HR: 0800h
AN: V31D-0649    [Abstracts]
TI: Numerical Simulations of Multicomponent Convection in a volatile-rich Replenished Magma Chamber
AU: * Longo, A
EM: longo@pi.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via della Faggiola 32, Pisa, I-56126 Italy
AU: Vassalli, M
EM: vassalli@pi.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via della Faggiola 32, Pisa, I-56126 Italy
AU: Vassalli, M
EM: vassalli@pi.ingv.it
AF: Dipartimento di Fisica, Universita' di Bologna, V.le Berti Pichat 6/2, Bologna, I-40127 Italy
AU: Papale, P
EM: papale@pi.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via della Faggiola 32, Pisa, I-56126 Italy
AB: The dynamics of multicomponent convection in a volatile-rich magma chamber have been studied by means of numerical simulations. The investigated system is an elliptic chamber with 4 km horizontal and 2 km vertical axes, replenished from below with new magma. Magma volatiles are H₂O and CO₂. The composition and volatile content of magma initially present in the chamber are uniform or stratified. The input magma is equal to or different from the resident magma in terms of liquid composition and volatile content, and enters the chamber on its axis at a constant velocity of 1 cm/s over 200 m of width. Numerical simulations are carried out by using the recently developed numerical code GALES (Longo at al., 2005). GALES is a finite element algorithm that solves the 2D, transient, multicomponent dynamics of compressible to incompressible homogeneous flows. The conservation equations for mass, momentum, energy and composition are discretized in time and space with Galerkin least-squares and discontinuity-capturing stabilizing techniques. The code is previously validated on several test cases spanning a wide range of flow conditions in terms of Mach, Reynolds, Prandtl and Schmidt numbers. Constitutive equations for magma properties employ recent viscosity measurements and parameterizations, as well as non-ideal multicomponent thermodynamic modeling. The numerical results show the complex dynamics of convection triggered by magma replenishment, displaying the formation and evolution of rising plumes and vortexes. Cases of injection of magma having the same composition and volatile content of resident magma do not produce convection in the examined range of conditions, resulting in accumulation of new magma around the inlet area and progressive decrease of the gas volume fraction over the entire magma chamber. On the contrary, the ingression of CO₂-rich magma is a very efficient mean of producing large-scale convection. CO₂ contents increasing to a few wt% correspond to progressively more efficient dynamics. Lower CO₂ contents produce the rise of a gas-rich plume along the chamber axis, and its subsequent lateral spreading. Higher CO₂ contents can produce plumes detached from the chamber axis, and large vortexes which can involve the entire chamber, or be localized in its middle portion. A few hours of magma injection result in overall pressure increase of the order of 10 MPa, suggesting that wall fracturing and dyke propagation can be associated with convection in the magma chamber.
UR: http://www.pi.ingv.it/user/longo
DE: 0545 Modeling (4255)
DE: 0560 Numerical solutions (4255)
DE: 3618 Magma chamber processes (1036)
DE: 8412 Reactions and phase equilibria (1012, 3612)
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005