Pohyb skalních věží u Holštejna na severním okraji Moravského krasu

Rock towers are in the Moravian Karst quite a rare phenomenon. The biggest group of seven is situated west of the Holštejn village near the Vaňous walls in the half blind valley of the Bílá voda stream. Surrounding area is made up of the Vilémovice Limestone of Frasnian age, which are folded into SW steeply inclined folds with subhorizontal fold axes, very gently dipping towards SSE. Three systems of cleavage were detected in the locality. The most prominent cleavage system K0 is NE–SW striking moderately dipping towards SW. Based on the orientation, it is likely that this system is the axial cleavage of the main folds. The other two cleavage systems are K1 and K2, which have very similar orientation. Both are W–E striking, dipping towards S, K2 is slightly steeper than K1. All rock towers show signs of toppling. This was proven via an orientation analysis of the two cleavage systems K1 and K2. More traditional bedding planes could not have been used, because there were none detected in any of the towers and because they are folded, they would be unreliable anyway. These two cleavage systems have an almost constant angle of 16° ±4° between them and can be therefore used as a rotation gauge instead. The rotation angle of these towers increases more or less systematically downslope up to 20°. The mean rotation axes for both cleavages are the same and have a very similar orientation as the NNE–SSW striking fault. Two structures control this toppling: the NNE–SSW striking fault system, which is the main subvertical separation plane of the towers forming a pronounced crest above the towers and bedding planes generally dipping gently towards E, which served as a “basal” plane of the limestones block on which they toppled. Opening of fault planes was detected also in the Sonda pod Jedničkou cave system located SW of the rock towers in the same slope. This, in combination with several small warm air exhalation spots near the crest around the rock towers, suggests quite a deep reach of the slope deformation (40 meters). This was possible because the Bílá voda stream valley was originally empty with much higher and steeper slopes than today and was subsequently filled by Quaternary sediments.