ABSTRACT: Topographic influences on recent changes of small cirque glaciers in the Torngat Mountains of northern Labrador.

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Abstract

Small alpine glaciers (<1.5 km2) in the Torngat Mountains, northern Labrador, have experienced marked decline in areal extent between 2005 and 2007 with an average change of -21%. Not all glaciers have responded the same, however, with a third either growing in area by an average of 0.02 km2 (n=10) or shrinking in area by less than 0.02 km2 (n=9), which given the spatial resolution of the aerial and satellite imagery used for change detection likely means an undetectable change. The dramatic overall recent decline in areal extent of Torngat glaciers is interpreted as a glaciological response to a regional, multidecadal trend towards lower winter precipitation, coupled with anomalously warm summers in the past decade. Small mountain glaciers in western Canada and Alaska have also exhibited varied responses to recent climate warming, which was in part attributed to local topographic factors (DeBeer & Sharp, 2009; Manley, 2009). On the basis of a short interval of glacier monitoring in the early 1980s, Rogerson (1986) hypothesized that topography is an important controlling factor for glacier survival in the Torngat Mountains. This presentation describes the current topographic setting of glaciers in the Torngat Mountains and reports preliminary results of analysis of recent glacier change in the context of local topographic controls. Glacier mapping from 2007 SPOT5 HRS satellite imagery revealed a total of 59 glaciers covering an area of 16.7 km2 and ranging in size from 0.05 to 1.24 km2. The glaciers occur within a coastal region defined by latitude 58° 40’ and 59° 50’ North. Most of the glaciers (56%) are smaller than 0.25 km2 and only one is larger than 1 km2. Glaciers in the Torngat Mountains typically occupy cirque basins with high backwalls, averaging 272 m above the ice surface, with a mean upslope contributing area of 0.41 km2. Relative upslope area, a ratio of the upslope contributing area to the glacier surface area, has a mean value of 1.5, indicating a high potential for snow accumulation and avalanching from the upslope catchment. Many glaciers are heavily debris-covered at lower elevations, with on average half the glacier surface covered by debris. Most (63%) have a northerly aspect (315-45° azimuth), which would maximize the shading effect from high backwalls, but 15% face south (135-235° azimuth). The elevations of the glacier termini vary from 245 m to 1080 m above sea level (asl), with 9 (15%) having a terminus above 1000 m asl. Approximately 70% of the glaciers are located within 30 km of the Labrador coast. Correlation of topographic variables with changes in areal extent suggest that shading of the glacier surface by high backwalls and large upslope catchment areas,which increase accumulation through snow drifting and avalanching, are signifi cant factors infl uencing local glacier response in the Torngat Mountains. Surface debris cover, which reduces ablation, was another important factor related to changes in glacier extent.

Bibliography of Canadian Geomorphology