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CHA P T E R 1 1


                  Hydrothermal Fluid Circulation and

                  its Effect on Caldera Unrest


                  Micol Todesco




                  Contents

                  1. Introduction                                                 394
                  2. The Hydrothermal Fluid Circulation                           395
                  3. Modelling of Hydrothermal Fluid Circulation                  397
                  4. Hydrothermal Systems and Volcano Monitoring                  400
                    4.1. Geochemical monitoring                                    401
                    4.2. Geophysical monitoring                                   402
                  5. An Example of Assessing the Role of Hydrothermal Processes
                     During Unrest: Solfatara (Phlegrean Fields Caldera, Italy)   404
                  6. Discussion and Conclusions                                   409
                  Acknowledgments                                                  410
                  References                                                       410




                  Abstract
                  This paper focuses on the role that hydrothermal systems may play in caldera unrest.
                  Changes in the fluid chemistry, temperature and discharge rate of hydrothermal systems
                  are commonly detected at the surface during volcanic unrest, as hydrothermal fluids
                  adjust to changing subsurface conditions. Geochemical monitoring is carried out to
                  observe the evolving system conditions. Circulating fluids can also generate signals that
                  affect geophysical parameters monitored at the surface. Effective hazard evaluation
                  requires a proper understanding of unrest phenomena and correct interpretation of their
                  causes. Physical modelling of fluid circulation allows quantification of the evolution of a
                  hydrothermal system, and hence evaluation of the potential role of hydrothermal fluids
                  during caldera unrest. Modelling results can be compared with monitoring data, and
                  then contribute to the interpretation of the recent caldera evolution. This paper:
                  (1) describes the main features of hydrothermal systems; (2) briefly reviews numerical
                  modelling of heat and fluid flow through porous media; (3) highlights the effects of


              Corresponding author. Tel.: +39 051 4151 468; Fax: +39 051 4151 499
             E-mail address: todesco@bo.ingv.it
             Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, via Donato Creti, 12, 40128 Bologna, Italy
             Developments in Volcanology, Volume 10                     r 2008 Elsevier B.V.
             ISSN 1871-644X, DOI 10.1016/S1871-644X(07)00011-3            All rights reserved.
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