Between 1987 and 1995, gases were sampled from various manifestations on Vulcano Island including various fumaroles at La Fossa crater and Baia di Levante and diffuse soil gas emissions in several areas which are characterized by high CO2 fluxes. Since the end of 1987, volcanic activity has increased considerably, showing a marked rise in temperature (300 degrees C in 1987 to 670 degrees C in December, 1992) and in output of steam from crater fumaroles. In addition, variations have been observed in the chemical and isotopic compositions of gases and thermal waters, which can be attributed to an increased inflow of deeper fluids. The isotopic composition of fumarolic steam seems to be the result of mixing processes between a positive endmember of deep origin (delta D = +10 parts per thousand similar to +15 parts per thousand; delta(18)O = +6 parts per thousand similar to +8 parts per thousand) and two endmembers of meteoric origin with different oxygen-shifts. Variations observed in the CO2 isotopic composition suggest that all sampled manifestations are fed by a single deep source which may be magmatic. Such a source would be characterized by the delta(13)C(CO2) values of high-temperature fumaroles (delta(13)C(CO2) congruent to 0 parts per thousand); these values are noticeably more positive than those generally attributed to magmatic gases (delta(13)C(CO2) = -5 parts per thousand similar to -8 parts per thousand) implying crustal contamination processes of the magma. The observed decrease in delta(18)O(CO2) values of the crater fumaroles (from +20 parts per thousand in 1978 to between +12 parts per thousand and +15 parts per thousand in 1993-1994) was probably caused by two different processes. The first is a reduction of the enrichment factor between CO2 and H2O which is related to the increased temperature of the gases, and the second is a mixing with more negative waters of meteoric origin. Finally, CO2 addition or removal processes caused by interactions between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions in the Vulcano Porto area and the crater fumaroles. Copyright (C) 1997 Elsevier Science Ltd.
