Towards a Better Understanding of Subsurface Processes in the Evolution of Sandstone Tablelands—Patterns and Controls of Contemporary Sand Removal from Sandstone Caprock, Stołowe Mountains Tableland, SW Poland

This paper reports the results of two-years’ monitoring of sand evacuation from a sandstone tableland through fissure systems and discusses the findings in the context of geomorphic evolution of tablelands, especially addressing the role of subterranean processes. A field experiment using specially designed sand collectors and involving sampling in approximately monthly intervals was carried out at six sites in SW Poland, representing two adjacent but contrasting settings: a mesa and a cuesta front. Data about sand deposition were then analyzed against precipitation data from a station located next to the sites. Sediment volumes deposited during the monitoring period were considerably different between the sites, with those at the mesa much higher than those at the cuesta. This is attributed to strong structural control influencing groundwater circulation pathways and the size of underground drainage systems, which were much smaller next to the cuesta front. Relationships between denudation and precipitation are complex, although the role of very high rainfall events appears clear, especially for the mesa. In general, precipitation in excess of 70 mm during a few consecutive days typically resulted in a considerable outflow of sand. This study highlights the role of mechanical underground erosion in sandstone tablelands, long neglected, and quantifies the denudation process.