Is the asymmetry of dolines in the Central Styrian Karst determined by periglacial processes?

The formation of dolines (or sinkholes) lasts commonly for long periods of time exceeding 10 ka or even 100 ka. Climatic conditions over such long timescales might vary substantially and thus dolines in nowadays temperate climatic conditions were substantially shaped during markedly different climates, namely the colder conditions which dominated during the Pleistocene. In this contribution we focus on a specific form of dolines which are located at the eastern boundary of the European Alps in the so-called Central Styrian Karst (CSK) where periglacial conditions dominated during the colder periods of the Pleistocene. The CSK comprises the occurrence of karst formations in carbonate rocks near Graz, Austria. Unlike in alpine regions further west, this area remained unaffected by Pleistocene glacial erosion and was never glaciated. Given the absence of glacial erosion and the dominance of subaerial processes, (karst-) morphological features are assumed to exist since a long period of time. Consequently, the CSK is a prominent area to investigate landscape evolution in a non-glaciated Alpine area where karstifiable rock were also affected by periglacial processes during the colder periods of the Pleistocene. In addition, the landscape comprises numerous planation surfaces grouped into several levels dating to several Mio. yrs BP. Previously unknown for the CSK are the asymmetries of many dolines detected recently due to airborne laser scanning data. These dolines exhibit a NW-SE elongation, with steeper slopes facing S-to-SE, and flatter ones facing N-to-NW. Some authors have attributed asymmetric dolines in other regions to tectonic influences. However, dolines in close proximity to main fault systems in the CSK do not display these peculiar asymmetries. In addition, dolines further away from the main fault systems show obvious asymmetries. The detected asymmetries of dolines occur at various levels ranging from 540 to 780 m a.s.l. indicating possibly different ages of formation. This contradicts a syngenetic origin of elongation and suggests subsequent re-shaping after primary formation of dolines. Similar asymmetries observed in the Northern Calcareous Alps further to the north have been interpreted as the result of snow-patches, where prevailing wind directions cause snow accumulation in the lee side of doline rims. This type of karst is known as nival karst, which requires the absence of glacial erosion and permafrost to impede subsurface drainage. The CSK satisfies the climatic conditions for the development of nival karst during colder periods of the Pleistocene as judged from past periglacial climate estimations for this area. We hypothesize that the morphometry and formation of asymmetric dolines in the CSK must be seen in relation to a severe periglacial influence and are thus a legacy of (severe/long-term?) periglacial conditions of the past.