The evolution of the thermal state of Mt.Vesuvius after the 1631 eruption (during an almost continuous eruptive cycle until the last episode in 1944) and in the subsequent quiescent period until present, has been investigated. An axysimmetric,twodimensional, finite-element model accounting for conduction and phase changes in an homogenous, isotropic medium endowed with realistic physical constants calculated on the basis of the geochemical available data has been worked out. An initial thermally stratified state is arbitrarely guessed. Since direct information on the real shape of the conduit is lacking, we adopt the usual approximation of a vertical cylinder, which represents the simplest possible case consistent with mechanical isotropy. During the 1631-1944 eruptive cicle, magma reaches the surface through a fracture systems leaving an open conduit from the magma reservoir to the surface.We assume that the magma is continuously supplied and that its cooling is nil, so that the surrounding host rock is heated essentially by conduction from the conduit, thus determining the thermal state in the volcanic edifice. At the end of an eruption cicle there are two extreme possibilities: the magma level in the conduit may either stop near the surface, leaving the conduit essentially full, or stop near the magma chamber, leaving the conduit essentially empty. If the last case, it has been demonstrated that the the conduit closes in a few years due to the deformation induced by the overburden pressure. In this work, we assume that after the 1944 eruption the conduit remains filled, but because the supply of magma stops, the melt in the conduits solidifies and creates a plug. The initial state of the cooling phase is taken from the solution obtained at the end of the eruptive cicle. Numerical solution are discussed in light of the available data and observation.
FINITE-ELEMENT, TIME-DEPENDENT MODELLING OF THE THERMAL STATE OF MT.VESUVIUS FROM 1631 TO PRESENT
MORETTI, Roberto;
2003
Abstract
The evolution of the thermal state of Mt.Vesuvius after the 1631 eruption (during an almost continuous eruptive cycle until the last episode in 1944) and in the subsequent quiescent period until present, has been investigated. An axysimmetric,twodimensional, finite-element model accounting for conduction and phase changes in an homogenous, isotropic medium endowed with realistic physical constants calculated on the basis of the geochemical available data has been worked out. An initial thermally stratified state is arbitrarely guessed. Since direct information on the real shape of the conduit is lacking, we adopt the usual approximation of a vertical cylinder, which represents the simplest possible case consistent with mechanical isotropy. During the 1631-1944 eruptive cicle, magma reaches the surface through a fracture systems leaving an open conduit from the magma reservoir to the surface.We assume that the magma is continuously supplied and that its cooling is nil, so that the surrounding host rock is heated essentially by conduction from the conduit, thus determining the thermal state in the volcanic edifice. At the end of an eruption cicle there are two extreme possibilities: the magma level in the conduit may either stop near the surface, leaving the conduit essentially full, or stop near the magma chamber, leaving the conduit essentially empty. If the last case, it has been demonstrated that the the conduit closes in a few years due to the deformation induced by the overburden pressure. In this work, we assume that after the 1944 eruption the conduit remains filled, but because the supply of magma stops, the melt in the conduits solidifies and creates a plug. The initial state of the cooling phase is taken from the solution obtained at the end of the eruptive cicle. Numerical solution are discussed in light of the available data and observation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
