The role of landslides in downslope transport of caprock-derived boulders in sedimentary tablelands, Stołowe Mts, SW Poland

Abstract

Escarpment slopes in sedimentary tablelands are often mantled by extensive boulder blankets. While lithology shows beyond doubt that caprock is the source of boulders, the processes involved in boulder movement and their distribution patterns are rarely examined. In this paper we investigate the role of landslides initiated within middle and lower escarpment slopes in redistributing boulder covers, on the example of the Stołowe Mountains in SW Poland. Quartz sandstones form caprock and give rise to precipitous, albeit rather low (30m high at most, typically 10–15m) uppermost slope sections, and are the source of boulders which occur at distances even 1km away from the caprock, on the nearly flat footslope. Sedimentary series beneath caprock include fine-grained rocks such as mudstones, claystone and calcareous sandstones. Geomorphological mapping and geomorphometric analysis of a high-resolution DEM allowed us to identify landform patterns interpreted as resulting from landslides, both rotational and translational. The latter produced distinctive tread-and-riser topography, with risers up to 10m high. Results of geophysical prospecting using Electrical Resistivity Tomography (ERT) confirm the presence of allochthonous, sandstone-derived upper layer that wedges out downslope and indicate resistivity contrasts at depth of 5–15m, interpreted as basal boundaries of landslide material. Sandstone boulders rafted on top of slid masses and reached very distant footslope settings. The primary role of landsliding consists of transporting allochthonous boulders further than would be possible otherwise and accumulating boulders in clusters and linear belts across the slope, notably on risers.