Geografie 1972, 77, 219-225
Extensive Landslide Near Oznice, Hostýnské vrchy (Hills)
In the Carpathian flysch zone in frontal part of the Magura nappe (Hostýnske vrchy) an extensive landslide occurred in 1967 north of the village Oznice, south-west of Valašské Meziříčí. Judging from its geological situation it is a shallow structural landslide which - according to P. F. Savarenský (1937) - is a consequent landslide. A claystone layer in the Zlín strata in the brachysynclinal closure served as the shear plane enabling the rotation movements of the sliding masses. The comparatively large extent of the slide as well as the proportion of its length to its width show that it was a plane landslide covering some 27 000 m2. With regard to structural conditions - which made it possible for extensive masses of rock to move without suffering much harm - it is a block landslide. It originated along the rotation shear plane in the brachysynclinal structure where a higher hypsometric and gravity potential of the northern stream caused overpressure in the southern lower-situated stream in a place where pressure was relieved in the direction towards an abrut gorge situated under the eastern margin of the landslide. In the course of the landslide two main blocks affected each other, i. e. the main mass sliding in the direction of the axis of the structural basin (of about 3.105 t), and the north-eastern block (D) of about 1.105 t. In the place of their contact mounds of soil were formed rising some 3 m above the surface of both blocks. From the hydrogeological point of view, the area - where the landslide occurred - represented a closed hydrogeological unit drained by a spring situated in the mouth of the abrupt gorge. The normal regime of percolation water in sand rocks alternated in periods of increased precipitation with periods of increased water supply to fissures and porous levels. Consequently, the gravitational potential of the whole structure was increased on the one hand, on the other hand the water-washed surface af the underlying claystone layer was enlarged, and transformed into a shear plane. The occurrence of such an extensive structural landslide is a warning of the danger that a similar phenomenon might be repeated in similar natural conditions. It may happen if otherwise seemingly stabile geological structures (such as the structural basin) are exposed to increased activity in periods of greater precipitation.
