Abstract:The Buda Thermal Karst System is located under the densely populated hills of Budapest. One of its caves (Pál-völgy Cave System) is the longest cave of Hungary with 30.1 km. The research was done in this area as a methodological study to estimate karst porosity parameters of aquifers or hydrocarbon reservoirs. In this study two modeling methods are demonstrated. The volumetric modeling method was primarily aimed to determine the macro-scale (>0.5 m) conduit porosity (referred as macroporosity) of the study area as percentage of the incorporating limestone and marl. This method is based on archive survey data (maps and records). Through this method, morphometric parameters and the approximate sizes of the unexplored cave parts were also calculated. The porosity modeling was aimed at the estimation of the meso-scale (0.02-0.5 m) and macro-scale conduit porosity. It is based on rock face measurements near the Pál-völgy Cave System and image analysis. The matching macroporosity estimations of the two methods suggest that the map-based volumetric modeling method can be a useful tool for karstologists and modeling experts to extract as much information as possible from existing cave maps, even if the records of the original survey were lost or scanty. With the matrix porosity data published earlier from this area, and the conduit porosity calculated from the models, hydrological models of the area can be completed.cave surveys; karst porosity; 3D models; Buda Thermal Karst System; porosity model

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In 1995 LEÉL-ŐSSY Sz. published in this bulletin an overview of the caves of the Buda Hills. Due mainly to the progress in investigation methods and to new building construction sites in the area, since LEÉL-ŐSSY's work there have not only been new discoveries but new results have emerged from research into the genetics and minerals of local hypogene caves. To give one example, in 1995 30 km of cave pasages were known in the Rózsadomb; now that figure is 55 km. Among the new theories related to genetics, the most important one focuses on altered zones and the source and the mixing of the ascending thermal water that created the caves. The number of known mineral species in the Buda caves has increased from 15 to 31. This was the time of the first age determinations, which provided us with actual dates.Today there are 239 known caves in the Buda Hills and 176 caves in Budapest (including the caves in Róka Hill, which belongs to the Pilis Hills). In the area of Rózsadomb there are 102 caves on the list of the Hungarian Cave Register.In the last 20 years, the most important cave discoveries in the Rózsadomb area were in Molnár János Cave (mainly in the phreatic zone), and in the Hideglyuk, Harcsaszájú and Pál-völgy Caves. After the discovery of the connecting passages between the last three mentioned caves and the Mátyás-hegy Cave, this Pál-völgy Cave System is recently the longest known cave system (31 km long) in Hungary. Its length exceeds the Baradla Cave in Aggtelek-Jósvafő (together with the part of the Baradla Cave in Slovakia -there known as the Domica Cave). Furthermore, a major result of the speleogical investigations has been the discovery of the Mélyszint (deep part) of the Ferenc-hegy Cave; formerly, knowledge about this cave was based on the surface-close passages. The discovery of three "new" small caves -the Citadella Crystal Cave, the Királylaki Cave and the József-hegy No. 4 Cave -is also significant. This is due to their having valuable mineral precipitations and their potential for further investigations. In addition to these three important caves, over the last 20 years 28 small caves have been found by explorers: mainly in the Rózsadomb area and in the Buda Hills.Keywords: hypogenic speleogenesis, Pál-völgy Cave System, Citadella Crystal Cave, Királylaki Cave, altered zones, age of the speleothems Összefoglalás LEÉL-ŐSSY Sz. 1995-ben közölt összefoglalót a Budai-hegység barlangjairól e lap hasábjain. Az azóta eltelt időszak -ban -a kutatási módszerek fejlődésének, és a megszaporodott hegyvidéki építke zéseknek köszönhetően -nemcsak új feltárások történtek (főként a Rózsadomb térségében, ahol az 1995-ben ismert 30 km-es járathossz csaknem a duplájára, 55 km-re növekedett), hanem az itteni hipogén barlangok genetikájával, ásványvilágával kapcsolatban is számos új eredmény született. A keletkezéssel kapcsolatos új elméletek közül az elvál tozott (kovás) zónákkal és a barlangot kioldó aszcendens termálvizek eredetével és keveredésével kapcsolatos új eredményeket kell kiemelnünk. A Budai-he...

Budapest is famous for its thermal springs and spas and outstanding thermal water resources. In the 21 st century renewable energy utilization -including the use of geothermal energy -became the focus of interest. Improving the use of the different forms of geothermal energy requires the assessment of their possibilities. The potential for deep geothermal doublet systems for direct heating in Budapest was evaluated based on the temperature conditions, the depth and reconnaissance of the carbonate reservoir. NW Buda is not appropriate for thermal water exploration. SW and SE Budapest have better temperature conditions but the lithology of the reservoir is uncertain. Beneath Pest the thermal water is well exploitable. It is obvious from the map of the region that the area is promising; however, due to the hydraulic continuity of the system, reinjection is desirable. Considering the reliability of the employed data the geothermal potential map is suitable only for general orientation and guidance.The geothermal potential map for Groundwater-sourced Heat Pump Systems (GHPS; scale = 1:40,000) was assembled by evaluating the thickness and appearance of the gravel strata and water table, complemented by the sulfate content as an aggressive component of groundwater. The original geothermal potential map series can be used for the evaluation of potential sites in Budapest. It can be concluded that the Buda side of the Danube River is almost entirely unsuitable for shallow groundwater-based heat pump installations. The only areas under consideration are Óbuda and the riverbanks. On the Pest side, there is no gravel in the central part; the largest areas close to the river and in the immediate surroundings are uncertain, with patches of suitable and possible categories. The southern and eastern area of Pest is the most prospective for GHPS installation. The potential maps only consider natural parameters; however, installation may be strongly influenced by the urbanization and the city environment.

Travertine precipitated during the past ca. 120 years, from thermal waters in one of the historical Spas of the Buda Thermal Karst (Hungary) was investigated using radiocarbon (14C). The age of the deposit is based on the historic date of the structure on which the travertine was deposited. A textural study of the travertine buildup using a ~22-cm-long diamond-core crosscutting was undertaken. The original aim of the study was to improve our understanding of the controls and possibly also the rate of travertine-precipitation. In addition to characteristic, mm-scale, regular laminations, 0.5–1.0 cm dark-colored intervals were also observed in the core. Correlation of these latter textural changes with well-known changes in the water management of the Spa was greatly hindered by the lack of age data from the interior of the core. Therefore, in addition to the two known points (beginning in 1883 AD and ending 2004 AD) at least one age-datum point, somewhere inbetween, was necessary. Since the timespan of the core obviously included the 1960s of the last century, we expected that the 14C anomaly related to the atmospheric nuclear tests of those years could be detected by isotope-geochemistry. This paper gives a brief overview of the textural features of the investigated travertine and presents the dataset proving the incorporation of considerable amounts of atmospheric carbon in the carbonate precipitate, which, indeed, facilitated the indirect dating of the part of the core containing “bomb” 14C, and this helped us to unfold the factors controlling the observed textural changes of the travertine.

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