THERMOMECHANICAL MODELS AS A FRAMEWORK TO STUDY THE EVOLUTION OF MAGMA CHAMBERS USING CONSTRAINTS FROM PETROLOGY, GEOPHYSICS AND GEODESY (Invited Presentation)

Subduction zone volcanoes are active for 10s – 100s kyr, and the magma composition, volatile content, eruption style, frequency and size change over time, reflecting changes in the underlying magma reservoir, crust and rates of magma inputs. Progression towards more silicic, colder and wetter eruptions is thought to reflect long-term storage, crystallization and differentiation in the crust. Reversals to this pattern may be linked to caldera-forming events or varying rates of mafic recharge from depth. However, the factors that control the growth and evolution of magma reservoirs and the ratio of magma erupted versus stored in the crust remain poorly understood, obscuring the interpretation of the present-day state of volcanoes within the context of their eruptive histories.

Developments on a box model designed to track the thermomechanical evolution of crustal magma chambers shed light on the complex interactions between a multiphase open-system magma body and its host crust. Chamber growth and eruption frequency is strongly modulated by the efficiency of the crust/magma chamber system to accommodate recharges (crust rheology and magma compressibility). A highly compressible magmatic volatile phase may dampen pressure buildup, yet lead to larger eruptions, which affects chamber growth and longevity as well as the rate and magnitude of surface deformation during unrest over shorter timescales.

In a recent effort to extend the model to more directly integrate petrologic and geodetic datasets, we have introduced two significant updates: (1) a more realistic magmatic volatile phase based on the solubility of H₂O-CO₂ in magmas and (2) coupling to surface deformation models.

Advances in volcano monitoring allow us to capture details about magma migration and mass/volume changes of magma reservoirs on daily to decadal timescales. Episodes of surface uplift commonly are interpreted using Mogi or other kinematic models for magma chamber inflation, yet kinematic models alone cannot uniquely determine if specific patterns of uplift are caused by magma recharge, influx/exsolution of volatiles, or viscoelastic effects. By coupling surface deformation to thermomechanical models, we can place tighter constraints on the nature and rate of magma recharge, causes of uplift, and link present-day observations to the longer-term evolution of the magmatic system.