Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Indications of karst cavities in marbles using the ERT method demonstrated on an example of the Branná Group
Published online: 29 June 2017 Barnet, I. - Čurda, J. - Holásek, O. - Koverdynský, B. - Manová, M. - Müller, V. (ed.) - Opletal, M. - Rejchrt, M. - Skácelová, D. - Šalanský, K. - Večeřa, J. (1999): Vysvětlivky k souboru geologických a ekologických účelových map přírodních zdrojů v měřítku 1 : 50 000, list 14-41 Šumperk. - Čes. geol. úst. Praha. Čeleda, V. (1984): Zpráva o geoelektrickém měření na akci Olšany - hydrogeologie. - Ochrana Přír. 4, 21-23. Koverdynský, B. - Holásek, O. - Opletal, M. - Rejchrt, M. (1996): Geologická mapa 1 : 50 000, list 14-41 Šumperk. - Čes. geol. úst. Praha. Kubalák, P. - Morávek, P. (2010): Nové objevy v krasovém území Na Pomezí. - Ochrana Přír. 4, 21-23. Morávek, R. (2009): Kras pásma Branné. In: Hromas, J. (ed.) et al. (2009): Jeskyně, 331. Chráněná území ČR, sv. XIV. 608 str. - Agent. ochr. přír. kraj. ČR, Praha - EkoCentrum Brno. Putiška, R. - Kušnirák, D. - Dostál, I. - Lačný, A. - Mojzeš, A. - Hók, J. - Pašteka, R. -Krajňák, M. - Bošanský, M. (2014): Integrated geophysical and geological investigations of karst structures in Komberek, Slovakia. - J. Cave Karst Studies 76, 3, 155-163. Sklenčka, J. - Životský, L. (1988): Zpráva o geofyzikálním měření na akci Ramzovské nasunutí - krystalinikum. - 20 str., MS Čes. geol. služba, Praha. Valois, R. - Guérin, R. - Pigeaud, R. - Rodet, J. (2009) : Geophysical study to characterize input karst water circulation in the saulges cave (Mayenne, France). - ArcheoSci. 33 (suppl.), 163-166. http://mapy.geology.cz/geocr_25/ - aplikace ČGS, mapy 1 : 25 000 http://mapy.geology.cz/geocr_50/ - aplikace ČGS, mapy 1 : 50 000Abstract
The electrical resistivity tomography method (ERT) was used to establish the extent and depth of karst cavities and/or the thickness of Quaternary sediments at two localities: Raškov Dvůr and Ruda nad Moravou. Both sites are located in a flood plain of the Morava River. Geophysical profiles at the Raškov Dvůr locality were 93 and 69 m long, and one profile coincided with a shallow hydrogeological borehole 6432_6 (30 m deep). The Ruda nad Moravou profile consisted of two overlapping 235 m long sections giving together a 350 m long common profile. The Ruda nad Moravou profile runs across a tectonic zone between the two great geological units of the Lugicum and the Silesicum so that the effect of this tectonic feature on the geophysical image is to be taken into account.
Discussion of the results:
The sites showing lower resistivity (Fig. 6) at the Raškov Dvůr locality at depths between 5 and 16 m indicate karstified marbles and gouge-filled fissures saturated with water. This area coincides with the collapsed surface close to the borehole thus representing a risk factor for this settlement.
A lower resistivity layer at the Ruda nad Moravou profile (Fig. 7) was proved to exist up to a depth of 30 m. Its interpretation is more problematic because of the absence of another borehole or relevant geophysical data. It is recommended to continue with using ERT and also to apply seismic methods, and drilling new boreholes at the locality.References
