Abstract
A magma plumbing system with dual magma chambers beneath active volcanoes is commonly observed through petrological and geophysical measurements. This paper developed a physical model for the dynamics of a dual-magma-chamber system during volcanic eruptions. The model consists of the plumbing system where two elastically deformable magma chambers are connected in series with non-deformable conduits. Based on this model, we obtained an analytical solution that describes temporal changes in pressures at the two chambers accompanied by the eruption. The analytical solution showed that the feature of the chamber pressure changes is mainly controlled by two non-dimensional numbers C' and Omega '. Here, C' is the ratio of the parameter controlling the magnitude of pressure change in the shallower chamber to that in the deeper chamber, and Omega ' is the ratio of conduit’s conductivity (inverse of resistivity to magma flow) between the shallower chamber and the surface to that between the chambers. For smaller C' and Omega ', the shallower chamber’s pressure is kept constant during the decrease in the pressure at the deeper chamber in the initial phase of the eruption. This corresponds to a deformation pattern commonly observed in some eruptions, in which the deflation of the deeper chamber was predominant. The estimation of C' and Omega ' based on the parameters related to magma properties and geometries of the chambers and the conduits revealed that the smaller C' and Omega ' conditions are satisfied under realistic magmatic and geological parameters. This indicates that the magma dynamics in the dual-chamber system generally cause the dominance of the deeper chamber’s deflation.
Highlights
A magma plumbing system beneath an active volcano shows a wide variation in size, geometry, and magma properties inside it
We developed the physical model of the co-eruptive magma dynamics in the plumbing system, where the two elastically deformable magma chambers are connected in series with the conduits
The solution showed that the feature of the pressure changes is mainly controlled by the non-dimensional numbers C′ and ′ : C′ is the ratio of the parameter controlling the magnitude of the pressure change in the shallower chamber to that in the deeper chamber, and ′ is the ratio of the conduit’s conductivity between the shallower chamber and the surface to that between the chambers
Summary
A magma plumbing system beneath an active volcano shows a wide variation in size, geometry, and magma properties inside it This variation causes complex features of geodetic and petrological observations during volcanic eruptions (e.g., Dvorak and Dzurisin 1997; Cashman et al 2017; Edmonds et al 2019). In geodetic analyses for volcanic activities such as based on GPS, tiltmeter, strainmeter, and InSAR, multiple deformation sources are sometimes detected to explain the surface deformation patterns (e.g., Kohno et al 2008; Foroozan et al 2011; Reverso et al 2014). In this case, the chamber depth is directly estimated from the depth of the deformation source
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