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

METHODS

from water-courses leaves through conduits which form in the zone of flowing karst water. Pseudobathycapture occurs along hidden rock boundaries (where limestone karstifies under cover sediments). In this case, water is conducted through chimneys created by water infiltrating from the surface through cover sediments and opening onto the valley floor (see below). According to HEVESI (1980), bathycapture (in our classification: true bathycapture) can occur if the rate of karst water table subsidence exceeds the rate of valley incision. The valley floors of the study area, however, are in a hanging position above the karst water table and, to author's present knowledge, no recent bathycapture exists. A possible way of resolving this contradiction is to consider the type of superimposed valley and the altitude of the floor of the superimposed valley and of the upper limit of the cavitation zone (ie. the highest karst water table existed to date). Then the following cases can be distinguished. - At the beginning, the karst water table is found at the elevation of the valley floor (syngenetic or postgenetic valley). Because of the more rapid subsidence of the karst water table the cavities in the flowing karst water zone develop into water-conducting passages and true bathycapture takes place. True bathycapture can occur when the karst water table was close to the surface of carbonate rock at the beginning of karstification and the inheritance of the superimposed valley happens in an early stage of geomorphic evolution. There is no such a geomorphological and hydrological situation in the mountains, in the initial stage of the present karstification period, however, it occurred in several isolated spots (eg. on the Tés Plateau, Som Hill and Hajag). The valley floor ponors formed by bathycapture have filled ap and fossilized by now. - Superimposed valleys have not yet inherited over the surface or only partly (postgenetic valley) but valley floors are subsequently partly lined with cover sediments. Valley incision has stopped or slowed down considerably. The valley floor does not reach the cavitation zone of the flowing karst water zone. The water collected and running off on the valley floor may trigger karstification where cover sediments are thinning out (chimney development). From the intermittent or permanent water-courses of valley sections, water infiltrates into covered karst depressions (pseudobathycapture). The developing superimposed valleys of the mountains belong to this type. The developed varieties of pregenetic valleys could have reached cavities of former karst water. At that time subsequently exposed cavities could occur in the valley side. On the valley floor, however, there were no bathycapture sites since in the active period of rapid valley incision potential conduits may have been destroyed (see below) or by the time bathycapture could occur, the valley had lost its water-course. JASKÓ (1961) observed how water conduits are eroded. He describes a crack in the channel of the Vörös János-séd which tapped the water-course entirely (at 50 litres per minute discharge). There the upper part of the ponor funnel have been eroded entirely or could not form at all because of channel deepening. The lower part, the water conduit, could take shape and it can function as a ponor to some degrees. Bathycapture, however, is interrupted here as with lack of a surface depression the water-course overflows the site. Probably bathycapture can only be complete if a surface depression can form and more water is collected by the conduit, the passage can develop more quickly and the surface depression can widen. (Bathycapture is most probably the result of a positive feedback mechanism.) Bathycapture cannot happen if the cavitation zone lies close to the surface but it is of limited vertical extension. (Due to the periodically more intensive subsidence of the karst water table a new cavitation zone develops in greater depth or the evolution of a contiguous zone is hindered by the intercalation of impermeable strata.) In this case the incising