Diverse and unpredictable behavior of eruption styles results from complex dynamics of magmas during their ascent towards the surface.
Complexity arise from the non-linear interaction between the different phases (exsolved volatiles and bubbles, solid crystals and fragments of viscous melt) which separate during magma ascent as a result of fluid and thermodynamic processes. In the atmosphere, the different degrees of coupling and concentration of the disperse particulate phase characterize the distinct regimes of gas-particle flows, ranging from dilute, turbulent particle-laden flows to concentrated collapsing columns.

Despite the well-established foundation and verification in laboratory regimes, multiphase flow processes in volcanic systems are still poorly understood or oversimplified. Degassing mechanisms have been described in experiments, observed in natural samples and geophysical signals and modeled. While new techniques such as tomographic imaging and spectroscopic analysis allow insights into microscopic scales of volatile pathways and distributions, numerical models can help us to understand the impact of such observations on the complex system of processes of volcanic degassing during magma ascent. On the other hand, the difficulty of properly scaling volcanic multiphase flows have made numerical simulations very attractive to study non-equilibrium processes, especially in the light of the advancements of High-Performance Computing techniques.

The session gathers contributions related to experimental and theoretical (including numerical modeling) studies on magma degassing and on the multiphase physics of volcanic eruptions, from subsurface flows to volcanic jets and plumes.