Controls on conduit magma flow dynamics during lava dome building eruptions

Abstract

[1] Lava dome eruptions commonly display fairly regular alternations between periods of high and low or no activity with timescales typically of weeks to years and sudden transitions between effusive and explosive activity. We develop a transient model of the magma flow in a volcanic conduit from an open-system magma chamber with continuous replenishment. The model incorporates gas exsolution, bubble growth, gas escape through the magma, and decompression-induced crystallization and considers variations in magma temperature, water content, conduit diameter, phenocryst size, chamber volume, and magma rheology. Calculations show the presence of periodic variations in discharge rate due to the transition from a stable regime, when discharge rate is low and crystals grow efficiently leading to high magma viscosity, to another stable state, when discharge rate is high and crystallization is negligible. The difference in discharge rates between these regimes can be several orders of magnitude. Periods are similar to the observed timescales and mainly depend on the chamber volume. The system shows strongly nonlinear responses to the variation of governing parameters. If magma has a Bingham rheology pauses in discharge rate occur between peaks of discharge and the peaks are much higher than for the case of Newtonian rheology. Large changes in discharge rate and eruptive behavior can occur as the consequence of small changes in magma temperature, water content, phenocryst size distribution, or conduit diameter. The system can fluctuate between low and high discharge rates with transitions to explosive activity.Citation: Melnik, O., and R. S. J. Sparks (2005), Controls on conduit magma flow dynamics during lava dome building eruptions,

Physics-based models of ground deformation and extrusion rate at effusively erupting volcanoes

“…However, because the focus of this work is the development of a relatively simple model capable of fitting geophysical time series within a modest solution time, we do not attempt to incorporate all possible physical-chemical processes in an erupting magma and the model is significantly simplified relative to some models of conduit flow [e. g., Melnik and Sparks, 2005].…”

“…While early work considered primarily the elastic compressibility of the host rock surrounding the chamber [Stasiuk et al, 1993], more recent work has suggested that the compressibility of the magma plays a dominant role due to the high compressibility of the exsolved gas phase [Huppert and Woods, 2002;Melnik and Sparks, 2005].…”

“…In simple form, these models consist of the laminar 1D steady state ascent of magma through a rigid cylinder [e.g., Jaupart, 1996;Sparks, 1999, 2002;Mastin and Ghiorso, 2000]. Even these simple models may display strongly nonlinear behavior and have multiple steady state solutions due to nonlinearity in constitutive laws and dependencies between different parameters, and additional complexity is introduced by consideration of lateral variation of magma properties in the conduit [Massol et al, 2001;Collier and Neuberg, 2006;Mastin, 2005], non-Newtonian rheologies [Melnik and Sparks, 2005], noncylindrical or depth-varying conduit geometries [Costa et al, 2007a[Costa et al, , 2007bde' Michieli Vitturia et al, 2008], and elastic or viscoelastic behavior of the conduit walls and/or inclusion of the magma chamber feeding the eruption [Maeda, 2000;Barmin et al, 2002;Costa et al, 2007a].…”

Conditions for detection of ground deformation induced by conduit flow and evolution

“…Melnik and Sparks [2005] proposed a transient model of magma flow in an open volcanic conduit including gas exsolution and escape, bubble growth as well as crystallization effects. They show that the system can fluctuate between two stable states, one being characterized by a high flow rate of less viscous magma and the other by a low flow rate of more viscous magma.…”

“…Large fluctuations in discharge rate are correlated with fluctuations of various signals such as ground deformation, seismicity and gas emissions. For long-term cycles, (months to years), the mechanism invoked is pressure changes occurring within a magma reservoir [Melnik and Sparks, 2005]. In some volcanic areas such as Soufrière Hills, Mt.…”