The rheological contrast between the viscous magma in the magmatic chambers and the surrounding rocks, having an elastic behavior, has allowed for a disturbance of the stress field, which, at a magmatic pressure unequal to the lithostatic one, can give rise to various modes of rock failure, leading to an eruption. In this context, one of the most important problems is represented by the mechanical stability of both large and extra-large magmatic chambers, such as the Yellowstone magmatic chamber. Due to its large volume, the critical overpressure necessary to start the volcanic eruption requires large added volumes of magma and fluids. The viscous relaxation of deviatoric stresses in the thermal areole of large chambers on a time scale of more than few years increases the critical volumetric flow rate of magma to 0.1–1 km3/yr. In this chapter, we have demonstrated that the deep CO2 flux related with the underplating of basaltic magma has significantly enhanced the expansion of the magmatic chamber. In Yellowstone, the CO2 fluxing can be the driver of its cyclic uplift and subsidence having a period of several decades. The extraction of water from the silicic melt by CO2 increases the volume of the fluid up to 4 times, thus multiplying the pumping effect of the fluid. In a long term, simple estimates have also indicated that the CO2 flux can significantly contribute to the heat balance, which can be up to the half one with respect to the value associated with the basaltic magma. The integrated stability index of a magma chamber has been tested during the beginning of the interglacial periods, when the rate of generation of the basaltic magma in a plume setting is of an order of magnitude higher than the normal one. The spikes of rhyolitic magmatism in some periods of the last Quaternary interglacials have been weakened for the Yellowstone case history. The last Pleistocene glaciation activated only strong hydrothermal eruptions, which may imply that at present, the level of CO2 and basalt supply rate is not high enough to cause a major eruption in Yellowstone in the near future.
Part of the book: Volcanoes