harrison lake glacier retreat – From a Glaciers Perspective

Icemantle Glacier in Landsat images from 2000-2022 illustrating the retreat exposing a new lake (Point A) and separation at Point D. Also the lack of snowcover in 2009, 2015 and 2022 indicative of mass balance loss that drives retreat.

Icemantle Glacier is on the north side of Greenmantle Peak just north of Snowcap Lake in the Lilloet River Basin of southwest British Columbia. Here we focus on the retreat and thinning of the glacier this century using Landsat imagery and then lack of snowcover extending into mid-October in 2022 using Sentinel images.

In 2000 the glacier extended across the basin where the new lake would soon form. The Landsat image from July 31, indicates near complete snowcover at the halfway point of themelt season. By 2009 a frining lake is evident between Point A and B. Snowcover is limited to the upper reaches above 2100 m. By 2015 the lake is evident and has numerous icebergs. Below Point B a bedrock knob is just emerging. At Point D the tributary is completing separation. In 2022 the glacier is receding from the lake basin. The bedrock knob below Point B in Landsat image and at Point A in Sentinel image has emerged. The snowline rises from 2000-2050 m in early September to 2100-2150 m by mid-October. At this point the glacier should have new snowcover, and not still be actively melting.

The lake has an area of 0.3 km2 and will not expand much more. The glacier has retreated 600 m this century and given the lack of consistent retained snowcover cannot survive current climate (Pelto, 2010). The thinning of this glacier has led to expansion and emergence of bedrock knobs at Point A-C. The retreat of this glacier fits the local pattern seen at nearby Stave Glacier. The surface darkening due to less snowcover and snowcover that has more light absorbing particles at its surfaces enhances melt. Forest fires do result in some darkening of the glacier surface (Orlove, 2020).

Icemantle Glacier in early September, when snow melt is usually largely offset by occassional new snowfall, and mid-October 2022 after a month of continue ablation reduced snowcover significantly. Notice the expansion and emergence of bedrock at Point A-C.

“Big Bend” Glacier is an unnamed glacier west of Big Bend Peak north of Harrison Lake in Southwest British Columbia. In 1985 the glacier was 2.6 km long filling a low valley with a surface elevation of 1600-1800 m elevation, the topographic map indicates this basic size. Here we utilize Landsat imagery to identify the changes in the glacier from 1985-2014 due to climate change. In essence the glaciated basin is transitioning to an alpine lake basin, quickly.

Topographic map of the Big Bend Glacier area.

In 1985 the glacier extends to the big bend in the valley marking its eastern end, red arrow. the yellow arrow indicates an area near 1800 m where the glacier extends across the valley. In 1992 there has been little retreat but evident thinning is leading to lake formation at the terminus and narrowing of the glacier at the red arrow. In 2002 thinning is leading to expansion of a proglacial lake both west and south of the red arrow. The terminus retreat has still been limited, thinning is evident at the yellow arrow.

In 2013 a new alpine lake that is approximately 1 km long has formed, as the terminus area of the glacier has collapsed. In 2014 an area of bedrock and a small lake has developed at the yellow arrow. There is no retained snowpack below the yellow arrow in 2013, and no retained snowpack in at all in 2014. This will likely be the case in 2015 as well. This glacier has a lower top elevation than most in the region and will be more impacted by the warm winter conditions and high snowline of 2015. The retreat from 1985 to 2014 has been 1.1 km. This is 40% of the entire glacier length gone in 30 years. The lake itself has a deep blue color suggesting limited glacier sediment input, further indicating a lack of motion of the glacier currently or in the near past.

The glacier retreat has been more extensive than Stave Glacier or Snowcap Glacier to its east. Koch et al,(2009) observed a widespread retreat and glacier area loss in Garibaldi Provincial Park just to the west, with 20% area loss from 1988-2005. Place Glacier is a short distance north of Big Bend Glacier has its mass balance has lost an average of 25 m of water equivalent (28 m ice) thickness since 1984, see bottom chart. This has been higher but similar in trend to other glaciers in the region. Big Bend will disappear soon just as we obsserved already happened at Milk Lake Glacier, North Cascades, Washington.

1985 Landsat Image