Gneissic tors in the central European upland: Complex Late Pleistocene forms?

Bedrock outcrops punctuating regolith-covered surfaces in the summit/upper slope and hillside positions (torsand crags) have long been a subject of inquiry in geomorphology for their evolutionary trajectories and now alsoas valuable geoheritage sites. Methodological advances in research, such as DTM-based geomorphologicalanalysis and terrestrial cosmogenic nuclide inventories, create new perspectives to decipher the spatial andtemporal context of tor emergence and decay. The shape, structural controls, 10Be inventories and relation tosurrounding medium-scale landforms were studied at thirteen conspicuous bedrock outcrops developed inmetamorphic and sedimentary lithologies in the Bohemian-Moravian Highland, Czechia. The shapes of studiedbedrock outcrops indicate significant litho-structural controls. The general outline is mainly governed by (sub)vertical joints, whereas the inclination of foliation or bedding planes dictates summit and cliff morphology. Someof the tors described in this study developed in exceptionally densely foliated and jointed gneiss, which does notcomply with the generally accepted view of tors as massive rock compartments resisting weathering. A series ofrock hardness measurements performed at three gneissic tors using Schmidt hammer show statistically significant within-tor variability of R-values, indicating different exposure times to subaerial weathering. Thecomplexity of landform assemblages, within which studied tors/crags are developed, varies from isolatedbedrock outcrops surrounded by smooth slopes covered with debris-rich soils to outcrops accompanied by lowrock cliffs, debris-covered steps, slope benches, boulder fields and isolated large blocks. The 10Be inventoriesreveal ages mostly from the Late Pleistocene and rarely from the Holocene. Summit/upper slope tors and hillsidecrags show considerable variability in maximum denudation rates ranging from 6.4 ± 0.2 to 105.6 ± 4.8 m/Ma.Paired samples from the summits and cliffs of eight outcrops indicate three possible post-emergence evolutionaryscenarios with summit downwearing while keeping the outcrop outline, balanced cliff and summit degradationrate, and backwearing as the dominant degradation process