly ascending magma basaltic lava-fountain eruptions, and Plinian or sub-Plinian eruptions of intermediate or silicic magmas that contains abundant nucleation sites microlites, for example for bubble growth. The numerical parts of the program were written in Fortran 90 and can be compiled on any platform DOS, Unix, Macintosh etc. that has a Fortran 90 compiler.
- Geology, Geochemistry and Mineralogy