Okay, 98 years technically. I’ve recently obtained high-quality scans of the Alberta/British Columbia Boundary Commission Survey maps, courtesy of Bob Sandford. They are real, and they are amazing. So after doing a quick georeferencing I’ve combined one of the maps with some recent imagery and datasets to produce this:
The survey maps from 1919 show glacier boundaries that line up well with the maximum glacier extents. Look for the trimlines that mark boundaries between vegetated areas and deglaciated areas. Significant retreats of Peyto Glacier, Bow Glacier, and Baker Glacier are clear from the animation. What’s less obvious is the change in surface height: not only are these glaciers melting back faster than they are advancing, but they are essentially deflating. Surface lowering is probably reducing the total volume of this ice mass faster than the retreat itself.
The topographic maps were constructed A.O. Wheeler, a pioneer of photogrammetry, and his survey team. Traversing up the divide between Alberta and British Columbia, Wheeler and his team set up and surveyed benchmark positions, and collected photographs from passes and high points all the way from the US border to north of Mt. Robson. Their expeditions took place over multiple seasons, with a median year of around 1919. Christina Tennant and Brian Menounos published a neat study in 2012 on historical glacier area change in the Rockies using these maps.
Having skiied the Wapta traverse a few years ago (okay, more like 15 years ago) the rate of glacier change that these historical data show really puts things in perspective. As in, you might be able to do the traverse without worrying about crevasses by the middle of the century. Thanks, #climatechange.