A transient model for explosive and phreatomagmatic eruptions

Abstract

We develop a model for explosive eruptions in cylindrical conduits generated by plug disruption at the top of the conduit. The eruption is calculated for a standard set of parameters for rhyolite. The model takes into account temperature variations and non-Newtonian magma rheology. We analyzed the influence of principal parameters such as fragmentation criteria, magma rheology, and initial conditions. We conclude that the variation of magma temperature is less than 70 K during eruption, and the model with bubble concentration-dependent viscosity leads to the increase of the steady discharge rate by about 40%. The eruption model is extended to include interaction between magma in the conduit and water in a surrounding aquifer. The phreatomagmatic eruption is also initiated by plug disruption. Two cases of initial aquifer pressure are considered: magmastatic and hydrostatic. These cases are valid for confined and unconfined aquifers. For the first case (confined aquifer), water influx influences the conduit flow soon after plug disruption and leads to the additional peaks of discharge rate; for the second case (unconfined aquifer), a purely magmatic, explosive eruption of longer duration is followed by a phreatomagmatic phase. In both cases, magma discharge rate increases by 10-100% in comparison with purely magmatic eruption.

Models of maar volcanoes, Lunar Crater (Nevada, USA)

“…Relevant problems relate to natural length and time scales, geological setting, confining rock properties and pressures, and interaction under the imposed shear of multiphase magma flowing through dikes. Previous experiments (e.g., Zimanowski et al 1997a, b) identified the magma:water mass ratios that result in different explosion efficiencies under relatively static conditions and for a specific range of scales, but the relationship between magma and water fluxes within the volcanic plumbing and the geohydrological setting of a volcano has yet to be quantified (e.g., Starostin et al 2005). Also unresolved is the effect of dike emplacement on the movement of groundwater.…”

Temperature evolution during magma ascent in basaltic effusive eruptions: A numerical application to Stromboli volcano

“…Melnik and Sparks (2002a) calculated a temperature profile within the conduit, but as a function of the dissolved water content, rather than an energy conservation equation. Starostin et al (2005), proposed a transient model where they solved also for the energy conservation equation, but considering no crystals in the magmatic mixture, and a single gas phase. In recent years, further models were proposed in the literature (e.g.…”

Multiphase flow above explosion sites in debris-filled volcanic vents: Insights from analogue experiments

“…Discrete volcanic eruptions, in contrast, involve non-steady conditions and are comparatively poorly understood and difficult to model (e.g., Clarke et al, 2002;Dufek and Bergantz, 2005;Starostin et al, 2005). Discrete eruptions imply that volcanic vents are filled by more-orless stagnating debris between eruptive pulses (White, 1991), and this results in eruptive styles different from open-vent conditions.…”