Abstract:The ice surface of the glacier in the 7 km long valley Scharffenbergbotnen in Heimefrontfjella, Dronning Maud Land, is characterized by blue ice fields and is partly covered by supraglacial moraine complexes. The debris cover of the supraglacial moraines is generally less than 50 cm thick and rests on glacial ice, and most of the surface morphology of ridges and numerous sink holes reflects irregularities in the underlying ice. The debris consists of angular to sub-angular clasts of local bedrock. We interpret the moraines to have an entirely supraglacial history, where colluvium and pre-existing moraines were brought into Scharffenbergbotnen primarily from the south/south-west by an advancing glacier during the last ice maximum in the region. The debris cover of the supraglacial moraines extends up to 200-250 m above the present ice surface on surrounding slopes in Scharffenbergbotnen, and generally to less than 100 m above the present ice surface on slopes outside the valley. We interpret this as marking the ice surface elevation in the area during the last ice maximum (probably LGM). The deposition of supraglacial moraines in the valley at that time, and their survival in the area until the present day, indicate that a local ablation centre and probably blue ice fields were present in Scharffenbergbotnen at LGM, and has been a persistent feature since. In a wider context, we argue that supraglacial moraines constitute a hitherto unexploited resource when reconstructing the former extent of blue ice areas.
We report here on cirque infills mapped in the Khibiny Mountains, Kola Peninsula, Russia. Cirque infills are morainic deposits located near the headwalls of valleys and cirques. Their location and shape, often with concave margins towards the valley side, indicate that they were deposited by ice flowing up-valley, into the mountains, rather than by local glaciers. We suggest that they formed during the last deglaciation, when Khibiny was a nunatak and Fennoscandian ice sheet lobes extended into valleys and cirques of the massif. The formation of cirque infills is probably more related to ice sheet dynamic factors, occurring when the ice margin retreated from the cirques, than to climate-driven interruption in the ice-marginal retreat. Glacial conditions similar to those prevalent when the Khibiny cirque infills were formed, occur today in Antarctica where the ice sheets engulf nunatak ranges. In Heimefrontfjella, Antarctica, the formation of supraglacial moraines at the head of cirques are linked to blue-ice conditions, indicating locally low accumulation rates, a dry continental climate and sublimation dominated ablation. We suggest that these Antarctic moraines are modern analogues of cirque infills on the Kola Peninsula, and possibly, that the cirque infills may be used as palaeoenvironmental indicators.
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