Reduced melt on debris-covered glaciers: investigations from Changri Nup
Glacier, Nepal

Vincent, Christian; Wagnon, Patrick; Shea, J. M.; Immerzeel, Walter W.; Kraaijenbrink, Philip; Shrestha, Dibas; Soruco, Álvaro; Arnaud, Yves; Brun, Fanny; Berthier, Étienne; Sherpa, Sonam Futi

doi:10.5194/tc-10-1845-2016

Cited by 139 publications

(171 citation statements)

References 54 publications

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“…Given that these features typically contribute ∼ 10-20 % of the total melt (Sakai et al, 2000;Reid and Brock, 2014), it is unlikely that they can lower the glacierwide mean melt rate on debris-covered glaciers sufficiently so that it matches that on the debris-free glaciers. Field measurements by Vincent et al (2016) seem to confirm this. It was also conjectured that a reduction in ice flux from upstream areas to the stagnant tongue may be behind the largerthan-expected thinning of debris-covered glacial ice (Kääb et al, 2012;Gardelle et al, 2012).…”

supporting

confidence: 69%

“…Also, it was reported that in the Pamir-Karakoram-Himalayas, depending on the region chosen, geodetic measurement yielded decadal thinning rates of debris-covered ice that were either larger or smaller than, or similar to that of debris-free ice (Gardelle et al, 2013). The present scenario is summed up neatly by Vincent et al (2016), "This question of areaaveraged melting rates over debris-covered or clean glacier ablation areas remains unanswered".…”

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confidence: 99%

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Brief communication: Thinning of debris-covered and debris-free glaciers in a warming climate

Banerjee

2017

The Cryosphere

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Abstract. Recent geodetic mass-balance measurements reveal similar thinning rates on glaciers with or without debris cover in the Himalaya-Karakoram region. This comes as a surprise as a thick debris cover reduces the surface melting significantly due to its insulating effects. Here we present arguments, supported by results from numerical flowline model simulations of idealised glaciers, that a competition between the changes in the surface mass-balance forcing and that of the emergence/submergence velocities can lead to similar thinning rates on these two types of glaciers. As the climate starts warming, the thinning rate on a debris-covered glacier is initially smaller than that on a similar debris-free glacier. Subsequently, the rate on the debris-covered glacier becomes comparable to and then larger than that on the debris-free one. The time evolution of glacier-averaged thinning rates after an initial warming is strongly controlled by the time variation of the corresponding emergence velocity profile.

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confidence: 69%

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confidence: 99%

Brief communication: Thinning of debris-covered and debris-free glaciers in a warming climate

Banerjee

2017

The Cryosphere

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“…The energy balance drives the melt of the debris-covered tongues and several studies point toward a yet unexplained faster surface lowering of the tongues of these glaciers than what can be expected based on the melt suppression by thick debris (Kääb et al, 2012;Gardelle et al, 2013;Pellicciotti et al, 2015;Azam et al, 2018). It is unclear whether this behavior can be attributed to turbulent fluxes, supra-glacial features such as cliffs and ponds, a reduced emergence velocity or other processes (Vincent et al, 2016;Azam et al, 2018). Highly detailed information about the surface temperature provides LW ↑ , a term often assumed to be spatially constant and only measured point-scale at a weather station (Reid et al, 2012;Steiner and Pellicciotti, 2016).…”

Section: Applications Of Thermal Uav Imagerymentioning

confidence: 86%

Mapping Surface Temperatures on a Debris-Covered Glacier With an Unmanned Aerial Vehicle

et al. 2018

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A layer of debris cover often accumulates across the surface of glaciers in active mountain ranges with exceptionally steep terrain, such as the Andes, Himalaya, and New Zealand Alps. Such a supraglacial debris layer has a major influence on a glacier's surface energy budget, enhancing radiation absorption, and melt when the layer is thin, but insulating the ice when thicker than a few cm. Information on spatially distributed debris surface temperature has the potential to provide insight into the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Here, we deploy an unmanned aerial vehicle (UAV) equipped with a thermal infrared sensor on three separate missions over one day to map changing surface temperatures across the debris-covered Lirung Glacier in the Central Himalaya. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous in situ temperature measurements as well as with Landsat 8 thermal satellite imagery. Results show that the UAV-derived surface temperatures vary greatly both spatially and temporally, with −1.4 ± 1.8, 11.0 ± 5.2, and 15.3 ± 4.7 • C for the three flights (mean ± sd), respectively. The range in surface temperatures over the glacier during the morning is very large with almost 50 • C. Ground-based measurements are generally in agreement with the UAV imagery, but considerable deviations are present that are likely due to differences in measurement technique and approach, and validation is difficult as a result. The difference in spatial and temporal variability captured by the UAV as compared with much coarser satellite imagery is striking and it shows that satellite derived temperature maps should be interpreted with care. We conclude that UAVs provide a suitable means to acquire surface temperature maps of debris-covered glacier surfaces at high spatial and temporal resolution, but that there are caveats with regard to absolute temperature measurement.

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“…The emergence velocity (w e ) of ice for debris-covered glaciers has been found to be significantly different from zero for 25 some cases, but it has typically been neglected in the calculation of p. Values of w e equal to 5.7-6.4 ± 3.9 m a −1 (Nuimura et al, 2011), 0.41 ± 0.05 m a −1 (Vincent et al, 2016) and 0.00-0.35 ± 0.10 m a −1 (Nuimura et al, 2017) have been found for, respectively, the debris-covered tongues of Khumbu, Changri Nup and Lirung glaciers in Nepal. Emergence velocities will affect the thinning rates of debris-covered ice and ice cliffs equally.…”

mentioning

confidence: 99%

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

Brun

Wagnon

Shea

et al. 2018

Preprint

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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.

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Reduced melt on debris-covered glaciers: investigations from Changri Nup Glacier, Nepal

Cited by 139 publications

References 54 publications

Brief communication: Thinning of debris-covered and debris-free glaciers in a warming climate

Brief communication: Thinning of debris-covered and debris-free glaciers in a warming climate

Mapping Surface Temperatures on a Debris-Covered Glacier With an Unmanned Aerial Vehicle

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

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