On the influence of magma chambers in controlling the evolution of explosive volcanic eruptions

The influence of magma chambers on the evolution of explosive volcanic erup tions is examined by coupling a model of an elastic chamber containing comp ressible magma [Bower, S.M., Woods, A.W., 1997. The control of magma volati le content and chamber depth on the mass erupted during explosive volcanic eruptions. J. Geophys. Res. 102, 10273-10290] with a model of conduit flow [Wilson, L., Sparks, R.S.J., Walker, G.P.L., 1980. Explosive volcanic erupt ions: IV. The control of magma properties and conduit geometry on eruption column behaviour. Geophys. J. R. Astr. Sec. 63, 117-148]. It is found that for a given magma volatile content and conduit geometry, variations in the chamber volume, depth and aspect ratio have a significant impact on the mas s erupted and the eruption duration. Shallow volatile-saturated chambers of large cross-sectional area tend to erupt a much larger fraction of the cha mber volume (similar to 10%) than deep, volatile-unsaturated chambers of th e same magma (similar to 0.1-1.0%). However, in either case, the steady dec rease in chamber pressure over the course of an eruption only leads to a de crease in eruption rate of 10-50%. Therefore, for a given chamber volume, s hallow chambers of large cross-sectional area produce much more long-lived and voluminous explosive eruptions. In contrast, we show that for a given c hamber geometry, variations in magma volatile content can lead to significa nt changes in both the eruption rate and the erupted volume; in turn, this also affects the eruption duration. Finally, we note that, as described by Wilson et al., increases in conduit radius lead to very large increases in eruption rate and hence a decrease in eruption duration. (C) 1998 Elsevier Science B.V. All rights reserved.