THE VERTICAL ELECTRICAL SOUNDING (VES) OF THE EPIKARST: A CASE STUDY OF THE COVERED KARST OF THE BAKONY REGION (HUNGARY) VERTIKALNO ELEKTRIČNO SONDIRANJE EPIKRASA: ŠTUDIJA PRIMERA POKRITEGA KRASA V REGIJI BAKONY (MADŽARSKA) Márton VERESS 1, György DEÁK 2 & Zoltán MITRE 3 Abstract UDC 550.837:551.435.88(234.373.1) Márton Veress, György Deák & Zoltán Mitre: The vertical electrical sounding (VES) of the epikarst: A case study of the covered karst of the Bakony region (Hungary) The epikarsts of five covered karst areas in the Bakony region are compared. The comparison is based on the specific resist- ances of the bedrock resistance averages measured by vertical electrical sounding (VES). The average largest specific resist- ance differences (per area) and the mean values (per profile) were calculated to investigate the characteristics of the epikarst. The mean values of specific resistance were compared using analysis of variance (ANOVA) to determine whether the spe- cific resistances of the areas showed significant differences. The studied karst areas can be categorised as high or low specific resistance areas, and the ANOVA method could be applied to three areas based on the available data. It can be concluded that the mean values of their specific resistances are significantly different. The mean values ( ) and standard deviation (S) of the specific resistances of the different areas were analysed. It is described that the karst receives less water in the case of areas with lower specific resistance, while it receives more water in the case of areas with higher specific resistance. Areas with a high specific resistance are less karstified, while areas with a low specific resistance are more karstified. Low specific resistances and small mean values ( ) indicate a higher degree of cavity formation in the epikarst, while the decrease in mean values and standard deviation (S) indicates increasing uniformity of the degree of cavity formation in the epikarst. The different de- gree of cavity formation is explained by the different karstifica- tion rates and the exposure of different time of certain areas. Keywords: Bakony Region, epikarst, VES measurement, spe- cific resistance, karstification, covered karst. Izvleček UDK 550.837:551.435.88(234.373.1) Márton Veress, György Deák & Zoltán Mitre: Vertikalno električno sondiranje epikrasa: študija primera pokritega krasa v regiji Bakony (Madžarska) Avtorji so primerjali epikraške značilnosti petih območij pokrite- ga krasa v regiji Bakony. Primerjava temelji na specifični upor- nosti z vidika povprečne upornosti matične podlage, izmerjene z vertikalnim električnim sondiranjem (VES). Za proučevanje značilnosti epikrasa so bile izračunane povprečne največje razlike specifične upornosti (za posamezno območje) in srednje vred- nosti (za posamezni profil). Z analizo variance (ANOVA) je bila izvedena primerjava srednjih vrednosti specifične upornosti, da bi ugotovili, ali specifična upornost območij kaže pomembne raz- like. Proučevana kraška območja je mogoče razvrstiti v območja z veliko ali majhno specifično upornostjo, metodo ANOVA pa je bilo mogoče na podlagi razpoložljivih podatkov uporabiti za tri območja. Ugotoviti je mogoče, da se srednje vrednosti njihove specifične upornosti pomembno razlikujejo. Avtorji so anal- izirali srednje vrednosti ( ) in standardni odklon (S) specifične upornosti različnih območij. Iz opisa izhaja, da na območjih z manjšo specifično upornostjo kraško območje prejme manj vode, na območjih z večjo specifično upornostjo pa prejme več vode. Območja z veliko specifično upornostjo so manj zakra- sela, območja z majhno specifično upornostjo pa so bolj zakra- sela. Majhna specifična upornost in majhne srednje vrednosti ( )kažejo na višjo stopnjo prevotljenosti epikrasa, zmanjševanje srednjih vrednosti in standardnega odklona (S) pa kaže na bolj enakomerno prevotljenost epikrasa. Avtorji različne stopnje pre- votljenosti posameznih območij razlagajo z različno hitrostjo zakrasevanja in različno časovno izpostavljenostjo zakrasevanju. Ključne besede: regija Bakony, epikras, meritve z vertikalnim električnim sondiranjem (VES), specifična upornost, zakra- sevanje, pokriti kras. ACTA CARSOLOGICA 52/2-3, 245-258, POSTOJNA 2023 1 Department of Geography, Savaria University centre, Eötvös Lóránd University, 9700 Szombathely, Hungary, e-mail: veress.marton@sek.elte.hu 2 Department of Geography, Savaria University centre, Eötvös Lóránd University, 9700 Szombathely, Hungary, 3 Institute of Geography, University of Pécs, 7600 Pécs, Hungary, e-mail: zoltan.mitre@gmail.com Prejeto/Received: 31. 5. 2023 DOI: https://doi.org/10.3986/ac.v52i2-3.12149 1. INTRODUCTION In this study, the epikarsts of the covered karst areas of the Bakony Mountains with various degree of karstifica- tion are compared. These are the following: eastern part of Tés Plateau (Tés 1 which is the area of Tábla Valley, Tés 2 which is the tributary valley of Tábla Valley, Tés 3 which is the area between the two valleys), Homód Val- ley area (Hárskút Basin), Eleven-Förtés doline group (Kőris Mount), Mester Hajag and the marginal part of Fehérkő Valley. The relationship between the degree of karstification of karst areas and the specific resistance of the karstic bedrock is described. Based on the specific re- sistance values of karst areas, the different maturity of the epikarst and the different degree of karstification of karst areas can be presented. The epikarst is the upper, subsurface part of the vadose zone with cavities (Williams, 1972, 1983, 1985; Mangin, 1975; Klimchouk, 1987, 2004; Bakalowicz et al., 1974; Bakalowicz, 2005, 2019; Palmer, 2004; Jones, 2013; Tobin et al., 2021; De Waele & Gutierrez, 2022), (Figure 1), where secondary porosity may even be 20% (Williams, 2008). Since porosity decreases in the vadose zone below the epikarst (about to 2%), the infiltrating waters accumulate temporarily at the lower part of the epikarst and flow laterally (Klimchouk, 2004; Williams, 2008; Bakalowicz, 2019). The surface of the water of the epikarst, the piezometric surface, fluctuates depending on water supply. Its elevation and fluctuation depends on the degree of local cavity formation of the epikarst, on the degree and distribution of water supply, and on the drainage intensity out of the epikarst. Therefore, the piezometric surface is uneven, non-horizontal, and dis- sected by depressions (Williams, 2008). Its lower surface is the saturation level which also constitutes an uneven surface. It penetrates deeper and creates a depression at a site where water with higher dissolution capacity ar- rives at the epikarst. On covered karst the thickness and calcareous content of the cover affect the upper and low- er surfaces of the epikarst. The thicker the cover, to the higher degree the water is stored in it, and the higher its calcareous content, the more saturated water arrives at the epikarst. A lot of infiltrating water (at water catch- ment feature and in case of thin cover) rises the piezo- metric surface. If the cover is calcareous-free, the water has a higher dissolution capacity, the epikarst has more cavities, and the saturation level is deeper and thus, forms a depression. The epikarst plays an important role in the karstic development of the surface, but it itself develops too and becomes more and more dissected by shafts and the mo- tion of its water becomes more and more vertical (Klim- chouk, 2004). Klimchouk (2004) differentiated young epikarst, mature epikarst, and old epikarst development phases. Figure 2 presents epikarst with various maturity degree and environment. MÁRTON VERESS, GYÖRGY DEÁK & ZOLTÁN MITRE Figure 1: The epikarst (Bakalow- icz, 2019). ACTA CARSOLOGICA 52/2-3 – 2023246 THE VERTICAL ELECTRICAL SOUNDING (VES) OF THE EPIKARST: A CASE STUDY OF THE COVERED KARST OF THE BAKONY REGION (HUNGARY) 2. THE BAKONY REGION AND RESEARCH AREAS Our studies were made in the karstic terrain sections of the Bakony Region (Transdanubian Mountains, Hun- gary). The Bakony Region (4900 km2) is separated to the Bakony Mountains (2200 km2) and the surrounding mi- cro region groups. It is enclosed by the Little Hungarian Plain, the Great Hungarian Plain, the Vértes Mountains, and the Transdanubian Hills. The Bakony Mountains with an elevation of 200-700 m, is separated into the Northern Bakony and Southern Bakony, its eastern part is the Eastern Bakony, the most expanded part of which is the Tés Plateau. The main constituting rock of the Bakony Moun- tains is Triassic Main Dolomite (Main Dolomite Forma- tion) which is overlain by Triassic Dachstein Limestone (Dachstein Limestone Formation) in patchy develop- ment and mainly in small thickness (from some tens of metres to some hundreds of meters) and by Jurassic, Cre- taceous and Eocene Limestones (Kercsmár et al., 2022). The Late Cretaceous tropical karstic peneplain of the mountains (Szabó, 1968; Bulla, 1968) had become tectonically dissected since the Eocene (Pécsi, 1980) therefore the Late Oligocene-Early Miocene delta gravel (Korpás 1981) (Csatka Gravel Formation) covered a dis- sected surface. Younger limestones mainly developed at the marginal parts of the mountains (Lajta Limestone Formation, Tinnye Limestone Formation), and also Plio- cene freshwater limestones were formed (Császár et al., 1981). Pannonian clay also occurs in small expansion (Jaskó, 1961) and loess in wide expansion developed too. The Bakony Mountains is separated into blocks (horsts) and block groups with different elevation and landscape evolution (Pécsi, 1980, 1991). On lower Figure 2: Epikarst with various maturity degree and environment. A: Epikarst below soil-covered karst in the side of a road-cut (near the village of Galečic, The Dinarides, Bosnia): 1. epikarst part that was separated into blocks with soil wash, 2. grikes with different inclination and width. B: Epikarst of covered karst in the side of a doline (Pádis, Romania) 1. cover, 2. filled-in epikarst part, 3. unfilled epikarst part or only filled to a small degree, 4. wide filled-in grike opening to the bedrock surface, 5. narrow grike, 6. grike along bedding plane. C: Ma- ture epikarst that developed below weathering residue on a karst exposed to intensive dissolution in the side of a road-cut (the Dinarides, Bosnia), 1. the upper part of the epikarst that is separated into debris, 2. epikarstic part of the bedrock, 3. grikes along the bedding plane, 4. grikes that developed along fractures. D: Epikarst below weathering residue that is separated into parts (the Dinarides, Bosnia), 1. wide, filled-in grike, the site where the epikarst is separated into parts, 2. the block of the bedrock in the weathering residue. ACTA CARSOLOGICA 52/2-3 – 2023 247 elevated blocks (for example the Dudar Basin) their roof level is uniformly covered with superficial deposit, those with a larger elevation are covered in bigger patches (for example Mester-Hajag, Tés Plateau), while the most el- evated ones are uncovered or only small patches of the cover survived (for example Kőris Block). On the pe- neplains of the blocks, abrasion peneplains, pediments (Pécsi, 1963, 1970, 1980) and epigenetic valleys (these are often gorges or of gorge character) are widespread, while on terrains covered mostly with thin, permeable cover, suffosion dolines occur frequently (Veress, 2022). Under superficial unconsolidated (?) deposits, the bed- rock became karstified to a various degree and in differ- ent periods (Mindszenty & Sebe, 2022), which resulted in the development of terrains with dolines (Bíró, 1969), and poljes (Szabó, 1956). Among the studied karstic terrain sections, the eastern part of the Tés Plateau is on the Tés Plateau, the Homód Valley karst area is in the Hárskút Basin, while the Eleven-Förtés doline group can be found on the Kőris Block. The Mester-Hajag is a block with a small area, its northern part was studied (further on Mester-Hajag Northern karst area), the area next to Fehérkő Valley is the marginal area that was separated from Középső- Hajag and Felső- Hajag by Fehérkő Valley. The last two areas belong to the Hajag mountain group (Figure 3). The eastern part of Tés Plateau is separated into three parts: Tés 1 includes the Tábla Valley, Tés 3 involves its tributary valley, while Tés 2 includes the area between the two areas. The Homód Valley karst area is situated on an epigenetic valley floor at the southern part of Hár- skút Basin, Eleven-Förtés is an areic part of Kőris Block. Figure 3: Research sites. Legend: 1. boundary of the Bakony Region, 2. boundary of the micro region group, 3. gorge, 4. block roof, 5. pla- teau, 6. basin, 7. stream and its val- ley, 8. settlement, 9. research site, I. Tábla Valley and its environment, II. Homód Valley, III. Eleven-För- tés, IV. Mester-Hajag North, V. margin of Fehérkő Valley. MÁRTON VERESS, GYÖRGY DEÁK & ZOLTÁN MITRE ACTA CARSOLOGICA 52/2-3 – 2023248 On the karst areas of Mester-Hajag and Fehér-kő Valley, the terrains between mounds becoming exhumed are karstifying, where the cover has become thin as a result of its denudation. These karst areas are covered karsts where the cov- er thickness is predominantly 1-15 m. According to its composition, the cover may be loess (and its clayey and limestone debris variety), clay (limestone debris varieties also occur in this case), limestone debris and sand (mixed with any of the above mentioned rocks) in a smaller ex- pansion. The above superficial deposits are either fea- tures of dust waves (loess) or reworked or may have de- veloped by fluvial transport and the dissolution residues of limestone (clay) or they were formed by the physical weathering of the bedrock (limestone debris). Based on the data of VES measurements, the bedrock was karsti- fied and it is dissected by mounds and depressions. Some characteristics of sample areas are presented in Table 1. 3. METHODS Measurements were carried out in the chosen sample ar- eas by the Terratest Ltd. During VES measurement (Ver- ess, 2009), electric current is conducted into the bedrock through two grounded electrodes, other two electrodes measure the potential difference which is created by the current dispersion (Veress, 2009). The dispersion of the current power, the measured potential difference and the calculated apparent specific resistance depend on the specific resistance and the thickness of the beds. Curves can be constructed based on the measured potential difference values considering the distance between the electrodes and thus, with the help of an inverse program, in ideal case the specific resistances and thicknesses of the row of beds can be determined. Measurements were Table 1: Characteristics of sample sites. Name expansion (m2) altitude (m) rock and morphology of bedrock morphology number of subsidence dolines eastern part of Tés Plateau, Tés Plateau 312000 440-480 Jurassic karstified2 epigenetic valleys, with subsidence dolines on their floor, some of them are connected by creeks 19 (1375) Homód Valley doline group 117967 430-440 Middle Eocene, karstified epigenetic valley floor, some of them are connected by creeks, with several filled subsidence dolines and lake on their floor 22 Eleven-Förtés doline group 50000 670-680 Jurassic, karstified1 areic area deepening into a flat terrain, its subsidence dolines are mainly on flat terrain, a valley leads to one of them, there are also dolines on its floor, several filled dolines with lakes occur 9 Mester-Hajag North 216528 470-480 Upper Cretaceous karstified3: some mounds of the bedrock became exposed terrains covered with superficial deposit between exposed mounds, with small subsidence dolines without creek on the mounds, some dolines occur in more expanded, narrow depressions 32 (856) area next to Fehérkő Valley 10053 340-360 Upper Cretaceous weakly karstified4 small subsidence dolines aligned in a larger depression which is enclosed by partly exposed mounds 4 1 mounds and depressions on the bedrock 2 at Table Valley, valley inheritance also take place in the bedrock 3 the presently covered bedrock is less karstified (smaller mounds, less deep, more expanded depressions) 4 depressions on the bedrock 5 on the entire Tés Plateau 6 on the entire Mester-Hajag THE VERTICAL ELECTRICAL SOUNDING (VES) OF THE EPIKARST: A CASE STUDY OF THE COVERED KARST OF THE BAKONY REGION (HUNGARY) ACTA CARSOLOGICA 52/2-3 – 2023 249 carried out along planned and marked, in some cases intersecting lines which went through the subsidence dolines of the studied areas. Geoelectric-geological pro- files were constructed with the help of the data of VES measurements situated next to each along a certain di- rection. On these profiles the quality and the thickness of the cover and the morphology of the bedrock were de- scribed taking into consideration the measured specific resistances. The VES measurements penetrating into the bedrock provide information on the extent of cavity, formation of the bedrock and the degree to which the cavities are filled, to the penetration depth. In the case of rocks without cavities and unfilled cavities, the specific resistance of the bedrock is higher than at sites where more cavities occur and these are filled with water or wet sediment. Along the profiles of the latter sites, the specific resistances are lower. The lengths of the profiles were 40- 750 m and their number is included in Table 2. A profile comprised 1000-4000 m2. For example, an area of 3800 m2 belonged to the Eleven-Förtés karst area, while an area of 25000 m2 belonged to Tábla Valley 2 area. The data of three areas (the eastern part of Tési Pla- teau, Mester-Hajag North, Eleven-Förtés) were studied with the ANOVA method (Falus & Olé, 2008; Fodor, 2022). The karst area of Homód Valley and the marginal karst area of Fehérkő Valley were not included in the study with the ANOVA method due to the small number of cases. 4. RESULTS Specific resistance values were read from the profiles (specific resistances along two profiles are described in Figures 4 and 5 as an example), and the average of these values were calculated by karst areas (Table 2). The mini- mum and maximum values of specific resistances were chosen by profiles and their average was calculated. The average maximum and average minimum differences were calculated at each studied area. This is called the av- erage largest differences of specific resistances (Table 3). It was investigated whether the mean values of spe- cific resistances by profiles (the averages of maximum and minimum values) differ significantly from each oth- er. The definitions that were used for the procedure are given in Table 4. The significance of mean values can be determined if we calculate the F and p values of standard deviation intervals in the studied areas. If Fcalculated is larger than Fcritical and p is smaller than 0.05, then the studied data sets differ significantly from each other. In case of the three areas, the average specific resistances along the profile were graphically described (Figure 6) as well as the mean values calculated from specific resistances ( ) and the standard deviation of specific resistances (S). The mean values of the above areas, the averages of mean values ( ), the graphs of mean values and the standard deviation of specific resistances (S) were described in Figure 6. Bedrock specific resistances are lower (Figure 4), MÁRTON VERESS, GYÖRGY DEÁK & ZOLTÁN MITRE Table 2: Specific resistance values in the bedrock in various sample sites of the Bakony Region. area profile number number of VES measurement profile density [profile/ km2] approximate penetration into the bedrock [m] average of specific resistance [Ohmm] shaft specific length of shafts1 eastern part of Tés Plateau (Tés Plateau) 14 104 0.02 3-10 315 46 2.73 (Veress 2019) Homód Valley 2 33 0.06 4-20 303 1 1.732 Eleven-Förtés doline group 10 68 0.09 5-7 611 4 1.0 Mester-Hajag 18 137 0.01 3-8 1273 - - marginal area of Fehérkő Valley 2 17 0.005 3-7 1875 - - 1 specific shaft length: 2 on the entire area of the plateau 3 cave of Homód Valley (of the entire karst area, of the Hárskút Basin: 2.04) ACTA CARSOLOGICA 52/2-3 – 2023250 and higher at different profiles (Figure 5). The averages of specific resistance values show significant differences and alternate between wide values, however the different specific resistances are not profile specific, but show sig- nificant differences by sample areas. Among the studied areas, the lowest specific resistance average (303 Ohmm) can be detected on the Homód valley karst area, while the highest average (1875 Ohmm) can be found in the karst area near Fehérkő Valley (Table 2). Based on their specific resistance values, the stud- ied karst areas can be put into two groups. The Homód Valley karst area and the eastern part of Tés Plateau be- long to the group with low specific resistance value. The area of Mester-Hajag North and the marginal karst area of Fehérkő Valley are of high specific resistances. The area of the Eleven-Förtés doline group is of transitory specific resistance, but it may rather be put into the for- mer group. THE VERTICAL ELECTRICAL SOUNDING (VES) OF THE EPIKARST: A CASE STUDY OF THE COVERED KARST OF THE BAKONY REGION (HUNGARY) Figure 4: Geoelectric-geological profile from a bedrock part of low specific resistance (Tábla Valley, Tés Plateau). Legend: 1. limestone, 2. limestone debris (clayey), 3. loess (sandy or with limestone debris), 4. loess (clayey-silty), or clay with limestone debris, 5. clay, 6. number of VES measurement, 7. geoelectric specific resistance of the series (Ohmm), 8. basal depth of the geoelectric series (m), 9. geoelectric specific re- sistance of the bedrock (Ohmm) 10. approximate penetration of VES measurement, 11. boundary of geoelectric series, 12. code of depression. Figure 5: Geoelectric-geological profile from a bedrock part with high specific resistance (Mester-Hajag). Legend: 1. limestone, 2. limestone debris, 3. limestone debris (clayey), 4. loess (sandy or with limestone debris), 5. clay, 6. number of VES measurement, 7. geoelectric specific resistance of the cover (Ohmm), 8. basal depth of the geoelectric series (m), 9. geoelectric specific resistance of the bedrock (Ohmm), 10. ap- proximate penetration of VES measurement, 11. boundary of geoelectric series, 12. subsidence doline. ACTA CARSOLOGICA 52/2-3 – 2023 251 MÁRTON VERESS, GYÖRGY DEÁK & ZOLTÁN MITRE Table 3: Maximum and minimum differences of bedrock specific average specific resistances in the studied areas. karst area average maximum average minimum difference profile number total VES measurements Tábla Valley and its environs 430.5 238.5 192.1 14 90 Homód Valley 470 170 300 2 33 Eleven-Förtés 8810 405 476 10 68 Mester-Hajag 1750 911 835 18 137 margin of Fehérkő Valley 2925 740 2185 2 17 Table 4: Theory of variance analysis calculation with the ANOVA method. name of sum of squares Variance Degree of freedom Estimation of standard deviation F value p value between groups r - 1 Sk 2 Sk 2/ Sb 2 p within group n - r Sb 2 - - total n - 1 - - - r number of groups n number of profiles within the group (Mester-Hajag 17; Tés 14; Eleven Förtés 10) -xi mean value of i group calculation -xij j member of i group Sk 2 sums of squares between groups Sb 2 sum of squares within group p value: j member of i group, at an error of 0.05 with what probability can it be fitted into the standard deviation interval of i+1 group (into +/-S) Table 5: A comparison of mean values of the measurements of Mester-Hajag North and the Eastern part of Tés Plateau. Groups Number of profiles Sum of measured values Mean value of measured values Variance Mester-Hajag North (1) 17 22427.5 1319.26 86777.94 Eastern part of Tés Plateau (2) 14 4693 335.21 709.14 Table 6: ANOVA probe results of Mester-Hajag North and the eastern part of Tés Plateau. Factors S2 Degree of freedom (n-1) F calculated P value Fcritical Between groups (1.2) 7434469 1 7434469 154.25 3.91E-13 4.18 Within group 1397666 29 48195.58 - - - Total 8832135 30 - - - - Since Fcalculated (194.25) is larger than Fcritical (4.18) and p value is smaller than 0.05 (0,0062E-13), the mean values of the samples are significantly different. ACTA CARSOLOGICA 52/2-3 – 2023252 THE VERTICAL ELECTRICAL SOUNDING (VES) OF THE EPIKARST: A CASE STUDY OF THE COVERED KARST OF THE BAKONY REGION (HUNGARY) It can be established that the average highest spe- cific resistance differences of the studied areas are sig- nificantly different. In case of the areas with high specific resistances, the average largest differences are big, while in case of the areas with low specific resistances, the aver- age largest differences are small (Table 3). The eastern part of Tés Plateau and the northern part of Mester-Hajag are significantly different at p<0.05 ran- dom variable level since Fcalculated is larger than Fcritical and value p is smaller than 0.05 (Tables 5 and 6). The signifi- cant difference can also be established in mean values re- garding the eastern part of Tés Plateau, the Mester-Hajag North and Eleven-Förtés since Fcalculated is larger than Fcriti- cal and the p value is smaller than 0.05 when the three ar- eas are compared (Tables 7 and 8). In case of these areas, the lower the specific resistance (Figure 6), the smaller its deviation from the mean value ( ) and partially from the standard deviation (S). In case of smaller and smaller averages of mean values ( ), which expresses the absolute value of the specific resistances of the areas, the mean values of certain areas and partly their standard deviation are smaller and smaller (Figure 6). With the decrease of specific resistances, these gather more and more along the line of the average of mean values ( ). Table 7: A comparison of the mean values of Mester-Hajag North, the eastern part of Tés Plateau and Eleven-Förtés. Groups Number of profiles Sum of measured values Mean value of measured values Variances Mester-Hajag North (1) 17 22427.9 1319.26 86777.94 Eastern part of Tés Plateau (2) 14 4693 335.21 709.14 Eleven-Förtés (3) 10 6425 64.25 20823.61 Table 8: Mester-Hajag North, eastern part of Tés Plateau, Eleven Förtés ANOVA probe. Factors S2 degree of freedom (n-1) F calculated P value Fcritical Between groups (1,2,3) 7842676.96 2 3921338.48 94.01 1.94E-15 3.24 Within group 1585078.41 38 41712.59 - - - Total 9427755.37 40 - - - - Since Fcalculated (94.01) is larger than Fcritical (3.24) and P value is smaller than 0.05 (1.94E-15), the mean values of the samples are significantly different. Figure 6: Average of mean values ( ), graphs of mean values and standard deviations (S) per profiles from the areas of Mester-Hajag North (a), Eleven-Förtés (b) and Tés Plateau East (c). ACTA CARSOLOGICA 52/2-3 – 2023 253 5. DISCUSSION The epikarst has not been studied by VES measurements yet. However, the statistical method used for the evalua- tion of measurements (ANOVA) has not been applied ei- ther. The analysis of specific resistances and the statistical analysis are suitable for the objective differentiation or the determination of the similarity of the epikarst of cer- tain areas. By the applied measurement method and the statistical data processing, the epikarst of different karst areas can be compared. To our knowledge, no compara- tive epikarst studies or no attempts on drawing a parallel between the maturity of the epikarst and surface karsti- fication (the frequency and size of surface karst features) have been made yet. The essence in the relationship be- tween the epikarst and surface karstification (is that there is more water at the level of penetrations in areas of lower specific resistance thus, they were more karstified. Areas of higher specific resistance were karstified to a larger de- gree (since there is less water at the level of penetrations) because there are no cavities or only some cavities occur in them since there is less water in the epikarst and no pi- ezometric surface occurs either. Since during sounding, electrical penetrations reached the bedrock in a depth of 5-10 m from its surface, the specific resistance provide information on the epikarst of the research sites. In study areas of high specific resistance which in- clude two karst areas (Table 2), the size of subsidence dolines is small (their diameter and depth does not ex- ceed 1-2 m). The bedrock does not crop out on the floors of dolines in no cases, at most there is a drainage passage (a passage that developed in the karst rock) in the cover of the floor at some of them (Mester-Hajag northern part). The water catchment area of dolines is small (it is often absent), there are no connecting creeks. The significant part of both Mester-Hajag North karst area and Fehérkő Valley marginal karst area have a surface drainage. The small size of dolines and the absence of bed- rock outcrop on the floor refers to low suffosion. This can be traced back to the fact that little water arrives at the dolines, and the sediment receiving capacity of the bed- rock is small (high specific resistances refer to the fact that there are small and few cavities in the epikarst). The lack of shafts in the two karst areas also refers to this. However, the low degree of water inflow also indicates that only a small proportion of the cavities of the epikarst is filled with water and washed-in superficial deposit or if they are filled, it is of low degree. In areas of low specific resistance which also involve two areas (Table 2), the size of subsidence dolines is large (those with a diameter of 5-10 m and deeper than 2 m are frequent). The bedrock often crops out on doline floors and shafts also occur. For example, in the eastern part of Tés Plateau, surface karst is characterised by the followings. There are 19 dolines in the karst area of the eastern part of Tés Plateau. On the floor of 9 dolines, the limestone crops out and there are shafts in case of 8 dolines. The specific shaft length, which is the quotient of the shaft length and the vertical depth, is large (Table 2; Veress, 2019), which refers to a significant degree of cav- ity formation. The water catchment area of the dolines is large, creeks are often connected to them. Creeks, lakes that developed in depressions during rainfalls refer to in- tensive water inflows in these karst areas. The karst areas of the eastern part of Tés Plateau and Homód Valley, but also the area of Eleven-Förtés are areic. Thus, the mete- oric waters of these areas infiltrate into the karst, which results in significant water surplus in the epikarst. The large size of dolines, the great degree of water transport refers to significant suffosion, the low specific resistance, the large number of shafts and the high aver- age specific shaft length indicate a significant degree of cavity formation particularly on Tés Plateau. Here, there are 6 shafts, the depth of which exceeds 50 m, but the av- erage shaft depth is also 30.13 m (Veress, 2019). The high degree of shaft frequency and their large depth also refer to the maturity of the epikarst and according to Klim- chouk’s classification (2004) it is in the old epikarst phase regarding its maturity. Intensive infiltration increases the chance of the filling of cavities with water, while intensive suffosion results in a higher chance of the filling of the cavities with sediment at the epikarst of the area. Figure 7 describes the interpretation of the relation- ship between different specific resistances and the matu- rity of the epikarst. In the karst area of Mester-Hajag North and Fehérkő Valley marginal karst areas which are of high specific resistance, the quantity of waterless (dry), but unfilled cavities is large as compared to the proportion of cavities filled with water as well as to cavities which are waterless, but filled with sediment (Figure 7a). The reason for this is that because of lower water level, there are less cavities with water, but more dry cavities. This is caused by sur- face infiltration of lower degree, but less water arrives at the bedrock too because there are fewer cavities opening to the bedrock surface as a result of a lower degree of cav- ity formation. However, it is also contributed by the fact that in narrower (smaller) cavities, the degree of water level subsidence is higher even in case of the same quan- tity of water drainage than at wider cavities. The presence of cavities without superficial deposit is the result of suf- fosion of lower degree. The eastern part of Tés Plateau and the Homód Val- ley karst areas which are of low specific resistance, the MÁRTON VERESS, GYÖRGY DEÁK & ZOLTÁN MITRE ACTA CARSOLOGICA 52/2-3 – 2023254 proportion of cavities of the bedrock which are filled with water is larger than that of dry cavities, and also the proportion of dry, but filled cavities is larger as compared to that of unfilled cavities (Figure 7b). This can be ex- plained by the fact that because of the infiltration with larger degree and thus, due to the effect of more elevated water level, the number of cavities with water increases and the number of dry cavities decreases. However, an- other reason is that in wider cavities, the degree of water level decrease is lower than at narrower cavities even in case of the same degree of drainage. The degree to which dry cavities are filled increases due to a larger degree of suffusion (Figure 7b). The absolute value of specific re- sistances and the average of mean values ( ) refer to the degree and state of cavity formation, while the mean val- ue and the standard deviation indicate the expansion of the degree of cavity formation. In case of areas with low specific resistances and in case of low averages of mean values ( ), the degree of cavity formation is larger, while if the mean values and the standard deviation show a smaller difference from the average of mean values (), the degree of cavity formation is evener. The epikarst of more karstified areas has more cavi- ties and is more mature (Tés Plateau and its environs, Homód Valley). The epikarst of less karstified areas has less cavities and is less mature (Mester-Hajag North and Fehérkő Valley marginal area). A direct evidence for the degree of cavity formation of areas with high and low specific resistances is the different number of shafts and different specific shaft lengths. Different degree of cavity formation results in different doline frequency. Thus, for example in the area of Homód Valley, doline density is 0.6889 dolines/100 m2 due to the mature epikarst, while this value is only 0,0339 dolines /100 m2 in the area of Mester Hajag North which has a little quantity of water supply. In the area of Eleven-Förtés, although there is com- plete lack of surface runoff, specific resistance is higher than in the eastern part of Tés Plateau and in the area of Homód Valley. This is an evidence for the fact that water supply of high degree is not a sufficient condition for the development of low specific resistances of the bedrock. The different development age and different development rate of the epikarst may contribute to different specific resistances. Different development rate may be increased by the different degree of primary porosity (for example fracture density or the type of fractures). Different surface denudation may contribute to the development or activation of the epikarst with different duration. Mester-Hajag North and Fehérkő Valley mar- ginal karst areas are enclosed and bordered by valleys. In these areas, karstification may have become active by the thinning out of superficial deposits that took place during their partial transportation. Here, the present epikarst and may have developed from an inactive epi- karst preceding covering following a longer development break. However, in the karst area of the eastern part of the Tés Plateau and the karst area of Homód Valley, the thinning out of the cover is less intensive due to arheism (which did gradually develop by the already beginning karstification). Thinning out is local under the dolines because the superficial deposit is transported into the karst. Therefore, in the latter areas, the activation of for- mer epikarst (paleoepikarst) began earlier or it did not reach an inactive state at all. Average largest differences indicate anomalies of the epikarst zone. In case of great differences, there are sig- nificant differences in the degree of cavity formation and filling of the epikarst, while in case of small differences, the epikarst is more uniform. This value is the lowest in the eastern part of the Tés Plateau in spite of the fact that (while average specific resistance is the lowest in the THE VERTICAL ELECTRICAL SOUNDING (VES) OF THE EPIKARST: A CASE STUDY OF THE COVERED KARST OF THE BAKONY REGION (HUNGARY) Figure 7: Models of immature (a) and more mature (b) epikarst. Leg- end: 1. caprock, 2. bedrock, 3. frac- ture, bedding plane, 4. approxi- mate penetration of VES measure- ment, 5. water motion, 6. cavities, 7. water along the fractures and on the rock surfaces that border the bedding planes, 8. cavity parts that are filled with water, 9. cavity part filled with washed-in sediment, 10. piezometric surface, 11. doline. ACTA CARSOLOGICA 52/2-3 – 2023 255 MÁRTON VERESS, GYÖRGY DEÁK & ZOLTÁN MITRE Homód Valley area) although shafts separated the epi- karst into parts, they were not able to change the uniform image of the epikarst. All in all, it can be established that in case of mature epikarst with several cavities, the aver- age largest differences are small. In other words, during its development, the epikarst is more and more uniform even if it is separated into parts regarding its area. Even the subsidence dolines that were formed in the cover are not able to change it probably because their effect (wa- ter surplus, sediment transportation) prevails not only directly below them, but also in their environs. The rela- tively great difference value occurring at Homód Valley is notable. This refers to the fact that although the epikarst also receives a lot of water here, it is not as uniform as in the area of the eastern part of the Tés Plateau thus, it does not reach its maturity. The epikarst of the studied areas can be put into a development order based on the different degree of cov- eredness and on the exposure and infiltration that trig- ger coveredness as follows: Fehérkő Valley marginal area, Mester-Hajag North, Eleven-Förtés, Homód Valley area, and the eastern part of Tés Plateau. 6. CONCLUSIONS The epikarsts of various karst areas may be significantly different on the same karst (Bakony Region) since the epikarst of karst areas became differentiated during karstification. The epikarst of certain karst areas could stay in the early phase of its development, while the epikarst of other areas may reach a more mature stage. The epikarst of karst areas of lower specific resistance has more cavities, but at the same time these cavities may be filled to a larger degree, and surface karstifi- cation is more intensive. During its development, the epikarst has a more and more uniform face. Taking into consideration the different specific resistances and their statistical characteristics, the epikarst of the studied areas can be put into a development order. The specific resistance of the epikarst of more karstified ar- eas is lower, which can be traced back to the fact that during its penetration, the VES measurement reaches the piezometric surface. Thus, the areas with a greater degree of karstification have more cavities and the pi- ezometric surface is of higher elevation. In areas which were karstified to a lesser degree, the epikarst has less cavities and the piezometric surface is below the pen- etration depth of VES measurements or the epikarst is without water fill. Different maturity can be traced back to the fact that the epikarst of different part areas had different develop- ment onset, the epikarst sections became active differ- ently, and the development rate of epikarst parts was also different. The former can be explained by different expo- sure, the latter by different water supply, but the different primary porosity of certain areas may also contribute to this. Different water supply is controlled by surface run- off conditions and the composition of the cover. Since in the area of Homód Valley, where the specif- ic resistance is a bit lower than in the eastern part of Tés Plateau, low specific resistance values do not necessar- ily coincide with the abundance and maturity of features which directly represent karstification (for example the number of shafts is much higher on the Tés Plateau than in the area of Homód Valley. This refers to the fact that the average highest specific resistance values, which are lower on Tés Plateau than in the area of Homód Valley better describe the maturity of the epikarst of the karst than the average values of specific resistances. REFERENCES Bakalowicz, M., 2005. A challenge for new resources. 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