Alberta glacier thinning – From a Glaciers Perspective

Bonnet Glacier in Sentinel 2 images indicating the emergence of bedrock due to thinning in the former accumulation zone, Point A. Note the lack of retained snowcover in both years with at least a month left in the melt season.

Bonnet Glacier, Alberta drains north from Bonnet Peak in the Sawback Range 30 km east of the Rocky Mountain Crest. It is at the headwaters of Douglas Creek that feeds into the Red Deer River. In 2017 we reported on the formation of new alpine lakes and the 900 m retreat of the glacier, 20% of its length, from 1987-2016 (Pelto, 2017). Here we examine changes from 1987-2021, including developments in the accumulation zone that provide a future forecast. An inventory 0f glaciers in the Canadian Rockies indicated area loss of 15% from 1985 to 2005 (Bolch et al, 2010), with Alberta glaciers losing area at a higher rate. Tennant et al (2012) noted that from 1919-2006 the glaciers in the central and southern Canadian Rocky Mountains lost 40% of their area. Of the 523 glaciers they observed 17 disappeared and 124 separated. Columbia Icefield, 125km northwest, lost 23 % of its area from 1919-2009 (Tennant and Menounos, 2013).

In 1987 and 1990 the accumulation zone is limited to upper periphery of Bonnet Glacier. In 2015 and 2016 the accumulation zone is restricted to the northeastern periphery. This is indicative of a glacier without a significant persistent accumulation zone. The consistent mass loss is driving the retreat and glacier thinning. In 2018 in the midst of what had been the accumulation zone a small area of bedrock has emerged at Point A. By 2021 this area has expanded substantially with the two bedrock areas poised to merge soon. This thinning in the midst of the former accumulation zone is indicative of a glacier that cannot survive (Pelto, 2010). In 2015, 2018 and 2021 the accumulation area ratio was between 10-15%, a value that typically results in glacier annual mass balance of more than -2 m. The area of main proglacial expanded 50% from 2016 to 2021 to 0.33 square kilometers.

Bonnet Glacier in Landsat images from 1987, 2016 and 2021 indicating retreat. Red arrows indicate 1987 margin, yellow arrows 2016 and the green arrow 2021. Point A indicates the emerging bedrock.

Bonnet Glacier in Landsat images from 1990, 2015 and 2021 indicating retreat. Purple arrows indicate lakes that have formed due to retreat. Point A indicates the emerging bedrock.

Scott Glacier, Alberta in 1987 and 2019 Landsat images. Yellow arrow indicates the 2019 terminus location and Point A and B are areas of bedrock expansion amidst the glacier.

Scott Glacier is the largest outlet glacier of the Hooker Icefield the drains into the Whirpool River and then the Athabasca River. The icefield straddles the BC/Alberta border. Jiskoot et al (2009) examined the behavior of the Clemenceau-Chaba Icefield, 25 km south finding that from the mid 1980’s to 2001 the Clemenceau Icefield glaciers lost 42 square kilometers, or 14% of their area. On Columbia Icefield 60 km to the southeast Tennant and Menounos (2013) found that from 1919-2009 glaciers had a mean retreat of 1150 m and mean thinning of 49 m for glaciers, with the fastest rate of loss from 2000-2009.

The Scott Glacier in 1987 had terminated at 1500 m, within 300 m of an alpine lake. At Point A there is a convex aspect to the glacier as it passes over a subglacial knob. The snowline is near this knob at 2200 m. In 1998 there is limited retreat of the main terminus and Point A is still beneath the ice. The snowline is just above Point A at 2250 m. In 2014 the glacier has retreated to the base of a step at ~1800 m. The snowline is well above Point A at 2450 m. In 2019 the terminus has retreated 750 m since 1987. Point A has emerged as a bedrock knob at the glacier surface. At Point B a rock rib has widened since 1987 and extends further into the heart of the glacier. The snowline in 2019 is at 2400 m at the end of July.

Scott Glacier’s retreat is less extensive than other nearby glaciers such as Chaba Glacier , Cummins Glacier and Columbia Glacier.

Scott Glacier, Alberta in 1998 and 2014 Landsat images. Yellow arrow indicates the 2019 terminus location and Point A and B are areas of bedrock expansion amidst the glacier.

Scott Glacier map indicating the glacier margins in the 1990’s.

Scott Glacier Digital Globe image indicating 1987 terminus location (red arrow) and 2019 terminus location yellow arrow. Point A is where bedrock is emerging and Point B is where the bedrock ridge is extending across glacier. Both Point A and B indicate bedrock steps that the glacier steepens as it flows over. The glacier remains crevassed to the front indicating no stagnant zone.