WEICHSELIAN GLACIATION HISTORY IN THE RONDANE 'DRY VALLEYS' OF CENTRAL SCANDINAVIA

The Rondane mountains in east-central southern Norway is situated within the zone of inferred cold-based (low-erosive) ice-sheets during the Late Weichselian glacial maximum (LGM) in central Scandinavia. In the studied area, former meltwater flow patterns at high altitudes indicate drainage from east, south and west towards the ‘dry valleys' of Dørålen, Haverdalen, Grimsdalen and upper Folldal north of the Rondane mountains, and then further northwards across the main watershed to Trøndelag. At present, the region is among the driest in Scandinavia with most of the precipitation related to south/south-easterly winds. With a suggested ice divide south of Rondane during the build-up of continental ice sheets in central Scandinavia, the ‘rainshadow' may have been even more pronounced during glaciations.

An objective for this study has been to identify areas with cold based, low-erosive ice, its timing and duration. This was done by comparing the discrepancy between Optically Stimulated Luminescence (OSL) and 10Be exposure ages from contemporaneous settings. If OSL and 10Be exposure ages from contemporaneous settings are corresponding, the area is suggested to have been ice free since then.

The results indicate that no period during the Weichselian obtained a large enough lowering of the regional glacier equilibrium-line altitude (ELA) to produce glacier ice at the terrain surface in the valleys north of Rondane. All glaciers that entered this area were produced elsewhere. Three main glacier events have been recorded: the largest occurred about 100-90 kyr ago during the early Weichselian, the next largest took place during early parts of the Middle Weichselian about 70-60 kyr ago, and the third largest occurred during the Late Weichselian maximum c. 20 kyr ago. In areas covered by cold-based glaciers during the Late Weichselian maximum, 10Be exposure ages show that the last ice remnants melted away close to the Younger Dryas-Holocene transition.

Based on OSL-dated sections, long periods in between the major glacier advances were dominated by ice-dammed lakes in the upper valley of Folldal and its tributaries. Periglacial features like fossil rock glaciers and ice-wedge casts are related to several of the periods with glacier advances and/or periods with ice-dammed lakes.