Search for an artificially buried karst cave entrance using ground penetrating radar: a successful case of locating the S-19 Cave in the Mt. Kanin massif (NW Slovenia)

Abstract

Abstract:The S-19 Cave was with its explored depth of 177 m one of the most important caves of the Mt. Kanin massif, but after its discovery in 1974, a huge snow avalanche protection dyke was constructed across the cave entrance. To excavate the buried cave, the accurate location of the cave had to be determined first. Since the entrance coordinates were incorrect and no markers were available, application of geophysical techniques was necessary to do this. A Ground Penetrating Radar (GPR) with special 50 MHz rough terrain antennas was selected as the single suitable geophysical method for the given conditions where thick debris overlay a rugged limestone surface. Nevertheless, it was not possible to directly detect the relatively narrow cave entrance itself due to data resolution limits. However, a historical photo of the area showed that the cave entrance was located in a local depression, which therefore represented the main target of the GPR survey. Seven GPR profiles were measured across the rough and steep surface causing difficulties in traversing the area with sensitive research equipment. In all recorded radargrams a small depression was clearly imaged under debris, and recognized as a topographic feature with the cave entrance. Based on the GPR data interpretation, the exact location for digging was determined and the thickness of debris assessed at 6.5-7 m. A massive excavation by a dredger resulted in a successful opening of the cave entrance, confirming both its geophysically determined location and its estimated depth. The application of an advanced geophysical method was therefore proven successful in providing a solution to this specific case in karst exploration and an important cave was saved.ground penetrating radar, speleology, cavity detection, Mt. Kanin massif, S-19 Cave

Test of the maximum penetration depth of the Roteg GPR above the Hranice Abyss and in the Moravian Karst

“…Smith and Jol (1995) experimentally estimated that the penetration depth for a 25 MHz antenna and the Quaternary sedimentary environment (above the surface of mineralised water) is between 52 and 57 metres. For a 100 MHz antenna the penetration depth reduced to 37 m. The results of experimental measurements above the cave of Divaška Jama (Gosar 2012) and above the S-19 Cave on the Kanin massif (Gosar, Čeru 2016) correspond to such estimations.…”

Ground‐penetrating radar analysis of the Drimolen early Pleistocene fossil‐bearing palaeocave, South Africa

“…This indicates a total depth of 2.32 m in the radargram survey profiles. Previous GPR studies in similar limestone and dolomite landscapes indicate RDP values of between 7 and 9(εr) depending on the individual study (see Gosar, 2012; Gosar & Čeru, 2016; Dos Reis et al, 2014; Rodriguez et al, 2014). It should be noted that this calculated velocity represents an average value for a variable deposit consisting of parent dolomite, colluvial material, brecciated material and in some cases small voids.…”

3D Inversion of Transient Electromagnetic Data for Concealed Karst Cavern Detection

“…The basic theoretical background of the modeling algorithm can be found in Liu [4]. For a given computational domain Ω and time interval [0, tf], the time-varying electric field E and magnetic flux B excited by an loop source are governed by the time dependent Maxwell's equations: (2) where E and B are the electric field and magnetic flux respectively, μ is the magnetic permeability with μ=μ0, and ε is the permittivity with ε=ε0, σ is the conductivity in S/m and 𝑱 𝑟 (𝑡) is the current density from the impressed source. By employing the backward Euler method to discretize the above Maxwell's equations in time domain and using the FV method in spatial domain, we can obtain following discretized equations：…”

“…Although geological drilling is a precise method for karst caverns detection, geophysical methods play important roles for karst cavern detection based on the differences of the physical properties between the karst structures and the surroundings. Among them, the electrical resistivity tomography [1], ground penetrating radar [2], transient electromagnetic method [3] and shallow seismic exploration have been proven to be effective in karst caverns detection.…”