The Transient Snowline and Glacier Mass Balance in Southern British Columbia and Alberta, Canada

The transient snowline can be easily defined on air photographs of glaciers having a reasonably even topography, and its height can then be determined from topographic maps of good quality. A study of an extensive air photograph cover made almost simultaneously in two selected regions in western Canada in August, 1966, has shown that neigh-bouring glaciers often exhibit equal or very similar transient snowline heights. Exceptions can be found for glaciers in extreme positions, but such deviations can be more or less subdued by the calculation of a mean height for several glaciers within small areas.A definite trend of higher transient snowline altitudes from southwest towards northeast was found within both regions, and this trend is demonstrated by isohypses drawn on maps. Comparisons were made with the height of the glaciation level which was similarly plotted on the maps (contours redrawn from Östrem 1966). Both the glaciation level and the height of the transient snowline can be thought of as invisible surfaces intersecting the landscape at various altitudes, the glaciation level normally being the highest. The two surfaces are tilted with the highest elevation in their northeastern parts.Continuing detailed mass balance investigations on 5 glaciers disposed along an east-west section across the Cordillera were introduced in this study by the determination of the “present” height of the equilibrium line, i.e. its altitude in a year of steady state conditions regarding the mass balance. When this eqilibrium line height was plotted on southwest-northeast profiles across the investigated regions it was found to be just above the transient snowline as of 22–24 August 1966.The conclusion is drawn that if simultaneous air photograph cover or high-resolution satellite imagery were made available throughout the summer melt season one could closely follow the mass balance variations during the summer and relatively easily extrapolate results from field studies on a few glaciers to almost all glaciers within the photographed region. When the transient snowline reaches positions higher than the present equilibrium line height (for a “balanced year”) this indicates that the glaciers have a negative mass balance and extra amounts of melt water are yielded to rivers in glacierized basins.