Thermal Regimen of Firn on Upper Seward Glacier, Yukon Territory, Canada

Abstract

Temperatures were measured within the firn and ice of the upper reaches of the Seward Glacier (referred to in this paper as the "upper Seward Glacier") to a depth of 204 ft. (62.2 m.) by means of thermohms and a Wheatstone bridge. Thermal boring proved a feasible means of penetrating this glacier. The winter's chilled layer here develops a thickness of 40–50 ft. (12.2–15.2 m.) and attains temperatures of at least −13° C. Deterioration of the chilled Iayer is rapid and irregular in the final phase and is attributed largely to freezing of percolating melt water. Melt water exerts such a powerful influence on thermal regimen that bodies of firn in environments with mean annual temperatures below freezing may, nonetheless, be geophyaically temperate because of extensive warming by melt water in summer. In both 1948 and 1949, the annual chilled layer on the upper Seward Glacier disappeared within the first 10 days of July. The slow development and rapid deterioration of diurnal crusts on firn and the lag effects at depth reproduce in miniature the behavior of the annual chilled layer. On the basis of its thermal regimen the upper Seward Glacier is geophysically temperate.

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