British columbia glacier separation – 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.

Warm Creek, Norht Warm Creek (NW) and Bighorn (H) Glaciers in Northwest British Columbia in 1984 and 2017. Red arrows are the 1984 terminus location, yellow arrows the 2017 terminus locations and purple arrows where glaciers have separated.

In Northwestern British Columbia a group of unnamed glaciers drain into Tagish Lake via Warm Creek and Bighorn Creek. Here we examine the profound changes in three glaciers from 1984 to 2017 using Landsat imagery. 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 Bighorn Glacier (B) has two termini joined at 1500 m, with the northern terminus ending in two small proglacial lakes and the southern terminus extending down valley to the red arrow. In 1984 Warm Creek Glacier terminates in a small proglacial lake, red arrow. The North Warm Creek Glacier (NW) has two tributaries joining at 1350 m, 1 km above the terminus. In 1999 the snowline is at 1650 m on these glaciers leaving only 20% of Bighorn Glacier above the snowline. North Warm Creek Glacier tributaries have separated due to glacier retreat. Retreat has led to proglacial lake expansion at Warm Creek Glacier. In 2001 it is apparent that the retreat of the northern terminus of Bighorn Glacier has led to expansion of the proglacial lake. The snowline is lower in this 2001 image at 1500 m. By 2017 Bighorn Glacier has separated with nearly 1 km of bedrock separating the northern and southern sections. The southern terminus has retreated 1100 m and the northern terminus 500 m. The Warm Creek Glacier retreat from 1984-2017 is 1300 m, more than doubling the length of the lake. The North Warm Creek Glacier tributaries are now well separated. Retreat of the northern terminus has been 1000 m and 1200 m for the southern terminus. The snowline in 2017 is again at 1700 m, too high to sustain these glaciers. The retreat of these glaciers fit the pattern of other glaciers in Northwest British Columbia such as Llewellyn, Tulsequah and West Hoboe Glacier. Bolch et al (2010) noted a 11% loss in glacier area in the province from 1985-2005 and an 8% loss in the Northern Coast Mountains.

Warm Creek, Norht Warm Creek (NW) and Bighorn (H) Glaciers in Northwest British Columbia in 1999 and 2001. Red arrows are the 1984 terminus location, yellow arrows the 2017 terminus locations and purple arrows where glaciers have separated.