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Glaciological mass balance (MB) is considered the most direct, undelayed and unfiltered response of the glaciers to climatic perturbations. However, it may inherit errors associated with stake under-representation, averaging over the entire glacier and human bias. Therefore, proper validation of glaciological MB with geodetic MB is highly recommended by the World Glacier Monitoring Service (WGMS). The present study focuses on the Dokriani Glacier, central Himalaya which is one of the bench-mark glaciers in the region and has glaciological MB records from 1993 to 2013 with intermittent gaps. In the present study, firstly the glaciological MB series is extended to 2014 i.e., field-based MB for one more year is computed and, to compare with it, the geodetic MB is computed for the 1999–2014 period using high resolution Cartosat-1 digital elevation model (DEM) and SRTM DEM. Finally, the study assesses the regional representation of the Dokriani Glacier in terms of MB and evaluates the influence of the MB regime on its morphological evolution. Results show that the average glaciological MB (−0.34 ± 0.2 m water equivalent (w.e.) y−1) is more negative than the geodetic MB (−0.23 ± 0.1 m w.e. y−1) for the 1999–2014 period. This is likely because of the partial representation of glacier margins in the glaciological MB, where melting is strikingly low owing to thick debris cover (>30 cm). In contrast, geodetic MB considers all marginal pixels leading to a comparatively low MB. A comparative assessment shows that the MB of Dokriani Glacier is less negative (possibly due to its huge accumulation area) than most other glacier-specific and regional MBs, restricting it to be a representative glacier in the region. Moreover, continuous negative MB has brought a peculiar change in the epiglacial morphology in the lower tongue of the glacier as differential debris thickness-induced differential melting has turned the glacier surface into a concave one. This concavity has led to development of a large (10–20 m deep) supraglacial channel which is expanding incessantly. The supraglacial channel is also connected with the snout wall and accelerates terminus disintegration. Given the total thickness of about 30–50 m in the lower glacier tongue, downwasting at its current pace, deepening/widening of supraglacial channel coupled with rapid terminus retreat may lead to the complete vanishing of the lower one km glacier tongue.

Glaciers in Switzerland are shrinking rapidly in response to ongoing climate change. Repeated glacier inventories are key to monitor such changes at the regional scale. Here we present the new Swiss Glacier Inventory 2016 (SGI2016) that has been acquired based on sub-meter resolution aerial imagery and digital elevation models, bringing together topographical and glaciological approaches and knowledge. We define the process, workflow and required glaciological adaptations to compile a highly detailed inventory based on the digital Swiss Topographic Landscape model. The SGI2016 provides glacier outlines (areas), supraglacial debris cover and ice divides for all Swiss glaciers referring to the years 2013–2018. The SGI2016 maps 1,400 individual glacier entities with a total surface area of 961 ± 22 km2, whereof 11% (104 km2) are debris-covered. It constitutes the so far most detailed cartographic representation of glacier extent in Switzerland. Interpretation in the context of topographic parameters indicates that glaciers with moderate inclination and low median elevation tend to have highest fractions of supraglacial debris. Glacier-specific area changes since 1973 show the largest relative changes for small and low-elevation glaciers. The analysis further indicates a tendency for glaciers with a high share of supraglacial debris to show larger relative area changes. Between 1973 and 2016, an area change rate of –0.6% a−1 is found. Based on operational data sets and the presented methodology, the Swiss Glacier Inventory will be updated in 6-yr time intervals, leading to a high consistency in future glacier change assessments., Frontiers in Earth Science, 9, ISSN:2296-6463

It can easily be expected that debris-covered glaciers show a different response on external forcing compared to clean-surface glaciers. The supra-glacial debris cover acts as an additional transfer layer for the energy exchange between atmosphere and ice. The related glacier reaction is the integral of local effects, which changes strongly between enhanced melt for thin debris layers and considerably reduced melt for thicker debris. Therefore, a realistic feedback study can only be performed, if both the ice flow and the debris-influenced melt is treated with a high degree of detail. We couple a full Stokes representation of ice dynamics and the most complete description of energy transfer through the debris layer, in order to describe the long-term glacier reaction in the coupled system. With this setup, we can show that steady-state conditions are highly unlikely for glaciers, in case debris is not unloaded from the surface. For continuous and complete debris removal from the lowermost glacier tongue, however, a balance of the debris budget and the glacier conditions are possible. Depending on displacement and removal processes, our results demonstrate that debris-covered glaciers have an inherent tendency to switch to an oscillating state. Then, glacier mass balance and debris balance are out of phase, such that glacier advance periods end with the separation of the heavily debris-loaded lowermost glacier tongue, at time scales of decades to centuries. As these oscillations are inherent and happen without any variations in climatic forcing, it is difficult to interpret modern observations on the fluctuation of debris-covered glaciers on the basis of a changing climate only.

Debris-covered glaciers represent potentially significant stores of freshwater in river basins throughout High Mountain Asia (HMA). Direct glacier mass balance measurements are extremely difficult to maintain on debris-covered glaciers, and optical remote sensing techniques to evaluate annual equilibrium line altitudes (ELAs) do not work in regions with summer-accumulation type glaciers. Surface elevation and glacier velocity change have been calculated previously for debris-covered glaciers across the region, but the response of debris cover itself to climate change remains an open question. In this research we propose a new metric, i.e. the debris emergence elevation (ZDE), which can be calculated from a combination of optical and thermal imagery and digital elevation data. We quantify ZDE for 975 debris-covered glaciers in HMA over three compositing periods (1985–1999, 2000–2010, and 2013–2017) and compare ZDE against median glacier elevations, modelled ELAs, and observed rates of both mass change and glacier velocity change. Calculated values of ZDE for individual glaciers are broadly similar to both median glacier elevations and modelled ELAs, but slightly lower than both. Across the HMA region, the average value of ZDE increased by 70 +/− 126 m over the study period, or 2.7 +/− 4.1 m/yr. Increases in ZDE correspond with negative mass balance rates and decreases in glacier velocity, while glaciers and regions that show mass gains and increases in glacier velocity experienced decreases in ZDE. Regional patterns of ZDE, glacier mass balance, and glacier velocities are strongly correlated, which indicates continued overall increases in ZDEE and expansion of debris-covered areas as glaciers continue to lose mass. Our results suggest that ZDE is a useful metric to examine regional debris-covered glacier changes over decadal time scales, and could potentially be used to reconstruct relative mass and ELA changes on debris-covered glaciers using historical imagery or reconstructed debris cover extents.

Debris-covered glaciers, especially in high-mountain Asia, have received increased attention in recent years. So far, few field-based observations of distributed mass loss exist and both the properties of the debris layer as well as the atmospheric drivers of melt below debris remain poorly understood. Using multi-year observations of on-glacier atmospheric data, debris properties and spatial surface elevation changes from repeat flights with an unmanned aerial vehicle (UAV), we quantify the necessary variables to compute melt for the Lirung Glacier in the Himalaya. By applying an energy balance model we reproduce observed mass loss during one monsoon season in 2013. We show that melt is especially sensitive to thermal conductivity and thickness of debris. Our observations show that previously used values in literature for the thermal conductivity through debris are valid but variability in space on a single glacier remains high. We also present a simple melt model, which is calibrated based on the results of energy balance model, that is only dependent on air temperature and debris thickness and is therefore applicable for larger scale studies. This simple melt model reproduces melt under thin debris (

Current glaciation of the Central Caucasus is in the regressive stage of evolution. Observed long rising of the air temperature in the ablation seasons (almost 1 °C since 1968 on the Djankuat Glacier) together with insignificant growth of winter precipitation caused a long period of the glacier degradation: since 1871 the mass balance of the glacier, with rare exceptions, remained negative. During this time, the glacier has lost about 60 m w.e. mainly by areas of the smallest ice thickness, i.e. the steep slopes of the rocky framing of the fi n basin which become exposing from ice due to conditions of extreme instability. In parallel with the processes of freezing and thawing in cracks, this leads to a signifi ant increase in the frequency of rockfalls. In 2001–2003, huge rockfalls occurred on the glacier from the slopes, which had recently undergone deglaciation. The last one covered 4% of the glacier surface with about 70 000 m3of clastic products. The marine cover differs significantly from the open ice surface in its thermal characteristics, which affect the structure of the thermal balance and the absolute values of ablation. The temperature inside the moraine is positive throughout the ablation season, even at a depth of 60 cm, but the absolute values of daily maximum melting are five times lower than those on open ice. The influence of the moraine material layer on the ablation is determined not only by its thickness, but also by the structure. The fi ld experiment conducted in 2011 demonstrated that melting under a layer of coarse-grained material (particle diameter 16–17 cm) is four times faster than under a layer of fi e-grained (7–8 cm) material equal in thickness. The study of the influence of the surface moraine and the account of its further growth in thickness and area made it possible to predict changes in the surface of the glacier by 2025. The climatic forecast was made using the HadCM3 model (A2 climate change scenario). Data on air temperature and precipitation were used to construct a predictive fi ld of the mass balance of the Djankuat Glacier for each year until 2025. Th s became possible by the use of a quantitative parameterized relationship between the mass balance of the entire glacier and each of its points, identifi d in the study of the total mass transfer of the glacier, as well as parameterized linear regression equations. The forecast of hypsometry of the Djankuat Glacier made it possible to determine that by 2025 the depression of the tongue areas covered by the moraine will be 7–15 m (or 42–45%) smaller than areas of the open ice. Th s means that at the present stage of the glaciation development the surface moraine plays a role in the evolution of the glacier, commensurable with the climate factor.

Meltwater from the glaciers in High Mountain Asia plays a critical role in water availability and food security in central and southern Asia. However, observations of glacier ablation and accumulation rates are limited in spatial and temporal scale due to the challenges that are associated with fieldwork at the remote, high-altitude settings of these glaciers. Here, using a remote-sensing-based mass-continuity approach, we compute regional-scale surface mass balance of glaciers in five key regions across High Mountain Asia. After accounting for the role of ice flow, we find distinctively different altitudinal surface-mass-balance gradients between heavily debris-covered and relatively debris-free areas. In the region surrounding Mount Everest, where debris coverage is the most extensive, our results show a reversed mean surface-mass-balance gradient of −0.21 ± 0.18 m w.e. a−1 (100 m)−1 on the low-elevation portions of glaciers, switching to a positive mean gradient of 1.21 ± 0.41 m w.e. a−1 (100 m)−1 above an average elevation of 5520 ± 50 m. Meanwhile, in West Nepal, where the debris coverage is minimal, we find a continuously positive mean gradient of 1.18 ± 0.40 m w.e. a−1 (100 m)−1. Equilibrium line altitude estimates, which are derived from our surface-mass-balance gradients, display a strong regional gradient, increasing from northwest (4490 ± 140 m) to southeast (5690 ± 130 m). Overall, our findings emphasise the importance of separating signals of surface mass balance and ice dynamics, in order to constrain better their contribution towards the ice thinning that is being observed across High Mountain Asia., Remote Sensing, 12 (10), ISSN:2072-4292

Himalayan glacier changes in the context of global climate change have attracted worldwide attention due to their profound cryo-hydrological ramifications. However, an integrated understanding of the debris-free and debris-covered glacier evolution and its interaction with glacial lake is still lacking. Using one case study in the Gyirong River Basin located in the central Himalayas, this paper applied archival Landsat imagery and an automated mapping method to understand how glaciers and glacial lakes interactively evolved between 1988 and 2015. Our analyses identified 467 glaciers in 1988, containing 435 debris-free and 32 debris-covered glaciers, with a total area of 614.09 ± 36.69 km2. These glaciers decreased by 16.45% in area from 1988 to 2015, with an accelerated retreat rate after 1994. Debris-free glaciers retreated faster than debris-covered glaciers. As a result of glacial downwasting, supraglacial debris coverage expanded upward by 17.79 km2 (24.44%). Concurrent with glacial retreat, glacial lakes increased in both number (+41) and area (+54.11%). Glacier-connected lakes likely accelerated the glacial retreat via thermal energy transmission and contributed to over 15% of the area loss in their connected glaciers. On the other hand, significant glacial retreats led to disconnections from their proglacial lakes, which appeared to stabilize the lake areas. Continuous expansions in the lakes connected with debris-covered glaciers, therefore, need additional attention due to their potential outbursts. In comparison with precipitation variation, temperature increase was the primary driver of such glacier and glacial lake changes. In addition, debris coverage, size, altitude, and connectivity with glacial lakes also affected the degree of glacial changes and resulted in the spatial heterogeneity of glacial wastage across the Gyirong River Basin.

In this study, mass balance for Chorabari glacier of the Central Himalaya, India has been estimated. This glacier has been considered for the case study as it feeds the Mandakini River and was one of the reasons for flash floods in Rudraprayag district, Uttarakhand in 2013. The observations are based on glacier area/length change and rate of melting in the multi-decade (1976-2016) using Landsat data. The study estimates an overall decrease in area at 0.8% per year. Elevation change has been studied using geodetic method utilizing shuttle radar topography mission and TanDEM-X datasets, which have shown a decrease in elevation in 16 years (2000-16). From these remotely observed parameters, a negative mass balance for the decade 2000-11 indicates glacier retreat. This study highlights the applicability of optical and radar remote sensing for the Himalayan glaciers, for better disaster management and understanding glacier dynamics in response to climate change.

The site investigation of low-gradient slopes composed by marly rocks usually focuses on shallow slides in weathered mantling material as it is assumed that the underlying bedrock has higher strength, but deeper investigations may reveal larger, active, deep-seated movements. A typical example of this is found in Montemartano (Perugia, Central Italy). Here aerial photo interpretation and field observations indicate that active movements involve the shallower portion of the slope, formed by a very old and large landslide body extending over an area of about 0.5 km2. Borehole core logging and probe inclinometer monitoring reveal that the area corresponding to the deep-seated landslide is moving at a maximum rate of 70 mm/year down to a maximum depth of 40 m. A comparison of inclinometer and piezometer data indicates that the movement seasonally reactivates even when rainfall and piezometer levels are below average values and suggests that structural setting of the whole slope influences both groundwater flow and movement kinematics. This hypothesis is reinforced by seepage analyses and stability analyses yielding a mobilized shear strength close to residual strength of the clayey interbeds of the marly limestone formations. This implies that instability occurs along bedding over a large part of the slide. The importance of these phenomena in land management policy is discussed and the critical aspects of their investigation and monitoring are addressed. The reconstruction of landslide geometry/stratigraphy and geotechnical characterization of the materials is closely considered, particularly as these are complicated by the limited representativeness of field and laboratory investigations in this type of material.