The origin and evolution of small dry valleys in the last-glacial area on the example of the Pomeranian Lake District (Poland)

Short dry valleys forming a part of the relief characteristic of the temperate zone occur particularly frequently in areas related to the young-glacial zone. Two areas were selected for analysis – Piaski Pomorskie and Jasień, located in northern Poland, at the back of the Pomeranian phase of the Vistulian glaciation. The aim of the research was to determine the role of denudation processes in the landform transformation of the young-glacial areas, manifested in their cutting and creation of, among others, erosional-denudational valleys, and to compare their geomorphological features. The research included field work (recognition of the geological structure, levelling measurements) and laboratory work (grain size analysis, organic matter content, age determination of the deposits). The valleys from both areas vary in size, but have a similar structure of deposits on their bottoms and at the outlets. Within the bottoms of the valleys, the erosively dissected fossil surfaces of the fluvioglacial substrate are visible or there is an erosional pavement. Slope deposits were found in all the valleys, mainly in the form of massive sand or sand and silt series. Their youngest, topmost part lies on organic sediments dated to 81 (95.4%) 253 cal. AD and 1024 (95.4%) 1224 cal. AD. The most distinct difference in the structure of the valleys of both research fields is the presence of boulder levels only in the Jasień area. This may suggest that the genesis of boulder covers depends not only on climatic and plant conditions, which were similar in both areas, but also on the geological structure and morphometry of the valleys. The obtained results indicate that the valley development was dominated by linear erosion in the Bølling and Allerød, mass movements mainly in the cold stage of the late Vistulian and slopewash, which were especially strong in prehistoric and historic times. The differentiation in the size of valleys only to some extent affects their geological structure and processes that accompanied their evolution