Models of geomorphic evolution of tablelands vary as far as the patterns of cliff line degradation and hence, scarp retreat are concerned. Among surface processes rock slope failures from caprock cliffs, often induced by preferential seepage from rock faces, are emphasized. In this paper evidence is provided that mechanical removal of sand from inside the caprock through underground erosion may also play an important role in the long-term evolution of cliffed escarpments in sandstone tablelands. More than 140 sandy cones and nearly 80 sand sheets emerging from fissures in the sandstone cap were mapped and measured along six cliff sections of variable length in the Stolowe Mountains tableland in SW Poland. The density of sandy accumulation forms varies along the cliff length, with cones preferentially associated with intact cliffs and sand sheets being more common along degraded cliff sections. Further redistribution of sand downslope results in widespread sandy covers below cliff lines which extend for a few hundred metres and are 1-3 m thick, as demonstrated by electrical resistivity tomography. Sand removal from caprock accounts for progressive, non-catastrophic degradation of tableland margins through gradual subsidence of blocky compartments and the development of ruiniform relief behind the cliff lines. Thus, it may be an important component of long-term evolution of stepped relief in sedimentary terrains. (C) 2016 Elsevier B.V. All rights reserved.
