DEVELOPMENT, EVOLUTION AND TRIGGERING OF SUPERERUPTIONS

Supereruptions (>VEI 7.5 >450 km³ of magma) are a common feature of the geologic record and are typically associated with ignimbrite flare-ups. Although they may be dwarfed by some silicic eruptions associated with LIPS (VEI 9), supereruptions represent one of the most catastrophic of terrestrial geologic phenomena. While the field characteristics and timing of these massive silicic outpourings is becoming increasingly well documented, the conditions that lead to the development, evolution and eventual eruption of such large volumes are less clear. Increased mantle power input (thermal and material flux) and its impact on the thermomechanical evolution of the crust and magma production is clearly important in producing and growing large, viable silicic magma bodies. Under these conditions, current models of overpressure-driven eruption triggers are untenable for most supereruptions and a new model for triggering these eruptions is required. We have developed a 2D finite-element model (Gregg et al., 2011) that for the first time takes into account the viscoelastic behavior of the country rock and helps identify the conditions that lead to the triggering of supereruptions. We show that roof collapse is the inevitable result of growth of magma bodies beyond a threshold size and this results in catastrophic eruption. This model is consistent with the physical volcanology of many supereruptions and the structural development of many of the large caldera complexes that source such eruptions.

Gregg, P.M., S.L. de Silva , E.B. Grosfils, and J.P. Parmigiani, Temperature-dependent mechanics of triggering catastrophic caldera-forming eruptions, in review, 2011.