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

KARSTIFICATION

Development of karst depressions The counterparts of blind chimneys on the surface are covered karst depressions. Their shapes are controlled by blind chimney development and surface erosion. (If accumulate in considerable thickness, cover sediments probably fill in chimneys without the development of covered karst features on the surface.) Above the chimneys extending towards the surface, the thin enclosing rock caves in. Collapse also affects cover sediments and on the surface depressions of interior drainage, steep-sided or broadening with depth, originate (Picts. 7 and 8). The explanation probably lies in the fact that, instead of solution on the limestone surface, a chimney forms in the karstic rock. While chimney development is a relatively slow process, the blind chimney caves in and cover sediments collapse rather rapidly. If chimney widening continues in the karstic rock, the surface landforms keeps widening through the subsidence of cover sediments. Since rainwater from the environs collects in the chimney as solvent, the surface depression increases the intensity of chimney development. The genesis of a chimney and a surface covered karst depression mutually assume each other's existence and develop in close interaction. If a chimney opening to the surface reaches a channel floor, pseudobathycapture happens. If a single chimney forms at the intersection of fracture planes, a circular symmetric depression is created on the surface of the carbonate basement. If several chimneys develop in each other's immediate vicinity, twinned landforms originate on the surface (Pict. 12). If the main chimney is accompanied by one or more subsidiary chimneys which reach the surface relatively further away from the edge of the depression above the main chimney, there occur minor depressions next to the main one. If a composite chimney forms, the chimneys reaching the surface produce a row of depressions (VERESS 1982a). If the chimney formed along a bedding plane, the surface depression will have an elongated planform in the direction of the strike of beds and in cross-section its inclination is variable: the gentler side is composed of bedding planes, while the steeper side is of bed scarps. If the carbonate rock sequence contacts with a non-soluble rock (munierian series), in sculpting the steeper side retreat through solution (local corrosional scarp) may be also effective. The side slopes of the surface karst feature formed in cover sediment may become gentler to the effect of sheet wash or they may be dissected by erosional gullies. Creeps also produce gentler slopes. Measurements indicate that their rates can be as high as 1-2 cm per year (Table II). On side slopes of depressions cavings and slides may generate scars. Mass movements are evidenced by curved tree-trunks in depressions (Pict. 9). In the intermittent ponds deposition flattens the floors of depressions (Pict. 10). On the fill secondary features, partial depressions (Pict. 10; Fig. 9) can occur (VERESS 1982a, 1987a). The development of these small-size depressions takes place by the collapse (above upward-extending subsidiary chimneys) or by the subsidence (transportation of passage fill into depth) in the cover sediments. Partial depressions may fill from channels formed on their margins and deepen again. The cycles of generation and regeneration of partial depressions is an indication of the interrupted character of the karstification process. Partial depressions may also form in the channels of the main depressions. This is caused by chimney development. The formation of partial depressions and even of passages without partial depressions (Fig. 9a) results in the bathycaptures of intermittent water-courses in the channels. These are pseudobathycaptures on hidden rock boundaries (where cover sediments are thinning