RHEOLOGIC CONTROLS ON MODELS OF VOLCANO UNREST

The ability to forecast volcanic unrest and evaluate precursory signals to assess whether a volcano is trending towards an eruptive state is a paramount goal in volcanology. The submarine volcano Axial Seamount, located on the Juan de Fuca Ridge has proven to exhibit an eruption predictable sequence of deformation resulting in the successful forecast of its 2015 eruption. However, the link between Axial’s deformation and the triggering mechanism of its eruption remains ambiguous. Recent models of volcano unrest suggest that eruptions are triggered when conditions of critical stress are achieved in the host rock supporting a magma reservoir. However, many approaches to modeling volcano behavior have traditionally relied on host-rock rheologies which are elastic and temperature independent. Low-pressure, high-temperature deformation experiments reveal that Young’s modulus in particular is highly temperature dependent at brittle-ductile transition temperatures of 600-750 °C and thermomechanical models of volcano deformation have shown that Young’s modulus greatly affects model predicted surface deformation and stress accumulation. We utilize 3D finite element models to address the role of rheology on such predictions. Specifically, we identify the magma flux rates necessary to generate mechanical failure of the host rock surrounding an expanding magma reservoir with both temperature- and non-temperature-dependent rheologies. Model advancements influencing rheology such as a temperature-dependent Young’s modulus and hydrothermal circulation are investigated to evaluate their contributions to predictions of stability. The presented numerical experiments provide constraints on model sensitivity to rheology, which may have considerable implications for interpreting existing models of unrest. Additionally, this approach provides insight into the triggering mechanics of eruptions at Axial Seamount. Preliminary results suggest that Axial’s eruptions are dynamic, exhibiting strong characteristics of an eruption triggered by reservoir overpressurization. However, precursory microearthquakes mimicking tidal signals may indicate possible external controls on the stress evolution of the host rock in the lead up to Axial’s eruptions.