The Origin of Instability Phenomena Along the Karst-Flysch Contacts

This paper presents the origin and the type of instability phenomena in the Rjecina and Sušacka draga valleys near the town Rijeka, Croatia. Both locations are part of unique morphostructural unit. Karstified carbonate rocks prevail in this area. Paleogene siliciclastic sedimentary rock complex, i.e. flysch, has a form of a squeezed syncline between carbonate rocks. Geological boundaries between carbonate and flysch rock mass are tectonic, but with different mechanism of origin. Erosion processes and gravitational forces have caused disintegration of the carbonate rock mass, separation of blocks and their sliding over the flysch bedrock, as well as the accumulation of talus on the toe of rocky scarps. During the time, coarse grained fragments originating from the rockfalls were mixed with soil-like material from flysch weathered zone. Disintegration of carbonate scarps, rockfall and talus displacements are a permanent phenomena. The comparisons of a recent instability show a distinction between Rjecina and Sušacka draga valleys.