Sir, Patterned ground under ice fieldsFootnote *
The description which Dr. Stephenson gives of the occurrence of patterned ground adjacent to small ice fields in Antarctica (Reference StephensonStephenson, 1961) is in some ways similar to a situation which I recently noted while comparing air photographs of small ice fields in northern Baffin Island, District of Franklin, N.W.T., Canada.
Air photographs of a small ice field were made in 1949 and 1958 and comparison reveals that an average marginal recession of 180 m. took place in the nine-year interval. In the area thus exposed large high-centred tundra polygons with diameters of about 50 m. can be seen (Fig. 1). Similar polygons are visible on both sets of photographs extending over much of the surrounding country. No marked variation in size with distance from the ice field can be seen although some tundra polygons are elsewhere reported to form initially as large features and to divide up into progressively smaller polygons with age (Reference BlackBlack, 1952). A close examination of the 1949 and 1958 ice margin using a high magnification stereoscope indicates that the large polygons are actually melting out from under the glacier ice giving a slightly “scalloped” appearance to the ice margin. Reference GoldthwaitGoldthwait (1951) described patterned ground including fissure polygons (tundra polygons) immediately adjacent to the Barnes Ice Cap in central Baffin Island and considered them as partial evidence of the expansion of the Barnes Ice Cap in the recent past, asserting that the patterned ground could not have been disturbed by glacier movement for many decades. Patterned ground has been reported emerging from beneath receding glacier ice in northern Ellesmere Island (Reference SmithSmith, 1961), in addition to the examples in Antarctica described by Reference StephensonStephenson (1961).
Fig. 1. Patterned ground emerging from beneath small receding ice fields in northern Baffin Island, Northwest Territories, Canada, 1 September 1958. The black line indicates the position of the ice field margin on 8 August 1949
As Dr. Stephenson points out some of these features may predate the formation of the ice fields and this I believe may be the case in the example from northern Baffin Island. That tundra polygons can grow comparatively rapidly, probably in 50 to 100 years, has been shown by Reference MackayMackay (1958), but it seems unlikely that the large polygons in northern Baffin Island could have developed in nine years, apart from the fact that half-emerged polygons are visible at the ice edge. It is also difficult to imagine their formation wider the ice because of their very great size and raised centres. If the north Baffin Island polygons are “fossil” forms, then the ineffectiveness of the small ice fields as agents of direct erosion, or possibly their recent origin, is suggested. (Small ice fields on the Brodeur Peninsula of Baffin Island reveal incised V-shaped valleys on receding, similarly indicating their inability to alter the preexisting landscape.)
An extension of glaciological and geomorphological studies in north-central Baffin Island by the Geographical Branch is planned for the summer of 1962 and further light may be thrown on these problems.
23 November 1961
