Inventory of Glaciers in the Canadian Rockies
The first Canadian glacier inventory was carried out between 1969 and 1974. Canada’s Department of Energy, Mining and Resources used 1:30,000 to 1:60,000 scale aerial photos to identify perennial snow and ice.
The outlines of the identified glaciers were transferred to work maps and later digitized and compiled onto a 1:500,000 scale final map. The 1:500,000 maps are the published product and due to the scale, the area of the perennial snow and ice cannot be found with high accuracy. Furthermore, the published maps do not distinguish between only snow and presence of glacial ice. Glacier type (i.e. valley, cirque and hanging) is also not included in the final product.
In total, the initial inventory found 1,524 areas of perennial snow and ice in the Nelson River catchment. As the project came to a halt in 1974, glaciers north of the Nelson River Drainage basin were not counted or mapped.
In a subsequent effort, Natural Resources Canada produced 1:50,000 scale topographic maps of the Canadian Rockies. Glaciers from these maps were later digitized. This glacier layer is also not without its problems. For instance, it was produced using maps ranging from 1969 to 1998, a period during which glaciers experienced extensive retreat. Many of the glacier outlines are therefore not representative of present extents and the temporal resolution can be considered poor.
The compilation did point out some important statistics regarding the glacier size distribution: a total count of 3,271 glaciers in the Rocky and Columbia Mountains of Alberta and B.C. covered an area of 4,298 km2, giving an average glacier size of 1.3 km2. This means that the majority of glaciers in the interior ranges of western Canada are small and vulnerable to ongoing retreat.
Updated Maps of Glacier Coverage
The most recent and thorough inventory of glaciers in western Canada is the recently-completed compilation of Bolch et al. (2010) as part of the Western Canadian Cryosphere Network (WC2N). This dataset has been contributed as a public resource to the Global Land Ice Measurement from Space (GLIMS) glacier inventory. Two complete time slices have been compiled for the glaciers of Alberta and B.C. (1985 and 2005).
In comparison to the NRCan glacier layer, the WC2N outlines appear to be of higher resolution and have less smoothed borders. It follows that the WC2N inventory and glacier outlines are the best option for both spatial and temporal resolution, although it is not without some shortcomings.
Area and Number of Glaciers in Alberta
The WC2N or Bolch et al. (2010) inventory estimates a total of 17,595 glaciers in B.C. and Alberta in 2005, covering 26,728 km2. Since most of these glaciers reside west of the continental divide, the 2005 inventory identified only 1,167 glaciers in Alberta, covering an area of 786 km2. Note that fragmentation of ice masses gave rise to an increase in Alberta’s glaciers from 926 to 1,167 (over the period 1985 to 2005), despite a 25.4% loss in total glaciated area.
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Glacier Volumes in Alberta
Glacier volume measurements require a labour and capital-intensive approach. Volume-area (V-A) and other scaling relations have been derived from the available global ice-thickness data. Glacier thickness data is available from six sites in the Rocky Mountains: the Grinnell (Montana), Dinwoody (Wyoming), Haig, Rae, Peyto, and Athabasca Glaciers. The latter four are in Alberta. Glacier volumes are estimated to be 55km3 (± 15km3) for all of the glaciers in the eastern slopes, with 47km3 (± 15km3) in Alberta and the remainder in the eastward-draining ice masses of the Peace River Basin in B.C.
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Classification and Types of Glaciers
The report classifies the glacier inventories by type: cirque glaciers, hanging glaciers, valley glaciers, or icefields. Of the 662 snow and ice features identified on three EMR maps, 403 resided within regions with high-resolution satellite imagery, but only 151 glaciers could be clearly identified and categorized. Within the areas with high-resolution imagery, 41 (~10%) of the original snow/ice patches are no longer present.
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