The Potential Use of Geophysical Methods to Identify Cavities, Sinkholes and Pathways for Water Infiltration

Abstract

The use of geophysical characterization of karst systems can provide an economical and non-invasive alternative for extracting information about cavities, sinkholes, pathways for water infiltration as well as the degree of karstification of underlying carbonate rocks. In the present study, three geophysical techniques, namely, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLFEM) methods were applied at three different locations in relation to fluvial karst, which is listed as an environmentally sensitive area in Rio Vermelho, Mambaí, Goiás, Brazil. In the data acquisition phase, the GPR, direct-current (DC) resistivity and VLFEM profiles were obtained at the three locations in the area. Data were analyzed using commonly adopted processing workflows. The GPR results showed a well-defined lithology of the site based on the amplitude of the signal and radar typologies. On the other hand, the inverted resistivity cross-sections showed a three-layered stratigraphy, pathways of water infiltration and the weathered structures in carbonate (Bambui group). The interpretation of VLFEM as contours of current density resulted from Fraser and Karous–Hjelt filters, indicated the presence of conductive structures (high apparent current density) that might be linked to the weathered carbonate and other conductive and resistive anomalies associated with the water-filled and dry cavities (cave), respectively. The results encourage the integrated application of geophysical techniques such as the reconnaissance for further detailed characterization of the karst areas.

Detection of Cover Collapse Doline and Other Epikarst Features by Multiple Geophysical Techniques, Case Study of Tarimba Cave, Brazil

“…There is strong geological control over the emergence of geomorphological units in the region with highlands and escarpment adjusted (i.e., eroded to the base level) to the cretaceous sandstone and karst terrain and lowlands within the carbonate. The study area presents a covered karst system, where the karst features are often located under claystone (Neoproterozoic) [2].…”

“…In the northeastern region of the State of Goiás, the following soil classes and sediments were found: oxisoils, podzolic, cambisols, plinthsol, gleysol, sands, hydromorphic quartz, organic soils, quartz sands, alluvial soils and petroplinthic soils. It is important to note that the BambuÍ Group is seldom found exposed, but is mostly covered by claystone, forming covered karst [2]. The cave systems in the area include vadose conduits (shallow) and phreatic conduits (deep).…”

“…This current encounters resistance from the subsurface soil conditions (i.e., depending on the degree of fractures, material types and degree of saturation), and the developed potential is measured by two other metal electrodes known as potential electrodes. Resistivity tomographic techniques that provide a 2D image of the area are adopted as standard geophysical imaging techniques for the study of karst [2].…”

“…Karst landform is a geological feature that usually develops from the dissolution effect of groundwater on soluble carbonate rocks [1,2]. Such a process is very complicated to predict [3,4], but it may create underground cavities, which distresses the overburden, leading (sometimes) to an opening in the ground surface in the form of sinkholes [5].…”

“…However, no previous study has applied geophysical investigation to characterize the caves in the preserved area of the Mambaí, Goiás (River Vermelho) where borehole drilling is prohibited. The latest study, conducted in this area by the authors [2], indicated that Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLF-EM) are more effective than Ground Penetrating Radar (GPR), as the latter approach could not reach the required depth because of the highly attenuated nature of the cover material.…”