The Editor,
Journal of Glaciology
Sir
Depth of the “frost table” on Arctic beaches, Cornwallis and Devon Islands, N.W.T., Canada
Although it seems unlikely that permafrost extends for any great distance offshore (Reference BrewerBrewer, 1958). permanently frozen ground at shallow depth is encountered below the intertidal zone of Arctic beaches. Experience on the gravel beaches of southern Cornwallis and Devon Islands in the Canadian Arctic Archipelago (lat. 74°N.) indicates that the depth of the active layer, clown to the frost table, in the con temporary beach zone reaches a maximum of 50-60 cm in mid- to late August. These values accord with those reported from engineering investigations at Milne Inlet in northern Baffin Island (Reference Samson and TordonSamson and Reference Samson and TordonTordon. 1969).
The data on the depth of the frost table presented below were collected over three held seasons at three sites as part of a broader program of investigations of beach conditions (Reference McCann and OwensMcCann and Owens, 1969,1970; Owens and Reference McCann and OwensMcCann, 1970), In each case the depths were determined by hand augering along a series of profile lines reaching from the lowest raised beaches to the intertidal zone. Figure 1 shows a typical frost-table profile from Radstock Bay, Devon Island, and the whole of the data are summarized in Table I. The depths recorded represent the depth at which very firm resistance was met in augering. If ice chippings were not brought up on the auger tip, a second boring was undertaken. Several trenches were also cut across the intertidal zone as a check to the auger figures. The actual beach surface profiles below which the depth of the frost table was measured remained almost static during the period of observations at the first two sites and, though there were changes on the Radstock Bay beach between 17 and 29 August 1969, these were not such as to affect the comparability of the two sets of figures. The data reveal a progressive increase in the depth of the active layer throughout the summer, from 0.25 m in late June-early July to 0.60 m in late August. There appears to be no significant increase in depth seawards across the intertidal zone.
Frost-table profile, Radstock Bay beach, 17 August 1969.
Depth or "FROST TABLE" on three heaches on cornwallis and devon islands, N.W.T.
In 1969, a scheme was devised for recording sub-surface temperatures in the Radstock Bay beach down to depths of 1 m at high- and low-tide levels. Instrumentation involved the use of copper-constantan thermocouples mounted at 10 cm intervals along wooden dowelling rods, which were to be inserted into holes drilled into the beach gravels and permafrost by a petrol-driven drill. Unfortunately for the beach project, it proved loo difficult to install a thermocouple rod at low tide due to pack-ice conditions, but a high-tide rod was successfully inserted on 31 July and readings were taken on that day and on 1, 4, 7 and 8 August. Somewhat unusual storm conditions of erosion, with large waves driving pack ice onto the beach smashed the rod on the night of 11 August and made it impossible to re-establish the position. However, the method of observation of sub-surface beach temperatures was shown to be viable and the five sets of readings plotted in Figure 2 are regarded as accurate to within 0.2°F (0.11°C)
Sub-surface temperatures, Radstock Bay beach.
Below a depth of 30-40 cm, sub-surface temperatures were below freezing point and remained relatively constant throughout the 8 d of observation, indicating that the frost table lies at this level and that little heat was passing downwards into the permafrost. Between 30 cm depth and the beach surface there is considerable variation in temperature from day to day. All the readings were taken at a similar time of day—late evening between 20.15 and 22.00 h—and these variations can be related to variation in daily weather conditions.
Department of Geography,
McMaster University,
Hamilton,
Ontario, Canada
15 June1970
S. B. Mccanh
F. G. Hannell
