Karst geomorphology in the Oštarije–Tounj area and its significance in the geomorphological evolution of the broader area

The Oštarije–Tounj area lies in the contact zone of two large geomorphological units: the Ogulin-Plaški basin and the Una-Korana plateau, along the northern edge of Dinaric karst in Croatia. This is a highly karstified landscape, with numerous surface and subterranean karst forms. The objective of this study was to determine the significance of the karst relief and the processes of its formation, with the aim of examining the interaction of these two large units during their geomorphological evolution. General and specific digital geomorphometric analyses were used, with geomorphological mapping. Within the morphogenetic approach, the morphostructural conditions of karstification, spatial distribution and significance of karst, and fluviokarst relief forms were analysed. Several dry valleys were established, indicating that this area was the important corridor for surface runoff from the Ogulin-Plaški basin towards the Una-Korana plateau. Tectonic up-lifting of the narrow zone between these two units created an orographic barrier, which hindered any further surface runoff and created the conditions for the development of karst subterranean watercourses. This paper provides a proposal of the morphogenesis model of the Ogulin-Plaški basin, summarised with the description “flattening and closure”.