Modeling hydrothermal fluid circulation and gravity signals at the Phlegraean Fields caldera

The Phlegraean Fields caldera is an active volcanic system where episodes of ground deformation are accompanied significant changes in geochemical and geophysical parameters monitored at the surface. These changes derive from a complex interaction between magmatic system and hydrothermal fluid circulation. We calculate the gravity changes associated with variable density of hydrothermal fluids. We simulate the multi-phase and multi-component fluid circulation triggered by a pulsating magma degassing, periodically increasing the discharge of CO2-enriched fluids into the shallow hydrothermal system. The simulated evolution of the hydrothermal system successfully reproduces the observed composition of gas discharged at the surface, At the same time, results indicate that changes in average fluid density generate it detectable gravity signal that is of the same order of magnitude of the observed changes. This contribution to gravity changes can explain the peculiar behavior of gravity data collected at Solfatara, where surface hydrothermal phenomena are present, Simultaneous filling of two independent sets monitoring data (gas composition and gravity changes) confirms the conceptual model proposed for the hydrothermal system Solfatara, and it provides new insights for the interpretation of gravity data, (C) 2005 Elsevier B.V. All rights reserved.