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A conduit model coupling two-phase magma flow with gas chemistry

Alain Burgisser 1, Mouloud Kessar2

  • Affiliations: 1 Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, ISTerre, Grenoble, France; 2 LAMA UMR5127 CNRS, Université Savoie Mont Blanc, Le Bourget du lac, France

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 194

  • Programme No: 3.2.17

  • Theme 3 > Session 2

Abstract

Conduit flow models have long produced outputs of total gas content, which often consists of only H2O. Such outputs are notoriously difficult to relate to natural data because gas measurements are mostly done on species, such as SO2, that are neglected by conduit flow models. This gap introduces large uncertainties when trying to match model outputs and natural data, which in turn weaken the model capability to explain crucial aspects of eruptive dynamics.  We present the coupling of a chemical model of degassing with a two-phase conduit flow model. The initial chemical model, D-Compress, calculates the equilibrium composition of volatiles in the CSHO system of a degassing parcel of magma. We extended D-Compress to address disequilibrium degassing so that the rate of degassing is controlled by a combination of volatile diffusion and decompression rate. We coupled this chemical disequilibrium model to a recent two-phase conduit flow model that ensures strict conservation of mass and volatile species. Such coupling enables us to simulate the combined effects of diffusion-limited exsolution of volatiles and those of outgassing. Our coupled model thus takes into account both the migration and mixing of gas through the permeable bubble network and the changes of gas composition due to volatile exoslution. Such coupling opens the full gamut of behaviors lying between the two end-member scenarios of closed- and open-system degassing. Preliminary results show how the gas emitted at the vent changes its composition (H2O, SO2, H2S, CO, and CO2) during a typical transition from effusive to explosive behavior.