ABSTRACT
Monitoring fluid and gas compositions at active and dormant volcanoes is becoming increasingly important, both as a tool for recognizing precursory geochemical changes associated with impending activity, as well as for increasing our understanding of magmatic and hydrothermal systems and how they interact. This chapter discusses geochemical changes in both thermal waters and soil gases at a number of volcanic localities. At the present time the modelling of active volcanoes using geochemical methods is in its infancy, and to date there have been few opportunities to monitor the geochemical changes of fluids and gases through a volcanic crisis which has culminated in eruption. Volcanic fluids and gases can be analyzed using a number of very different methods, although some attempt has been made in recent years to standardize analytical techniques. The chapter looks at geochemical variations in fumaroles in more detail, with particular reference to recent studies at Campi Flegrei and Vulcano island.
