Surface lowering of the debris-covered area of Kanchenjunga Glacier in the eastern Nepal Himalaya since 1975, as revealed by Hexagon KH-9 and ALOS satellite observations

Lamsal, Damodar; Fujita, Koji; Sakai, Akiko

doi:10.5194/tc-11-2815-2017

Cited by 20 publications

(14 citation statements)

References 50 publications

(95 reference statements)

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“…After 1988 the thinning has in general become stronger but also more homogeneous along the glacier tongue. Table 1), which are derived as the standard deviation over stable terrain and therefore represent the upper bound of the uncertainty (Magnússon et al, 2016). Except for the periods 1879-1946 and 1977-1988, these uncertainties are significantly lower than the glacier changes and thus have little impact on the final decadal elevation change rates.…”

Section: Tongue-wide Surface Elevation Change and Patternsmentioning

confidence: 99%

Unravelling the evolution of Zmuttgletscher and its debris cover since the end of the Little Ice Age

et al. 2019

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Abstract. Debris-covered glaciers generally exhibit large, gently sloping, slow-flowing tongues. At present, many of these glaciers show high thinning rates despite thick debris cover. Due to the lack of observations, most existing studies have neglected the dynamic interactions between debris cover and glacier evolution over longer time periods. The main aim of this study is to reveal such interactions by reconstructing changes of debris cover, glacier geometry, flow velocities, and surface features of Zmuttgletscher (Switzerland), based on historic maps, satellite images, aerial photographs, and field observations. We show that debris cover extent has increased from ∼13 % to ∼32 % of the total glacier surface since 1859 and that in 2017 the debris is sufficiently thick to reduce ablation compared to bare ice over much of the ablation area. Despite the debris cover, the glacier-wide mass balance of Zmuttgletscher is comparable to that of debris-free glaciers located in similar settings, whereas changes in length and area have been small and delayed by comparison. Increased ice mass input in the 1970s and 1980s resulted in a temporary velocity increase, which led to a local decrease in debris cover extent, a lowering of the upper boundary of the ice-cliff zone, and a strong reduction in ice-cliff area, indicating a dynamic link between flow velocities, debris cover, and surface morphology. Since 2005, the lowermost 1.5 km of the glacier has been quasi-stagnant, despite a slight increase in the surface slope of the glacier tongue. We conclude that the long-term glacier-wide mass balance is mainly governed by climate. The debris cover governs the spatial pattern of elevation change without changing its glacier-wide magnitude, which we explain by the extended ablation area and the enhanced thinning in regions with thin debris further up-glacier and in areas with abundant meltwater channels and ice cliffs. At the same time rising temperatures lead to increasing debris cover and decreasing ice flux, thereby attenuating length and area losses.

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Section: Tongue-wide Surface Elevation Change and Patternsmentioning

confidence: 99%

Unravelling the evolution of Zmuttgletscher and its debris cover since the end of the Little Ice Age

et al. 2019

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“…In High Mountain Asia (HMA) many debris-covered and debris-free glacier tongues are thinning at similar rates (e.g., Kääb et al, 2012;Brun et al, 2018). This apparent paradox is known as the 'debris-cover anomaly' (Pellicciotti et al, 2015), and has been documented in HMA and the European Alps (Nuimura et al, 2012;Pellicciotti et al, 2015;Agarwal et al, 2017;Lamsal et al, 2017;Wu et al, 2018;Mölg et al, 2019). But the debris-cover anomaly also occurs on glaciers in the Wrangell Mountains of southern Alaska (Das et al, 2014 ).…”

Section: Introductionmentioning

confidence: 99%

Debris cover and the thinning of Kennicott Glacier, Alaska, Part B: ice cliff delineation and distributed melt estimates

Anderson

Armstrong

Anderson

et al. 2019

Preprint

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Abstract. The mass balance of many valley glaciers is enhanced by the presence of ice cliffs within otherwise continuous debris cover. We assess the effect of debris and ice cliffs on the thinning of Kennicott Glacier in three companion papers. In Part A we report in situ measurements from the debris-covered tongue. Here, in Part B, we develop a method to delineate ice cliffs using high-resolution imagery and use empirical relationships from Part A to produce distributed mass balance estimates. In Part C we describe feedbacks that contribute to rapid thinning under thick debris. Ice cliffs cover 11.7 % of the debris-covered tongue, the most of any glacier studied to date, and they contribute 19 % of total melt. Ice cliffs contribute an increasing percentage of melt the thicker the debris cover. In the lowest 4 km of the glacier, where debris thicknesses are greater than 20 cm, ice cliffs contribute 40 % of total melt. Surface lake coverage doubled between 1957 and 2009, but lakes do not occur across the full extent of the zone of maximum glacier thinning. Despite abundant ice cliffs and expanding surface lakes, average melt rates are suppressed by debris, the pattern of which appears to reflect the debris thickness-melt relationship (or Østrem’s curve). This suggests that, in addition to melt hotspots, the decline in ice discharge from upglacier is an important contributor to the thinning of Kennicott glacier under thick debris.

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“…ice at similar elevations across HMA (Gardelle et al, 2013;Kääb et al, 2012), in the Khumbu region (Nuimura et al, 2012), the Langtang catchment , the Kangri Karpo Mountains (Wu et al, 2018), for the Kanchenjunga Glacier (Lamsal et al, 2017) and the Siachen Glacier (Agarwal et al, 2017). This has been referred to as the "debris-cover anomaly" .…”

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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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Surface lowering of the debris-covered area of Kanchenjunga Glacier in the eastern Nepal Himalaya since 1975, as revealed by Hexagon KH-9 and ALOS satellite observations

Cited by 20 publications

References 50 publications

Unravelling the evolution of Zmuttgletscher and its debris cover since the end of the Little Ice Age

Unravelling the evolution of Zmuttgletscher and its debris cover since the end of the Little Ice Age

Debris cover and the thinning of Kennicott Glacier, Alaska, Part B: ice cliff delineation and distributed melt estimates

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

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