The Solfatara area

The Solfatara area has been characterized by intense and diffuse fumarolic and hydrothermal activity since Roman times. The area was investigated by means of a detailed soil-gas survey in the inter crater sector, during which 32 soil gas flux measurements (1 sample/100 m) were carried out using an accumulation chamber and a portable gas-chromatograph. OCO2 is typically 1127.32 gr/m2*d, although the highest flux values were found in the "La fangaia" and near the "Bocca Grande" and "Bocca Nuova" fumaroles. These fumaroles have the highest outlet temperatures (145°-165°C) amongst the several fumaroles present in the area (mean discharge temperature = 100°C). Fumarole effluents have similar chemistry, with H2O as the main component, followed by CO2 and H2S (Chiodini et al., 2001).

Figure 4. Ternary diagram (N2-He-CH4) for gas samples at Panarea island. Data from the literature (white dots, Italiano & Nuccio, 1991) have values typical of hydrothermal fields, whilst samples collected from November 2002 to December 2004 have concentrations typical of volcanic field suggesting an evolution of the system controlling Panarea emissions.

Figure 4. Ternary diagram (N2-He-CH4) for gas samples at Panarea island. Data from the literature (white dots, Italiano & Nuccio, 1991) have values typical of hydrothermal fields, whilst samples collected from November 2002 to December 2004 have concentrations typical of volcanic field suggesting an evolution of the system controlling Panarea emissions.

Based on their stable isotopes, the fumarole fluids were interpreted as magmatic fluids which are variably contaminated by metamorphic and meteoric components (Panichi & Volpi, 1999; Allard et al., 1991b). On the basis of outlet temperatures and the content of H2O, CO2 and of un-reactive gases (i.e., Ar, N2 and He) from fumarole fluids it was possible to estimate the flux of steam and thereby the heat flux involved in the diffusive degassing process. Chiodini et al. (2001) calculated that the entire Solfatara area releases 1500 t/d of hydrothermal CO2 through diffusive degassing. The contour map (Fig. 5) shows an area of about 0.5 km2 of high 0CO2 values representing an important diffuse degassing structure crossed by a NW-SE band of low fluxes. The highest 0CO2 values overlap with faults and fractures, confirming that the degassing process is strictly related to tectonic structures. In fact, the area is characterised by a regional extensional tectonic feature and by transverse structures considered as transfer faults along which the main regional volcanoes are located (Acocella et al., 1999).

Figure 5. CO2 flux contour map of the inter crater sector of the Solfatara area. Highest ®CO2 values overlap faults and fractures confirming that the degassing process is strictly related to tectonic structures.
+1 0

Post a comment