Genesis of Deep Lakes of the łęCzna-WłOdawa Lakeland – Case Study of Lake Piaseczno (Polesie Lubelskie, East Poland)

The origin of the lake basins in the Łęczna-Włodawa Lakeland is not clearly explained. Therefore, field and desk research were undertaken to clarify the origin and development of the deep lake basins. These lakes have basins formed in loose Quaternary rocks, situated above deep, fossil valleys in tectonic zones, and bordered by lacustrine and fluvial sediments. These sediments originate from the Odranian and Vistulian glaciations. The basins have a funnel-like shape and consist of one or two depressions. Based on the conducted research and literature analysis concerning the studied lakes, it was determined that these basins are polygenetic. In the initial stage, shallow closed depressions were formed because of fluvial or thermokarst processes. During the main stadial of the Vistulian glaciation, the development of permafrost led to increased groundwater pressure and hydraulic breakthrough within shallow water bodies located in tectonically active zones. Water emerging from the resulting limnocrenes carried sands and silts to the forefield. The remnants of these flows are preserved as winding and narrow valleys. Therefore, the deep lake basins have a fluvio-ascensional origin.