Ice cliff contribution to the tongue-wide ablation of Changri Nup Glacier, Nepal, central Himalaya

• Published in: The cryosphere Vol. 12; no. 11; pp. 3439 - 3457
• Main Authors: Brun, Fanny, Wagnon, Patrick, Berthier, Etienne, Shea, Joseph M., Immerzeel, Walter W., Kraaijenbrink, Philip D. A., Vincent, Christian, Reverchon, Camille, Shrestha, Dibas, Arnaud, Yves
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 01-11-2018; Copernicus; Copernicus Publications
• Subjects: Ablation; Aerial surveys; Cliffs; Debris; Detritus; Earth Sciences; Glacial drift; Glacier ice; Glacier tongues; Glaciers; Glaciology; Ice; Imagery; Photogrammetry; Sciences of the Universe; Surveys; Terrestrial environments; Thinning; Unmanned aerial vehicles; Nepal
• ISSN: 1994-0424; 1994-0416; 1994-0424; 1994-0416
• DOI: 10.5194/tc-12-3439-2018

Ice cliff backwasting on debris-covered glaciers is recognized
as an important mass-loss process that is potentially responsible for the
“debris-cover anomaly”, i.e. the fact that debris-covered and
debris-free glacier tongues appear to have similar thinning rates in the
Himalaya. In this study, we quantify the total contribution of ice cliff
backwasting to the net ablation of the tongue of Changri Nup Glacier, Nepal,
between 2015 and 2017. Detailed backwasting and surface thinning rates were
obtained from terrestrial photogrammetry collected in November 2015 and 2016,
unmanned air vehicle (UAV) surveys conducted in November 2015, 2016 and 2017,
and Pléiades tri-stereo imagery obtained in November 2015, 2016 and 2017.
UAV- and Pléiades-derived ice cliff volume loss estimates were
3 % and 7 % less than the value calculated from the
reference terrestrial photogrammetry. Ice cliffs cover between 7 % and
8 % of the total map view area of the Changri Nup tongue. Yet from
November 2015 to November 2016 (November 2016 to November 2017), ice cliffs
contributed to 23±5 % (24±5 %) of the total ablation observed
on the tongue. Ice cliffs therefore have a net ablation rate 3.1±0.6
(3.0±0.6) times higher than the average glacier tongue surface.
However, on Changri Nup Glacier, ice cliffs still cannot compensate for the
reduction in ablation due to debris-cover. In addition to cliff enhancement,
a combination of reduced ablation and lower emergence velocities could be
responsible for the debris-cover anomaly on debris-covered tongues.