The evolution of river valleys in Lithuania from deglaciation to recent changes and data from the sediment infill of oxbow lakes

Abstract

Generalized analysis of geological-geomorphological structures of river valleys in Lithuania has been carried-out. Lithuania's fluvial topography results from the retreat of the Scandinavian Nemunas (= Vistulian and/or Valdaian) Glaciation, as is shown by the study of geomorphological structures in the recent river valleys (representing the last 15,000 years), which were formed as the ice sheets progressively retreated and ice-barrier lakes were drained. Oxbows in the river valleys are most often located on the floodplain itself and on the first terrace above the floodplain. The oxbow lakes are subdivided into two groups: (1) formed in the near-river stage and (2) formed in the lake-bog stage. Separate development phases can be recognized within both groups of oxbow lakes. The more organic components of oxbow deposits provide specific information for palaeoecological reconstructions. Anthropogenic changes to the natural landscapes of Lithuania have resulted in considerable geological transformation of rivers. Increased sediment volume, shallowing, silting and overgrowing of channels, lateral erosion of floodplains and the spread of ravine erosion on valley-side slopes are all phenomena characteristics of all the valleys in Lithuania. At present the natural components of river valleys and their ecosystems are being changed, mainly with negative consequences for humans.