Geophysical Researches to Detect Karst Caves in the Main Polje of Apulia

Canale di Pirro, the main polje in Apulia, extends for 12 km in the Low Murge karst area. It hosts the deepest cave in the region, reaching the depth of −324 m. Geophysical analyses have been performed in correspondence of two sites of interest. The first is located about 0.5 km upstream of the cave and is the main swallow hole in the polje. During rainstorms, most of the water accumulated in this sector is drained at this site, with time of absorption ranging from a few hours to some days, in function of the saturation condition of the sediments. The survey was addressed to verify the existence of caves, and the possibility to open a passage in the cover deposits. By adopting a multi-array and multi-scale strategy, based on the acquisition and joint inversion of geoelectrical data collected by using different arrays and with electrode spacing ranging from 5 to 20 m, a high-resolution model of the electrical subsurface structure was obtained. With an investigation depth up to ~150 m below the ground and high surficial resolution, the model shows features compatible with the presence of large caves, providing useful information on their possible extension and the thickness of the cover deposits. The second site is a small sinkhole (3 m depth, 7 m diameter) within a vineyard in the eastern sector of the polje. The survey was addressed to detect likely ways of water infiltration at the site and possible presence of underground voids.