GNGTS 2014 - Atti del 33° Convegno Nazionale

has increased in time due to the rapid population expansion in such active and active volcanic areas of the Earth. The reconstruction of the temporal evolution and the definition of the present state of the magmatic system feeding an active volcano are essential data for hazard assessment. Therefore the restless Campi Flegrei caldera (CFc) is one of the most dangerous volcanic areas on Earth. It is inhabited by more than 1.5 million people, most of whom concentrated in the city of Naples, as also recently indicated by the upcoming emergency evacuation plan for the Campi Flegrei area which as included different neighbourhood (i.e. Chaia, Fuorigrotta, Bagnoli, a part of Vomero). The magmatic system is still active as demonstrated by the widespread fumaroles and thermal springs (Allard et al. , 1991), and by bradyseismic episodes that occurred in 1969–1972 and 1982–1984 (Corrado et al. , 1977; Barberi et al. , 1984, 1989; Orsi et al. , 1999). ��� ������� ������ ������ ��� ��� ����������� �������� ������ ��� ������ ��� ������� The maximum ground uplift and the earthquakes location during the crises are focused in the center of the Campi Flegrei caldera, near the fumarolic field of Solfatara volcano. The Solfatara volcano is a tuff cone that consists of hydrothermally altered breccias and dunebedded ash to lapillus beds (Rosi and Sbrana, 1987). The tuff cone was formed between 3.8 and 4.1 ka (Di Vito et al. , 1999), and historical chronicles report that a phreatic event occurred in the 12th century. At the present moment, the Solfatara area is affected by an intense, diffuse degassing and fumarolic activity. Detailed geochemical study of Solfatara fumaroles (Caliro et al. , 2007), coupled with soil diffuse degassing measurements (Chiodini et al. , 2001) and with physical numerical simulations of the hydrothermal system (Todesco et al. , 2003; Troiano et al., 2011) suggests that magma degassing episodes have a relevant role in triggering the volcanic unrest periods that periodically affect the area (Chiodini et al. , 2003). The Solfatara volcano is located inside the CF caldera, at about 2 km east–northeast of the town of Pozzuoli. A low-magnitude explosive eruption in 1198 AD ejected tephra over a small area (Di Vito et al. , 1999). The crater has a roughly elliptical shape with axes of 580 and 770 m, and the highest relief along its rim reaches 199 m asl. The Solfatara crater is located very close to the area of maximum ground uplift and is the most active seismic area. It hosts large and spectacular fumarole vents, with maximum flow temperatures in the range of 150–160 °C at the Bocca Grande (BG) and Bocca Nuova (BN) fumaroles and approximately 100 °C at Le Stufe (LS) and La Fangaia (LF) ones (Chiodini et al. , 2001). Systematic measurements of the gas fluxes from the soil evidenced up to 1500 tonnes/day of CO2 emission through the main fault system and temperature up to 95 °C far from the fumaroles (Granieri et al. , 2010). During the first 16 years of systematic monitoring of the geochemical composition of the BG and BN fumaroles, from 1984 to 2000, the CO 2 /H 2 O concentration ratio has shown three clear peaks, in 1986, 1991 and 1995–96, respectively of 0.30, 0.26 and 0.34 over a background average value of 0.17, peaked about one year later of related peaks in ground deformation. Since 2000 to nowadays the CO 2 /H 2 O concentration ratio has progressively increased with a nearly linear trend from the background value of 0.17 up to about 0.32 (Chiodini et al. , 2010). Pisciarelli field site and experimental set-up. The Pisciarelli area is � ������������� a fault-related fumarolic field ������� �������� ������� ��� ������� ��� �� ��� ��������� ������ ����� ���� ���� located slightly outside the caldera rim of the Solfatara crater (Fig. 1a). This area is characterized by the presence of fractures and is affected by phenomena of emission of gases and fluids. The fumaroles are mainly composed by H 2 O followed by CO 2 and H 2 S and with a range of temperature between 100-110 °C (Chiodini, 2009). ��������� ��� ���������� Currently the increasing temperature of the fumaroles above the average background temperature, local seismicity and occurrence of fumaroles mixed with jets of boiling water, ���� �� ������� �������� �� show an evident increase of the activity compared to previous inspections� ������ ����� ������� ���� �� ��� ���� ���� �� . During field surveys made in the year 2006 in Pisciarelli area, compared to similar surveys conducted in the past (the year 2005), changes in the phenomena of gases and fluids emissions were observed. In addition, along the eastern side of the small hill to the east of this place pool the points of greenhouse gas emissions have increased. Fractures are mostly trending N110-120E and the area is dominated by two main features NW-SE and NE-SW. Also accumulations of material from surface gravitational movements of recent formation were not observed. 212 GNGTS 2014 S essione 1.3