Veress Márton: A Bakony természettudományi kutatásának eredményei 23. - Covered karst evolution... (Zirc, 2000)
METHODS
sediment types (plant detritus series, charcoal series, limonite concretions) can be detected. The roots of some curved trees in the side of a karst object (Gy-9) were excavated and they were found to have adjusted to the strain produced by mass movements. During the excavation of collapse dolines rich assemblages of corrosional features (spherical niches, ruined chimneys) were found on limestone surfaces. The rock fragments of small thickness recovered from fills mey derive from the ceiling of the cavity. Truncated fragmetns of ceilings also occur in the sides of collapse dolines in some places. The morphological evidence confirms the collapse origin of these landforms. Corrosional features are identified at several decimeters' depth from the limestone surface (ie. the present-day surface). It allows the conclusion that cavitation took place close to the limestone surface and this means that the karst water table of the flowing karst water zone was close to the present-day surface or may have even located above it. The gravels found in some chimneys of summit position or in caves (like in cave M-7) clearly indicate that during cavitation it was a covered karst. Measurements The investigations also involved measuring the geological properties of mass movements and of the enclosing rocks and their statistical processing. Mass movements In order to measure mass movements in cover sediments, rows of piles were placed down to ca 30 cm depth in the sides of some karstic depressions of the central Hárskút Plateau. Displacements were measured related to the outer piles. During repeated measuments the direction between two outer piles was set by tachymeter and displacement was calculated from the distance between the measuring pole (placed in the fixed direction) and the pile. Measurements have been made at karst objects like G-5/a for more than 10 years (repeated twice annually in approximately the same time of the year). In some places displacements reached rates of 1-2 cm per year. Remeasuring the distances between trees in some karstic depressions (Gy-3 and Gy-9), author wanted to obtain new data on the activity and rate of mass movement. Repeated measurements, however, did not indicate changes in distances between trees. In these depressions rapid accumulation was observed. The conclusion was drawn that as a consequence of accumulation the material transport in covered karst depressions was being rearranged or the input gradually reduced. Comparisons between the spatial positions of chimneys and enclosing rocks The investigations involved the comparative study of the spatial patterns of chimneys (water conduits) of surface karstic depressions and structures formed in the enclosing rocks. In the case of vertical chimneys the dip of enclosing rock was less than 10-20°. Such chimneys formed at the intersection of fractures. When intersections occurred close to each other, chimneys developed in each other's immediate vicinity. When dip was above 10-20°, the spatial position of the chimney coincided with the spatial position of the stratum, ie. the chimney developed along a bedding plane. In case of steeper dipping strata, if the rock is properly fractured, composite chimneys develop. Composite chimneys are built up of