Veress Márton: A Bakony természettudományi kutatásának eredményei 23. - Covered karst evolution... (Zirc, 2000)

OBJECTIVES

leys become inactive. Except for superimposed ones, no valleys dissect the karst surface. Rapid denudation in the neighbouring areas lead to the isolation of karst regions as nondissected plateaus. Infiltrated rainwater may percolate downwards in the rocks until it reaches down to the level of the neighbouring terrain. Flowing sideways and impounded, this water creates the zone of flowing karst water. Its surface is the karst water table. Where flowing karst water issues, karst springs occur. If there are impermeable strata above the karst water table, another, higher-lying flowing karstwater zone may develop. The flowing karstwater approximately in the level of the neighbouring terrain is called middle karst water zone, while that in lower position is the deep karst water zone. The middle karst water zone in the Bakony Mountains is mentioned as „main karst water" since it is found in Triassic „Hauptdolomit" (main dolomite). In humid periods water may percolate downwards in the rock mass above the karst water table (descending karst water zone). As it was mentioned, there are covered and open karsts. In the first case, carbonate rocks are buried under non-karstic rocks, while in the latter, there is no sediment cover, only soil at most. The sediment cover is either impermeable (buried karst) or permeable (cryptokarst). In the Bakony Mountains open and covered karsts alternate. Buried karsts have gravel mantles, while cryptokarsts are loess-covered carbonate surfaces. Another way of classification of karst is by water budget and age. Allogenic karsts receive water from adjacent non-karstic areas, while authigenic karsts do not. If karstification took place earlier during Earth history, it is paleokarst. Recent (Holocene) karsts are either active or fossil features. (Naturally, all paleokarsts are fossil.) Karstic landforms are grouped as surface or underground features. All surface karst forms are undrained, either located on open or on covered karsts. The most common landform on open karst is the solution doline, a depression of variable size and bowl shape without water conduit. Solution dolines are formed directly below soils. There are several varieties. (If adjacent dolines merge, uvalas result.) Collapse dolines are not generated by solution but by the cave-in of cave ceilings. Ponors develop along rock boundaries of allogenic karsts since water-courses over nonkarstic rocks cut valleys and continue underground when reach the rock boundary. The valley terminates in a counterslope there (blind valley). At its terminal point a depression without drainage but with a water conduit to depth is created (ponor). In buried karsts, where the valley is inherited over the underlying carbonate rocks, a valley rock boundary with ponor develops. With progressing incision, the rock boundary is shifting towards the head valley. Accordingly, the site of ponor development is also shifting. The previously formed ponors are transformed into dolines-with-ponors. In cryptokarsts, the solvent percolating through the sediment cover dissolves carbonates and a deficit of matter is generated in or on the underlying rock. A corresponding depression is created on the surface. The dolines on covered karsts are grouped as follows. A superimposed doline is formed if the cover is a cohesive sediment. Due to its higher strength, this rock only fills the surface depression if the strength of the cover sediment is reduced by weakened support. Cover sediments move rapidly (collapse) and the resulting karst feature will have steep walls. A subsidence doline is created if the cover sediments are non-cohesive. Although there is only a minor deficit of matter in this case and the strength of the cover is so low that it cannot remain in its previous position. The increasing deficit of matter on or in the underlying sediment is compensated by per-