The Editor,
Journal of Glaciology
Sir,
In a previous letter to the Editor (Reference McCann and HannellMcCann and Hannell, 1971) data were presented about the depth of the frost table on three gravel beaches in the Canadian Arctic. Their observations indicated that in the summer permanently frozen ground exists at relatively shallow depths across the intertidal zone. A further investigation of beaches north of lat. 72º, at widely separated sites in the Canadian Arctic, has shown similar conditions even though the beaches were characterized by varying sediment types and exposure to wave action. The observations presented here, which are summarized in Table I, are thus intended to be more widely representative of conditions throughout the eastern Archipelago.
The frost-table depths were recorded by hand auger, as described previously, at a series of common points along the lines of beach profiles surveyed from the back shore to low-water mark. Between five and ten profiles were surveyed at each site, depending on local conditions, and the values recorded in columns 5–9 of Table I are thus the mean of several observations. The frost-table depths presented in column 4 are the mean of all observations taken at each site regardless of position on the beach. The data, though obtained at different times from different localities, are arranged sequentially and the seasonal pattern is evident. Early in the open-water season the frost table tends to be nearest the beach surface toward low-tide level, but at the end of the season when air temperatures have fallen below freezing the opposite applies. The greatest individual measurements of frost-table depth, over 90 cm, were recorded on the sandy beaches at Pond Inlet in late August; elsewhere few depths greater than 75 cm were recorded. An exception to the latter occurred on the lower beach slope in late September at Radstock Bay where depths of up to 1.2 m were found; however, the increased depth is actually less because of the occurrence of buried lenses of frozen material less than 15.0 cm from the beach surface. An attempt to correlate frost-table depths with beach sediment size, and with aspect, was unsuccessful due to the considerable local variations in these controls at each site. Investigations of the changes in frost-table depths over short time intervals gave the following results: at the site on northern Somerset Island the frost table increased, across the whole foreshore, by 2.4 cm in the 10 day period, 3–13 July 1972; at the site on Hooker Bay the frost-table depth increased, across the whole foreshore, by 3.8 cm in the 8 day period 2–10 August 1972.
10 December 1973
