Revealing the ongoing speleogenetic processes in an underwater cave through the application of natural radionuclides and stable isotopes: case study from the hypogene Buda Thermal Karst

Authors

Anita Erőss, ELTE Eötvös Loránd University, Institute of Geography and Earth Sciences, Department of Geology, Budapest, HungaryFollow
Katalin Hegedűs-Csondo, ELTE Eötvös Loránd University, Institute of Geography and Earth Sciences, Department of Geology, Budapest, HungaryFollow
Petra Kovács-Bodor, General Directorate of Water Management, HungaryFollow
Dénes Szieberth, Budapest University of Technology and Economics, Department of Inorganic and Analytical Chemistry, Budapest, HungaryFollow
Ákos Horváth, ELTE Eötvös Loránd University, Institute of Atomic Physics and Astronomy, Department of Atomic Physics, Budapest, HungaryFollow
György Czuppon, HUN-REN Research Centre for Astronomy and Earth Sciences, Institute for Geological and Geochemical Research, HungaryFollow
Andrea Mindszenty Dr, ELTE Eötvös Loránd University, Institute of Geography and Earth Sciences, Department of Geology, HungaryFollow
Szabolcs Leél-Őssy, ELTE Eötvös Loránd University, Institute of Geography and Earth Sciences, Department of Geology, Budapest, HungaryFollow
Judit Mádl-Szőnyi, ELTE Eötvös Loránd University, Institute of Geography and Earth Sciences, Department of Geology, HungaryFollow

Highlights

• Karst development is studied in real-time in a regional discharge area
• Cave forming process connected to lukewarm groundwater of intermediate flow system
• Free convection results in an upper warmer water layer
• Mixing corrosion is connected to a fault zone
• Danube level regulates thermal water discharge and temporal variations in mixing

Abstract

The underwater Molnár János Cave in the hypogene Buda Thermal Karst system (Budapest, Hungary) provides a unique site to study the effects of flowing groundwater and the interplay of fluids of different origin. The aim of the present study is to characterize the groundwater in different parts of the cave with temporal resolution, hence describe the recent speleogenetic processes within the cave. This study uses natural radioisotopes (uranium, radium, and radon) besides stable isotope ratios of oxygen and hydrogen to identify the different fluid components. The results show that the majority of the cave is situated in the flow path of the intermediate flow system, discharging in the Boltív Spring. Thus, the dominant recent speleogenetic processes are connected to this lukewarm groundwater. In contrast to previous views, typical hypogene processes, such as mixing corrosion involving thermal waters, are restricted to a narrower area in the cave, to the contact zone of lukewarm waters and the warmer upper water layer around the largest partially air-filled chamber (Kessler Hall). The warmer water layer is the result of free convection. In the air-filled chambers condensation-corrosion might be active. However, its effect is limited to the largest room (Kessler Hall), as it is open to surface conditions. More active mixing corrosion probably occurs deeper, in the area of the Northeastern Margin Fault, which is indicated by the radon content in the Boltív Spring. Regarding the temporal processes, the main driving force can be linked to the water level fluctuations of the Danube, which regulates the discharge of the regional flow-related thermal water upwelling, thus affecting the mixing ratio of the lukewarm waters transported by the intermediate flow systems and the thermal waters, representing the regional flow path, including basinal components.

DOI

https://doi.org/10.5038/1827-806X.53.2.2510

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Recommended Citation

Erőss, A., Hegedűs-Csondor, K., Kovács-Bodor, P., Szieberth, D., Horváth, Á., Czuppon, G., Mindszenty, A., Leél-Őssy, S., Mádl-Szőnyi, J., 2024. Revealing the ongoing speleogenetic processes in an underwater cave through the application of natural radionuclides and stable isotopes: case study from the hypogene Buda Thermal Karst. International Journal of Speleology, 53(2), 147-158. https://doi.org/10.5038/1827-806X.53.2.2510