LAND-BASED ICE STREAMS OF THE SOUTHERN SCANDINAVIAN ICE SHEET: MOVEMENT MECHANISMS AND ICE/BED INTERACTIONS

The Peribaltic area between Denmark and Estonia experienced repeated and non-synchronous ice streaming during the last glaciation. These ice streams are believed to have been major dynamic elements of the southern periphery of the Scandinavian Ice Sheet (SIS), controlling regional-scale mass balance and sediment redistribution patterns. The most prominent of them was the Baltic Ice Stream that has operated for hundreds of kilometres along the Baltic Sea basin and fed numerous second-rank ice streams along the ice sheet margin. All ice streams in the area were soft-bedded and land-based, and their terminal areas are accessible to direct geological studies.

Geomorphological data (attenuated drumlins, subglacial meltwater channels and eskers), together with geological (striated boulder pavements and soft-sediment deformations) and hydrogeological data (substratum hydraulic conductivity) indicate that ice streams’ fast flow was facilitated by temporarily and spatially transient mosaic of enhanced basal sliding and bed deformation. Subglacial water pressures were in the vicinity of glacier flotation point and small variations of water pressures, possibly caused by local parameters such as the drainage capacity of the substratum, controlled the ice movement mechanism.

The outermost parts of the ice streams were highly dynamic in the sense of local flow directions and contrasting flow velocities. In some areas along past ice margins thick accumulations of boulder gravel deposited from high-energy subglacial meltwater conduits occur. Close to the ice limits, meltwater channels containing eskers are found side-by-side with drumlins. It is suggested that only models involving complex interactions between subglacial hydraulics and soft sediment rheology can constrain flow dynamics of ice streams along the southern margin of the SIS.