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

KARSTIFICATION

Fig. 24. Types of wallow (modified after VERESS 1998) Legend: 1. limestone; 2. unconsolidated cover sediment; 3. present-day valley floor; 4. previous valley floor; 5. surface karst feature with water conduit; 6. wallow; 7. asymmetric hidden rock boundary; 8. symmetric hidden rock boundary; a. development of ponor-type wallow in blind valley (a,, initial stage; a

2

. present stage); b. development of ponor-type wallow in valley (b

r initial stage; b

r present stage); c. development wallow of doline-with-ponor type within pseudodepression The wallow is regarded an inactive and completely fossilized karst feature with the formation of a secondary basin in the sediment fill, to the effect of various geochemical processes. The conditions of these processes are created by the buried karst feature. Wallows may evolve from syngenetic covered karst ponor (ponor-type wallow) but also from postgenetic karst features (Fig. 24). The wallows of doline-with-ponor type are the most common (Picts. 24, 25), which include wallows of pseudoponor type. Phenomena of karst depression activity The further evolution, sediment transport and thus fossilization and environmental impact of covered karst depressions primarily depends on their water budget. The phenomena related with the water budget of depressions are called phenomena of activity (VERESS 1987a). During its activity the karst depression receives water recharge from the background area from a stream or by sheet wash. The latter occurs during prolonged rainfalls or snowmelt if the surface is bare or frozen and the soil is saturated. The two ways of water recharge may alternate even during a single phase of activity. External sediment influx particularly happens during phases of activity.