Can ice-cliffs explain the debris-cover anomaly? New insights from Changri Nup Glacier, Nepal, Central Himalaya

Abstract

Abstract. Ice cliff backwasting on debris-covered glaciers is recognized as an important process, potentially responsible for the so-called "debris-cover anomaly", i.e. the fact that debris-covered and debris-free glacier tongues appear to have similar thinning rates in Himalaya. In this study, we assess the total contribution of ice cliff backwasting to the net ablation of the tongue of the Changri Nup Glacier over two years. Detailed terrestrial photogrammetry surveys were conducted on select ice cliffs in November 2015 and 2016, and the entire glacier tongue was surveyed with unmanned air vehicles (UAVs) and 5Pléiades tri-stereo imagery in November 2015, November 2016, and November 2017. The total difference between the volume loss from ice cliffs measured with the terrestrial photogrammetry, considered as the reference data, and the UAV and Pléiades was less than 3 % and 7 %, respectively, demonstrating the ability of these datasets to measure volume loss from ice cliffs. For the period November 2015-November 2016 (resp. November 2016-November 2017), using UAV and Pléiades over the entire glacier tongue, we found that ice cliffs, which cover 7 % (resp. 8 %) of the planar area, contribute to 23 ± 5 % (resp. 24 ± 10 5 %) of the total net ablation of Changri Nup Glacier tongue. Ice cliffs have a net ablation rate 3.1 ± 0.6 (resp. 3.0 ± 0.6) times higher than the average glacier tongue surface. However, on Changri Nup Glacier, ice cliffs cannot compensate for the reduction of ablation due to debris-cover. Reduced ablation and lower emergence velocities on debris-covered glacier tongues could be responsible for the debris-cover anomaly.

Glacier area and the variability of glacier change

“…1a). Overall, this analysis supports the observed area-independent thinning of glaciers in the Himalaya (Salerno et al, 2017;Brun et al, 2018) and the Alps (Fischer et al, 2015;Rabatel et al, 2016) as discussed above.…”

“…The area-independent thinning rate of glaciers have also been observed in the Khumbu region of the Himalaya (Salerno et al, 2017). Strong evidence in favour of this trend in several glacierised regions of High Mountain Asia has recently been provided by an analysis of thinning data from more than 6000 glaciers larger than 2 km 2 (Brun et al, 2018).…”

“…Thus, the area-volume scaling law (Bahr et al, 2015), together with the empirical scaling ofȦ with A, provide an understanding of the area-independent thinning rate as observed in the Himalaya (Salerno et al, 2017;Brun et al, 2018) or Alps (Fischer et al, 2015;Rabatel et al, 2016).…”

“…Apart from the above factors, which exert influence by altering the surface mass-balance forcing, various geometrical variables like slope, area, aspect and hypsometry of glaciers have also been investigated for their possible influences on the glacier-to-glacier variability of thinning rates. These studies have revealed, for example, a significant control of glacier slope on regional-scale glacier thinning rate distribution in the high mountain Asia (Salerno et al, 2017;Brun et al, 2018) or in the Alps (Huss, 2012;Fischer et al, 2015;Rabatel et al, 2016), with gently sloping glacier showing higher loss rates. These trends may be understood in terms of a larger climate sensitivity and response time of the gently sloping glaciers (Oerlemans, 2001).…”

Contextualizing lobate debris aprons and glacier-like forms on Mars with debris-covered glaciers on Earth

“…The latest comprehensive studies on select glaciers found that debris-covered ice can exhibit less melt than clean ice (e.g. Brun et al, 2018; Sherpa et al, 2017; Vincent et al, 2016), and while regional mass balance is not entirely negative (e.g. Bolch et al, 2017; Brun et al, 2016, 2019; Kääb et al, 2012, 2015), glacier loss and slowdown are generally the dominant modern signals that have been observed (e.g.…”