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Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards
Abstract and Figures
In areas of high relief, many glaciers have extensive covers of supraglacial debris in their ablation zones, which alters both rates and spatial patterns of melting, with important consequences for glacier response to climate change. Wastage of debris-covered glaciers can be associated with the formation of large moraine-dammed lakes, posing risk of glacier lake outburst floods (GLOFs). In this paper, we use observations of glaciers in the Mount Everest region to present an integrated view of debris-covered glacier response to climate change, which helps provide a long-term perspective on evolving GLOF risks.
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... Supraglacial lakes and ice cliffs, which are regularly formed on debris-covered glaciers, mainly due to reduced glacier velocity and gentle slope angles in the ablation zone, can both increase ablation rates (Bhambri et al. 2023;Brun et al. 2016;Huo et al. 2021;Pellicciotti et al. 2015;Salerno et al. 2017). As a consequence, mass loss rates can be higher in the middle parts of the glacier than in the debris-covered terminus (Benn et al. 2012). In contrast, other studies from the Himalayas showed that the lowering rates of debris-covered glaciers are the same or even higher than for clean-ice glaciers . ...
... Furthermore, the impact of ice cliffs, which are often connected to supraglacial lakes and increase mass loss (Bhambri et al. 2023;Brun et al. 2016;Pellicciotti et al. 2015;Salerno et al. 2017), needs to be analysed in more detail. Especially, as the typical inversion of the ablation gradient along debris-covered glaciers as shown for the debris-covered glaciers in the Khumbu region, Himalaya (Benn et al. 2012) does not exist. In contrast, the lowermost part and the transition zone of the Belvedere Glacier both showed a more pronounced thinning than the central part. ...
This study describes and analyses elevation changes in the debris-covered tongue of the surge-type Belvedere Glacier (Western Italian Alps) between 1951 and 2023 using remote sensing data, including historical aerial photographs, Lidar and drone acquisitions. High-resolution digital surface models from 1951, 2009 and 2023 enabled detailed observation of the spatially heterogeneous patterns of change caused by debris cover, avalanches, a surge-type event, supraglacial meltwater, and glacial lake outburst floods in the context of global warming. In the period of 1951–2009, the mean rate of downwasting was quantified as 0.24 metres per year (14 metres in total), ranging from −83.5 to 32.2 metres. During the second observation period from 2009 to 2023, the mean downwasting rate was estimated to be 1.8 metres per year (25 metres in total), varying from −73.9 to 26.9 metres. The 2001–2002 surge-type event, meltwater streams and supraglacial lakes are considered to be the main drivers forcing elevation changes and shaping its spatial variation and surface structures. In general, the changes in the glacier have accelerated between 2009 and 2023. This paper demonstrates the high potential of differenced digital surface models with high spatial resolution to detect the processes of glacier dynamics in high detail.
... Debris dammed lakes appear when glacial debris flows downstream and blocks or deposits in ablation zones or rivers, causing water to accumulate [111]. ...
Due to climate change, the Northwesterner Gilgit Baltistan's, Ghizer district is highly susceptible to glacial lake outburst floods (GLOFs). Nearly 24 GLOFs have occurred in this area in the last ∼200 years, demonstrating the growing recurrent nature of these incidents. Taking this into account, the assessment of risks associated with GLOFs was investigated in this study. All regional glacial lakes were identified in the first phase, and changes between 2000 and 2023 were mapped using moderate-resolution satellite images (Landsat). To map built-up and agriculture areas, Landsat's lower resolution limited its use in such complex topography. Therefore Sentinel-2 data was used, and images from 2016 to 2023 were classified using a random forest (RF) classifier. A total of 617 glacial lakes covering ∼31.67 km2 of the area were mapped in 2023. Since 2000, ∼88 glacial lakes have appeared, showing an increasing trend in the number of lakes. In the second phase, categorization and susceptibility to GLOFs were assessed using multi-criteria decision analysis (MCDA). The grass GIS tool, r.avaflow, was used to generate GLOFs simulations based on friction, density, release area, travel time, and two travel time scenarios, i.e., 1800 and 3600 seconds, for four high-weighted glacial lakes. Results showed that the glacial lake near Darkut village, Yaseen Valley, poses a significant threat to downstream communities. In contrast, two other lakes in Gupis valley will have a moderate effect on the infrastructure and agriculture. The glacial lake of Punyal Valley poses no significant threat.
... Ice cliffs absorb more solar radiation, accelerating local melting and potentially triggering collapse events; supraglacial ponds collect meltwater, and as their volume increases, they can cause catastrophic outburst floods, posing significant threats to downstream communities and ecosystems [23,24]. Monitoring the spatiotemporal dynamics of supraglacial debris cover is essential for understanding glacier melt patterns and accurately quantifying runoff [25,26], which provides critical data for understanding glacier dynamics, mass balance, hydrological modeling, and disaster risk reduction, in addition to water resource management in downstream areas [27,28]. In eastern Pamir, the supraglacial debris cover spans an extensive area, with Scherler et al. [20] estimating it to be approximately 330 km 2 , or about 11% of the total glacier area. ...
Supraglacial debris cover considerably influences sub-debris ablation patterns and the surface morphology of glaciers by modulating the land–atmosphere energy exchange. Understanding its spatial distribution and temporal variations is crucial for analyzing melting processes and managing downstream disaster mitigation efforts. In recent years, the overall slightly positive mass balance or stable state of eastern Pamir glaciers has been referred to as the “Pamir-Karakoram anomaly”. It is important to note that spatial heterogeneity in glacier change has drawn widespread research attention. However, research on the spatiotemporal changes in the debris cover in this region is completely nonexistent, which has led to an inadequate understanding of debris-covered glacier variations. To address this research gap, this study employed Landsat remote sensing images within the Google Earth Engine platform, leveraging the Random Forest algorithm to classify the supraglacial debris cover. The classification algorithm integrates spectral features from Landsat images and derived indices (NDVI, NDSI, NDWI, and BAND RATIO), supplemented by auxiliary factors such as slope and aspect. By extracting the supraglacial debris cover from 1994 to 2024, this study systematically analyzed the spatiotemporal variations and investigated the underlying drivers of debris cover changes from the perspective of mass conservation. By 2024, the area of supraglacial debris in eastern Pamir reached 258.08 ± 20.65 km², accounting for 18.5 ± 1.55% of the total glacier area. It was observed that the Kungey Mountain region demonstrated the largest debris cover rate. Between 1994 and 2024, while the total glacier area decreased by −2.57 ± 0.70%, the debris-covered areas expanded upward at a rate of +1.64 ± 0.10% yr⁻¹. The expansion of debris cover is driven by several factors in the context of global warming. The rising temperature resulted in permafrost degradation, slope destabilization, and intensified weathering on supply slopes, thereby augmenting the debris supply. Additionally, the steep supply slope in the study area facilitates the rapid deposition of collapsed debris onto glacier surfaces, with frequent avalanche events accelerating the mobilization of rock fragments.
... When a glacier retreats, its terminus leaves open an empty bowl in the surface due to repeated erosion actions and sometimes meltwater collects in it to form glacial lakes (Carrivick and Tweed 2013). Another way of formation of glacial lakes can be from the fusion of several supraglacial lakes (small lakes or ponds of the meltwater forming atop the glacier's surface) on a debris covered glacier (Benn et al. 2012). The presence of glacier-fed lakes can start a chain reaction or a positive feedback loop because it can cause more ice to melt and collapse inside the lake and causing further addition to the extent of the lake (King et al. 2019). ...
This term paper explores the global risk assessment of Glacial Lake Outburst Floods (GLOFs), emphasizing the interplay of hazard, exposure, and vulnerability. It examines the formation and triggers of glacial lake outbursts, their social and environmental impacts, and the unequal distribution of risks across regions. The research highlights key findings on population exposure in high-risk areas like the Himalayas and Andes, while addressing critical gaps in vulnerability assessment and mitigation strategies. Submitted as part of the coursework for the Joint Master Program at the University of Bonn and UNU-EHS (2023), this work aims to contribute to the understanding and management of GLOF-related risks globally.
... Tropical cyclones and westerly disturbances are responsible for heavy snowfall in autumn and winter. However, snow can accumulate at high altitudes throughout the month (Benn et al. 2012). ...
Due to the lack of high-altitude observational datasets, a better understanding of snow cover changes and meteorological forcing for their variation in the Mount Everest region is still insufficient. This study examined changes in snow cover over the Mount Everest region and their relationship to air temperature, albedo (surface and snow), and total precipitation. This study used data from the MERRA2, ERA5-Land, JRA55, FLDAS, and CERES products spanning 41 years (1981–2021). For comparison and evaluation, we also used a ground station, Pyramid, located at a high elevation (5050 masl) at the foot of Mount Everest on the southern slope. The results confirmed a significant decline in snow cover during winter and post-monsoon seasons, which was observed in all datasets. Changes in surface and snow albedo and total precipitation positively correlate with the variation in snow cover; however, this relationship reverses with air temperature. This research suggests that atmospheric warming caused a decline in snow cover in the Mount Everest region. This decline affected snow and surface albedo, causing further warming and contributing to the continued decline in snow cover in the study area. The reduction in precipitation further contributes to the decrease in snow cover in the Mount Everest region. The variations in snow cover in this study correspond to those found in earlier studies on glacier thinning in cryosphere regions. Anthropogenic activities have linked these variations to increasing air temperatures while decreasing snowfall, precipitation, and albedo.
... A second factor is the availability of water. The highest position of the zero isotherm during the melt season defines the upper maximum level of SGLs occurrence (Benn et al. 2012;Sakai 2012). To consider the influence of debris cover, it is necessary to acknowledge that a thick cover prevents ice melting, and that the lower boundary of occurrence may be shifted to higher altitudes (Miles et al. 2017). ...
Understanding of the formation and evolution of supraglacial lakes in high mountain regions is crucial for accurately assessing their impact on glacier behaviour, hydrology, and potential hazards such as outburst floods. This article examines the annual spatio-temporal evolution of supraglacial lakes on the Belvedere Glacier between 2000 and 2023. Very high-resolution aerial photography and high-resolution satellite imagery were used to identify supraglacial lakes as small as 37 m2 and narrow bands of ice-marginal lakes. The mapping revealed that the well-known Lake Effimero is stable in its position but unstable in size, with variations from 428 m2 to 99.7 × 103 m2. These changes are potentially due to snowmelt or glacier dynamics. In 2002, the area of Effimero was at its largest extent observed during the study period. The first appearance of the Lake Effimero was revelated by the Landsat imagery on 27 May 2001, which differed from the findings of other studies. New lakes were observed to form in a manner independent of Effimero formation, exhibiting a consistent annual occurrence with nearly linear area growth up to 9.7 × 103 m2 in 2023. The formation of the lakes is shown to be influenced by their morphological characteristics.
... Reduced mass transfer leads to localized surface lowering and a decrease in downglacier surface gradient. This, in turn, lowers driving stress and glacier velocity, causing the lower ablation zones to become increasingly stagnant (Benn et al. 2012;Nuimura et al. 2017). As downwasting progresses in the future, formerly efficient supraglacial and englacial drainage networks will break up, and supraglacial lakes will probably form in surface depressions. ...
Glacier retreat is a key indicator of climate change, with significant implications for geomorphological hazards and ecosystem stability. This article focuses on the surface evolution of the Belvedere Glacier from 1951 to 2023. Using high-resolution orthophotos and manual mapping, we tracked changes in the glacier’s area and shape over time. The results show three significant phases of change: the separation of the Nordend Glacier from the Belvedere Glacier (1951–1991), the partial separation of the central accumulation basin from the debris-covered tongue (2006–2015), and the separation of the Locce Nord Glacier (2018–2021). These changes, combined with a surge event from 1999 to 2002, have significantly altered the glacier’s dynamics and accelerated its retreat. Manual mapping was accurate in areas with scarce debris cover but faced challenges in debris-covered areas due to limited image resolution, snow cover, and debris characteristics. Despite these difficulties, we observed that the glacier remained stable until the late 1990s, when it began a rapid retreat. This recent retreat is consistent with rates observed in the early 20th century. The study highlights the importance of surface mapping to quantify the areal loss and to understand broader changes in glacier structure and mass flow that drive its retreat. Our results provide key data for future studies and highlight the need for continued monitoring of Alpine glaciers in the context of accelerating climate change.
Glacier dynamics in the Himalayan mid-latitudes, particularly in regions like the Shishapangma, are not yet fully understood, especially the localized topographic and climatic impacts on glacier deformation. This study analyzes the spatiotemporal characteristics of glacier surface deformation in the Shishapangma region using the Small Baseline Subset (SBAS) Interferometric Synthetic Aperture Radar (InSAR) technique. The analysis reveals an average deformation rate of −4.02±17.65 mm/yr across the entire study area, with glacier regions exhibiting significantly higher rates of uplift (16.87±13.20 mm/yr) and subsidence (20.11±14.55 mm/yr) compared to non-glacier areas. It identifies significant surface lowering on the mountain flanks and localized uplift in certain catchments, emphasizing the higher deformation rates in glacial areas compared to non-glacial ones. We found a strong positive correlation between temperature and cumulative deformation (correlation coefficient of 0.63), particularly in glacier areas (0.82). The research highlights the role of temperature as the primary driver of glacier wastage, particularly at lower elevations, with strong correlations found between temperature and cumulative deformation. It also indicates the complex interactions between topographic features, notably, slope gradient, which shows a positive correlation with subsidence rates, especially for slopes below 35°. South-, southwest-, and west-facing slopes exhibit significant uplift, while north-, northeast-, and east-facing slopes predominantly subside. Additionally, we identified transition zones between debris-covered glaciers and clean ice as areas of most intense deformation, with average rates exceeding 30 mm/yr, highlighting these as potential high-risk zones for geohazards. This study comprehensively analyzes the deformation characteristics in both glacier and non-glacier areas in the Shishapangma region, revealing the complex interplay of topographic, climatic, and hydrological factors influencing glacier dynamics.
Supraglacial debris modulates the thermal regime and alters glacial melt rates depending on its thickness. Thus, the estimation of debris thickness becomes imperative for predicting the hydrological response and dynamics of such glaciers. This study tests the performance of empirical and thermal resistance-based debris thickness approaches against field measurements on the Hoksar Glacier, Kashmir Himalaya. The aim of this study was accomplished using thermal imageries (Landsat 8 Operational Land Imager [Landsat-OLI], 2017 and Advanced Spaceborne Thermal Emission and Reflection Radiometer [ASTER] Surface Kinetic Temperature Product [AST08], 2017) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA-5) datasets. First, the spatially resolved estimates of debris thickness for the entire debris-covered zone were achieved by establishing an empirical relationship between debris thickness and debris surface temperature (both field and satellite thermal imageries). Second, debris thickness for every pixel of thermal imagery was executed by calculating thermal resistance from the energy balance model incorporating primary inputs from (ERA-5), debris temperature (AST08, Landsat OLI), and thermal conductivity. On comparison with field temperature and thickness measurements with satellite temperature, homogenous debris thickness pixels showed an excellent coherence ( r = 0.9; p < 0.001 for T AST08 and r = 0.88; p < 0.001 for T Landsat OLI for temperature) and ( r = 0.9; p < 0.001 for T AST08 and r = 0.87; p < 0.002 for T Landsat OLI for debris thickness). Both approaches effectively captured the spatial pattern of debris thickness using Landsat OLI and AST08 datasets. However, results specify an average debris thickness of 18.9 ± 7.9 cm from the field, which the empirical approach underestimated by 12% for AST08 and 28% for Landsat OLI, and the thermal resistance approach overestimated by 6.2% for AST08 and 5.1% for Landsat OLI, respectively. Debris thickness estimates from the thermal resistance approach (deviation 11.2% for AST08 and 11.6% for Landsat OLI) closely mirror the field measurements compared to the empirical approach (deviation 26.9% for AST08 and 35% for Landsat OLI). Thus, the thermal resistance approach can solve spatial variability in debris thickness on different heavily debris-covered glaciers globally without adequate knowledge of field measurements.
The Tsho Rolpa Glacier Lake stores about 100x 106 m3 of water behind an unconsolidated moraine dam in the Roiwaling Valley of central Nepal. The 150 m high terminal moraine has been deteriorating rapidly since the last 4-5 years, as buried dead-ice is being exposed. Displacement waves formed by the calving of the Trakarding Glacier terminus into the Tsho Rolpa are increasing in magnitude. Seepage from springs on the distal flank of the end moraine some 50 m below the dam crest and shallow slumps were also observed, and all of these phenomena indicate deterioration of the moraine dam. The majority of past studies suggested lowering the lake level to prevent a glacier lake outburst flood. Engineering work to lower the lake level down to 3 m by constructing an open channel on the terminal moraine began in May 1999 and ended successfully in July 2000. Several studies, including the ground penetrating radar survey, were conducted in association with the construction work. They provided the detailed information on subsurface conditions of the lake area. The construction of the open channel reduced the volume of water available to form a potential glacier lake outburst flood by about 20%. This work demonstrated for the first time in Nepal that such remediation of a glacier lake outburst is quite effective.
Field and geophysical studies have allowed us to identify processes leading to ice-cored moraine degradation for three natural dams investigated in Peru and Nepal. As potentially hazardous lakes form on the snouts of debris-covered glaciers they may separate a stagnant ice body from the upper reaches of the glacier to form an ice-cored end-moraine complex. The ice-cored moraines appear to degrade through ablation beneath the debris cover, by localized thermokarst development, and by associated mass movement. Relict glacier structures serve as a focal point for the onset of accelerated thermokarst degradation. Once exposed, the ice core then undergoes accelerated wastage through the combined affects of solar radiation and mechanical failure due to the rheological response of the ice to deepening kettle forms. Continuing degradation reduces the lake freeboard, weakens the moraine dam, and can lead to its catastrophic failure.
Analyses of satellite imagery obtained in 1989-1990 and topographic maps from 1966 have been undertaken for the glacierized areas of Bhutan. It has been found that where supraglacial lakes have formed since 1966, surface gradients of the glaciers concerned were in all cases less than 2°. At gradients of 2-10°supraglacial ponds can form but tend to be transient due to the opening and closing of crevasses. By identifying the conditions under which large supraglacial lakes form it is possible to use these criteria to predict where such lakes may develop in the future. This will allow suitable monitoring programmes to be introduced and, where necessary, suitable engineering remediation works to be undertaken in order to prevent the collection of large volumes of water that may be liable to form glacier lake outburst floods in the future.
Patterns of annual variation of air temperature in the world provide two types of the patterns of ablation rate of the glacier, namely the “summer-maximum” and the “non-maximum” through a year, while those of precipitation and air temperature provide three types of accumulation rate, namely, the above two and the “winter-maximum”. In six combinations of these types, annual variation of balance rate can be classified into the types of the winter-maximum, the non-maximum and the summer-maximum. The “summer-accumulation type glaciers” in the Nepal Himalaya, which have more accumulation in summer than winter in the whole area of a glacier, belong to the non-maximum type of balance rate.
In the case of this type glacier, direct observations of accumulation and ablation are quite difficult, since accumulation and ablation mainly occur simultaneously in summer. Therefore, the methods of estimation of accumulation and ablation are discussed. Accumulation can be estimated on the basis of the linear relation between surface air temperature and the probability of occurrence of solid precipitation in all cases of precipitation. Local characteristics of melting process of precipitation elements which control such relation are described. For the estimation of ablation, the effect of high albedo of new snow is important for the summer-accumulation type. The variation of mass balance through the balance year in the case of the summer-accumulation type is compared with that of the winter-accumulation type.
In 1978, the first detailed glaciological studies were carried out on the small glacier AX010 in a glacier inventory of Dudh Kosi region, in the Nepal Himalaya. Its length, area and highest and lowest elevations in 1978 were 1.7 km, 0.57 km2, 5360 and 4950 m a.s.l., respectively. Two resurveys of its terminus position and/or surface elevations were carried out in 1989 and 1991. The glacier retreated by about 30 and 28 m during the periods 1978–89 and 1989–91, respectively.
In 1995, annual monitoring of this glacier by means of ground survey, stake method and topographical mapping began, in order to obtain its mass balance, surface flow velocity and extent, and link them with climatic conditions. The results obtained in 1995 are summarized as follows: (1) During the period 1991–95, the glacier retreated by 12 m. (2) Associated with the ice-thickness loss in the lower part of the glacier, the horizontal surface velocities along the center line in 1995 (June–October) showed a remarkable decrease on the glacier tongue, to about 50% of those in 1978.
Shrinkage of the glacier in the near future is predicted from a simple model calculation for the case that climatic conditions remain unchanged from 1995. The results show that the present shrinkage should continue and accelerate.
The thickness of supraglacial debris on the Khumbu Glacier, Nepal Himalaya, has been mapped by a combination of direct measurements and morphological and lithological studies. All three processes, englacial, supraglacial, and subglacial, must be considered in establishing the distribution of debris. Taking advantage of the lithological characteristics of the debris and their bedrock source, the denudation rate of the schistose bedrock was estimated to be about 0.02 mm a−1. A rough estimate of the production rate of supraglacial debris indicated that most of the present debris has formed since the last advance of the glacier, which took place a few hundred years B.P.
The debris-covered area of Khumbu Glacier was topographically mapped in 1995 and the morphological evolution was determined by comparing the 1995 maps with those made in 1978. There had been significant changes in the surface morphology during this 17-year period: The area with a rough uneven surface with large relative relief had extended both upglacier and downglacier, and area of high ablation had increased. The glacier shrinkage in the ablation area where there was a thick debris cover was associated with an increase in surface relief and relative height, mainly caused by rapid ablation on exposed ice and lateral erosion at streams and ponds.
The Neoglacial evolution of the Tasman Glacier is reconstructed from the distribution of ice-marginal moraines and from the subglacial topography. The glacier has overridden its margins, creating two shelves of thin ice by c. 3700 years before present (BP) and c. 2000 years BP. The proglacial foreland is dominated by outwash aggradation and lacks pre-nineteenth century terminal moraines. The glacier has experienced successively larger expansions over the Neoglacial period (c. 5000 years), prior to drastic twentieth-century thinning and retreat. Over the same period, uncovered glaciers have shown progressively smaller re-advances. The expansionary tendency of the debris-covered glacier is interpreted as a response to long-term (millennial) accumulation of both subglacial and supraglacial debris. Subglacial aggradation has probably raised the bed of the glacier, promoting debris cover growth and reducing ablation even as less favourable balance regimes developed. Comparison with other glaciers shows that the expansionary tendency is widespread but may be manifest in a variety of sediment-landform associations.
ABSTRACT: 15.1 INTRODUCTION The concept of the glaciated valley landsystem was introduced by Boulton and Eyles (1979) and Eyles (1983b), to describe the characteristic sediments and landforms associated with valley glaciers in upland and mountain environments. By focusing on the scale of the whole depositional basin, the glaciated valley landsystem has a broader compass than most of the other landsystems explored in this book, which are specific to particular depositional environments. Indeed, glaciated valley landsystems may incorporate ice-marginal, supraglacial, subglacial, proglacial, periglacial and paraglacial landsystems, recording the juxtaposition and migration of very different depositional environments. Additionally, because glaciated valleys occur in every latitudinal environment from equatorial to polar regions, the dimensions of climate and glacial thermal regime add even more variability. Thus the 'glaciated valley landsystem' should be regarded as a family of landsystems, which exhibits considerably more variety than suggested by the original Boulton and Eyles model (Fig. 15.1). Despite this variability, landsystems in glaciated valleys tend to have certain recurrent features, as a result of two main factors: 1. the strong influence of topography on glacier morphology, sediment transport paths and depositional basins 2. the importance of debris from supraglacial sources in the glacial sediment budget. In this chapter, we emphasise the contrasts between glaciers with limited supraglacial debris ('clean glaciers') and glaciers with substantial debris covers in their ablation zones ('debris-covered glaciers'), although it should be recognized that intermediate forms occur between these end members. Before examining the landsystems of glaciated valleys, we begin by considering debris sources and transport pathways through valley glaciers, and the ways in which debris cover influences glacier dynamics. 15-Evans-Glacial-15-ppp 5/27/03 2:38 PM Page 372
Full-text · Article · Jan 2004