Accelerating recent mass loss from debris-covered Khumbu Glacier in Nepal, and projected response to climate change by 2200 CE

Thick supraglacial debris covers the ablation areas of many large Himalayan glaciers, particularly those in the Everest region where debris is typically several metres thick. Sustained mass loss from these high-elevation debris-covered glaciers is causing supraglacial debris layers to expand and thicken. However, at the same time, regional satellite observations have demonstrated that debris-covered glaciers in High Mountain Asia are currently losing mass at the same rate as clean-ice glaciers. This greater than expected mass loss&#8212;sometimes referred to as the &#8220;debris-cover anomaly&#8221;&#8212;could be due to surface processes that locally enhance ablation, including the formation and decay of ice cliffs and supraglacial ponds.We tested the hypothesis that the presence of ice cliffs and supraglacial ponds is responsible for the rapid decay of debris-covered Himalayan glaciers, using a numerical glacier model that includes the feedbacks between debris transport, mass balance and ice flow. We show that parameterising differential ablation processes in our higher-order ice flow model of Khumbu Glacier in Nepal does increase glacier-wide mass loss, but is not sufficient to match the observed glacier surface elevation change between 1984 and 2015 CE. Additional mass balance forcing is required to simulate the remaining mass balance change, which may represent the impact of rising air temperatures on englacial and supraglacial hydrology or englacial ice temperatures. Under a moderate future warming scenario (RCP4.5), Khumbu Glacier is projected to lose 59% of ice volume by 2100 CE, and 94% by 2200 CE accompanied by a dynamic shutdown that causes the death of this iconic glacier by 2160 CE.

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Debris cover and the thinning of Kennicott Glacier, Alaska, Part A:in situ mass balance measurements

10.5194/tc-2019-174 ◽

2019 ◽

Author(s):

Leif S. Anderson ◽

Robert S. Anderson ◽

Pascal Buri ◽

William H. Armstrong

Keyword(s):

Mass Balance ◽

High Mountain ◽

Glacier Surface ◽

Ice Dynamics ◽

Air Temperatures ◽

High Resolution Imagery ◽

Debris Cover ◽

The Alps

Abstract. The mass balance of many Alaskan glaciers is perturbed by debris cover. Yet the effect of debris on glacier response to climate change in Alaska has largely been overlooked. In three companion papers we assess the role of debris, ice dynamics, and surface processes in thinning Kennicott Glacier. In Part A, we report in situ measurements from the glacier surface. In Part B, we develop a method to delineate ice cliffs using high-resolution imagery and produce distributed mass balance estimates. In Part C we explore feedbacks that contribute to glacier thinning. Here in Part A, we describe data collected in the summer of 2011. We measured debris thickness (109 locations), sub-debris melt (74), and ice cliff backwasting (60) data from the debris-covered tongue. We also measured air-temperature (3 locations) and internal-debris temperature (10). The mean debris thermal conductivity was 1.06 W (m C)−1, increasing non-linearly with debris thickness. Mean debris thicknesses increase toward the terminus and margin where surface velocities are low. Despite the relatively high air temperatures above thick debris, the melt-insulating effect of debris dominates. Sub-debris melt rates ranged from 6.5 cm d−1 where debris is thin to 1.25 cm d−1 where debris is thick near the terminus. Ice cliff backwasting rates varied from 3 to 14 cm d−1 with a mean of 7.1 cm d−1 and tended to increase as elevation declined and debris thickness increased. Ice cliff backwasting rates are similar to those measured on debris-covered glaciers in High Mountain Asia and the Alps.

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Modelling the contribution of ice cliff melt to glacier mass loss at the catchment scale

10.5194/egusphere-egu21-7026 ◽

2021 ◽

Author(s):

Pascal Buri ◽

Evan S Miles ◽

Jakob Steiner ◽

Silvan Ragettli ◽

Francesca Pellicciotti

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Meteorological Data ◽

High Mountain ◽

Catchment Scale ◽

Glacier Surface ◽

Surface Mass ◽

Mass Losses ◽

Weather Stations ◽

High Elevations

The melt rates of debris-covered glaciers in High Mountain Asia are highly heterogeneous and poorly constrained. Supraglacial cliffs are typical surface features of debris-covered glaciers and act as windows of energy transfer from the atmosphere to the ice, locally enhancing melt and mass losses of otherwise insulated ice. Despite this, their contribution to the glacier mass budget has never been quantified at the glacier scale.Here we simulate the specific melt of all supraglacial ice cliffs individually in a Himalayan catchment (Langtang Valley, Nepalese Himalayas), using a process-based ice cliff melt model that has previously been validated in the catchment. Cliff outlines and initial topography are derived from high-resolution stereo SPOT6-imagery and the model is forced by meteorological data from on- and off-glacier automatic weather stations within the valley, both for the 2014 melt season. The model simulates ice cliff backwasting by considering the cliff-atmosphere energy-balance, reburial by debris and the effects of adjacent ponds. We estimate the contribution of ice cliffs to glacier surface mass balance derived from ensemble mean geodetic thinning observations and emergence flux calculations for the same glaciers 2006-2015.We show that ice cliffs, although covering only 2.1 &#177;0.6 % of the debris-covered tongues, are partially responsible for the high thinning rates of debris-covered glacier tongues, leading to a catchment mass loss underestimation of 17 &#177;4 % if not considered. We show that cliffs enhance melt where other processes would suppress it, i.e. at high elevations or where debris is thick, and confirm that they contribute relatively more to glacier mass loss if oriented north.Our approach bridges a scale gap in our understanding of the processes of debris-covered glacier mass losses, and a new quantification of their catchment wide melt and mass balance.

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The Causes of Debris-Covered Glacier Thinning: Evidence for the Importance of Ice Dynamics From Kennicott Glacier, Alaska

Frontiers in Earth Science ◽

10.3389/feart.2021.680995 ◽

2021 ◽

Vol 9 ◽

Author(s):

Leif S. Anderson ◽

William H. Armstrong ◽

Robert S. Anderson ◽

Dirk Scherler ◽

Eric Petersen

Keyword(s):

Mass Balance ◽

Flow Direction ◽

Surface Velocity ◽

Glacier Surface ◽

Ice Dynamics ◽

Ice Flow ◽

Thickness Change ◽

Air Temperatures ◽

Compressive Flow ◽

Wide Range

The cause of debris-covered glacier thinning remains controversial. One hypothesis asserts that melt hotspots (ice cliffs, ponds, or thin debris) increase thinning, while the other posits that declining ice flow leads to dynamic thinning under thick debris. Alaska’s Kennicott Glacier is ideal for testing these hypotheses, as ice cliffs within the debris-covered tongue are abundant and surface velocities decline rapidly downglacier. To explore the cause of patterns in melt hotspots, ice flow, and thinning, we consider their evolution over several decades. We compile a wide range of ice dynamical and mass balance datasets which we cross-correlate and analyze in a step-by-step fashion. We show that an undulating bed that deepens upglacier controls ice flow in the lower 8.5 km of Kennicott Glacier. The imposed velocity pattern strongly affects debris thickness, which in turn leads to annual melt rates that decline towards the terminus. Ice cliff abundance correlates highly with the rate of surface compression, while pond occurrence is strongly negatively correlated with driving stress. A new positive feedback is identified between ice cliffs, streams and surface topography that leads to chaotic topography. As the glacier thinned between 1991 and 2015, surface melt in the study area decreased, despite generally rising air temperatures. Four additional feedbacks relating glacier thinning to melt changes are evident: the debris feedback (negative), the ice cliff feedback (negative), the pond feedback (positive), and the relief feedback (positive). The debris and ice cliff feedbacks, which are tied to the change in surface velocity in time, likely reduced melt rates in time. We show this using a new method to invert for debris thickness change and englacial debris content (∼0.017% by volume) while also revealing that declining speeds and compressive flow led to debris thickening. The expansion of debris on the glacier surface follows changes in flow direction. Ultimately, glacier thinning upvalley from the continuously debris-covered portion of Kennicott Glacier, caused by mass balance changes, led to the reduction of flow into the study area. This caused ice emergence rates to decline rapidly leading to the occurrence of maximum, glacier-wide thinning under thick, insulating debris.

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Glacier Surface Mass Balance in the Suntar-Khayata Mountains, Northeastern Siberia

Water ◽

10.3390/w11091949 ◽

2019 ◽

Vol 11 (9) ◽

pp. 1949 ◽

Cited By ~ 1

Author(s):

Yong Zhang ◽

Xin Wang ◽

Zongli Jiang ◽

Junfeng Wei ◽

Hiroyuki Enomoto ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Surface Mass Balance ◽

Negative Mass ◽

Glacier Surface ◽

Surface Mass ◽

Northeastern Siberia ◽

Response To Temperature ◽

Rapid Mass

Arctic glaciers comprise a small fraction of the world’s land ice area, but their ongoing mass loss currently represents a large cryospheric contribution to the sea level rise. In the Suntar-Khayata Mountains (SKMs) of northeastern Siberia, in situ measurements of glacier surface mass balance (SMB) are relatively sparse, limiting our understanding of the spatiotemporal patterns of regional mass loss. Here, we present SMB time series for all glaciers in the SKMs, estimated through a glacier SMB model. Our results yielded an average SMB of −0.22 m water equivalents (w.e.) year−1 for the whole region during 1951–2011. We found that 77.4% of these glaciers had a negative mass balance and detected slightly negative mass balance prior to 1991 and significantly rapid mass loss since 1991. The analysis suggests that the rapidly accelerating mass loss was dominated by increased surface melting, while the importance of refreezing in the SMB progressively decreased over time. Projections under two future climate scenarios confirmed the sustained rapid shrinkage of these glaciers. In response to temperature rise, the total present glacier area is likely to decrease by around 50% during the period 2071–2100 under representative concentration pathway 8.5 (RCP8.5).

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Geodetic Mass Balance of Haxilegen Glacier No. 51, Eastern Tien Shan, from 1964 to 2018

Remote Sensing ◽

10.3390/rs14020272 ◽

2022 ◽

Vol 14 (2) ◽

pp. 272

Author(s):

Chunhai Xu ◽

Zhongqin Li ◽

Feiteng Wang ◽

Jianxin Mu ◽

Xin Zhang

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Laser Scanning ◽

Mean Value ◽

Tien Shan ◽

Glacier Mass Balance ◽

Topographic Map ◽

Glacier Surface ◽

Elevation Changes ◽

Geodetic Mass Balance

The eastern Tien Shan hosts substantial mid-latitude glaciers, but in situ glacier mass balance records are extremely sparse. Haxilegen Glacier No. 51 (eastern Tien Shan, China) is one of the very few well-measured glaciers, and comprehensive glaciological measurements were implemented from 1999 to 2011 and re-established in 2017. Mass balance of Haxilegen Glacier No. 51 (1999–2015) has recently been reported, but the mass balance record has not extended to the period before 1999. Here, we used a 1:50,000-scale topographic map and long-range terrestrial laser scanning (TLS) data to calculate the area, volume, and mass changes for Haxilegen Glacier No. 51 from 1964 to 2018. Haxilegen Glacier No. 51 lost 0.34 km2 (at a rate of 0.006 km2 a−1 or 0.42% a−1) of its area during the period 1964–2018. The glacier experienced clearly negative surface elevation changes and geodetic mass balance. Thinning occurred almost across the entire glacier surface, with a mean value of −0.43 ± 0.12 m a−1. The calculated average geodetic mass balance was −0.36 ± 0.12 m w.e. a−1. Without considering the error bounds of mass balance estimates, glacier mass loss over the past 50 years was in line with the observed and modeled mass balance (−0.37 ± 0.22 m w.e. a−1) that was published for short time intervals since 1999 but was slightly less negative than glacier mass loss in the entire eastern Tien Shan. Our results indicate that Riegl VZ®-6000 TLS can be widely used for mass balance measurements of unmonitored individual glaciers.

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Greenland high-elevation mass balance: inference and implication of reference period (1961–90) imbalance

Annals of Glaciology ◽

10.3189/2015aog70a967 ◽

2015 ◽

Vol 56 (70) ◽

pp. 105-117 ◽

Cited By ~ 21

Author(s):

William Colgan ◽

Jason E. Box ◽

Morten L. Andersen ◽

Xavier Fettweis ◽

Beáta Csathó ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Greenland Ice Sheet ◽

Mass Gain ◽

High Elevation ◽

Reference Period ◽

Input Output ◽

Specific Mass ◽

Ice Dynamics ◽

Dynamic Mass

AbstractWe revisit the input–output mass budget of the high-elevation region of the Greenland ice sheet evaluated by the Program for Arctic Regional Climate Assessment (PARCA). Our revised reference period (1961–90) mass balance of 54±48 Gt a–1 is substantially greater than the 0±21 Gt a–1 assessed by PARCA, but consistent with a recent, fully independent, input–output estimate of high-elevation mass balance (41±61 Gt a–1). Together these estimates infer a reference period high-elevation specific mass balance of 4.8±5.4 cm w.e. a–1. The probability density function (PDF) associated with this combined input–output estimate infers an 81% likelihood of high-elevation specific mass balance being positive (>0 cm w.e. a–1) during the reference period, and a 70% likelihood that specific balance was >2 cm w.e. a–1. Given that reference period accumulation is characteristic of centurial and millennial means, and that in situ mass-balance observations exhibit a dependence on surface slope rather than surface mass balance, we suggest that millennial-scale ice dynamics are the primary driver of subtle reference period high-elevation mass gain. Failure to acknowledge subtle reference period dynamic mass gain can result in underestimating recent dynamic mass loss by ~17%, and recent total Greenland mass loss by ~7%.

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Sensitivity of mountain glacier mass balance to changes in bare-ice albedo

Annals of Glaciology ◽

10.1017/aog.2017.25 ◽

2017 ◽

Vol 58 (75pt2) ◽

pp. 119-129 ◽

Cited By ~ 9

Author(s):

Kathrin Naegeli ◽

Matthias Huss

Keyword(s):

Mass Balance ◽

Balance Model ◽

Glacier Mass Balance ◽

Landsat 8 ◽

Glacier Surface ◽

Mountain Glacier ◽

Albedo Feedback ◽

In Situ Data ◽

The Impact ◽

Near Future

ABSTRACT Albedo is an important parameter in the energy balance of bare-ice surfaces and modulates glacier melt rates. The prolongation of the ablation period enforces the albedo feedback and highlights the need for profound knowledge on impacts of bare-ice albedo on glacier mass balance. In this study, we assess the mass balance sensitivity of 12 Swiss glaciers with abundant long-term in-situ data on changes in bare-ice albedo. We use pixel-based bare-ice albedo derived from Landsat 8. A distributed mass-balance model is applied to the period 1997–2016 and experiments are performed to assess the impact of albedo changes on glacier mass balance. Our results indicate that glacier-wide mass-balance sensitivities to changes in bare-ice albedo correlate strongly with mean annual mass balances (r 2 = 0.81). Large alpine glaciers react more sensitively to bare-ice albedo changes due to their ablation areas being situated at lower elevations. We find average sensitivities of glacier-wide mass balance of −0.14 m w.e. a−1 per 0.1 albedo decrease. Although this value is considerably smaller than sensitivity to air temperature change, we stress the importance of the enhanced albedo feedback that will be amplified due to atmospheric warming and a suspected darkening of glacier surface in the near future.

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Structure and evolution of the drainage system of a Himalayan debris-covered glacier, and its relationship with patterns of mass loss

The Cryosphere ◽

10.5194/tc-11-2247-2017 ◽

2017 ◽

Vol 11 (5) ◽

pp. 2247-2264 ◽

Cited By ~ 26

Author(s):

Douglas I. Benn ◽

Sarah Thompson ◽

Jason Gulley ◽

Jordan Mertes ◽

Adrian Luckman ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Satellite Image ◽

Drainage System ◽

Ablation Zone ◽

Negative Mass ◽

Long Distance ◽

Glacier Surface ◽

Base Level ◽

Englacial Drainage

Abstract. We provide the first synoptic view of the drainage system of a Himalayan debris-covered glacier and its evolution through time, based on speleological exploration and satellite image analysis of Ngozumpa Glacier, Nepal. The drainage system has several linked components: (1) a seasonal subglacial drainage system below the upper ablation zone; (2) supraglacial channels, allowing efficient meltwater transport across parts of the upper ablation zone; (3) sub-marginal channels, allowing long-distance transport of meltwater; (4) perched ponds, which intermittently store meltwater prior to evacuation via the englacial drainage system; (5) englacial cut-and-closure conduits, which may undergo repeated cycles of abandonment and reactivation; and (6) a "base-level" lake system (Spillway Lake) dammed behind the terminal moraine. The distribution and relative importance of these elements has evolved through time, in response to sustained negative mass balance. The area occupied by perched ponds has expanded upglacier at the expense of supraglacial channels, and Spillway Lake has grown as more of the glacier surface ablates to base level. Subsurface processes play a governing role in creating, maintaining, and shutting down exposures of ice at the glacier surface, with a major impact on spatial patterns and rates of surface mass loss. Comparison of our results with observations on other glaciers indicate that englacial drainage systems play a key role in the response of debris-covered glaciers to sustained periods of negative mass balance.

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Long-term records of glacier surface velocities in the Ötztal Alps (Austria)

10.5194/essd-2018-153 ◽

2019 ◽

Author(s):

Martin Stocker-Waldhuber ◽

Andrea Fischer ◽

Kay Helfricht ◽

Michael Kuhn

Keyword(s):

Mass Balance ◽

Glacier Mass Balance ◽

Data Sets ◽

Climatic Forcing ◽

Glacier Surface ◽

Ice Flow ◽

Strong Indicator ◽

Length Changes ◽

Flow Velocities

Abstract. Climatic forcing affects glacier mass balance and ice flow dynamics on different time scales, resulting in length changes. Mass Balance and length changes are operationally used for glacier monitoring, whereas only a few time series of glacier dynamics have been recorded. With more than 100 years of measurements of ice flow velocities at stakes and stone lines on Hintereisferner and more than 50 years on Kesselwandferner, annual velocity and glacier fluctuation records have similar lengths. Subseasonal variations of ice flow velocities have been measured on Gepatschferner and Taschachferner for nearly a decade. The ice flow velocities on Hintereisferner and especially on Kesselwandferner show great variations between advancing and retreating periods, with magnitudes increasing from the highest to the lowest stakes, making ice flow records at ablation stakes a very sensitive indicator of glacier state. Since the end of the latest glacier advances from the 1970s to the 1980s, the ice flow velocities have decreased continuously, a strong indicator of the negative mass balances of the glaciers in recent decades. The velocity data sets of the four glaciers are available at https://doi.pangaea.de/10.1594/PANGAEA.896741.

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Simulating ice thickness and velocity evolution of Upernavik Isstrøm 1849–2012 by forcing prescribed terminus positions in ISSM

The Cryosphere ◽

10.5194/tc-12-1511-2018 ◽

2018 ◽

Vol 12 (4) ◽

pp. 1511-1522 ◽

Cited By ~ 5

Author(s):

Konstanze Haubner ◽

Jason E. Box ◽

Nicole J. Schlegel ◽

Eric Y. Larour ◽

Mathieu Morlighem ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Surface Mass Balance ◽

Position Change ◽

Ice Flow ◽

Surface Mass ◽

Total Mass Loss ◽

Negative Surface ◽

Ice Velocity ◽

Glacier Velocity

Abstract. Tidewater glacier velocity and mass balance are known to be highly responsive to terminus position change. Yet it remains challenging for ice flow models to reproduce observed ice margin changes. Here, using the Ice Sheet System Model (Larour et al., 2012), we simulate the ice velocity and thickness changes of Upernavik Isstrøm (north-western Greenland) by prescribing a collection of 27 observed terminus positions spanning 164 years (1849–2012). The simulation shows increased ice velocity during the 1930s, the late 1970s and between 1995 and 2012 when terminus retreat was observed along with negative surface mass balance anomalies. Three distinct mass balance states are evident in the reconstruction: (1849–1932) with near zero mass balance, (1932–1992) with ice mass loss dominated by ice dynamical flow, and (1998–2012), when increased retreat and negative surface mass balance anomalies led to mass loss that was twice that of any earlier period. Over the multi-decadal simulation, mass loss was dominated by thinning and acceleration responsible for 70 % of the total mass loss induced by prescribed change in terminus position. The remaining 30 % of the total ice mass loss resulted directly from prescribed terminus retreat and decreasing surface mass balance. Although the method can not explain the cause of glacier retreat, it enables the reconstruction of ice flow and geometry during 1849–2012. Given annual or seasonal observed terminus front positions, this method could be a useful tool for evaluating simulations investigating the effect of calving laws.

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