Height of the Glaciation Level in Northern British Columbia and Southeastern Alaska

Abstract

In glacierized areas there exists a critical height under which glaciers do not normally develop. Above this height glaciers will form on mountains with a favourable topography (e.g., not too steep slopes). It is of glaciological interest to determine this critical height because it has relevance to certain climatological elements, e.g., continentality.

A previously developed method, the so-called “summit method” was used in this study to determine the critical height which it is necessary for mountains to exceed—within a given area—to obtain a glacier. This critical height is termed “glaciation level”. Studies of topographic maps, in general covering a unit area of 15×27 km (one “half-sheet” 1: 50,000 map), revealed the summit elevations of the highest glacier-free and lowest glacier-carrying mountains. The height of the glaciation level was calculated as the arithmetic mean of these two summit elevations. To check the quality of source maps, a comparative study was performed in areas where maps of various scales were available. In general, a somewhat higher glaciation level was found when the 1: 250,000 maps were used. This is thought to be a result of generalization and omittance of small glaciers on these maps.

Resulting heights, valid for each single unit of area, were plotted on a glacier map at a scale of 1: 2,000,000 and 100-m contours were drawn. The resulting map indicated that the height of the glaciation level increases from about 900 or 1000 m at the coast to a maximum of 2700 m in the Rocky Mountains. However, there are certain exceptions from this general rule—local maxima and certain depressions occur.

Depressions in the height of the glaciation level are thought to be related to large-scale topographic openings in the Coast Mountain system, allowing maritime air masses to penetrate further inland in certain areas. Detailed winter precipitation studies in the Kitimat—Terrace area support this assumption. Comparisons were also made with a map of continentality for Canada that indicated a similar depression in the same area. Snow-line investigations in Scandinavia have also shown local depressions in transient snow line altitude in areas of maritime influence.