Solfatara is situated within the Phlegraean Fields volcanic area. Geological evidence and historical records show that volcanic activity is mainly explosive. The last eruption took place in 1538 (Monte Nuovo). In 1970-71 and in 1982-84 the area was affected by a shallow seismicity and by a ground uplift totalling 170 and 180 cm respectively. In both cases large sections of population had to be evacuated. Complete chemical analyses of the Solfatara fumaroles have been carried out since 1978. Samplings and analyses were more frequent and regular after the ground had started inflating (August 1982), before the onset of the shallow seismicity (March 1983). During the period in which physical changes were observed, changes were also noticed in the chemical composition of the fumaroles: H2O and H2S increased before and during the first part of the crisis (until January-March 1984), then decreased together with H2 and CH4 and began declining a little earlier. N2 exhibited a sudden increase at the same time as the decrease of H2O and H2S. Some geochemical variations, e.g. the gas/steam ratio, occurred in response to an increase of the heat flow from the magma chamber underlying the Solfatara volcano before the onset of both local seismicity and ground uplift. Hydrogen and methane returned to their "normal" conditions about 6 months before the seismicity and the ground uplift had given any sign of subsiding (January 1985). At the same time the gas composition allowed an interpretation to be made of the chemical equilibria in the geothermal system under Solfatara. The gas/steam variation was utilized in order to obtain a rough estimation of the P and T variations in the aquifer supplying the fumarolic fluids. A 10°C increase in temperature would be sufficient to explain the gas/steam decrease between the end of 1982 and the beginning of 1984. Yet it is not enough to explain the variations of some chemical parameters, e.g. H2S, H2 and CH4. These changes occurred several months after the onset of both seismic activity and ground uplift. An input of high temperature fluids of deep origin should then be assumed. The delay was due to the buffer role played by the main aquifer present underneath Solfatara, while other geochemical parameters, the Ar isotopic composition and the N2/Ar ratio, accompanied discrete seismic swarms.
Geochemical Precursors at Solfatara Volcano, Pozzuoli (ltaly)
G Magro;
1989
Abstract
Solfatara is situated within the Phlegraean Fields volcanic area. Geological evidence and historical records show that volcanic activity is mainly explosive. The last eruption took place in 1538 (Monte Nuovo). In 1970-71 and in 1982-84 the area was affected by a shallow seismicity and by a ground uplift totalling 170 and 180 cm respectively. In both cases large sections of population had to be evacuated. Complete chemical analyses of the Solfatara fumaroles have been carried out since 1978. Samplings and analyses were more frequent and regular after the ground had started inflating (August 1982), before the onset of the shallow seismicity (March 1983). During the period in which physical changes were observed, changes were also noticed in the chemical composition of the fumaroles: H2O and H2S increased before and during the first part of the crisis (until January-March 1984), then decreased together with H2 and CH4 and began declining a little earlier. N2 exhibited a sudden increase at the same time as the decrease of H2O and H2S. Some geochemical variations, e.g. the gas/steam ratio, occurred in response to an increase of the heat flow from the magma chamber underlying the Solfatara volcano before the onset of both local seismicity and ground uplift. Hydrogen and methane returned to their "normal" conditions about 6 months before the seismicity and the ground uplift had given any sign of subsiding (January 1985). At the same time the gas composition allowed an interpretation to be made of the chemical equilibria in the geothermal system under Solfatara. The gas/steam variation was utilized in order to obtain a rough estimation of the P and T variations in the aquifer supplying the fumarolic fluids. A 10°C increase in temperature would be sufficient to explain the gas/steam decrease between the end of 1982 and the beginning of 1984. Yet it is not enough to explain the variations of some chemical parameters, e.g. H2S, H2 and CH4. These changes occurred several months after the onset of both seismic activity and ground uplift. An input of high temperature fluids of deep origin should then be assumed. The delay was due to the buffer role played by the main aquifer present underneath Solfatara, while other geochemical parameters, the Ar isotopic composition and the N2/Ar ratio, accompanied discrete seismic swarms.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
