19. The Rax Karst massif: A Typical Plateau of the Northern Calcareous Alps?

The Rax massif is located at the border of the Austrian provinces of Styria and Lower Austria. The area is part of the Northern Calcareous Alps (NCA) and covers 104 km². The plateau is built up by a Triassic carbonate sequence with a thickness of more than 1 km. Similar to other plateaus of the NCA, the Rax massif indicates remnants of ‘Tertiary’ palaeosurfaces which carry Quartz-rich sediments of the Augenstein Formation. There is a long-lasting scientific controversy about the age and the evolution of these palaeosurfaces. Lichtenecker (Das Bewegungsbild Der Ostalpen. Naturwissenschaften 13:739–743, 1924) introduced the terms Augenstein-Landschaft and Rax-Landschaft. The latest model, introduced by Frisch et al. (Int J Earth Sci 90:500–518, 2001) proposed the term Dachstein-palaeosurfaces for karstified landscapes developed before the Augenstein sedimentation. The plateau area (approximately 27 km²) is characterized by intense karstification including entire underground drainage. The morphogenesis of the epikarst is influenced by the presence of soil-cover and sparse vegetation. Due to dominantly subsoil development, karren are characterized by rounded forms. Closed depressions (dolines) represent the dominating surface karst feature. Based on airborne LIDAR data and intensive field mapping 914 dolines, with a summarized area of approximately 0.15 km², are delineated and their morphometric characteristics analyzed. Although the study area comprises a large number of caves, deep pits or large cave systems are unknown so far, which is in contrast to other karst massifs of the NCA. The Rax plateau also comprises the catchment areas of springs captured for the Viennese water supply.