Mechanical and thermal-fluid-dynamical contributions to unrest phenomena at
active calderas are quantitatively evaluated, and a mixed mechanical-therm
al-fluid-dynamical model is developed, to explain the unrest phenomena at C
ampi Flegrei caldera. Mechanical modelling involves the use of analytical a
nd finite element formulations. Thermal-fluid-dynamical effects are conside
red in the framework of a one-dimensional approximation, solved by an analy
tical method. The results shed new light about the coupled effect of mechan
ically and thermally induced perturbations and variations in the geothermal
fluid circulation regime. Unrest episodes at Campi Flegrei are interpreted
in terms of the joint effect of a first, essentially mechanical, phase due
to overpressure in a magma chamber and to a progressive amplification and
final decay due to the circulating water. The elastic response of the rocks
to the migrating front of overpressure is shown to be strongly conditioned
by the caldera structure, which produces a concentration of strain in the
inner part, and a stress concentration, causing the local seismicity, aroun
d the caldera borders. Thermal-fluid-dynamical effects are also shown to ha
ve important implications on the evolution of the volcanic system towards c
ritical phenomena, which must be considered for a meaningful evaluation of
volcanic hazard. (C) 2001 Elsevier Science B.V. All rights reserved.