Volcanic deformation and degassing

: the role of volatile exsolution and magma compressibility

Integrating multi-parameter observations of volcanic processes is crucial for volcano monitoring. Qualitative models demonstrate that combining observations of volcanic deformation, gas emissions, and other parameters enhances the detection of volcanic unrest and provide insights into the magma plumbing system. Despite the progress made in this field, quantitative models that link these observations are still lacking. 

Thermodynamic models have been used to constrain the characteristics of magma properties and its plumbing system. In this thesis, I develop models based on melt inclusion data and thermodynamics to reconstruct magma properties such as compressibility, and investigate how magmatic volatile content and magma storage conditions influence observations of volcanic deformation and SO₂ degassing.

By comparing mafic systems in arc and ocean island settings, I provide evidence for the lack of deformation observed during water-rich arc eruptions. In contrast, despite having low magmatic volatile content, ocean island eruptions have high SO₂ emissions due to their high diffusivity, which results in co-eruptive degassing. By comparing model predictions and observations, I show that all magmatic systems experience a certain degree of outgassing prior to an eruption, consistent with current conceptual models of transcrustal magmatic systems. Additionally, integrating time series of deformation, degassing, and extrusion flux can reveal the evolution of magma properties. Using this framework, I provide evidence for the increase in bulk magma compressibility following the removal of the degassed magma during the 2004 eruption of Mount St. Helens. 

This study contributes to the better understanding of the effects of magmatic volatile content and pre-eruptive gas segregation on the physicochemical properties of magma, and provides a framework for modelling magma properties that can be applied to global volcano monitoring.