10:15 AM - 10:30 AM
[SVC31-12] Numerical study of effusive eruption based on coupled unsteady simulations of dike deformation and conduit flow
Keywords:Temporal change of eruptions, Conduit Deformation, Conduit Flow Modeling, dike
Geodetic observations suggest that magma intrusion into the shallow crust is mainly caused by dike propagation, which can be deformed during volcanic eruptions (Smittarello, 2019; Lengliné et al., 2021). Previous conduit flow modelings have revealed the influence of the microscopic processes within the ascending magma on the macroscopic behavior of volcanic eruptions (e.g., Melnik and Sparks, 1999; Kozono and Koyaguchi, 2009). Recent research has progressed to incorporate elastically deforming dike-like volcanic conduit to reveal the complex dynamics that govern the eruptive style and intensity (e.g., Costa et al., 2007; Massaro et al., 2017; Kozono et al., 2022). On the other hand, studies focusing on deformation and propagation processes of dikes have developed models that incorporate fracturing and deformation dynamics of the host rock to simulate nature manner and associated ground deformations (e.g., Pinel and Jaupart, 2000; Traversa et al. 2010; Roman and Lundgren, 2023). However, there are not enough steady conduit flow modeling studies that investigate the effects of both conduit flow and dike deformation on the temporal change of volcanic eruptions. In this study, we propose a coupled model for effusive eruptions to understand the dynamics of ascending magma and deformable conduits. Numerical simulations are performed to understand the basic behaviors of the spatio-temporal changes in the conduit geometry and the discharge rate.
In this study, the conduit geometry is an elliptical cylinder with a flat cross-section that resembles a dike in nature. Its deformation is based on the constitutive law of deformation of an elliptical cavity in an elastic medium (Muskhelishvili, 1953), where the dike width is driven by the difference between the internal magma and the lithostatic pressure at each depth. The conduit flow is simplified by approximating it as a one-dimensional flow of liquid single phase. The model incorporates pressure-dependent changes in the effective viscosity and bulk density to account for the effects of the exsolution of volatile components and crystallization during magma ascending. Under this assumption, the temporal evolution of the magma plumbing system was calculated by numerically solving the governing equation as a two-point boundary value problem, where the boundary condition at the lower end of the conduit is the chamber pressure and that at the upper end is atmospheric pressure.
Steady-state calculations revealed that the larger the chamber overpressure, the thicker the dike width, and the larger the discharge rate than in the case of the rigid conduit under similar conditions. When the unsteady calculations were performed by applying overpressure to the lower end of the conduit, the overpressure propagated upward as the dike expanded. The propagation velocity and its response to the magma properties were roughly governed by the coefficient of the linearized diffusion equation-like disturbance equation. Such behavior governs the timescale of the mitigation of chamber overpressure that drives the eruption. The expansion and contraction of dikes and the propagation of overpressure depend on the rheology of magma as well as the rigidity of the surrounding rock. Therefore, it is necessary to take into account the thermal effects on the surrounding rock caused by long-term contact with hot magma and the physical property distribution of magma in the cross-sectional direction for the discussion of the temporal changes in eruptive evolution.
This work was supported by JST SPRING, Grant Number JPMJSP2119.
In this study, the conduit geometry is an elliptical cylinder with a flat cross-section that resembles a dike in nature. Its deformation is based on the constitutive law of deformation of an elliptical cavity in an elastic medium (Muskhelishvili, 1953), where the dike width is driven by the difference between the internal magma and the lithostatic pressure at each depth. The conduit flow is simplified by approximating it as a one-dimensional flow of liquid single phase. The model incorporates pressure-dependent changes in the effective viscosity and bulk density to account for the effects of the exsolution of volatile components and crystallization during magma ascending. Under this assumption, the temporal evolution of the magma plumbing system was calculated by numerically solving the governing equation as a two-point boundary value problem, where the boundary condition at the lower end of the conduit is the chamber pressure and that at the upper end is atmospheric pressure.
Steady-state calculations revealed that the larger the chamber overpressure, the thicker the dike width, and the larger the discharge rate than in the case of the rigid conduit under similar conditions. When the unsteady calculations were performed by applying overpressure to the lower end of the conduit, the overpressure propagated upward as the dike expanded. The propagation velocity and its response to the magma properties were roughly governed by the coefficient of the linearized diffusion equation-like disturbance equation. Such behavior governs the timescale of the mitigation of chamber overpressure that drives the eruption. The expansion and contraction of dikes and the propagation of overpressure depend on the rheology of magma as well as the rigidity of the surrounding rock. Therefore, it is necessary to take into account the thermal effects on the surrounding rock caused by long-term contact with hot magma and the physical property distribution of magma in the cross-sectional direction for the discussion of the temporal changes in eruptive evolution.
This work was supported by JST SPRING, Grant Number JPMJSP2119.