Climatic Effects on Glacier Distribution Across the Southern Coast Mountains. B.C., Canada

Abstract

Over a distance of 150 km inland across British Columbia, glaciation level (altitudinal threshold for glacier generation) rises north-eastward from 1800 m near Jervis Inlet, to 2800m near Lillooet on Fraser River. The methods of Østrem (1966b) are revised for more detailed work from air photographs; inclusion of small but active glaciers gives a glaciation level some 200 m below Østrem’s from 1:250 000 maps, or 110 m below that from 1:50 000 maps.Mountains which rise slightly above the altitudinal threshold invariably support glaciers only on their northerly slopes. Mountain crests need to be some 300 m higher before they support glaciers on most slopes: this defines an “all-sided” glaciation level. Since summit heights vary from 2500 to 2900 m through most of the transect considered here, east- and west-facing glacier sources are found mainly in the coastal half; south-facing sources are rare outside icefields.For particular mountain ranges bounded by valleys and low passes, the aspects (azimuths) of glacier sources can be summarised by vector analysis. The higher the range rises above glaciation level, the more widespread the aspects represented and the weaker the resultant vector strength. Strengths as high as 90% are observed on landward ranges with a relatively sunny, continental climate, while 20-60% is found for coastal ranges where cloudiness reduces slope variations in incident solar radiation. Vector mean aspects throughout are close to north.Perennial lee drifts on icefields show that wind directions during and immediately after snowfalls are from the south or from south-south-west. Together with orographic details of the glaciation level, this suggests that snow-bearing winds come from the south rather than the west. These winds reinforce radiation contrasts, giving north-south asymmetry of glacier aspect even near the coast.