Thermomechanics of Triggering the Eruption of Large Magma Reservoirs: The Effects of Buoyancy and Magma Recharge

Tuesday, 16 December 2014: 2:25 PM
Patricia M Gregg, University of Illinois at Urbana Champaign, Urbana, IL, United States, Eric B Grosfils, Pomona College, Claremont, CA, United States and Shanaka L de Silva, Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States
The evacuation of large silicic magma reservoirs via catastrophic caldera forming eruptions that emplace 100s to 1000s of km3 of material is a devastating and rare natural disaster on Earth. Given the destructive nature of these eruptions, it is critical to better understand the evolution of large silicic systems and what parameters are responsible for either maintaining magma in storage conditions or triggering an eruption. The formation of large, shallow magma bodies requires thermal maturation of the upper crust through elevated magma fluxes over periods of 104-106 years. Once the crust is thermally primed, the viscoelastic response of the host rock buffers the reservoir and stifles the generation of significant overpressure, thus accommodating the accumulation of large magma volumes (103-104 km3). Given that overpressures are difficult to generate in magma reservoirs of this size, increasing attention has been focused on better understanding what mechanisms may trigger their eruption. Recent analytical models suggest that buoyancy may play a critical role in generating the necessary overpressures to trigger eruption of the largest systems. We build upon these findings and utilize numerical models to quantify overpressure generation due to buoyancy and magmatic recharge. Furthermore, the interplay between reservoir growth and fault formation is explored to determine whether eruption triggering is most likely to occur due to fault development within the overlying roof or due to rupture at the reservoir boundary. Specifically, we utilize viscoelastic finite element models with Mohr-Coulomb and von Mises failure criteria to explore foundering in the roof and failure development at the reservoir boundary during buoyant magma recharge. Presented results will compare temperature- and non-temperature dependent viscosities with elastic models to investigate end-member controls on fault formation and reservoir rupture.