Palaeohydrology of the rivers Ivalojoki and Oulankajoki, Finland

Abstract

Reconstruction of the past is mainly based on work with 14 palaeochannels, 22 stratigraphical sections, 15 pollen diagrams, 43 radiocarbon dates and geomorphological mapping. Of the results revealed the most important are: low water balance of (1) the Boreal and (2) the Early Subboreal (around 4800 B.P.), (3) step‑wise in­crease in water balance approx. 2000 B.P. connected with intense activation in meander shifting. (4) continuing of this situation in the present form 1500–1600 B.P., and (5) the highest level of all in fluvial activity during the Little Ice Age. None of these features were affected by Man. Changes in post‑glacial fluvial activity are reflected, first of all, in the reverse trends of lateral and vertical channel movements. the last‑mentioned being strongly regulated by the isostatic land uplift. The dominance of the climatic factors over those of the glacio‑isostatic origin in controlling Ho­locene fluvial work appears to increase the more the closer to the present day we come. These effects are to be seen in the activation of lateral shifting. The concentration of coarse lag deposits at the valley bottoms may have contributed in intensifying lateral movements in the near past. The research made calls for great methodological caution in palaeo­hydrological interpretation of fluvial environments.