Some hydro-geochemical fluctuations observed in Mexico related to volcanic activity

Some experiences obtained in Mexico pursuing the identification of geochemical precursors and changes associated to different kinds of volcanic activity are discussed. Three recent events of volcanic unrest are described in the context of an active geological environment. The identification of some geochemical precursors helped to evaluate the eruptive potential during two volcanic crises (Tacana´, 1986; Colima, 1991). The significant compositional fluctuations observed after a volcanic catastrophic eruption (El Chichon, 1982) are also discussed. It is concluded that even simple geochemical methods may provide a useful tool for the evaluation of the level of activity and the recognition of some eruption precursors.