ABSTRACT: Twentieth-Century change in glaciers of the Bendor and Shulaps Ranges, British Columbia Coast Mountains.

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Abstract

Recent mountain glacier wastage has been almost universal, but punctuated by readvances in some regions: c.1965-85 in the Alps, Caucasus and Iceland, and in the 1990s in Norway and New Zealand. The degree of recession has varied both regionally and with glacier size and position. Thus it is useful to make regional studies, to complement the annual monitoring of a small sample of glaciers (Haeberli et al. 1998). The southern Coast Mountains of British Columbia (Ryder, 1981) form a glacier region (Østrem, 1966) almost as extensive as the Alps but with relatively little published information other than for two glaciers monitored for mass balance (Sentinel and Place Glaciers, near Pemberton), and several glaciers near Whistler ski resort whose termini are checked annually by Karl Ricker. Topographic maps published at 1/50k in the 1970s and 1/20k in the 1990s omitted many small glaciers and show errors in interpretation due to snowbanks and debris cover: late summer air photography and/or fieldwork is necessary for accurate delimitation of small glaciers. Though very poorly known, these are important as they respond rapidly to climatic changes, especially increased temperature. On the landward side of the Coast Mountains, west of Lillooet and northeast of Pemberton, the Bendor and Shulaps Ranges of the Bridge River District had some 131 small glaciers and glacierets, based on my interpretation of 1947 and 1951 air photographs (Evans, 1977 and 1990). The latest air photographs are from 1997 but show too much snow to define glaciers shorter than about 1 km. Thus the glaciers were remapped from September 1993 Forest Service air photographs, which have very low snow cover. The fieldwork supported by the QRA was undertaken in August 2003 to reoccupy as many photo stations as possible and take ground photos comparable to those from 1965 and 1966, giving 38 years of change. Despite access problems, this was successful for the northern and western Bendor Range and the central Shulaps Range. All these glaciers have suffered net loss, both 1965-2003 and 1951-1993, but few have disappeared entirely. Glaciers which were thin and deteriorating in 1965 are still present. Some steep north-facing glaciers have receded very little since 1951, but those over 1 km long have lost hundreds of metres of their tongues. On Whitecap Mountain (2918 m), the length of the east-facing glacier, initially 1880 m, diminished by 760 m 1951-1993, while its neighbour facing northeast lost only 180 m of its initial 2020 m. Keary Glacier lost 160 m of its 1940 m length, and the bottom 50 m of its initial 750 m height range. Immediately northwest of Mount Truax in the northern Bendor Range, two lakes have enlarged considerably and the glaciers are no longer in contact with them. One glacier has lost 240 m of its 1250m length, the other, 260 of 600 m. The hanging glaciers on Shulaps Peak (2880 m) have lost very little. In general, where the 1/20k maps, based on 1988 air photographs, had accurately identified glacier margins, there was little change by 1993. A multi-temporal inventory of these glaciers is being produced, including their Little Ice Age (LIA) extents. Analysis of this will relate length and snout altitude change to glacier size, gradient, altitude and aspect. West of the Bendor Range and east of the Bridge - Lillooet Ice Field, there are numerous larger glaciers: these appear to be continuing their rapid post-LIA wastage. Their 1993, 1951 and LIA extents have been mapped and will provide useful comparisons with the small glaciers farther east. These small glaciers have shared the global trend of recession in the second half of the twentieth century, as shown also by negative mass balances for the Sentinel and Place Glaciers. However, it is not the smallest that have lost most either relatively or absolutely. The data will contribute to development of a model for differential response of glaciers to recent climatic change, in relation to size, altitude, aspect and detailed position.

Bibliography of Canadian Geomorphology