Unveiling the Rheological Control of Magmatic Systems on Volcano Deformation: The Interplay of Poroviscoelastic Magma-Mush and Thermo-Viscoelastic Crust

Understanding the mechanical evolution of magmatic systems requires careful assessment of their rheological characteristics, particularly in light of the growing evidence that magma reservoirs are dominated by magma-mush surrounded by thermally-altered host-rock. To address this complexity, we develop models for volcano deformation based on a poroviscoelastic source within a thermo-viscoelastic host. We use Finite Element modeling to investigate the rheological and mechanical response to melt injection in a Maxwell poroviscoelastic reservoir hosted in a temperature-dependent standard linear solid viscoelastic (thermo-viscoelastic) crust. Our models consider the competing roles of poroelastic diffusion, and viscoelastic creep and relaxation. All cause time-dependent post-injection deformation. Post-injection deformation of a poroviscoelastic reservoir in an elastic crust is dominated by poroelastic diffusion, a consequence of the short relaxation timescale of a hot and relatively low viscosity mush. For cooler, more viscous mush, the magnitude of viscoelastic deformation increases, supplementing the deformation caused by post-injection poroelastic diffusion. Thermo-viscoelasticity of the crust amplifies the poroelastic deformation response of the magma-mush, leading to increased time-dependent deformation both during and after melt injection. The rate of post-injection surface deformation decreases at a rate proportional to the reservoir temperature. Crucially, our model sensitivity analysis demonstrates that the wall rock thermo-viscoelastic response contributes more to surface deformation than the viscous effect of the magma-mush. For this reason, neglecting the viscoelastic properties of the host rock and the poroelastic properties of the reservoir in interpretations of surface deformation data could produce errors in inferred processes (e.g., injection duration) and subsurface characteristics (e.g., reservoir compressibility, shape and depth).Plain Language Summary Measurements of volcano deformation can provide crucial insights into the mechanical behavior of magmatic systems if the physical properties of the systems are known. Past assumptions of magma chambers as molten bodies surrounded by elastic rock are not sufficient, however, to model the behavior of more realistic reservoirs comprising a mixture of melt plus crystal-magma-mush-in thermally-altered wall rock. More appropriate are models that treat the magma-mush as poroviscoelastic and the wall rock as viscoelastic. In this study, we develop new numerical models that simulate volcano deformation caused by melt injection into a shallow poroviscoelastic magma reservoir that is surrounded by viscoelastic wall rock. Under these conditions, surface deformation continues after the injection has stopped. Our model further shows that for high temperature reservoirs, poroelastic diffusion, that is, the movement of melt through the mush, dominates surface deformation. Our results emphasize the importance of considering both the host rock and magma-mush viscoelastic properties to understand the processes that cause surface deformation during and after melt intrusion.

Automated summary

Understanding the mechanical evolution of magmatic systems requires careful assessment of their rheological characteristics, particularly in light of the growing evidence that magma reservoirs are dominated by magma-mush surrounded by thermally-altered host-rock. We develop models for volcano deformation based on a poroviscoelastic source within a thermo-viscoelastic host. Our models consider the competing roles of poroelastic diffusion, and viscoelastic creep and relaxation, and emphasize the importance of considering both the host rock and magma-mush viscoelastic properties to understand the processes that cause surface deformation during and after melt intrusion.