GNGTS 2014 - Atti del 33° Convegno Nazionale

Finally, the self-potential method (SP) is a passive geoelectrical technique and it consists in measuring the potential differences between two unpolarizable electrodes placed at the ground surface. These voltage differences result from the existence of an electric field produced by natural electrical sources distributed in the subsoil and generated by various phenomena (hydraulic, chemical, or thermal disequilibria). In particular, the SP method is sensitive to groundwater flow through the electrokinetic effect (Thony et al., 1997; Revil, 1999; Darnet and Marquis, 2004; Rizzo et al. , 2004). ���������� ��������� �������������� ������ ����� �� �� Therefore, detecting electrokinetic effect based on SP survey can allow zoning of infiltrating water recharge and run-off areas, and can determine the extent of effects of subsurface drainage works. Site description. The Sirino Lake (Fig.1), placed at 784 m above sea level is a major tourist place in the middle of a naturalistic interesting area, between the towns of Lauria, Lagonegro and Maratea (south Basilicata region, Italy). Almost elliptical in shape, the Lake Sirino extends for about 3 hectares with a 300 m length and a 150 m width; the depth varies according to the season but it doesn’t exceed 6 m depth. The landscape surrounding the lake is characterized by a complex orography, mostly mountainous with a steep morphology. Furthermore, the studied area is affected by severe and permanent landslides, involving relevant sectors of infrastructure systems, and a pervasive network of minor entity gravitational phenomena (Grassi et al. , 2001a, b; Guida and Siervo, 2005; Guida et al., 2006). The Sirino Lake is placed on the SE side of the Mount Sirino tectonic window at the base of the Costa del Capraro ridge . The area is characterized by a calcareous-siliceous marly succession attributable to Lagonegro I Unit (Flinty Limestone, Siliceous Schists and Galestrino Flysh), which constitutes the backbone of the Monte Sirino. Moreover, massive glacial debris accumulations, refer to the last Wurm glacial phase, and slope and/or landslide debris are present (Cotecchia et al. , 1993). The Sirino Lake rests on silty-clay sediments accumulated in the depression that houses the lake. These reddish clay deposits, due to the dissolution of Fig. 1 – Sirino Lake affected by piping phenomena in 1994, 2009 and 2014. 144 GNGTS 2014 S essione 3.2