2025-01-142025-01-142024Burgisser, A., Collombet, M.,...,Bresch, D. (2024). Two-phase magma flow with phase exchange. Part II. 1.5D numerical simulations of a volcanic conduit. (pp. 1-54). Wiley.0022-25261467-9590https://hdl.handle.net/11441/166625In a review paper in this same volume, we present thestate of the art on modeling of compressible viscousflows ranging from single-phase to two-phase systems.It focuses on mathematical properties related to weakstability because they are important for numerical res-olution and on the homogenization process that leadsfrom a microscopic description of two separate phasesto an averaged two-phase model. This review serves asthe foundation for Parts I and II, which present averagedtwo-phase models with phase exchange applicable tomagma flow during volcanic eruptions. Part I establishesa two-phase transient conduit flow model ensuring: (1)mass and volatile species conservation, (2) disequilib-rium degassing considering both viscous relaxation andvolatile diffusion, and (3) dissipation of total energy. Therelaxation limit of this model is then used to obtain adrift-flux system amenable to simplification. Here, in Part II, we summarize this model and propose a 1.5Dsimplification of it that alleviates three issues causingdifficulties in its numerical implementation. We com-pare our model outputs to those of another steady-state,equilibrium degassing, isothermal model under con-ditions typical of an effusive eruption at an andesiticvolcano. Perfect equilibrium degassing is unreachablewith a realistic water diffusion coefficient because con-duit extremities always contain melt supersaturatedwith water. Such supersaturation has minor conse-quences on mass discharge rate. In contrast, releasingthe isothermal assumption reduces significantly massdischarge rate by cooling due to gas expansion, which inturn increases liquid viscosity. We propose a simplifiedsystem using Darcy’s law and omitting several processessuch as shear heating and liquid inertia. This minimalsystem is not dissipative but approximates the steady-state mass discharge rate of the full system within 10%.A regime diagram valid under a limited set of condi-tions indicates when this minimal system captures theascent dynamics of effusive eruptions. Interestingly, thetwo novel aspects of the full model, diffusive degassingand heat balance, cannot be neglected. In some caseswith high diffusion coefficients, a shallow region whereporosity and velocities tend toward zero develops ini-tially, possibly blocking an eventual steady state. Thislocal porosity loss also occurs when a steady-state solu-tion is subjected to a change in shallow permeability. The resulting shallow porosity loss features many char-acteristics of a plug developing prior to a Vulcanian eruptionapplication/pdf54p.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Numerical simulationsTwo-phase modelsVolcanic eruptionsinfo:eu-repo/semantics/articleinfo:eu-repo/semantics/openAccess10.1111/sapm.12747