Numerical thermomechanical modelling of lava dome growth during the 2007-2009 dome-building eruption at Volcán de Colima

Abstract

Lava domes form during effusive eruptions due to an extrusion of highly viscous magmas from volcanic vents. In this paper we present a numerical study of the lava dome growth at Volcán de Colima, Mexico during 2007-2009. The mathematical model treats the lava dome extrusion dynamics as a thermomechanical problem. The equations of motion, continuity and heat transfer are solved with the relevant boundary and initial conditions in the assumption that magma viscosity depends on the volume fraction of crystals and temperature. We perform several sets of numerical experiments to analyse the internal structure of the lava dome (i.e. the distributions of the temperature, crystal content, viscosity and velocity) depending on various heat sources and thermal boundary conditions. Although the lava dome growth at Volcán de Colima during short (a few months) dome-building episodes can be explained by an isothermal model of lava extrusion with the viscosity depending on the volume fraction of crystals, we show here that cooling plays a significant role during long (up to several years) episodes of dome building. A carapace develops as a response to a convective cooling at the lava dome-air interface. The carapace becomes thicker if the radiative heat loss at the interface is also considered. The thick carapace influences the lava dome dynamics preventing its lateral advancement. The release of the latent heat of crystallization leads to an increase of the temperatures in the lava dome interior and to a relative flattening of the dome. Meanwhile, the heat source due to viscous dissipation inside the lava dome is negligible, and it does not influence the lava dome growth. The developed thermomechanical model of the lava dome dynamics at Volcán de Colima can be used elsewhere to analyse effusive eruptions, dome morphology and carapace evolution including its failure potentially leading to pyroclastic flow hazards.