Active Layer Changes (1968 to 1993) following the Forest-Tundra Fire near Inuvik, N.W.T., Canada

Abstract

Active layer changes after the 1968 forest-tundra fire at Inuvik, N.W.T., have been monitored from 1968 to 1993 at three burned and two unburned sites. In addition, a burned site has been used for field experiments on changes to the active layer. The active layer depths have been measured at the same points, marked initially by 58 permanent stakes, nearly every year and the vegetation described in general terms and frequently photographed. The changes to the active layer have been site specific so that broad generalizations for the three burned and the two unburned sites for the 25-yr period are limited. For brief periods, summer air temperatures correlated reasonably well with changes in the depth of the active layer at two sites. For only one summer (1993), active layer depth increases were controlled primarily by the previous winter's temperature and snow conditions. At all sites where the active layer deepened, the underlying ice-rich permafrost thawed to produce thaw settlement. The addition of thaw water to the bottom of the active layer at the more poorly drained sites created moist conditions which favored vegetation growth. In response to the vegetation growth which shielded the ground surface, active layer depths decreased, permafrost aggraded upward, and there was some ground uplift from the growth of aggradational ice. Although there was a pronounced winter warming during the observation period, the effects on ground warming were offset, to an unknown degree, by a decrease in winter snow depths which led to winter ground cooling.