FUNCTION OF THE ICE STREAMS IN THE SCANDINAVIAN ICE-SHEET - ANALYSES OF GLACIAL GEOLOGICAL DATA FROM SOUTHWESTERN FINLAND

Mapping of striae trends, macro-scale erosion forms, drumlins, moraini c ridges, eskers, till fabric and boulder fans has facilitated reconst ruction of glacial dynamics in terms of ice streams, marginal ice lobe s and interlobate zones. Data were recorded in a computerised geograph ical information system (GIS). Data on oriented glaciogenic elements a re compared with the evolving patterns of glacial flow. The oldest flo w occurred at a distance of several hundred kilometres inside the ice margin, while the later flows were dependent on the dynamics of the ic e streams and fan-shaped ice lobes. A model is developed for the zonat ion of subglacial processes such as erosion, deposition and till defor mation beneath the ice sheet. Most of the glacial forms, as well as lo wer till, were generated in a zone of basal melting and fast ice flow which existed some hundred kilometres from the receding margin and was associated with the formation of ice streams. These results are consi stent with recent reconstructions of basal hydrology using mathematica l models. Ice streams were important for deglaciation dynamics. In the course of deglaciation, decreased shear stress on the water-saturated substratum resulted in ice-bed uncoupling which lowered the profile a nd accelerated flow in the ice streams. This did not happen in interst ream areas as reflected by the glacial geomorphology typical of inacti ve ice.