**2. Study Area**

The description below is based on Veress's work [15]. The parts of the Bakony Region and the names of the features that are mentioned in this study are described in Figure 1. The Bakony Region is the southwestern part of the Transdanubian Mountains. It is surrounded by the Little Hungarian Plain in the NW, by Lake Balaton in the SE and the micro-regions of the Balaton Basin (Balaton Riviera, Tapolca Basin), the Great Hungarian Plain (Mez˝oföld) and the Vértes Mountains in the NE (and Mór Graben with graben structure). Its elevation is 150–700 m and its area is 4300 km2. Its largest area is the Bakony Mountains (2200 km2). Parts of the Bakony Region are the Keszthely Mountains, Northern Bakony, Southern Bakony, Balaton Uplands and Bakonyalja (Figure 1).

The mountains are of horst structure, where more elevated horsts are mountains, while less elevated horsts are basins. They are mainly built up of Triassic dolomite which is significantly widespread on the surface too [16]. However, Triassic, Dachstein and Jurassic limestones frequently occur in great extension on the horsts of higher elevation. Cretaceous and Eocene limestones of smaller thickness can mainly be found in larger and smaller areas on horsts with medium elevation, mostly covered with loess. Horsts of lower elevation (basins) are mostly covered by non-karstic rocks (Middle Oligocene–Lower Miocene gravels, Figure 2).

**Figure 1.** Parts of the Bakony Region. Legend: 1. boundary of mountains, 2. boundary of microregion group, 3. stream, 4. horst, 5. basaltic horst, 6. plateau, 7. basin, 8. karst spring, 9. karst lake, 10. doline group, 11. cave, 12. settlement, 13. Northern Bakony, 14. Southern Bakony, 15. Balaton Uplands, 16. Keszthely Mountains, 17. K˝oris Mountain, 18. Som Mountain, 19. Mester-Hajag, 20. Kab Mountain, 21. S ˝ur ˝u mountain group, 22. Porva basin, 23. Lókút basin, 24. Hárskút basin, 25. Tapolca basin, 26. Dudar basin, 27. Cuha valley, 28. Gerence valley, 29. Ördög valley, 30. Ördög-lik of K˝oris Mountain, 31. Alba-Regia cave, 32. Lóczy cave, 33. Öreg-köves inflow cave, 34. Cserszegtomaj caves, 35. Devecser, 36. Szentbékálla, 37. Tapolca, 38. Márkó, 39. Hajmáskér, 40. Balatonfüred, 41. Hévíz, 42. Eleven-Förtés doline group, 43. Lake Hévíz and its spring cave, 44. Tihany Peninsula, 45. Tapolca cave system.

**Figure 2.** Geological map of the Bakony Region [17]. Legend: 1. fluvial sediment, 2. Holocene peat, 3. Holocene wind-blown sand, 4. Pleistocene loess, 5. Pliocene basalt, 6. Upper-Miocene freshwater limestone, 7. Middle Miocene limestone, 8. Oligocene gravel, 9. Eocene limestone, 10. Upper Cretaceous limestone, 11. Lower Cretaceous limestone, 12. Jurassic limestone, 13. Triassic limestone, dolomite, 14. Permian sandstone, 15. old Paleozoic phyllite.

The uniformly developed karstwater reserves of the mountains (regional groundwater, Figure 3), mostly stored in the main dolomite and preceding karstwater; pumping it resurged not only in karst springs, but also fed karstic swamps and lakes (Lake Balaton) [18,19]. However, it is also transmitted into the basin sediments of the environs [20,21] (Figure 3).

**Figure 3.** Karstwater map of the Bakony Mountains [21]. Regional groundwater of the mountains according to the state of January 2006. Legend: 1. infiltration area, 2. boundary of groundwater storage, 3. altitude of the isoline of groundwater level, 4. hypogene branch, 5. former hypogene branch, 6. termination boundary is not known.

In the Bakony Region, where impermeable intercalations are mainly in the Middle-Eocene limestone (Sz˝oc Limestone Formation) and in Cretaceous limestones, perched water tables developed in some horsts and horst groups [22,23]. Particularly, the percolating water of the gorges of the Bakony Mountains [22] may significantly feed the perched water tables, however, at sites where the aquifuge is absent or already removed by erosion, it feeds the regional groundwater [24].

As the horsts of the mountains performed oscillating movements since the Late Cretaceous period, Pécsi [25] put them into different genetic types (Figure 4). He distinguished

cryptopeneplain (up to 300 m elevation, it is covered with non-karstic impermeable rocks, morphologically basin), low-threshold surface (up to 300 m, its surface is built up of Triassic carbonates), horst elevated to summit position (surface elevation is 400–550 m, constituting rocks are Cretaceous and Eocene limestones, on which mainly permeable loess accumulations are found, morphologically mountain), horst in summit position (surface elevation is 600–700 m, Triassic and Jurassic carbonates are widespread at its surface, cover only occurs in patches) and horst type with basalt cover (basalt caprock and widespread loess cover).

**Figure 4.** Horst types of the mountains [26]. 1. non-karstic rock, 2. Triassic carbonates, 3. Jurassic, Cretaceous and Eocene limestones, 4. impermeable intercalation, clay, marly limestone, silica, etc., 5. basalt, 6. gravel, 7. loess, 8. karst water table, 9. fault, 10. karst water storey, 11. main karst water, 12. basin, graben, 13. mount, 14a. horst in summit position, 14b. horst elevated to summit position, 14c. threshold surface, 14d. cryptopeneplain, 14e. horst covered with basalt.

#### **3. Factors Influencing Its Karstification**

In the Bakony Region, two flow systems are present, a regional and a local. At the ascending branches of regional flows, hypogene karst systems are present, while at the descending branches of regional flows and at local flows, epigene karst systems are present. The main constituent of regional flow is the regional groundwater, which is not exclusively fed by descending waters, but also by the water of the perched water table, which percolates along fractures and faults. The regional flow with a NW–SE direction partly resurges in the karst springs of mountain margins, and, to a larger extent, it arrives at the sediment and at carbonate rocks on the floor of surrounding basins. In the SW, the former hypogene branch extended from the Keszthely Mountains nearly to the NE termination of Lake Balaton (Figure 3). Members of this branch are the Cserszegtomaj Caves [27,28] and the Lóczy Cave [29,30]. The hypogene branch still exists at Lake Hévíz, which is represented by the water of the spring cave of Lake Hévíz with a temperature of 40 ◦C [31].

Local flow occurs at sites where the limestones constituting the horsts are interbedded with impermeable or partly impermeable intercalations (marl, chert, clay). Such local flow is particularly characteristic of the Cretaceous limestone horsts of Northern Bakony (for example on Mester-Hajag Figure 5).

**Figure 5.** Water flow system of Mester-Hajag: Legend: 1. limestone, 2. impermeable intercalation, 3. permeable cover, 4. fault, 5. karstwater level, 6. infiltration, 7. local water inflow, 8. water motion above aquifuge, 9. water drainage along fault, 10. linear seepage, 11. spring, 12. epigenetic valley.

As has already been mentioned, the mountains are separated into horsts of different elevations, expansions and evolutions [21]. The distribution of horst types in the mountains is described in Figure 6.

**Figure 6.** Distribution of horst types in the Bakony Region. Legend: 1. boundary of the mountains, 2. boundary of micro-region group, 3. stream, 4. horst, 5. basaltic horst, 6. plateau, 7. basin, 8. karst spring, 9. karst lake, 10. boundary of horst type, 11. Northern Bakony, 12. Southern Bakony, 13. Balaton Uplands, 14. Keszthely Mountains, 15. horst in summit position, 16. horst elevated to summit position, 17. cryptopeneplain, 18. threshold surface, 19. horst with basalt cap, 20. buttes with basalt cap in karstic and non-karstic environments, 21. hilly country covered with superficial deposit (fluvial sediment, dune sand).

The majority of the mountains are covered by impermeable or permeable non-karstic sediment (mainly loess). The caprock thins out in some places (at the mounds of the bedrock or at creeks) as compared to its environment. On horsts covered with impermeable beds, epigenetic valleys of different stages of maturity emerged. These valleys may also have permanent streams at sites where a horst is surrounded by terrains covered with impermeable beds. As a result of the elevated position of the horst relative to its environment of covered terrain, some parts of these valleys are of epigenetic-antecedent origin and constitute gorges. On terrains covered with impermeable beds (for example on Kab Hill which is covered with basalt), mixed allogenic–autogenic karst developed.

The bedrock, therefore, became karstified and dissected into mounds and depressions. The mounds of Cretaceous limestones are partly exhumed. On the terrains between them, the caprock thinned out (Mester-Hajag). However, some parts of threshold surfaces that are uncovered and have a low elevation (below 300 m) are also dissected by mounds.
