We are pleased to announce a School Seminar by Dr Alain Burgisser on the topic of: Modelling crystal-rich magmas and volcanic eruptions.
Abstract:
The common point between the dynamics of a magma flowing inside a reservoir and of an ash cloud generated by an explosive eruption is that both involve particles (crystal or ash) suspended in a fluid (silicate melt or a mixture of air and volcanic gases). Both cases can thus in principle be simulated by two-phase flow models where the melt/gas is treated as a fluid and the behaviour of suspended crystals/ash is averaged into a granular continuous phase. We will see that it is not so simple. In the case of magma reservoirs, we should have been able to use the many rheology relationships stemming from the study of immersed granular systems. We show that, unfortunately, the high viscosity of silicate melts yields dynamical regimes that are not captured by these relationships. We thus define a new, two-phase flow rheology that includes the full jamming expected to occur in magmas. We then present a two-phase flow model based on this new rheology that has the potential to simulate a wide range of processes controlling the evolution of magmatic systems. To counterbalance these glorious promises with concrete scientific results, we will present a two-phase flow model already able to simulate volcanic ash cloud dispersal. We used this model to quantify how much volcanic gas reaches stratospheric levels during a caldera-forming eruption, which is a strange question to ask unless one wishes to understand the rise of the Roman empire.
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