| dc.description.abstract | This thesis explores the mechanical behaviour of magma mush - a crystal-dominated magma - in the context of volcano deformation models, contributing towards a more comprehensive understanding of volcanic processes and enhancing the potential for hazard assessment. Traditional volcano deformation models assume shallow, melt-dominated magma reservoirs, contradicting evidence for extensive, crystal-rich systems. In this thesis, I propose a more realistic conceptual model that incorporates the poro(visco)elastic behaviour of magma mush and the (thermo-visco)elastic behaviour of the surrounding rock.
This research progresses in a coherent, interconnected sequence of objectives. Through analytical and numerical deformation models, I first explore magma intrusion dynamics into a shallow melt-dominated magma reservoir using inlet pressure and mass flow boundary conditions. Results show the strong influence of reservoir geometry and applied boundary conditions on the spatiotemporal evolution of the surface deformation.
Subsequently, I explore the impact of a poroelastic mechanical response to melt intrusion or withdrawal on the reservoir pressure evolution and the resultant spatiotemporal surface deformation. Incorporating mush poroelasticity in the deformation models shows that melt diffusion through the crystal framework causes continued post-injection/eruption displacements dependent on mush properties. Moreover, the melt withdrawal location affects the relative vertical and radial post-eruption deformation magnitudes over time. I then developed more advanced deformation models integrating a poroviscoelastic mush reservoir within a thermo-viscoelastic host, providing a more realistic representation of the system’s rheology. Poroelastic and viscoelastic effects of both the mush and the wall rock all cause competing time-dependent deformation. Thermo-viscoelasticity amplifies the deformation response, emphasizing the need to consider host rock rheology and, to a lesser degree, the poroviscoelastic behaviour of the mush.
Finally, this thesis applies these insights to Soufrière Hills Volcano, Montserrat. Optimization of continuous GPS data suggests a decreasing melt injection rate into a low-permeability shallow mush reservoir is driving current surface inflation and unrest. While potential cessation of the melt source is projected by June 2024 (± 2 years), ongoing poroelastic diffusion could continue driving low-magnitude surface deformation and potential instability.
This thesis provides implementable recommendations for integrating mush poroelasticity into volcano deformation models, furthering understanding of volcano deformation generation. The progressive analyses within this thesis foster a more holistic understanding of the crystal-rich systems dominating many volcanic settings. Overall, this work extends our understanding of magmatic systems, highlighting the need for more sophisticated models to interpret geodetic data and help inform hazard assessments. | en_GB |
