Degassing processes of Popocatépetl and Volcán de Colima, Mexico
To understand the behaviour of a volcano and try to predict future eruptive activity, it is imperative to investigate its degassing processes. Areas of study include direct degassing of the magma through the conduit, the interaction between the hydrothermal system and volcanic gases and fluids, and diffuse degassing through the volcanic edifice. Various aspects of the degassing processes of Popocatepetl and Volcan de Colima in Mexico have been studied. The results are summarized in this chapter, and new data on diffuse degassing at both volcanoes and analyses of fumarolic gases from Volcan de Colima are presented.
Variations in the flux of SO2 at both volcanoes have led to models of the degassing processes. At Colima, isotopic analyses of condensates suggest a shallow degassing magma body. Volcan de Colima showed geochemical precursors prior to its 1998/9 eruption and variations in certain parameters continue to relate to the behaviour of the volcano during its on-going eruption. Both volcanoes yield interesting data on their diffuse degassing of CO2 and radon: at Popocatepetl, the large plume degassing contrasts with a small diffuse contribution. Volcan de Colima has anomalous concentrations of diffuse CO2 associated with faults. The challenge is how to interpret the geochemical data to provide a fresh insight into the mechanics of the volcanic system.