Time-dependent chamber and vent conditions during explosive caldera-forming eruptions

We use a modified version of the CPIUC model [Macedonio, G., Neri, A., Martí, J., Folch, A., 2005. Temporal evolution of flow conditions in sustained explosive eruptions, Journal of Volcanology and Geothermal Research, 143, 153-172] to simulate chamber and vent conditions during the different phases of a piston-like caldera-forming eruption. Our idealized caldera-forming scenario assumes an initial central-vent conduit that, after critical chamber decompression, migrates to a fissure-vent peripheral conduit(s). Further decompression leads to final piston-like subsidence which stops only after the virtual destruction of the magmatic reservoir. The simulations find that the pressure at the conduit entrance drops during the decompression phases at a rate depending on the conduit geometry, chamber volatile zonation and fragmentation threshold. The higher the volume contrast between the initial central-vent and the final peripheral fissure-vent conduits, the higher the pressure drop and the jump in the mass eruption rate. Pressure increases back to lithostatic during piston subsidence while some compressible magma remains within the chamber. Finally, during the later phase, pressure experiments a gentle increase or decrease depending on the balance between deposition of intra-caldera material and decrease in the contents of volatiles as deeper chamber levels are tapped.