A nunatak is an upland surface that protrudes above the surface of an ice sheet, ice cap, or ice field. The term nunatak derives from the Inuit language and was initially used by Greenlanders to refer to the mountains that protruded above the surface of the Greenland Ice Sheet.
Some nunataks are steep mountains, whose slopes are too precipitous and summits too narrow to support permanent ice. Additionally, some nunataks have a minimal snow cover during the summer months because of their low albedo and high rates of heat absorption from solar radiation. This heating during extended periods of sunshine may result in unusually high rates of ablation on the adjacent ice surface, resulting in localized lowering of the glacier surface. Other localized climatic effects of nunataks on glacier surfaces include wind scouring and snow drifts. Scouring can produce windscoops on the upwind sides of a nunatak, whereas lee eddies can construct wedge-shaped snowdrifts on the lee sides. Where mountain ranges have been overwhelmed by an ice sheet or ice field, chains of nunataks may protrude from the ice surface to form a “nunatak landscape” (Sugden and John, 1976), such as on the Prince of Wales Icefield and Agassiz Ice Cap on Ellesmere Island. The eastern margin of the Greenland Ice Sheet is also characterized by nunatak landscapes. Because of the potentially large number of freeze-thaw cycles that could take place on nunatak rock surfaces that receive sunshine, they are likely to be areas of intense frost shattering and blockfield (felsenmeer) accumulation.
Paleo-ice sheet reconstructions utilize geomorphological evidence for paleo-nunataks in the landscape. Specifically, the upper limit of former glaciation is often marked in upland terrain by “periglacial trimlines” that separate ice-scoured bedrock below from in situ frost-shattered bedrock (autochthonous blockfield/felsenmeer) above. Although such evidence has been used to delimit “weathering zones” that have developed during sequentially more restricted glaciations (“nunatak/refugia hypothesis”; e.g. Dahl, 1961; Boyer and Pheasant, 1974; Ives, 1978; Nesje and Dahl, 1990; McCarroll et al., 1995; Ballantyne, 1997), some researchers have proposed that blockfields, sometimes including Tertiary weathering residues, can persist beneath cold-based ice and therefore do not necessarily constitute evidence in support of paleonunataks (e.g., Sugden, 1977; Kleman, 1994; Kleman and Borgstrom, 1994; Rea et al., 1996).
See also Ice caps; Ice Sheets; Quaternary Paleogeography
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pronunciation (1877) : a hill or mountain completely surrounded by glacial ice