December 9, 2021
Swanson River Glaciers Retreat: Two Very Bad Summers in 2018 & 2019
Posted by Mauri Pelto
Swanson River glaciers, British Columbia in Landsat images from 1984 and 2019. EM=East Meade Glacier, CG=Canning, red arrows=1984 terminus, yellow arrow=2019 terminus, purple dots=snowline. Points 1-8 are specific glacier locations with very limited to no retained snowcover.
The Swanson River feeds into Tagish Lake in NW British Columbia. The watershed is host to dozens of glaciers. Here we exaine the retreat of the two largest glaciers in the watershed from 1984-2019, referred to as “East Meade” and “Canning Glacier” in this post. We also look at the loss of snowcover on glaciers across the watershed in 2018 and 2019. These glaciers are in the northeast sector of the Juneau Icefield, sharing a divide with the retreating Meade Glacier, Alaska. The Juneau Icefield Research Program focuses on glaciers to the south of these including the retreating Llewellyn Glacier.
In 1984 the two glacier tongues terminated at 1000 m, red arrow and the snowline was at 1350 m, purple dots. This was a year of positive glacier mass balance on the Juneau Icefield, where I was working that summer. By 1998 there has ben modest retreat and the snowline is at 1400-1450 m. The retained snowpack at the end of the summer is limited to the upper reaches of the tributary glaciers. This year was a negative balance year on the Juneau Icefield where I was busy probing snowpack.
By 2018 Canning Glacier had retreated 1400 m since 1984 and terminated at 1100 m. East Meade Glacier had retreated 1100 m since 1984 and terminated at 1100 m. In 2018 there is no retained snowpack on East Meade Glacier. There is limited snowpack at the top of some of the tributaries in wind deposition zones, but many ofthe small alpine glaciers in the area have no accumulation zone. This summer led to the highest snowline ever observed on the Taku Glacier (Pelto, 2019). In 2019 the snowlineis even higher and the glaciers of the Swanson River basin are laid bare. There is no snowpack on East Meade (1) or on the adjacent tributaries at Point 2 and 3. There is no snowpack retained on Canning Glacier (4) or on the alpine glaciers east of the Juneau Icefield at Point 6 and 8. At Point 5 and 7 each has a small patch of retained snowpack at its upper margin close below a peak.
These back to back summers are the type of conditions that lead to the loss of alpine glaciers when they become frequent enough to remove any retained snowpack not just from that year, but from previous years. The retreat of East Meade and Canning Glacier is much less than Meade Glacier, 4 km 1986-2018, and similar to Warm Creek Glacier.
Swanson River glaciers, British Columbia in Landsat images from 1998 and 2018. EM=East Meade Glacier, CG=Canning, red arrows=1984 terminus, yellow arrow=2019 terminus, purple dots=snowline.
Canadian Topographic map of the area EM=East Meade Glacier, CG=Canning Glacier and TL=Tagish Lake