Sir, Cold glaciers in the central. Transantarctic Mountains, Antarctica: dry ablation areas and subglacial erosion
In the course of glacial geological work in the central Transantarctic Mountains in 1964-65 and 1969-70 (Mercer, 1968, in press), I have observed some properties and activities of cold glaciers that may be of glaciological interest.
At high elevations, independent glaciers with permanently dry ablation areas occur: ablation is solely by sublimation, except perhaps for a small amount of mechanical deflation. An example of such a glacier (Fig. 1) is on the north-west side of Heathcock Peak, in the Caloplaca Hills adjacent to Reedy-Glacier (lat. 86° 06’ S., long. 40° W.; snout elevation about 1 800 m). No measurements were made on this glacier but, on a blue-ice distributary lobe of Reedy Glacier at a similar elevation, sublimation averaged 7.5 mm of ice/week between mid-November 1964 and mid-January 1965. Because of the complete absence of run-off or surface melting, this is a more extreme type of polar glacier than Meserve Glacier in the Transantarctic Mountains of south Victoria Land (lat. 77° 35’S., long. 162° 23’ W.; snout elevation 440 m), where about 55% of the ablation is by sublimation (Bull and Carnein, 1970).
No basal ice movement was measured on Meserve Glacier. However, there is evidence that in the same climatic environment (average annual air temperature about — 40°C), as with the small cold glaciers with dry ablation areas, large glaciers can both pluck and abrade their beds. These glaciers are probably, but. not certainly, cold at their bases.
Plucking is shown by englacial rock debris that reaches the surface of McCarthy Glacier, a tributary of Reedy Glacier, in a blue-ice area of net ablation, adjacent to Mims Spur (lat. 86° 03’ S. long. 125° 40’ W., elevation 1 900 m). The material consists of fresh and unweathered granitic fragments of all sizes from gravel to boulders 3 m in diameter. McCarthy Glacier is a local glacier that originates on the nearby Wisconsin Plateau, and the granitic debris must have been quarried beneath the glacier, probably where the ice descends steeply from the plateau.
Abrasion is shown by abundant striated clasts in the modern and recent (ice-cored) moraines on the east side of Buckley Island, a nunatak in upper Beardmore Glacier (lat. 84° 55’ S., long. 164° 30’ E.: elevation 1 800 m). Probably the abrasion occurs a short distance up-glacicr beneath the Shackleton Icefalls. At the sampling point, chosen at random, more than half the clasts, of cobble size and larger, on the surface (excluding those of sandstone and shale) were striated; this would be an unusually high proportion even for till from a temperate glacier. The abrasion is evidently the result of exceptional local factors, perhaps fast-moving ice, because elsewhere alongside Beardmore Glacier—for instance, in the Dominion Range or on The Cloudmaker—no striated clasts were found.
J. H. Mercer
Institute of Polar Studies, Ohio State University 125 South Oval Drive, Columbus, Ohio 43S10, U.S.A. 8 November 1970