Geochemistry applied to volcanic surveillance

The selection and use of chemical indicators to understand and possibly predict volcanic activity depends upon the geological framework and the geochemical model of the volcano in question. Monitoring of volcanic plumes is often carried out by measuring the SO2 flux. Where an hydrothermal system buffers the uprising gases released from a deep-seated magma body, gas-geobarometry is an effective tools to evaluate the risk of impending hydrothermal eruptions. At Vulcano crater, where deep magmatic gases mix with shallower hydrothermal fluids, main chemical constituents as well as radon activity indicate the extent of the mixing process, whereas minor rective species (H2, CO) re-equilibrate fast during the ascent. Most geochemical surveillance programmes currently under way are carried out through discontinuous sampling at relevant sites. Continuous monitoring is relatively new and yet not completely tested. (author). 18 refs, 8 figs