Chapter 11 Hydrothermal Fluid Circulation and its Effect on Caldera Unrest

Abstract

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 hydrothermal fluids on unrest processes and (4) describes some model applications to the Phlegrean Fields caldera. Simultaneous modelling of different independent parameters has proved to be a powerful tool for understanding caldera unrest. The results highlight the importance of comprehensive conceptual models that incorporate all the available geochemical and geophysical information, and they also stress the need for high-quality, multi-parameter monitoring and modelling of volcanic activity.