The Evolution and Development of Solution Dolines with Horizontal Growth and the Processes of Their Floors: A Case Study on the Plate-Shaped Dolines of the Bükk Mountains, Aggtelek Karst and P á dis Plateau

: This study investigated the evolution and development of plate-shaped dolines (depressions with a large diameter, small depth and plain ﬂoor) within the framework of a case study. For the determination of their morphological characteristics, the morphological parameters of 16 dolines were measured and calculated (their average values were compared to the parameter average values of the dolines of other doline types). Based on the data from the vertical electrical sounding measurements, the superﬁcial deposit and the morphology of the bedrock of six dolines were studied. It can be stated that the plate-shaped dolines increased in size by widening. They were formed at sites where the water drainage and material transport capacities of the epikarst of the bedrock ceased on doline ﬂoors, while the drainage and material transport took place at the margin of the dolines. Their genetic varieties were plate-shaped dolines with a karren, plate-shaped dolines with a drawdown doline, plate-shaped dolines with a subsidence doline, plate-shaped dolines without a drawdown doline and plate-shaped dolines with a partial doline.


Introduction
The aim of this study was to investigate and describe the characteristics, the evolution and the development of plate-shaped dolines of some study areas, the karstic features of their floors and the effects of these dolines on the geomorphic evolution of karsts.
The study of dolines of various types is an important area of karst research [1][2][3][4][5][6][7][8][9]. A variety of solution dolines is the plate-shaped doline, which is a flat-floored depression with a large diameter (80-200 m), according to Hevesi [10,11]. These dolines are widespread in the Bükk Mountains on Aggtelek Karst (Hungary) and on the Pádis Plateau (Apuseni Mountains, Romania), but they also occur in some karst areas of the Alps (for example the Asiago Plateau, Italy) and probably in other karst areas as well. The nature of their slopes changes during their growth. Primarily taking into consideration the lengths of the concave and convex slope sections compared to each other, the dolines may be categorised into four kinds [1]: doline widening at rim and base (the concave slope section is dominant), doline widening at the base (the concave slope section is dominant but the slope becomes steep during its development and the floor becomes plain), doline widening at the rim (the convex slope becomes longer compared to the concave slope, while the slope becomes gentle) and doline deepening but not widening (the length of the convex slope section increases compared to the concave section, while the slope becomes increasingly steeper).
According to their development, solution dolines may be categorised into either point recharge dolines, drawdown dolines or inception dolines [12]. Point recharge dolines develop in valleys inherited by the karst. Surface water inflow takes place in the developing proto caves, ensuring the transportation of both the surface water and the dissolved material, and thus, the deepening of the depression [12][13][14][15]. Inception dolines are formed where there is an impermeable bed close to the surface. Where the water gets through this, both the drainage and the transmission of the dissolved material will be concentrated. Therefore, depression formation takes place above this site [12]. Drawdown dolines develop during feedback processes [15,16]. In the epikarst, where drainage is accelerated, passages develop faster along the fractures (in the case of a subsoil karren [17,18]. The faster drainage that also takes place above these sites results in more intensive dissolution, and thus, the deepening of the developing depression will also be faster towards the increasingly more developed passages. Even more water arrives at the deepest point of the depression, which enhances the dissolution here, as well as the increase of secondary porosity in the epikarst. The growth of the secondary porosity of the epikarst makes the flow more intensive, which also contributes to the increase of dissolution at the deeper section of the doline and below it in the epikarst. The outlined development results in the fact that the doline floor (and the bedrock at the floor) will be increasingly deeper towards the center of the doline.
On a glaciokarst, different varieties of solution dolines are distinguished: giant solution doline (paleodoline), small-sized (recent) solution doline and a schachtdoline (a depression with a steep slope and flat floor that is small-sized and with a diameter and depth of some meters), but subsidence dolines and buried dolines also occur [5,[19][20][21][22][23].
The floor of various solution dolines may be covered not only by soil in large and small thicknesses but by nonkarstic cover too. In this case, covered (concealed) karstic dolines (subsidence dolines) are often formed on the cover [5,14,20,23,24].

Methods
Dolines have measurable and calculable parameters that were studied by several researchers [1,[25][26][27][28][29][30][31][32][33][34][35]. Bondesan et al. [30] distinguished 65 kinds of dolines. The size, morphology, occurrence, distribution, orientation and pattern of dolines can be described using these parameters (for instance, density, change in density, the closest neighbour). Measurable parameters can be determined using field measurements, maps or aerial photographs. In this study, such parameters were used, created (since plate-shaped dolines have partly different morphological characteristics from other dolines) and calculated, which are methods that are suitable for characterising and describing plate-shaped dolines, as well as comparing dolines belonging to other doline types. Geophysical methods are used to determine the composition of doline cover and to investigate their structure and morphology of their bedrock [24,[36][37][38][39][40]. Our methods are described below: On the Aggtelek karst in the Bükk Mountains on the Pádis and Asiago Plateaus, which were identified as plate-shaped dolines during field studies. These dolines were chosen and their topographic maps were created, where the maps were drawn at 1:250 or 1:500 scales and the contour lines were constructed at every 0.5 m or 1.0 m.
To determine the morphological characteristics of the plate-shaped dolines, the following parameters were measured and plotted on the topographic maps ( Figure 1): the longitudinal diameter of the doline (d d ), the longitudinal expansion of the plain doline floor (b d ), the largest elevation difference of the bottom (b ed ) and the length of its slope (s l ). Both the depth and the slope length were given and compared to the mound next to the doline and also to the margin of the doline. In the case of a doline where there was a karst saddle, the contact between the floor and the slope was given by the contour line that left the doline at the karst saddle. In the lack of a karst saddle, the contour line was determined by the line from where the contour line density is smaller towards the centre of the doline than towards the margin. The degree of the lack of the side slope was determined by the size of the angle at the centre of the floor (α). The centre point was taken at the cross point of the longest and ridge of the dividing wall (margin of the doline), (5) inner side slope of the dividing wall (side slope of the doline), (6) floor of the doline, (7) karst saddle, where bd-the longer diameter of the doline floor, pd-diameter that is perpendicular to the longest diameter, dc-centre of the doline floor, α1 and α2-angles expressing the expansion of the karst saddle, ddf-depth of the doline floor (apparent depth), dfb-depth of the doline (actual depth), Sl-length of the side slope of the doline, dd-the diameter of the doline along the longer axis, bed-the largest elevation difference of the floor, tsd-thickness of the superficial deposit, Vs-apparent shape, As-actual shape, P-plate shapedness value of the doline, Be-expansion of doline floor and Se-expansion of the side slope of the doline.
The vertical electrical sounding (VES) method was applied to determine the quality, the thickness and the structure of the superficial deposit. The method involved the following. During the VES measurement, an electric current was conducted into the rock through two grounded electrodes, where another two electrodes measured the strain that was created by the current dispersion. Curves were constructed from the measured strain values as a function of the distance between the current  (5) inner side slope of the dividing wall (side slope of the doline), (6) floor of the doline, (7) karst saddle, where b d -the longer diameter of the doline floor, p d -diameter that is perpendicular to the longest diameter, d c -centre of the doline floor, α 1 and α 2 -angles expressing the expansion of the karst saddle, d df -depth of the doline floor (apparent depth), d fb -depth of the doline (actual depth), S l -length of the side slope of the doline, d d -the diameter of the doline along the longer axis, bed-the largest elevation difference of the floor, t sd -thickness of the superficial deposit, V s -apparent shape, A s -actual shape, P-plate shapedness value of the doline, B e -expansion of doline floor and S e -expansion of the side slope of the doline.
The vertical electrical sounding (VES) method was applied to determine the quality, the thickness and the structure of the superficial deposit. The method involved the following. During the VES measurement, an electric current was conducted into the rock through two grounded electrodes, where another two electrodes measured the strain that was created by the current dispersion. Curves were constructed from the measured strain values as a function of the distance between the current electrodes, and based on these, the resistivity and thickness of the array of beds were determined. Matching the arrays of beds of different places and cross-sections (geoelectric-geological profiles) were constructed along the measurement lines.
The shape of the doline was calculated using the quotient of the longitudinal diameter and the depth. If the depth was given compared to the surrounding mound, the shape that was obtained in this way is presented in brackets in Table 1. The apparent shape (V s ) and the actual shape (A s ) were determined separately. In the case of the apparent shape, the depth was given compared to the doline floor (d df ) from the margin of the doline, while in the case of the actual shape, the depth was given compared to the bedrock of the floor (d fb ) from the margin of the doline. The calculation of the latter was possible at sites where the thickness of the cover (t sd ) was determinable with the help of the data of VES measurements and where the doline floor was uncovered (an average was calculated to the cover thickness for each doline). The value describing the extent to which a doline is plate-shaped (P) was determined using the quotient of the longer diameter of the doline and the longitudinal expansion of the floor. In addition, the expansions of the floors of the plate-shaped dolines (B e ) were also determined using the quotient of the floor-length and one of the slopes of the doline. The proportion of the expansion of the side slope of the plate-shaped doline with an incomplete side slope and the angle α (S e ) was given compared to the side slope of the plate-shaped doline with complete side slopes (which was regarded as a circle) (100%) in the following way: Based on the data of the VES measurements (this method is unsuitable for detecting the passages and shafts of the bedrock), geoelectric-geological profiles were constructed by the colleagues of Terratest Ltd. for three plate-shaped dolines in the Bükk mountains, one in Aggtelek, and two in Padis.
The average apparent shape values of the studied dolines were compared with the average apparent shape values of other temperate non-plate-shaped dolines (drawdown doline), namely, those of the giant dolines, schachtdolines and small-sized recent solution dolines of glaciokarsts. The average value of the plate-shapedness and average value of the floor expansion of the plate-shaped dolines and schachtdolines were compared to each other (schachtdolines were involved in the comparison because they have a plain floor too). In addition, the average size and shape values of the temperate drawdown dolines and those of the small-sized, recent solution dolines of glaciokarsts were compared to the average size and average shape values of the depressions occurring on the bedrock of the floor of plate-shaped dolines. Notice: In the cases with a number in brackets, when calculating the shape of the doline, the depth is given compared to the surrounding mound.

Research Sites
The locations of the research sites are presented in Figure 2.

Research Sites
The locations of the research sites are presented in Figure 2. The Bükk Mountains are part of the North Hungarian Mountains but structurally belong to the Alpaca Macrostructural Unit [41]. Its rocks are Carboniferous dolomites, limestones and shales, Permian sandstones and shales, Triassic limestones and subordinately Jurassic limestones, Middle-Triassic volcanic rocks, Oligocene clays and Miocene andesite [42,43]. The mountains have a nappe structure [42], where its central part is the Bükk Plateau with an 800-900 m elevation, which is divided by the Garadna valley in the Little Plateau in the north and the Great Plateau in the south.
Our research sites were located on the Great Plateau (its constituting rock is Triassic limestone) which were Fekete-Sár, Big Plateau and Nyavalyás-tető. Fekete-Sár is situated in the south-western part of the plateau, near Tarkő mound. Fekete-Sár was a soil-covered karst, where its karst features were located in a zone with an almost NS direction. Here, solitary but mostly coalesced (uvalas) drawdown dolines and plate-shaped dolines occurred adjacent to each other. Dolines representing a morphological transition between drawdown dolines and plate-shaped dolines were also common. In the southern part of the area, which was a polygonal karst at some sites, the dolines occurred on a plain surface in a summit position, while in its northern part, they were located on the floor of an epigenetic valley. The latter also coalesced with dolines of the valley margin position at some sites.
In the area of Big Plateau, plate-shaped dolines occurred in an irregular pattern, where some of them coalesced. These dolines were infilled to various degrees (covered karst and covered karst patches occur on their floor). This can be attributed to the fact that an epigenetic valley led to its area from the northern direction (probably a former blind valley with a ponor). On the floor of the plateshaped dolines with a covered floor, subsidence dolines also developed [44].
Only one plate-shaped doline (L6) was situated in a summit position on Nyavalyás Hill. This mound was also situated on the Great Plateau, on its northern part, between the valleys of Lusta and Garadna, whose terrain was soil-covered karst.
The Aggtelek Karst also belongs to the North Hungarian Mountains and is built up of Upper Permian-Lower Triassic, gypsum-anhydrite and Triassic carbonates [45]. The karst is part of the Szilice Nappe [46] and is separated into plateaus. Among them, the most elevated was Alsó Hill (the elevation of its surface is 450-550 m and its constituting rock is Triassic limestone), where one mound The Bükk Mountains are part of the North Hungarian Mountains but structurally belong to the Alpaca Macrostructural Unit [41]. Its rocks are Carboniferous dolomites, limestones and shales, Permian sandstones and shales, Triassic limestones and subordinately Jurassic limestones, Middle-Triassic volcanic rocks, Oligocene clays and Miocene andesite [42,43]. The mountains have a nappe structure [42], where its central part is the Bükk Plateau with an 800-900 m elevation, which is divided by the Garadna valley in the Little Plateau in the north and the Great Plateau in the south.
Our research sites were located on the Great Plateau (its constituting rock is Triassic limestone) which were Fekete-Sár, Big Plateau and Nyavalyás-tető. Fekete-Sár is situated in the south-western part of the plateau, near Tarkő mound. Fekete-Sár was a soil-covered karst, where its karst features were located in a zone with an almost NS direction. Here, solitary but mostly coalesced (uvalas) drawdown dolines and plate-shaped dolines occurred adjacent to each other. Dolines representing a morphological transition between drawdown dolines and plate-shaped dolines were also common. In the southern part of the area, which was a polygonal karst at some sites, the dolines occurred on a plain surface in a summit position, while in its northern part, they were located on the floor of an epigenetic valley. The latter also coalesced with dolines of the valley margin position at some sites.
In the area of Big Plateau, plate-shaped dolines occurred in an irregular pattern, where some of them coalesced. These dolines were infilled to various degrees (covered karst and covered karst patches occur on their floor). This can be attributed to the fact that an epigenetic valley led to its area from the northern direction (probably a former blind valley with a ponor). On the floor of the plate-shaped dolines with a covered floor, subsidence dolines also developed [44].
Only one plate-shaped doline (L6) was situated in a summit position on Nyavalyás Hill. This mound was also situated on the Great Plateau, on its northern part, between the valleys of Lusta and Garadna, whose terrain was soil-covered karst.
The Aggtelek Karst also belongs to the North Hungarian Mountains and is built up of Upper Permian-Lower Triassic, gypsum-anhydrite and Triassic carbonates [45]. The karst is part of the Szilice Nappe [46] and is separated into plateaus. Among them, the most elevated was Alsó Hill (the elevation Earth 2020, 1 55 of its surface is 450-550 m and its constituting rock is Triassic limestone), where one mound of its western, lower part is called Magas Hill. One of the uvalas of Magas Hill was a plate-shaped uvala marked Ag1, which was involved in this study.
Padis (Ponor-Bâtrina) is a plateau of the Bihor Mountains with an elevation of 1100-1400 m and dissected by mounds. The Bihor Mountains is a structurally autochthonous tectonic fenster [47]. It is built up of Triassic and Jurassic limestones and dolomites, Permian sandstones and metamorphic rocks [48]. Here, the research areas were the floors of the main partial doline (P3) of the large-sized Răchite and that of one of its tributary partial dolines (P3), which developed on the Triassic limestone Răchite as an uvala, which was surrounded by mounds and karst saddles of various elevations, and was constituted by a main and its surrounding tributary partial dolines. The karst saddle that bordered it from an eastern direction fit into its floor level since sedimentary cover with debris arrived there via fluvial transport and also at other parts of the plateau from the mass of Kék-Magura bordering the plateau from the east and was built up of sandstone. The lower terrain section of Padis, and thus, the floor of the main partial doline marked P1, were covered karst areas, while there were solution dolines on the surrounding mounds thus, which was a soil-covered karst. Similarly, the partial dolines at lower elevations that were connected to this large-sized depression, such as the tributary doline marked P3 (partial doline), became covered too. Several subsidence dolines developed on the floor of the main doline but also on the floor of its connecting tributary partial dolines [24].
The Asiago Plateau is situated between the Vald'Astico, Valsaguno and Brenta valleys in the Southern Alps. It is built up of Upper Triassic, Jurassic and Cretaceous limestones and is an autochthonous part of the Apulian Plate [49]. Our research area was on the lower, southern part of the plateau (below 1500 m), which was a solitary plate-shaped doline (marked as 1) on Triassic limestone.

Qualitative Characteristics of the Morphology of Plate-Shaped Dolines
The morphological elements of the dolines were the expanded and plain floors, as well as the short side slope, which was the part of the dividing wall (or threshold) that separated adjacent dolines in the case of those that occurred in clusters (Figures 3 and 4). Its most elevated part was the ridge. In the case of the dolines in a summit position, if they were widened enough, there was a circular, barrier-like mound that was arcuate similarly to the dividing wall. In this case, the dividing wall was narrow and its side slopes not only tilted toward the centre of the surrounded doline but also in the opposite direction, towards its surroundings. The ground plan of the dividing wall was arcuate and circular. It developed where the original terrain became narrow due to the widening of the surrounding dolines. The dividing walls were occasionally broken through (half dividing wall, half-threshold). Karst saddles developed at these sites; the same doline occasionally had several karst saddles when the dividing wall or the ridge was denuded at several sites. The dolines of valley margin position or the dolines with a hanging position of the uvalas were often not closed but rather open. In this case, the surface at the saddle exclusively tilted towards the valley or the depression to which the partial doline was connected. The roof level of the dividing walls was not plain, where it was occasionally dissected by mounds. These mounds developed during the local denudation of the dividing walls (the process may be of non-karstic origin too). Mounds occasionally occurred among several dolines (mounds between dolines or karst hills). These features were higher, more expanded and less elongated than the mounds of the dividing walls. Their ground plan was not arcuate, though their margins were parallel to the side slopes of the dolines. Their roof level was the relict landform of the original (preceding karstification) terrain. Earth 2020, 1, FOR PEER REVIEW 8 of 26   Depressions of two kinds may occur on the floor with a superficial deposit of plate-shaped dolines. One of them is a feature with a large diameter compared to its depth and has gentle side slopes, which is regarded as a compaction doline (see below). The other is a depression that is deep compared to its diameter and has steep walls; these are the subsidence dolines. Depressions of two kinds may occur on the floor with a superficial deposit of plate-shaped dolines. One of them is a feature with a large diameter compared to its depth and has gentle side slopes, which is regarded as a compaction doline (see below). The other is a depression that is deep compared to its diameter and has steep walls; these are the subsidence dolines.

Quantitative Characteristics of the Morphology of Plate-Shaped Dolines (Morphometric Characteristics)
The calculated parameters from the measured parameters of the studied dolines are shown in Table 1. Plate-shaped dolines and drawdown dolines cannot be undoubtedly distinguished from each other based on only their morphological characteristics since non-plate-shaped dolines may also have saddles and plain floors. A flat floor develops if the doline floor is filled up (pseudo-plate-shaped doline). Therefore, these dolines can be regarded as plate-shaped dolines, whose shape values are not smaller than the shape values of those dolines, which have a plain bedrock floor. During the study, there were two possibilities for the recognition of plate-shaped dolines.
A flat-floored doline being exposed in a natural way (such a doline was the doline marked as As1 in the Asiagó plateau, the shape value of which was 11.25; Figure 5) is regarded as a plate-shaped doline. This results in the fact that these dolines that are exempt from glacial erosion are plate-shaped dolines whose shape values are larger than the shape value of this doline.

Quantitative Characteristics of the Morphology of Plate-Shaped Dolines (Morphometric Characteristics)
The calculated parameters from the measured parameters of the studied dolines are shown in Table 1. Plate-shaped dolines and drawdown dolines cannot be undoubtedly distinguished from each other based on only their morphological characteristics since non-plate-shaped dolines may also have saddles and plain floors. A flat floor develops if the doline floor is filled up (pseudo-plateshaped doline). Therefore, these dolines can be regarded as plate-shaped dolines, whose shape values are not smaller than the shape values of those dolines, which have a plain bedrock floor. During the study, there were two possibilities for the recognition of plate-shaped dolines.
A flat-floored doline being exposed in a natural way (such a doline was the doline marked as As1 in the Asiagó plateau, the shape value of which was 11.25; Figure 5) is regarded as a plate-shaped doline. This results in the fact that these dolines that are exempt from glacial erosion are plate-shaped dolines whose shape values are larger than the shape value of this doline. Out of the flat-floored dolines that were demonstrated as such using VES measurements, the doline that had the smallest apparent shape value was regarded as relevant when we chose the dolines. Among the flat-floored dolines that were investigated using VES measurements, the doline marked N11/a (Bükk Mountains) had the smallest apparent shape value, which was 13.86 (Table 1).
The shape values of the two dolines that were chosen based on the two principles were close to each other (which strengthened the objectivity of the choice). It can be seen that the apparent shape values of all the dolines that qualified as plate-shaped dolines were larger than the apparent shape values of the above-mentioned dolines.
Based on the parameters of the chosen plate-shaped dolines, it can be stated that this doline type was characterised by a large average apparent shape (33.04). However, even the average of the actual doline shapes was large (23.11). Similarly, the value of the floor expansion was large (6.41) and the value of the plate-shapedness was small (1.59). The shape was large because the depth of the dolines was small compared to their diameter. The reason for the large value of the floor expansion was that the floor was dominant compared to the length of the side slope, while the cause of the low value of the plate-shapedness was that the expansion of the flat floor was approximately the diameter of the dolines. The plain nature of the floor was proved by the low values of the largest elevation differences within the floor (average 1.03 m). However, not only was the floor with the superficial deposit or Out of the flat-floored dolines that were demonstrated as such using VES measurements, the doline that had the smallest apparent shape value was regarded as relevant when we chose the dolines. Among the flat-floored dolines that were investigated using VES measurements, the doline marked N11/a (Bükk Mountains) had the smallest apparent shape value, which was 13.86 (Table 1).
The shape values of the two dolines that were chosen based on the two principles were close to each other (which strengthened the objectivity of the choice). It can be seen that the apparent shape values of all the dolines that qualified as plate-shaped dolines were larger than the apparent shape values of the above-mentioned dolines.
Based on the parameters of the chosen plate-shaped dolines, it can be stated that this doline type was characterised by a large average apparent shape (33.04). However, even the average of the actual doline shapes was large (23.11). Similarly, the value of the floor expansion was large (6.41) and the value of the plate-shapedness was small (1.59). The shape was large because the depth of the dolines was small compared to their diameter. The reason for the large value of the floor expansion was that the floor was dominant compared to the length of the side slope, while the cause of the low value of Earth 2020, 1 59 the plate-shapedness was that the expansion of the flat floor was approximately the diameter of the dolines. The plain nature of the floor was proved by the low values of the largest elevation differences within the floor (average 1.03 m). However, not only was the floor with the superficial deposit or with soil almost flat or had a low inclination but the bedrock did too. This was shown by the profiles (Figure 6) but also by the fact that the distance between the two subsidence doline groups of Răchite (which were situated along the tracks of the profiles marked I-I' and VII-VII') was 100 m, while the elevation difference of the bedrocks of the two sites was only 7-11 m.
Earth 2020, 1, FOR PEER REVIEW 11 of 26 with soil almost flat or had a low inclination but the bedrock did too. This was shown by the profiles (Figure 6) but also by the fact that the distance between the two subsidence doline groups of Răchite (which were situated along the tracks of the profiles marked I-I' and VII-VII') was 100 m, while the elevation difference of the bedrocks of the two sites was only 7-11 m. Compared to other doline types, it can be stated that the average apparent shape value of the plate-shaped dolines was the largest (Table 2). Even their actual average shape values were larger than the average apparent shape values of other dolines belonging to other types of solution dolines. Among the solution doline types, schachtdolines have the lowest average apparent shape value (1.45) ( [5], Table 2). The apparent average shape value of plate-shaped dolines was double the apparent average shape value of the old, giant dolines that were widened by glacial erosion. Other parameters of the plate-shaped dolines can only be compared with those of the schachtdolines because this doline type also has a plain floor. According to the data of Table 2, the average value of the plate-shapedness of schachtdolines (2.30) was close to the average value of the plate-shapedness of plate-shaped dolines (1.59). This was possible not because of the expansion of the flat floor but because schachtdolines have steep slopes and therefore their diameter and floor hardly differ from each other Compared to other doline types, it can be stated that the average apparent shape value of the plate-shaped dolines was the largest (Table 2). Even their actual average shape values were larger than the average apparent shape values of other dolines belonging to other types of solution dolines. Among the solution doline types, schachtdolines have the lowest average apparent shape value (1.45) ( [5], Table 2). The apparent average shape value of plate-shaped dolines was double the apparent average shape value of the old, giant dolines that were widened by glacial erosion.
Other parameters of the plate-shaped dolines can only be compared with those of the schachtdolines because this doline type also has a plain floor. According to the data of Table 2, the average value of the plate-shapedness of schachtdolines (2.30) was close to the average value of the plate-shapedness of plate-shaped dolines (1.59). This was possible not because of the expansion of the flat floor but because schachtdolines have steep slopes and therefore their diameter and floor hardly differ from each other in size. However, the expanded nature of the floor was significantly different: in the case of plate-shaped dolines, this value was 6.41, while it was 0.85 in the case of schachtdolines. The reason for the significant difference was that in the case of schachtdolines, because of their relatively large depth, the length of their side slopes was similar to the value of the diameter of the floor and could even exceed it. However, in the case of the plate-shaped dolines, the expansion of the floor significantly exceeded the length of the side slope as a result of the small depth.

The Characteristics of the Bedrock and Superficial Deposits of Plate-Shaped Dolines
The plain bedrock ranged from non-dissected and hardly dissected ( Figure 6) to dissected to a large degree (Figures 7 and 8). Shafts and depressions occurred on the bedrock. A shaft was seen on the floor of the plate-shaped doline marked N-13 (Bükk Mountains), where a shaft can be seen that opened up to the surface with a superficial deposit. Bedrock depressions with plate-shaped dolines of various shape values are shown in Table 3. The shape of the bedrock depressions could be large (average shape is 15.33) and small (average shape is 5.32) compared to the shape of the doline marked As1 (shape 11.25). There were subsidence dolines (Figures 7 and 8) on the cover above the small-shaped depressions, but their lack was also possible ( Figure 9). Among the 14 studied depressions with a small shape value, there were 8 above which there was a subsidence doline on the cover. Among the depressions with a large shape value, there were depressions whose margins coincided with the margin of the bearing depression, where the partial depressions were separated from each other by a dividing wall. An example of this is the plate-shaped uvala at Magas-tető ( Figure 10).      boundary, (10) subsidence doline, (11) large-sized depression on the bedrock with the identification code and (12) inner depressions of the large-sized depression with the identification codes.  At profile VII-VII', d1/1 and d1/2 were on the floor of the doline marked d1, where the subsidence dolines occurring here were taken into consideration at the dolines marked d1/1 and d1/2. Average 1: Average of the depressions in the cases where the shape was smaller than at the doline marked As1. Average 2: Average of depressions in the cases where the shape was larger than at the doline marked As1 (when calculating the average, the doline marked d3 in profile B-B' and the doline marked d4 in profile P1 I-I' of Magas Hill were left out).
The superficial deposits covering the floor of the plate-shaped dolines could be lenticular ( Figure 6) and bedded (Figures 7-10). The structure of the bedded superficial deposits could be the following:

•
The lower and upper surfaces of the beds were not parallel to each other. In this case, the upper surface of the bed was inclined (right part of Figures 9 and 10) or horizontal (the middle bed of the left part of Figure 9). When the upper surface of the bed was inclined, although the lower surface of the bed was also inclined, the two surfaces were not parallel to each other. The lower surface adjusted to the surface of the bearing depressions or to the incurved surface of the bedrock.

•
The surfaces of the beds were not inclined, i.e., the beds were horizontal (the uppermost bed of the left part of Figure 9).

•
The lower and upper surfaces of the beds were parallel but the beds were inclined (Figures 7 and 9).

•
The two structures could also occur together: An incurved cover layer was deposited on the inclined upper surface of the bedrock. The incurvation of the cover layer filled in the depression that developed due to the incurvation of the bedrock layer. The lower surface of the latter was inclined to a larger extent than the upper (Figures 7 and 8).   The superficial deposits covering the floor of the plate-shaped dolines could be lenticular ( Figure  6) and bedded (Figures 7-10). The structure of the bedded superficial deposits could be the following: • The lower and upper surfaces of the beds were not parallel to each other. In this case, the upper surface of the bed was inclined (right part of Figures 9 and 10) or horizontal (the middle bed of the left part of Figure 9). When the upper surface of the bed was inclined, although the lower surface of the bed was also inclined, the two surfaces were not parallel to each other. The lower surface adjusted to the surface of the bearing depressions or to the incurved surface of the bedrock.

•
The surfaces of the beds were not inclined, i.e., the beds were horizontal (the uppermost bed of the left part of Figure 9).

•
The lower and upper surfaces of the beds were parallel but the beds were inclined (Figures 7  and 9).

The Development of the Plate-Shaped Dolines
The dolines did not deepen if their floor reached an impermeable bed or the level of the local base level of erosion. Below the floor of the studied dolines, there was no impermeable bed and they were situated high above the local base level of erosion. Therefore, the flat floor of the plate-shaped dolines could only develop and survive if no dissolution occurred on the doline floor. However, if there was a local depression on the flat floor, local dissolution must have happened. However, the large diameter proved that the side slopes were dissolved.
Therefore, the morphology of the plate-shaped dolines (thus, their plain floor) and their morphological parameters (for example, their large shape) proved that the growth of these dolines took place via widening. Thus, these were dolines that arose from doline widening of a base type with a small depth. However, according to the data of Table 1, the shape values of the plate-shaped dolines were significantly different from each other. This refers to the fact that the growth of the diameter was of various intensities in the case of different dolines. The degree of widening depended on the duration and intensity of the dissolution and on the morphological environment; it depended on this latter factor since the lateral growth of the doline was limited, for example, it was located on the valley floor, where its widening was restrained because the slope reached the valley side during its retreat.
Regarding the nature of the doline development, the plate-shaped dolines and the schachtdolines represented two extreme methods of doline growth: plate shaped dolines widen and do not deepen (or it is only characteristic of their development for a short time), while the schachtdolines deepen but do not widen.
As a result of their extreme widening, the plate-shaped dolines may have been of various maturities. Thus, the juvenile, mature and destroyed plate-shaped dolines could be distinguished. Disregarding the solitary dolines of the plain terrains, juvenile plate-shaped dolines constituted an uvala and they had a karst saddle. The mature plate-shaped dolines had a dividing wall and a surrounding mound. The dividing walls of the destroyed plate-shaped dolines were denuded and only some larger and smaller mounds could survive from them around their flat floor.
However, the different shape values of the plate-shaped dolines also referred to the fact that they could have deepened at the beginning of their development. Thus, in the case of the main partial doline marked P1 of the Răchite uvala, a large depth (22.00 m and 24.98 m) was associated with a large shape (45.00), while in the case of the doline marked Fs2, a small depth (2.00 m) was associated with a large shape (40.00) ( Table 1). Thus, there was a more significant deepening at the former doline than at the latter. In the case of dolines with the same or almost the same depth, the slope length could be different. For example, in the case of the tributary partial doline marked P3, the depth was 4.00 m and the slope length was 12.60 m, while in the case of the doline marked Fs10, the depth was 4.50 m and the slope length was 20.00 m. In the case of the same or nearly the same depth, the slope length was different because the steepness of the two slopes was different. This refers to the slope retreat of various types. The shorter slope became increasingly steeper during its retreat. Such a slope development could occur at dolines that were infilled to a larger degree for a shorter or longer time. The fill favoured horizontal dissolution since the water was transported to the side slope of the doline through the fill, and thus, the lower part of the slope that was covered by sediment was dissolved to a larger degree ( Figure 12). The slope becomes steeper and shorter during its retreat. Horizontal dissolution was less effective on the slopes of dolines that were filled to a lesser extent, where the slopes were dissolved uniformly across their whole length by subsoil dissolution. Therefore, they shortened to a lesser degree or possibly lengthened ( Figure 12).
Karst features may widen due to horizontal dissolution, such as with kamenitzas or poljes [50]. The horizontal dissolution in dolines and its resulting doline widening were demonstrated by ZÁMBÓ [51,52] and ZÁMBÓ, FORD [53]. According to them, this takes place when the grains of the clayey cover of the doline become swollen during the absorption of water and the sediment becomes impermeable. Thus, the water of the cover arrives at the side slope of the doline during a horizontal seepage and it produces a dissolution capacity there.
In epikarsts, the secondary porosity is 10-30%, while in the vadose zone, it is lower than 2% [18,54]. The drainage is either too fast as a result of its great porosity or it is slow (for example, because of the infilling of the cavities of the epikarst) such that no drawdown dolines are formed [15]. Thus, where the epikarst is absent or it is weakly matured, the doline does not deepen and no drawdown doline develops. Therefore, no drawdown dolines are formed on gypsum where there is no epikarst [55,56]. If the epikarst is locally absent, no deepening occurs. A condition of the drawdown doline development is that there must be water storage in the epikarst [18] and the surface of the water stored in the epikarst must form a depression [16]. If the epikarst does not transmit water and dissolved material (inactive epikarst), the dolines do not deepen since even if dissolution takes place on the doline floor, the dissolved material is not transported away from this place. However, if the epikarst is active in the environment of the doline (the dissolved material may be transported into the karst), the doline may widen. Active, well-developed epikarsts can develop on well-karstified rocks. Thus, it is not surprising that the investigated plate-shaped dolines developed on well-karstified, Triassic limestones. The above-mentioned factors together cause the doline to develop into a plate-shaped doline. An inactive epikarst may develop directly (the transmission of the epikarst ceases) or indirectly (no water with dissolution capacity arrives at the epikarst). A direct cause may be if, for example, the passages of the epikarst become filled with a washed-in superficial deposit [24,51], and thus, they do not transmit water. This can be triggered by the degradation of the vegetation of the doline slope because, at this time, the denudation of the soil and the superficial deposit may rise, which increases the chance of the plugging of the passages of the epikarst. A possible indirect cause occurs when the dissolution of the bedrock is hindered by the cover because it is impermeable [57] or there is percolation through the cover, but saturated water arrives at the bedrock) [5,23,24,51,57]. However, an indirect cause may occur when the infiltrating water does not reach the bedrock since the superficial deposit is thick and stores water [57] or the capillary porosity is great in the superficial deposit (in this case the superficial deposit is fine grained) because, in this case, the water motion is horizontal [58]. Karst features may widen due to horizontal dissolution, such as with kamenitzas or poljes [50]. The horizontal dissolution in dolines and its resulting doline widening were demonstrated by ZÁMBÓ [51,52] and ZÁMBÓ, FORD [53]. According to them, this takes place when the grains of the clayey cover of the doline become swollen during the absorption of water and the sediment becomes Therefore, the widening of plate-shaped dolines is only possible if water drainage takes place at their margins (this ensures the transport of the material being dissolved at the slopes into the karst) at the same time the epikarst directly or indirectly loses its activity in the area of the doline floor parts becoming exposed during the retreat of side slopes. The development of the plain floor is the result of two processes: the retreat of the side slope and the lack of deepening on the floor that developed during the process. The widening of the doline may happen in two ways. If the epikarst is inactive because the bedrock is unable to transmit water (inactive epikarst developing directly) into the karst, but there is no cover on the doline floor, then the widening of the doline also takes place without horizontal dissolution, and thus the side slope retreats parallel with itself and becomes gentle during subsoil dissolution (Figure 13. If horizontal dissolution takes place because there is a cover on the floor and the stored water moves laterally (inactive epikarst developing indirectly), the side slope of the doline becomes increasingly steeper during the widening of the doline. Both types of slope denudation may occur together. In this case, horizontal dissolution occurs on the lower part of the side slope that is covered with superficial deposits, while subsoil dissolution takes place on its upper, uncovered section ( Figure 13). deposit may rise, which increases the chance of the plugging of the passages of the epikarst. A possible indirect cause occurs when the dissolution of the bedrock is hindered by the cover because it is impermeable [57] or there is percolation through the cover, but saturated water arrives at the bedrock) [5,23,24,51,57]. However, an indirect cause may occur when the infiltrating water does not reach the bedrock since the superficial deposit is thick and stores water [57] or the capillary porosity is great in the superficial deposit (in this case the superficial deposit is fine grained) because, in this case, the water motion is horizontal [58].
Therefore, the widening of plate-shaped dolines is only possible if water drainage takes place at their margins (this ensures the transport of the material being dissolved at the slopes into the karst) at the same time the epikarst directly or indirectly loses its activity in the area of the doline floor parts becoming exposed during the retreat of side slopes. The development of the plain floor is the result of two processes: the retreat of the side slope and the lack of deepening on the floor that developed during the process. The widening of the doline may happen in two ways. If the epikarst is inactive because the bedrock is unable to transmit water (inactive epikarst developing directly) into the karst, but there is no cover on the doline floor, then the widening of the doline also takes place without horizontal dissolution, and thus the side slope retreats parallel with itself and becomes gentle during subsoil dissolution (Figures 13. If horizontal dissolution takes place because there is a cover on the floor and the stored water moves laterally (inactive epikarst developing indirectly), the side slope of the doline becomes increasingly steeper during the widening of the doline. Both types of slope denudation may occur together. In this case, horizontal dissolution occurs on the lower part of the side slope that is covered with superficial deposits, while subsoil dissolution takes place on its upper, uncovered section ( Figure 13). The higher the value of biogenic CO 2 in the water, the more intensive the denudation of the dolines slopes. Therefore, the macroorganisms and microorganisms of the doline floor and doline slope that produce CO 2 affect the dissolution intensity, and thus, the intensity and degree of the doline widening.
If such dolines are close to each other on the floor of the inactive epikarst, but it is active on their side slopes, the dolines that are not deepening but widening may coalesce during the retreat of the slopes. The so-developed plate-shaped doline has a not completely flat floor since it is dissected by the remnants of the partial dolines ( Figure 10).

Processes on the Floor of Plate-Shaped Dolines
The processes of the floor of plate-shaped dolines extend to the bedrock and the cover. The processes of the bedrock and the cover often cause each other's conditions or one of them is the cause of the other. The depressions of the bedrock develop via dissolution. Dissolution processes may create the following types of bedrock depressions.
A depression with a large shape, whose margins coincide with the margin of the bearing depression and that has a dividing wall are former plate-shaped dolines that have coalesced. Such partial dolines can be seen in Figure 10. Here, the plate-shaped uvala probably developed via the coalescence of four partial plate-shaped dolines. The shape value of a partial plate-shaped doline is lower than the shape value of an uvala that was formed by coalescence (Tables 1 and 3).
Depressions that also have a large shape but are located inside the bearing depression are plate-shaped dolines (inner, floor dolines). Finally, small-shaped bedrock depressions are drawdown dolines. This is proved by the fact that their actual average shape is similar or smaller than the apparent shape of temperate drawdown dolines. However, their drawdown doline character is also proved by the subsidence dolines situated on the cover above them since subsidence dolines may be formed by the fact that, at these depressions, the superficial deposit was transported into the karst. This is only possible because there are shafts on the floor of these depressions. The presence of the shaft is a characteristic feature of a drawdown doline (at depressions, where there is no subsidence doline, the shaft may be narrow and/or it is filled with superficial deposits). These depressions of the bedrock are due to a local dissolution for a shorter or longer time. Thus, an epikarst will be locally active at these sites.
The composition, structure and stratigraphy of the cover, as well as the morphology of the surface with superficial deposits, indicate the development method of the superficial deposit on the doline floor and the characteristics of its transport into the karst.
In the case of an unbedded sediment (Figure 6), the material of the cover was formed for a longer period and it was not formed during a material transport of fluvial origin. This sediment is weathering residue or of airborne dust origin. The sediment did not subside either during its accumulation or subsequently such that its structure did not change and no subsidence doline developed on its surface. The material of the cover was not transported into the karst.
The cover was bedded sediment (Figures 7-10) that developed during the transport of material of a fluvial origin. The surfaces of the beds being inclined at their upper part may have developed in two ways: the material of the bed compacted or a part of the material was transported into the karst. Compacted inclined surfaces are situated at partial dolines ( Figure 10) but may be found at some drawdown dolines that the floor position where there is no subsidence doline on the surface. The shaft of the latter probably becomes plugged early. Therefore, if there was any material transport from these bedrock depressions into the bedrock (and in this case, the inclined bed surface did not develop via material compaction, but it was formed via material loss), no subsequent material transport took place, only compaction occurred. The beds were horizontal at their upper part or horizontal beds developed from the cessation of material transport onwards or following compaction (Figure 9). In the case of the plate-shaped dolines ( Figure 11) where there was an inner floor depression (compaction doline) that developed during the compaction of the sediment of the floor, this did not become filled since no sediment from its environment arrived at the doline at all or following compaction.
Where the upper surface of the bed is inclined without a horizontal bed (or a bed with a horizontal surface at least at its upper part) but the inclined surface forms a subsidence doline and there is a drawdown doline below it, the bed lost one part of its material in such a way that it was transported into the karst. Where the bed is inclined above the drawdown doline and there is a subsidence doline here, material loss developed in the bedrock layer below this bed (also during transportation into the karst) and this bed subsided into the space caused by material loss (which was formed with the incurvation of the upper part of the latter bed). The upper surface of the cover bed above the drawdown doline may also be inclined to a lower degree than its lower surface (Figure 8).
Subsidence dolines develop at incurved bedding planes or incurved beds if these surfaces are at ground level. Subsidence dolines may also be formed in a way that the lower bed loses sediment, into which the upper is bent into (Figure 7) or the upper bed loses its sediment and maybe becomes partially compacted (Figure 8).

Genetic Types of Plate-Shaped Dolines
Taking into consideration the morphology of plate-shaped dolines, different varieties developed during their development in the studied areas, which were the following.
Karren plate-shaped doline ( Figures 5 and 13b1): Water drainage and material transport regenerated in the epikarst situated below the whole doline floor. As a result of homogenous water drainage, the bedrock was affected by the karren formation (this increased the chance of the plate-shaped doline to be transformed into a drawdown doline). The karren features forward the superficial deposit into the karst. The bedrock may become exposed if all the superficial deposit (soil) is transported into the karst [59].
Plate-shaped doline with a drawdown doline (Figures 6-9 and Figure 13b2-c1): Water drainage and material transport in the epikarst under the doline floor regenerate only locally. On its bedrock, drawdown dolines may develop but no subsidence dolines are formed on the cover since the regeneration of the epikarst has a short duration. Because of this, the shafts are probably not mature either. Thus, they become plugged quickly; therefore, there is no material transport from the cover, or if it occurs, it is limited. If a subsidence doline does develop, it is destroyed rapidly; since its drainage partially decreases, it becomes filled and then covered (Figure 9).
Plate-shaped doline with a subsidence doline (Figures 7, 8 and 13c2): Water drainage and material transport regenerate locally in the epikarst below the doline floor and this may be long-lasting. The depressions of the bedrock are drawdown dolines. Above them, on the cover, there may be subsidence dolines or they may be absent. At sites, where they are absent, the shafts of bedrock depressions become plugged. Since the superficial deposit is transported into the karst through shafts [13], subsidence dolines develop above drawdown dolines, where the shafts of the latter are not plugged. The sediment-forwarding shafts of the drawdown dolines of the bedrock may also become filled, their sediment-forwarding capacity disappears and the surface depressions become inactive and turn into shallow, marshy depressions (such features commonly occur in the area of Răchite). Subsequently, if they are reactivated, newer subsidence dolines are formed on the surface.
Plate-shaped doline without a drawdown doline (Figure 13a,d): The epikarst of the bedrock of the plate-shaped doline is inactive, where its water drainage and material transport do not regenerate. Thus, no drawdown dolines develop on the bedrock.
Plate-shaped doline with a partial doline: In the beginning, the epikarst is active on the floor of partial dolines and it later becomes inactive, while it is active on its side slopes for a short or long period. The plate-shaped doline develops via the coalescence of partial dolines (Figures 6 and 10).

Conclusions
Plate-shaped dolines with a large diameter and a flat floor develop from drawdown dolines if there is no dissolution on the floor but there is horizontal dissolution. The lack of floor dissolution can be explained by the lack of material transport from the surface of the bedrock due to an inactive epikarst.
Since plate-shaped dolines have a large diameter, their development in a karst area increases the chance of uvala formation. Their presence locally favours the planation of the karst area. Plate-shaped dolines develop as a result of the interaction of dolines, the epikarst below them and the environment (for example, inward sediment transport). Since their floor is flat, no significant dissolution takes place there. As an active epikarst is necessary for the material transport from the surface of the bedrock, they are formed at sites where the epikarst is inactive on the doline floors, while it is active in its environment. An inactive epikarst may be formed directly (the cavities of the epikarst are filled with washed-in superficial deposits) or indirectly (the water of the cover does not reach the bedrock or it arrives there in a saturated state). The development and morphology (the steepness of its side slope) of the doline is affected by whether the epikarst is indirectly or directly inactive. In the case of a directly inactive epikarst, the doline widens via subsoil dissolution, while in the case of an indirectly inactive epikarst, it widens via horizontal dissolution.
According to the data from investigations in the studied areas, genetically plate-shaped dolines could be those with karren dolines, with drawdown dolines, with subsidence dolines and without drawdown dolines or plate-shaped dolines with partial dolines. The morphology of the floor was caused by the lack of dissolution there or to its temporary appearance, which was interpreted via the various activities of the epikarst. According to this, below the floor of plate-shaped dolines, the water drainage and material transport of the epikarst regenerated; below the floor of plate-shaped dolines with drawdown dolines, this regeneration was local and of short duration; below the floor of plate-shaped dolines with subsidence dolines, the regeneration was local but long-lasting; below the floor of plate-shaped dolines without a drawdown doline, the epikarst did not regenerate at all. Plate-shaped dolines with partial dolines did not deepen since the epikarst lost its activity at the floor of partial dolines. However, the epikarst was active on their side slopes, and thus, the dolines coalesced via widening.
Since according to field data in the studied areas, drawdown dolines and plate shaped dolines (and their clusters) occurred adjacent to each other on the karst, the patches of active and inactive epikarsts had various expansions and patterns in these karst areas at a given time. The patterns of the drawdown doline and plate-shaped doline groups and their expansion on the karst indicated the former or current patterns of active and inactive epikarsts and the expansion of active and inactive epikarst patches.
The local activation of the epikarst may have resulted from the development of floor drawdown dolines with subsidence dolines above them in the studied areas where there waere superficial deposits on the floor of the plate-shaped dolines. Subsidence dolines contributed to the transport of the superficial deposit of plate-shaped dolines into the karst. The lack of subsidence dolines and the horizontal beds covering the drawdown dolines of the bedrock was due to the early plugging (or weak maturity) of the shafts of these dolines, and thus, to the blocking of the transportation of the superficial deposit into the karst. However, the presence of subsidence dolines indicated mature shafts in them and an active material-forwarding capacity.
According to the evidence of the presented profiles, the drawdown dolines with a floor position of plate-shaped dolines may have developed into uvalas; if an epikarst was active between them, an inner, floor plate-shaped doline could be formed. At these sites, the surface of the karst could be locally denuded with a small thickness at several levels via dissolution. During this process, older levels were increasingly used up. The joint occurrence of plate-shaped dolines and drawdown dolines show that in the studied areas, planation and vertically dissected surface sections possibly occurred on the karsts adjacent to each other.
Funding: This research received no external funding.