Preservation of block fields beneath Pleistocene ice sheets on Solen and Elgahogna, central-eastern Norway

For more than 100 years the vertical extent of the last ice sheets, and in particular during the Late Weichselian, in southern Norway has been debated. The nunatak hypothesis states that mountain summits with alpine topography or autochthonous block fields remained ice-free during the glaciation, thereby suggesting a thin Weichselian ice sheet ('the minimum model') in central-eastern Norway (NESJE et al. 1988). The alternative hypothesis proposes a thick, cold-based and non-erosive ice sheet ('the maximum model') covering even the Summits (SOLLID & SORBEL 1982, 1984, 1988, 1994). This paper presents results of traditional glacial-geomorphic mapping and a provenance study of glacial erratic boulders on the mountains Solen and Elgahogna in the Femunden area in central-eastern Norway. Erratics superimposed on the block fields and meltwater channels incised in the block fields indicate that the block fields have been covered by at least one ice sheet. The provenance study indicated two events with ice coverage; one with ice flow from the north, and the second and youngest with ice flow from the southeast. The second event was warm-based on Elgahogna, eroding on the stoss side, but preserving the block fields on the lee side. At least one event is of pre-Late Weichselian age, and no unequivocal traces are identified of a Late Weichselian ice sheet. A readvance of deglacial age indicate an active ice cap with an accumulation area during the late deglaciation of Fennoscandia. It is suggested that openwork block fields produce a self-conserving effect, in the way that a negative thermal anomaly in the block fields, associated with non-conductive cooling processes, provide permafrost and favor the build-up of a cold-based ice sheet.