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 eruptions is examined by coupling a model of an elastic chamber containing compressible magma [Bower, S.M., Woods, A.W., 1997. The control of magma volatile 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 eruptions: IV. The control of magma properties and conduit geometry on eruption column behaviour. Geophys. J. R. Astr. Soc. 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 mass erupted and the eruption duration. Shallow volatile-saturated chambers of large cross-sectional area tend to erupt a much larger fraction of the chamber volume (∼10%) than deep, volatile-unsaturated chambers of the same magma (∼0.1–1.0%). However, in either case, the steady decrease in chamber pressure over the course of an eruption only leads to a decrease in eruption rate of 10–50%. Therefore, for a given chamber volume, shallow chambers of large cross-sectional area produce much more long-lived and voluminous explosive eruptions. In contrast, we show that for a given chamber geometry, variations in magma volatile content can lead to significant 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.