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Investigation of karst features at Ogbunike area, south-eastern Nigeria using 3D resistivity and GIS methods

Okafor Innocent U, Anakwuba Emmanuel K, Okpara Augustine O, Udegbunam Innocent E, Onyebum Tochukwu, Aniwetalu Emmanuel U

3 Dimensional electrical resistivity and Geographic Information System (GIS) methods have been employed in the study of karst system at Ogbunike in south-eastern Nigeria. Hypsometric, slope and curvature map, both plan and profile were derived from the digital elevation or terrain model of the study area for surface analysis to identify landform features characteristic of karst terrains. Vertical Electrical Sounding (VES) and 3D Electrical Resistivity Tomography (ERT) was used to image, investigate and characterize the morphology of subsurface karst features at the study area. Morphometric analysis shows places of higher relief to be more dominant in the southern portion of the study area with the presence of characteristic mound features or isolated hills of karst terrain especially at the cave location. Slope maps showed values that range from 0-20 degrees with places predicted to be of karst terrain showing higher slope values. Curvature maps both plan and profile show that convex and concave landforms are more dominant in places that have undergone karstification. Ten Vertical Electrical Sounding (VES) curves were interpreted to identify lithological intervals that correspond to zones of equal average electrical resistivity. Zones of possible cavities were identified for VES locations 1, 2, 3, 4 and 6 as studied in current research that were associated to doline features and sediment-filled cavities. A possible interval of air-filled or open cavity was interpreted for VES 5 in current work. The volume slice of the 3-D ERT data shows common karst features such as solution doline, chimneys and caves. This study supports the knowledge that a karst system exists at the Ogbunike area. The results of this study also suggest the spatial extent of karstification to be extensive.

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