Mechanizmy i uwarunkowania rozwoju progów morfologicznych Gór Stołowych = Mechanisms and controls of escarpment evolution in Poland’s Stołowe Mountains

Abstract

The Stolowe Mountains,situated in the Middle Sudetes, form Poland’s only tableland, which is underlain by an alternating succession of sedimentary rocks, all of Permian and Late Cretaceous age. The morphology of the Stolowe Mountains is characterised by the presence of isolated mesas and plateaus. Nearly-level summits are bounded by precipitous escarpments up to 300 m tall. These are bipartite in profile, with stronger sandstones forming vertical cliffs and less-resistant marls and mudstones being truncated by concave slope sections. There seems to be general agreement that long-term escarpment retreat is the dominant pathway by which this tableland evolved geomorphically. However, ideas on the processes contributing to the scarp recession vary. Since the early 20th century, the dominant concept has ascribed a major role to catastrophic mass movements. Łozinski (1909) for example pointed to rock falls, and linked their origin with intense mechanical weathering. For their part, both Czeppe (1952) and Dumanowski (1961, 1967) underlined the crucial importance of subsurface water flow at the point of contact between the permeable sandstones and impermeable fine-grained rocks. In their opinion, that phenomenon results in the undercutting and destabilisation of rock faces. Pulinowa (1972, 1989) was of a similar view and suggested that plastic deformations of underlying marls and mudstones caused subsidence and the toppling of marginal parts of the sandstone caprock. Although deep clefts are a prominent feature of Mt Szczeliniec Wielki, no significant movements have been recorded in recent decades (e.g. Cacon, 2008). Thus, from a present-day standpoint, the different outlooks mentioned above can be considered highly influenced by paradigms, while lacking in support where empirical data are concerned. In contrast, systematic study based on quantitative measurements has been engaged in recently by Duszynski and Migon (2015) and Duszynski et al. (2016). They reveal that non-catastrophic disintegration of cliff lines appears to be a much more common phenomenon than rock failure. An alternative scenario assumes that the marginal parts of plateaus are separating along joints, due to underground erosion and removal of rock residuum. In this way, after a long period of time, a once-solid rock face becomes a mess of joint-bounded blocks. Transport downslope is then more apparent than real as progressively lower topographical positions are occupied, while the lower escarpment slope recedes. Landslides in the middle and lower parts of the slope (Duszynski et al., 2017), block ploughing (Pulinowa, 1989; Duszynski and Parzoch, 2016) and erosional incision (Migon and Kasprzak, 2016) all do contribute to escarpment retreat, but their role is limited to single localities. Although our knowledge regarding the evolution of the Stolowe Mountains has improved greatly, we still lack chronological data, and are hence unable to pinpoint the environmental conditions proving particularly favourable to escarpment recession. There is also a need to determine whether the arenisation process often described in the foreign literature (e.g. Wray and Sauro, 2017) is actually responsible for the slow detachment of sand grains from quartz sandstone.