Closed depressions in the European loess belt – Natural or anthropogenic origin?

© 2017 Elsevier B.V. Closed depressions (CDs) are typical geomorphological features of the loess belt in Europe. CDs have been reported in several regions of the European loess belt, where they are described as hollows, mardeles, wymoki, crovuri, bludtsa and zapadiny. The natural and anthropogenic origins of CDs are debated in literature. Moreover, no comprehensive review of the geomorphic properties or the evolution of these depressions exists. Therefore this paper reviews the characteristics of CDs in the European loess belt and attempts to better understand their genesis based on detailed case studies. The main morphometric features as well as sediment deposits within CDs in several sub-regions of Europe were analysed and compared. Morphometric properties of CDs from the West European and East European loess belt were investigated through a comparison of CDs from two representative regions, i.e. East Poland and Central Belgium. In both study areas, CDs under cropland are similar. However, a comparison of morphological features of CDs under forest, revealed clear differences, suggesting a different origin of CDs from both regions. Infilled sediments in CDs show various litho-genetical features in different regions of the European loess belt. The morphometric features, ages and stratigraphy of infillings clearly indicate that both anthropogenic and natural processes have shaped these landforms within the loess belt of Europe. CDs observed in Eastern Europe may have a very different origin than those documented in Western Europe. Detailed analysis of CDs in Poland and in neighbouring regions of East Europe, suggest that CDs are natural landforms: thermokarst, deflation and dissolution of loess are reported as probable genetic processes. In contrast, several studies in Western Europe indicate a dominant anthropogenic origin (i.e. digging of calcareous loess or marls, bomb and mining craters, collapse of underground limestone quarries), although CDs formed by natural processes (i.e. piping, dissolution of limestone and salt lenses below the loess cover) are reported as well. CDs act as important archives, allowing one to reconstruct both natural and anthropogenic processes operating in the past. As CDs store most sediments eroded within their catchment they provide ideal sediment traps to assess long-term erosion rates in these environments which have hitherto been under-researched. More research is needed to unravel the genesis and evolution of these depressions to better understand the importance of the Late Glacial and Holocene stages for the morphogenesis of the loess belt in Europe.status: publishe

Geotourism assets of loess relief in western part of the Lublin Upland

The characteristic group of loess relief in the western part of the Lublin Upland makes up a unique and varied landscape that is particularly attractive for tourists. Gullies, whose density exceeds 11 km/km2 in the Kazimierz Dolny area, are the best known element of the loess landscape. Along the gullies, tourist and interpretive trails have been established, but there is a lack of well-prepared geotourism trails. The southern part of the study area, the Urzędów Hills, is particularly underdeveloped in terms of tourism. This study presents the key characteristics of loess relief in the western part of the Lublin Upland, the current development of tourist infrastructure, and prospects for geotourism based on the unique landforms in the area. A few geotourism trails focusing on the unique loess relief features have been proposed, and attention has been drawn to threats to these landscape assets posed by certain forms of adventure tourism and problems related to private land ownership

The importance of geological conditions for the formation of past thermokarst closed depressions in the loess areas of eastern Poland

Closed depressions (CDs) are common forms occurring in the European loess belt. So far, investigations of CDs in Europe have suggested various natural or/and anthropogenic processes leading to their formation. The origins of CDs occurring in the loess areas of Poland have been the subject of few investigations, and their results have not clarified the problem. Most frequently, the age of CDs is linked with the post-glacial period, or the final stages of the formation of the loess cover. The investigations of CDs carried out in eastern Poland (Nałęczów Plateau) have so far revealed some patterns with regard to the morphometric characteristics and distribution of CDs on the regional scale. They also suggest the impact of thermokarst processes on the formation of the CDs. Five main lithogenetic types of sediment underlying the loess cover have been documented: glacial tills, clay and clayey loams, patches of glacial tills and sandy deposits, sands with gravels, and the bedrock. The relief under the loess cover has also been documented. The types of sediment as well as the relief under the loess cover have an impact on local differences of water content in the loess sediments. It was found that the variatiability of the geological conditions in the Nałęczów Plateau in the Pleistocene had an impact on the local variation of the ice content in the upper part of the former permafrost. This led to local predispositions for the development of thermokarst CDs during the Last Glacial. Areas with a high density of CDs have less permeable sediments (glacial tills, clay and clayey loams) and small relative heights under the loess cover. In the Pleistocene, these areas had higher ice content in the upper part of the permafrost. A model of thermokarst CDs development in the loess areas in eastern Poland is proposed. The model shows that the distribution and size of thermokarst CDs depends on the thickness of the loess cover as well as the types and relief of sediments underlying the loess. The development of thermokarst in the region studied may have consisted of multiple stages resulting in superimposed CDs. Between two and four stages of thermokarst CDs development can be distinguished on the Nałęczów Plateau. The two main stages occurred in MIS 4/3 (~58 ka or 55-50 ka Oerel and Glinde interstadials) and MIS 2/1 (~12 ka). These landforms may have developed also during the Denekamp Interstadial (32-28 ka) and ~15 ka. The present investigations indicate significant morphogenetic effects of permafrost melting on the contemporary relief of the loess areas

Geological conditions of the distribution of closed depressions in the Nałęczów Plateau (Lublin Upland, E Poland): are they an origin determinant?

Closed depressions (CDs) are landforms typical for loess areas. 1761 CDs have been inventoried within the Nałęczów Plateau. Large concentrations of CDs: 30–40 forms per km2 occur in areas where thick (more than 10 m) complex of glacigenic sediments (mainly glacial tills) or clay (limniglacial) deposits underlying loess cover. Areas with a low concentration of CDs (fewer than 10 forms per km2) correspond to areas where the loess cover lies on a bedrock (opokas) or on thin sandy-gravelly deposits. The distributions of CDs depends on the conditions of Pleistocene permafrost development and melting, linked with lithological properties of the sediments under loess cover

Geomorphosites of Poland : the role played by the Central Register of Geosites

Poland is a country of considerable geomorphological diversity and includes a range of physical landscapes, from high mountains through uplands, plains, glaciated lowlands, large river valleys, to coasts. Within them, numerous localities may be considered as geomorphosites, illustrating key stages in the geomorphic evolution of the territory, classic landforms and the recent operation of geomorphic processes. The only database that aims to cover all geosites in Poland, including sites of geomorphological interest, is the Polish Central Register of Geosites (PCRG), managed by the state geological survey – the Polish Geological Institute (PIG). Among more than 2200 geosites recorded about 30% can be considered as geomorphosites. Their spatial coverage is very uneven. Most are located in the upland belt of southern Poland (40%) and in northern part of the country, within the extent of the late Pleistocene ice sheet (29%), while the Carpathians are under-represented. Thematically, geosites illustrating various examples of denudational relief dominate (45%). Significantly less common are glacifluvial (13%), glacial (11%) and fluvial (10%) landforms. Tors and residual hills are most common among geomorphosites (205 sites), followed by moraines (52), dunes (49), gullies and their systems (45) and river valleys (34). Thus, PCRG does not yet adequately reflect the diversity of the geomorphological heritage of Poland