March 18, 2021
Bailang (B) and Angge Glacier (A) in 1995 and 2020 Landsat images indicating retreat and lake expansion. Red arrow is the 1995 terminus location, yellow arrow the 2020 terminus location, purple arrow rock ridges that expand separating tributaries. Chubda Glacier (C) to the south and an unnamed glacier Point D between Angge and Bailang.
Bailang Glacier and Angge Glacier, China are adjacent to the Chubda Glacier, Bhutan, They drain north from Chura Kang and are summer accumulation type glaciers that end in proglacial lakes. The glacier runoff feeds the Xung Qu River a tributary of the Kuri Chhu in Bhutan that powers the Kurichhu Hydropower plant a 60 mw run of river plant in Eastern Bhutan. Both lakes are impounded by broad moraines that show no sign of instability for glacier lake outburst flood. The number of glacier lakes in the adjacent Pumqu Basin to the west has increased from 199 to 254 since the 1970’s with less than 10% deemed dangerous (Che et al, 2014). In the Yi’ong Zangbo basin to the east Hongyu et al (2020) observed that from 1970 to 2016 total area of glaciers in the basin decreased by 35%, whereas the number of glacial lakes increased by 86. Here we compare Landsat images from 1995 and 2020 to identify their response to climate change.
Bailang Glacier in 1995 terminated in a proglacial lake that was 2.1 km long at an elevation of ~5170 m, red arrow. Angge Glacier terminated in a lake that was 1 km long at an elevation of ~5020 m. Between the two is an unnamed glacier labeled “D” here that does not end in a proglacial lake. By 2001 both glaciers experienced minor retreat of less than 250 m. By 2014 Bailang Glacier had retreated 800-900 m and the lake was now 3 km long and had no change in water level. A key tributary on the west side near the purple arrow had also detached. Angge Glacier retreat from 1995 to 2015 was 700 to 800 m, with the glacier retreating to a westward bend in the lake basin. The glacier has an icefall just above the current terminus suggesting the lake basin will soon end, which should slow retreat. The D Glacier between them has developed a proglacial lake as well. By 2020 the Bailang Glacier has retreated 1300 m since 1985 and has lost connection with tributaries on either side of the ridge on the west side of the glacier noted by the purple arrow. Angge Glacier has retreated 1100 m since 1995 and has a very narrow connection to the lake, which is now ~2 km long. The glacier in between Bailang and Angge, D Glacier, has developed a 900 m long proglacial lake which also matches the retreat during the last 25 years. This glacier has lost contact with its western tributary as well at western purple arrow.
Bailang (B) and Angge Glacier (A) in 2001 and 2014 Landsat images indicating retreat and lake expansion. Red arrow is the 1995 terminus location, yellow arrow the 2020 terminus location, purple arrow rock ridges that expand separating tributaries. Chubda Glacier (C) to the south and an unnamed glacier Point D between Angge and Bailang.