CR2.2

The creation and curation of environmental data present numerous challenges and rewards. In this study, we reflect on the maturity of freely available glacier data sets (inventories and changes), as well as on related demands by data providers, data users, and data repositories in-between. The amount of glacier data has increased significantly over the last two decades, especially as remote-sensing techniques have developed quickly. The portfolio of observed parameters has increased as well, which presents new challenges for international data centers, and fosters new expectations from users.

We assess the services of the Global Terrestrial Network for Glaciers (GTN-G) as the central organization for standardized data on glacier distribution and changes. Within GTN-G, different glacier data sets are consolidated under one umbrella, and the glaciological community supports this service by actively contributing their data sets and by providing strategic guidance via an Advisory Board. To assess each GTN-G data set, we present a maturity matrix and summarize achievements, challenges, and future ambitions.

Most challenges can only be overcome in a financially secure setting for data services and with the help of international standardization. Therefore, dedicated support and long-term commitment for certified data repositories build the basis for the successful democratization of data. In the field of glacier data, this balancing act has so far been successfully achieved through joint collaboration between data repositories, data providers, and data users. However, we also note an unequal allotment of funds for data creation and projects using the data, and data curation. Considering the importance of glacier data to answering numerous key societal questions (from water availability to global sea-level rise), this imbalance needs to be adjusted. In order to guarantee the continuation and success of GTN-G in the future, basic funding schemes, flexible adaptation measures, and regular evaluations are required.

How to cite: Gärtner-Roer, I., Nussbaumer, S. U., Raup, B., Paul, F., Welty, E., Windnagel, A., Fetterer, F., and Zemp, M.: Maturity of worldwide glacier data sets – history and future ambitions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3376, https://doi.org/10.5194/egusphere-egu22-3376, 2022.

Various interdisciplinary studies have shown substantial discrepancies between modeled and remotely sensed glacier surface elevation change.It is therefore crucial to better understand and quantify uncertainties associated to both methods. We design a probabilistic framework with the aim to filter outliers, fill data voids and estimate uncertainties in glacier surface elevation changes computed from Digital Elevation Model (DEM) differentiation. The technique is based on a Bayesian formulation of the DEM difference problem and specifically targets surging and debris-covered glaciers, both at glacier and regional scales. We first define a set of physically admissible surface elevation changes as an elevation-dependent probability density function.

In a second step, terrain roughness is defined as the main descriptor for DEM uncertainty. Each surface elevation change pixel is a probability distribution. We present validation experiments in High Mountain Asia and show that the model produces results consistent with conventional DEM differencing, while avoiding the caveats of already existing methods. We further demonstrate that accounting for unstable glacier dynamics is crucial for accurate outlier filtering and robust uncertainty estimation. The technique can be applied to other types of remotely sensed glacier quantities (surface velocity etc.) and would provide more reliable characterization of uncertainty associated with changes in glacier mass and dynamics.

How to cite: Guillet, G. and Bolch, T.: Probabilistic estimation of glacier surface elevation changes from DEM differentiation: a Bayesian method for outlier filtering, gap filling and uncertainty estimation with examples from High Mountain Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10073, https://doi.org/10.5194/egusphere-egu22-10073, 2022.

In recent decades, snowfalls, snow cover and duration over Central Italy have decreased and there have been some extreme snowfall events followed by extreme avalanche activities. In this regard, the Calderone Glacier (hereinafter Calderone) represents a geographical and geomorphological element of great interest and is defined as a sentinel of climate change in central Italy, as it is going through a strong phase of reduction, it is the only glacier in the Apennines,  and the southernmost in Europe, and for its position on the summit of the Italian Gran Sasso (2912 m asl), a mountain group located in the center of the Apennine belt in the Mediterranean area.

The Italian Glaciological Committee (Comitato Glaciologico Italiano (CGI) )  every year with ad hoc in-situ inspections in late spring and early autumn monitor the Calderone mass balance. The mass balance of a glacier depends on the interplay between the mass gains and losses associated with climate and those associated with the inherent flux, its monitoring is essential because it can contribute to the knowledge of the current ongoing evolution of glaciers. 

Continuation of the traditional type of monitoring, like the one performed by CGI, based on direct measurements of accumulation and ablation by means of a network of stakes, appears to be an unlikely prospect, because in-situ data gathering usually implies expensive field campaigns and with difficult access to the sites, resulting in limited spatial and temporal resolution.  In contrast, techniques based on remotely sensed data, among several techniques, those relying on Synthetic Aperture Radar (SAR) demonstrated to be very effective due to the instrument's capability of operating day and night independently of the weather conditions.

Differential interferometry or DInSAR is a tool for accurate displacement measurements, and it is useful in identifying footprints of progressing movement. DInSAR is interferometry itself, the only difference is that topographical effects are compensated by using a Digital Elevation Model (DEM) of the area of interest, creating what is referred to as a differential interferogram.

In this work we propose the mass balance for the Calderone through the DInSAR results and its comparison with CGI in-situ measurements for the winter period 2018-2020. The data used in this study consist of COSMO-SkyMed satellite X-band single-look complex images in slant geometry (SCS, level 1A product),  Stripmap Himage mode (HH polarization) at 3 m per pixel of spatial resolution, and acquisition geometry Right Descending. The processing of this satellite data was applied over the entire area covered by the images and then refined to Calderone area, it includes a pre-processing first step that include: coregistration, interferogram formation, filtering and speckle; and a second part focused on obtaining the average values, active area and total area for the calculation of the mass balance.

How to cite: Alvan Romero, N., Palermo, G., Raparelli, E., Tuccella, P., D'Aquila, P., Caira, T., Pecci, M., and Marzano, F.: Monitoring the Calderone glacieret in Central Italy from COSMO-SkyMed synthetic aperture radar at X band, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4377, https://doi.org/10.5194/egusphere-egu22-4377, 2022.

The intercomparison exercise by the IACS Working Group on Regional Assessments of Glacier Mass Change (RAGMAC) aims to provide an overview of good practises as well as spread of different processing approaches for assessing glacier volume changes from geodetic methods. It is composed of two experiments with mandatory and optional tasks. Participants are encouraged to contribute to all tasks.

Experiment 1 targets a comparison of spaceborne elevation changes to high-quality, high-resolution airborne data (either from laser scanning or aerial photogrammetry) as well as to in-situ surface glacier mass balance data. Test sites are Aletsch Glacier and Hintereisferner in the Alps as well as Vertisen in Norway. The expected outcome of the first experiment (with validation data) is to see how the participants account for the mismatch between DEM acquisition dates and to assess quantitatively the divergence between estimates as a function of this mismatch.

Experiment 2 is setup for regions (Northern Patagonian Icefield, Karakoram, Franz Joseph Land) where not direct validation data is available. The challenge posed here is on the intercomparison and influence of different processing steps and approaches on the elevation and volume change results. Observation periods are pre-defined and participants deliver different versions of the processing results.

The presentation will provide an overview of the exercise and the experiments and outline first results of the endeavour.

How to cite: Braun, M., Zemp, M., and Brun, F.: First results of the RAGMAC glacier elevation change intercomparison exercise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8606, https://doi.org/10.5194/egusphere-egu22-8606, 2022.

Debris-covered glaciers in the Manaslu region of Nepal have been scarcely studied. Here we aim to fill this gap using new, multi-sensor, freely available 2019 Planet high-resolution (3 to 5 m) imagery, 1970 Corona declassified imagery and UAV and stake ablation data acquired in the field to characterize the surface and evolution of these glaciers over the last five decades. We report regional area changes, glacier thickness, geodetic glacier mass balance and surface velocity changes and focus on Ponkar Glacier and Thulagi Glacier and Lake for an in-depth assessment of surface geomorphology and surface feature dynamics (ponds, vegetation and ice cliffs).

Glaciers in the Manaslu region experienced a mean area loss of -0.26 ± 0.0001 % a^-1 between 1970 and 2019, with a mean surface lowering of -0.20 ± 0.02 ma^-1 over the period 1970 to 2013, corresponding to a regional geodetic mass balance of -0.17 ± 0.03 m w.e.a⁻¹. Overall, debris-covered glaciers had higher thinning rates compared to clean ice glaciers. During the period 1970 to 2013, the debris-covered Ponkar Glacier had a geodetic mass balance of -0.06 ± 0.01 m w.e.a⁻¹, with parts of the central trunk thickening and a nine-fold increase in the thinning rates over the lower parts of the glacier tongue in the recent years (2013 to 2019). Ice-surface morphology changes between 1970 and 2019 include a decrease in ogives and open crevasses, an increase in ice cliffs and ponds and the expansion of the supraglacial debris and ice-surface vegetation, suggesting reduced ice-dynamic activity.

How to cite: Racoviteanu, A. E., Glasser, N. F., Robson, B. A., Harrison, S., Millan, R., Kayastha, R. B., and Kayastha, R.: Recent evolution of debris-covered glaciers in the Manaslu region of Nepal (1970 - 2019): the case of Ponkar Glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5467, https://doi.org/10.5194/egusphere-egu22-5467, 2022.

Climate change is affecting glaciers worldwide, leading to unprecedented melt rates. In this context, establishing systems that provide near-real-time glacier information can be of high interest. However, the effort for acquiring real-time, in situ glacier observations is large.

In a previous study, we investigated the potential for automated acquisition of real-time mass balance readings by using optical cameras installed in-situ and computer vision techniques. The setup proved to be useful for obtaining melt rates with a temporal resolution of 20 minutes. However, it is not feasible to cover an extensive portion of a glacier with such a setup.

In our contribution, we present a method to acquire glacier mass balance readings with a custom drone equipped with a camera. The principle is to acquire images of a color-coded stake, from which surface mass balance can be determined via the glaciological method. To autonomously approach and read the stake, we exploit a combination of computer vision techniques and geometrical triangulation.  The results of off-glacier test flights, as well as four flights on Rhonegletscher, Switzerland, prove that the system is successful in detecting the stake in the videos captured by the drone. The determined stake position has uncertainties of 2.4 - 4.6 m, thus being sufficient to safely approach the stake. We investigate the main factors influencing the performance of the method in more detail, and discuss potential future developments of the system.

How to cite: Cremona, A., Landmann, J., Sold, L., Borner, J., and Farinotti, D.: Testing drones and computer vision for acquiring glacier melt observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-243, https://doi.org/10.5194/egusphere-egu22-243, 2022.

Glaciers are an important component of the cryosphere and are key indicators of climate change. Observations of temporal changes in glacier extent are essential for understanding the impacts of climate change, but these observations are not widely available in many parts of the world. Research indicates that climate change has had a significant impact on glacier recession, particularly in the Arctic, where glacier meltwater is an important contributor to global sea-level rise. Therefore, it is important to accurately quantify glacier recession within this sensitive region. In this study, we mapped 480 glaciers in Russian Arctic, Novaya Zemlya, using object-based image analysis (OBIA) applied to multispectral Landsat satellite imagery in Google Earth Engine (GEE) to quantify the area changes between 1986-89 to 2019-21.  Our results confirm that in 1986-89, the total glacierized area was 22958.98 km² and by 2019-21 there was an 5.56% reduction in glacier area to 21680.63 km².  Comparison between manually corrected glacier outlines taken from the Randolph Glacier Inventory (RGI) and the mapped glacier outlines derived using the OBIA method shows there is a 90.26% similarity between both datasets. This confirms that OBIA, combined with the GEE platform, is a promising method for accurately mapping glaciers, reduces the time required for manual correction, and can be applied in other glacierized regions for rapid assessment of glacier change.

How to cite: Ali, A., Dunlop, P., Coleman, S., Kerr, D., W McNabb, R., and Noormets, R.: Quantifying glacier area changes using object-based image analysis in Google Earth Engine, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6853, https://doi.org/10.5194/egusphere-egu22-6853, 2022.

The motion of glaciers with a temperate base is highly variable in time and space as a result of glacier basal sliding being strongly modulated by subglacial hydrology. Here we investigate short term (diurnal to multi-diurnal) changes in horizontal velocity and vertical displacement caused by melt and rain water input events on the Argentière Glacier (French Alps). We use up to 13 permanent GNSS stations that have been operating continuously over three full years (since April 2019). We report observations of strong surface acceleration events occurring in response to late summer storms, during which a velocity pulse propagates from up to down glacier at a migrating speed of about 0.1 m/s, which is typical of flow drainage speeds in the distributed system. We thus suggest that transient changes in the surface velocity field during intense and short-term water input events reflect transient changes in the distributed system flow properties. Although the efficient drainage system is expected to be well developed at this time of the year, this latter does not appear to play a primary role in our observations. Using concomitant observations of subglacial flow discharge and seismic tremor amplitudes we are able to estimate the average height of cavities and the associated cavity-drainage conductivity. Examination of the vertical displacement suggests that a vertical motion of the glacier (uplift) is largely controlled by the volume increase in subglacial water cavities rather than by the vertical strain rate change. These observational constraints may be crucial to test subglacial drainage and transient friction theories.

How to cite: Togaibekov, A., Walpersdorf, A., and Gimbert, F.: Short-term surface velocity variations of the Argentière glacier monitored with a high-resolution continuous GNSS network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4654, https://doi.org/10.5194/egusphere-egu22-4654, 2022.

The PROMICE project runs 27 Automatic Weather Stations (AWSs) in Greenland. Most of these are located in the ablation zone of the Greenland ice sheet. From March to September 2020 a multi-frequency Global Navigation Satellite System (GNSS) antenna was installed on the AWS NUK-K at a small local glacier outside Nuuk with the purpose of testing the setup for high precision positioning. Due to the remote location, power supply is limited and the GNSS setup is constructed to minimize the power consumption. Therefore, data collection is limited to three hours each day, the antenna is passive and the data is stored on a local drive and not transmitted.

This study tests if the setup is feasible for GNSS Interferometric Reflectometry (GNSS-IR) measurements of snow depth. The method estimates the average snow depth over an area on the order 10-20 • 10³ m². GNSS-IR analysis shows good reflections during most of the covered time period. A sonic ranger is mounted on the PROMICE AWSs and used for measurement of snow depth. The GNSS reflector heights are compared to measurements from the sonic ranger. Though some differences are present, the GNSS-IR estimates capture the snow melt, as measured by the sonic ranger, well. The quality of the reflections decreases towards the end of the data series when the snow is melted. We expect that this is due to a rougher ice surface. However, useful reflections are still obtained but the uncertainty on the daily estimates increase significantly. The transition from snow to ice surface is confirmed by an albedo estimate based on measurements of shortwave radiation at the AWS.

How to cite: Dahl-Jensen, T., Khan, S. A., Citterio, M., Jakobsen, J., and Ahlstrøm, A.: GNSS-IR for snow studies at PROMICE automatic weather station in Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3609, https://doi.org/10.5194/egusphere-egu22-3609, 2022.

The turbulent exchange of heat at the surface, including the sensible heat flux (SHF), is an important component of the surface energy balance (SEB) over glaciers and ice sheets. Yet, the turbulent heat fluxes are parameterized in all SEB models, which makes their contribution to the modelled ice ablation uncertain.

In this study, we present several years of continuous, daily, in situ observations of SHF (eddy-covariance) and ice ablation, taken at multiple contrasting sites across the ablation area of the Greenland ice sheet. We then compare these measurements to several SEB models with different settings for the surface roughness lengths.

We show that it is possible to accurately model the SHF and the daily ice ablation, provided that the prescribed surface roughness lengths, for both heat and momentum, are accurate. We propose a simple parameterization of these roughness lengths, based on both in-situ measurements and remotely sensed data (UAV, ICESat-2).  This updated parameterization can be implemented in SEB- and climate- models for improved simulations of ice sheet ablation and surface mass balance.

How to cite: van Tiggelen, M., Smeets, P. C. J. P., Reijmer, C. H., van den Broeke, M. R., van As, D., Box, J. E., and Fausto, R. S.: Momentum- & heat- flux parameterization over the Greenland Ice Sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1480, https://doi.org/10.5194/egusphere-egu22-1480, 2022.

High mountain environments are characterized by highly glacierized, complex, dynamic topography, often exhibiting a heterogeneous debris mantle comprising ponds and exposed ice cliffs, associated with differing ice ablation rates. These has been an increased interest in understanding these supraglacial surface features, i.e., the formation and expansion of supraglacial ponds and implications for glacier hydrology and glacier-related hazards, notably glacier lake outburst flood (GLOF) events. Until recently, supraglacial debris surfaces and their features have received less attention compared to mapping of debris-cover extents due to methodological challenges posed by their ephemeral nature. As a result, they remain poorly quantified in global glacier databases including the Global Land Ice Measurements from Space (GLIMS) and the Randolph Glacier Inventory (RGI). Furthermore, remote sensing studies used to generate these datasets generally rely on traditional “whole pixel” image classification techniques, which do not allow decomposition of a pixel into constituting materials. In this talk I summarize the state-of-art remote sensing techniques to characterize supraglacial features, such as debris material, ice cliffs, supraglacial ponds and vegetation. I particularly highlight the potential of spectral unmixing routines multi-temporal Landsat and Sentinel data combined with high-resolution multispectral imagery to quantify the composition of debris cover at multiple scales across the Himalaya with an emphasis on supraglacial ponds. I summarize the current strengths and limitations of these methods and discuss steps needed such as automation and open-source tools.

How to cite: Racoviteanu, A. E.: Remote sensing tools for monitoring supraglacial debris cover features and their fluctuations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10241, https://doi.org/10.5194/egusphere-egu22-10241, 2022.

Supraglacial debris covers the tongue of many mountain glaciers. In the course of ongoing climate change and the rapid melting of glaciers, debris extent and thickness will continue to increase. The thickness and other inherent properties of the debris layer control sub-debris melt rates and influence how glaciers respond to climate change. It is therefore essential to consider the impact of supraglacial debris on ablation in glacier surface mass balance models and glacier evolution models. However, this requires detailed knowledge on the debris thickness distribution. As debris thickness is spatially very variable, it remains a challenge to map debris thickness across the entire ablation zone of a glacier. Here we present the preliminary results of a feasibility study on the Kanderfirn in the Swiss Alps, where we deployed an Unoccupied Aerial Vehicle (UAV) with a visible and thermal infrared camera to map and analyse spatial variations in debris surface temperature, debris thickness, and sub-debris melt rates. Two independent approaches originally developed for satellite data were tested and compared to map debris thickness in high resolution. First, we used the statistical relationship between spatial UAV observations and in-situ point measurements (mapped surface temperature vs. measured debris thickness) to derive spatial debris thickness variations from mapped surface temperature variations. Second, we calculated distributed sub-debris melt rates from UAV-based elevation-change maps and quantified debris thickness through the inversion of a sub-debris ice melt model. Both methods deliver promising results. Despite the remaining challenges, the results emphasise the potential of UAVs equipped with visible and thermal infrared cameras for glacier-wide debris thickness mapping.

How to cite: Groos, A. R. and Messmer, J.: Mapping debris thickness on alpine glaciers using UAV thermography and photogrammetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12672, https://doi.org/10.5194/egusphere-egu22-12672, 2022.

Glaciers in High Mountain Asia have been shrinking in the recent decades. They are a valuable indicator of climate change, and their meltwater plays an important role for regional water resources. Debris-covered glaciers, which are prevalent throughout the Himalayas, exhibit complex melt processes due to their heterogeneous surface.  Previous studies have demonstrated that ice cliffs disproportionally contribute to glacier melt, but their importance at the glacier scale has been quantified for only a few sites. In this study, we exploit measurements taken since 2016 on the lake-terminating Trakarding Glacier (27.9°N, 86.5°E; 2.9 km² spanning 4,500–5,000 m a.s.l.; ~5% ice cliff cover), eastern Nepal Himalaya, to investigate the importance of cliffs for debris-covered ice melt at the glacier scale from a remote-sensing inversion and energy-balance modeling. We generated super-high-resolution (0.2 m) terrain data from aerial photographs (UAV and helicopter-borne photogrammetry) during 2018-2019 and manually delineated ~500 ice cliffs to derive surface velocity, elevation change, and specific mass balance, providing an observational estimate of ablation across the debris-covered tongue and attributable to ice cliffs. Further we employed a process-based 3D-backwasting model to estimate continuous ice cliff mass-loss over the study period. The model calculates the energy balance of ice cliff surfaces and reproduces their evolutions (cliff expansion, shrinkage, and reburial), based on the characteristics of the glacier surface and location of individual ice cliffs. This method, forced with in-situ meteorological and terrain data and evaluated against the observed changes, provides ice cliff mass-loss from the scale of individual features to the entire Trakarding Glacier.

How to cite: Sato, Y., Buri, P., Miles, E., Kneib, M., Sunako, S., Sakai, A., Pellicciotti, F., and Fujita, K.: Ice cliff mass-loss of debris-covered Trakarding Glacier, Rolwaling region, eastern Nepal Himalaya, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8327, https://doi.org/10.5194/egusphere-egu22-8327, 2022.

Ice cliffs are important contributors to the mass balance of debris-covered glaciers, especially in High Mountain Asia where they can account for one sixth of the melt of  debris-covered glacier tongues, despite covering less than 10% of their area. These features have been shown to evolve, appear and disappear rapidly from year to year, with high variability in relative area and number. It has been hypothesized that ice cliffs expand and melt more rapidly during the monsoon (June-September), but there are very few observations during this period. Here, we use arrays of time-lapse cameras to reconstruct the geometry of four ice cliffs at a weekly timestep over a period of four to six months at two monsoon-affected sites: Langtang Glacier in Nepal, and 24K Glacier in South-Eastern Tibet. We use Structure-from-Motion photogrammetry to derive point clouds and Digital Elevation Models (DEMs) of the glacier surface, using the stable background terrain to constrain viewing geometries and DEM errors. This technique (time-lapse photogrammetry) enables a high accuracy, quantitative measurement of processes occurring at the cliff-scale (elevation uncertainties stay below 30cm at a distance of 300m from the cameras) and at high temporal resolution over the monsoon season, when dense cloud cover and intense precipitation prevent field- or satellite-based observations. We derive the melt patterns of these cliffs from the differencing of the weekly DEMs by accounting for glacier flow. We compare the observed melt patterns with the modeled energy-balance at the cliff surface and use these observations to quantify the influence of debris slumping and redistribution, as well as supraglacial ponds and streams on the melt patterns of these cliffs. The results highlight the seasonal variations of cliff melt, which occurs at up to 8 cm/day during the monsoon, twice as high as observed in the pre- and post-monsoon period. Our energy-balance results indicate that melt rates are driven by incoming long- and shortwave radiation, and are thus highly dependent on the cliff slope and aspect, as substantiated by our photogrammetric measurements. The observations also demonstrate the competitive influence of debris, which progressively reburies the cliff by accumulating at its surface, and supraglacial streams and ponds, which maintain the cliff slope by preventing debris accumulation at the base. These results will help in understanding the surface evolution of debris-covered glaciers and enable a better representation of ice cliff melt and evolution in glacio-hydrological models.

How to cite: Kneib, M., Miles, E. S., Buri, P., Fugger, S., McCarthy, M., Zhao, C., Shaw, T. E., Truffer, M., Westoby, M., Yang, W., and Pellicciotti, F.: Sub-seasonal evolution of ice cliffs captured with time-lapse photogrammetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6163, https://doi.org/10.5194/egusphere-egu22-6163, 2022.

Landslides or rockslides occur in unstable slopes around the world, of which many cases are related to changes in the cryosphere. They can result in natural hazards and are an indicator of climate change. Due to their inherent non-linearity, they are difficult to predict and often remain unobserved. Appropriate documentation allows for assessing their consequences and long-term impacts on ecosystems or the hydrological cycle.

We report on a particularly well-documented case of a supraglacial rockslide that occurred on Brenndalsbreen, an outlet glacier of Jostedalsbreen, Norway, in the period November 2009-June 2010. We assess its consequences on local glacier mass balance derived from surface elevation changes and explore potential changes in flow velocities. The rockslide occurred unobserved and did not obviously impact humans or the environment, yet, satellite imagery and aerial photogrammetrical surveys allow for a spatial and temporal quantification of the event. Furthermore, a series of digital elevation models from 2012-2021 is used to determine spatial heterogeneity in ablation rates, however, this is complicated due to the motion of the ice mass. According to the widely used Östrem curve, a debris-cover exceeding a certain threshold thickness protects the ice below from ablation, while a thin debris or dirt layer increases ablation rates. In fact, we find that during the first years after the rockslide, locally, ablation was reduced below the debris layer, while a recent high-resolution LiDAR survey that got complemented with a UAV survey a year later, clearly indicates increased ablation rates relative to the debris-free surroundings. Clear trends in surface velocities have not been found based on satellite remote sensing data. We discuss the significance of the observations on surface energy balance and geomorphological changes in the proglacial area.

How to cite: Seier, G., Abermann, J., Engen, S. H., Gjerde, M., Scheiber, T., Löffler, K., Carrivick, J. L., Andreassen, L. M., and Yde, J. C.: ‘Dancing around the Östrem curve’: High-resolution monitoring of a supraglacial rockslide on Brenndalsbreen, Norway, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11134, https://doi.org/10.5194/egusphere-egu22-11134, 2022.

We have derived the glacier-specific Østrem curve to quantify the influence of a supraglacial debris cover on the mass and surface energy balance components of the Djankuat Glacier, a northwest-facing and partly debris-covered temperate valley glacier in the Caucasus region, which has been selected as a ‘reference glacier’ by the WGMS. A 2D energy balance model, in combination with meteorological data from automatic weather stations and ERA5-Land reanalysis data, are used to assess the melt-altering effect of supraglacial debris on the overall glacier runoff during 1 complete balance year. The main results show that both the surface energy balance and mass balance fluxes are modified significantly due to the presence of debris on the glacier surface. For very thin debris, a slight relative melt-enhancement occurs due to a decreased surface albedo. If debris, however, further thickens, the insulating effect becomes dominant and reduces the melt and runoff of the underlying ice significantly, as thermal conduction becomes the dominant process to induce ice melt beneath such thick debris layers. The above-mentioned effects are modelled to be increasingly pronounced with an increasing thickness of the superimposed supraglacial debris cover, and can be of great importance with respect to future glacio-hydrologic regimes and glacio-geomorphological processes.

How to cite: Verhaegen, Y., Rybak, O., Popovnin, V., and Huybrechts, P.: Deriving the Østrem curve to quantify supraglacial debris-related melt-altering effects on the Djankuat Glacier, Caucasus, Russian Federation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4217, https://doi.org/10.5194/egusphere-egu22-4217, 2022.

As glaciers respond to climate change, the scientific community has dedicated increasing attention to the development of melt models for debris-covered glaciers. Here, we present an intercomparison aimed at advancing our understanding of the skills of models of different complexity to simulate ice melt under a debris layer. We compare 14 models with different degrees of complexity at nine sites in the European Alps, Caucasus, Chilean Andes, Nepalese Himalaya and the Southern Alps of New Zealand, over one melt season. We run the models with meteorological data from automatic weather stations and estimated or measured debris properties. Model performance is evaluated using on-site measurements of sub-debris melt (for all models) and surface temperature (for models based on the surface energy balance) at each site. We find that the two main categories of models considered, physically-based energy balance (EB) models and empirical temperature index (TI) models perform in a distinct manner. Temperature index models are reliably accurate when they are recalibrated, and show a range of results when parameters are uncalibrated. The most accurate energy balance models are those with the highest degree of complexity at the atmosphere-debris interface. However, we also find that additional complexity within the debris and at the debris-ice interface does not improve performance, which results from a lack of data to accurately force the models to represent these processes. The difficulty to properly estimate the physical properties of debris layers and within-the-debris processes are a likely cause. One of our main conclusions is thus that sophisticated models need high quality input data. An important data gap emerged from our experiment: the poor performance of all models at three sites was related to poor knowledge of debris properties; specifically, of thermal conductivity. Since debris properties are a major control on melt model simulations, we demonstrate that consistent data acquisition efforts are required to more rigorously evaluate existing models and support new model developments. Future work should seek to advance models by improving how they account for processes such as debris-snow interactions, moisture in the debris and refreezing. We suggest that a systematic effort of model development using a single model framework could be carried out in phase II of the Working Group.

How to cite: Pellicciotti, F., Fontrodona-Bach, A., Rounce, D. R., Fyffe, C. L., McCarthy, M., Miles, E., and Shaw, T. E.: DCG-MIP: The Debris-Covered Glacier melt Model Intercomparison exPeriment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11904, https://doi.org/10.5194/egusphere-egu22-11904, 2022.

Around 10% of glacier area in the Himalaya is debris-covered with heterogeneous distribution. Debris distribution, as a function of its thickness, induces differential melting and may lead to characteristic slope inversion. The spatial distribution of debris thickness is poorly quantified in the Himalaya with limited field-based measurements. In the present study we conducted a field expedition on the Panchi Nala Glacier (4.50 km², 60% debris-covered), western Himalaya during September 2021 and measured debris thickness at 73 points using a DGPS. Debris thickness ranges from <1 cm to 50 cm and reaches upto 1 m over extreme margins. In general, the debris is thicker (>25 cm) in the lower reaches (upto 1.5 km from snout) and decreases with increasing distance from snout. This generalization is, however, not always true as some patches of thin debris cover (<3.5 cm) in the lower portion and some patches of thick debris cover (~13 cm) at upper portion were also found. To assess the influence of debris thickness on melting, elevation difference data from Shean et al. (2020) is obtained. The correlation between debris thickness and elevation changes over corresponding pixels is negative (R = −0.58), suggesting that variation in surface elevation changes can partially be explained by the distribution of debris thickness. Spatially, the wastage is comparatively low (−0.69 m/y) around glacier snout where debris cover is thick (~15 cm) and higher (−1.14 m/y) at higher reaches (~3 km from snout) where debris cover is thin (~5 cm). Comparison of profiles derived from SRTM DEM and ASTER DEM along the central flowline for 2000 and 2020, respectively suggests that owing to differential melting, the concavity is developing on the glacier. Thus, debris thickness is playing an important role in regulating the melt and modifying the overall morphology of the Panchi Nala Glacier. 

How to cite: Garg, P. K. and Azam, M. F.: Impact of debris distribution on glacier morphology: a case study of Panchi Nala Glacier, western Himalaya using field and remote sensing measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10142, https://doi.org/10.5194/egusphere-egu22-10142, 2022.

It is common for temperate glaciers in mountainous regions to exhibit an extensive ablation-zone supraglacial debris cover. Although secondary reworking of surface debris and its role in modifying rates of glacier melt is receiving increasing attention, debris origin and primary distribution is poorly understood. Arguably, studies have tended to uncritically assume that debris supply is dominated by the passive transport of rockfall material that is dispersed within the ice (englacially) or is deposited onto the surface directly. We show that a substantial portion of the debris cover at Miage Glacier, Italy, can be attributed to release from medial moraine (MM) structures that can be observed englacially in debris-free ice cliffs and as supraglacial ‘melt out’ ridges containing vertically oriented clasts, occasionally supported by a fine matrix. Two MM types displaying contrasting debris characteristics were observed: one arising from the tributary confluences located near or below the equilibrium line position, and another derived from accumulation basin confluences. The former were reasonably continguous supraglacial features that in the upper- and mid-ablation area develop considerable relief that clearly acts as a primary control on debris redistribution across the glacier surface. The latter type are traceable for limited distances, and form more isolated areas of high topography in the mid-ablation area. We argue that ablation area debris cover and relief complexity in the upper- and mid-ablation area largely reflects debris entrainment at the point of medial moraine origin, though additional factors include the recent detachment of tributaries, the decline in mass contributed by specific accumulation basins, and the stochastic nature of headwall debris supply. Secondary debris redistribution processes appear to increase as glacier surface elevation declines, meaning in the lower ablation area surface relief decreases as debris distribution complexity increases.

How to cite: Swift, D., Jones, A., Westoby, M., Bryant, R., and Veness, R.: Structurally controlled englacial origin of supraglacial debris cover and relief at a debris-covered Alpine glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11900, https://doi.org/10.5194/egusphere-egu22-11900, 2022.

Debris-covered glaciers accumulate supra-glacial debris on the glacier surface in the ablation zone. As long as this debris layer is not at least partly removed, it can be expected that glaciers continue to grow in length, because the thickening debris layer continuously reduces surface melt rates. Removal of the debris layer, on the other hand, is a complicated process, which depends on a number of parameters, like surface slope, debris thickness, grain size distribution and water content to name just a few. However, the way how supra-glacial debris is removed might strongly influence the dynamic reaction of the glacier itself.

A realistic study of these interactions can only be performed, if the ice flow and the debris-influenced melt is treated with a high degree of detail. In our study, we coupled a 2-D full Stokes ice dynamic and surface debris transport model with a sophisticated description of energy transfer through the debris layer. This approach ensures that ice flow and surface melt rates are simulated at high detail, including the enhanced melt rates for very thin debris cover just below the equilibrium line. We restricted our experiments to rather simple initial conditions, in order investigate the fundamental feedback mechanisms between melt rates and glacier dynamics. Therefore, we introduced rather simple, but realistic formulations of debris unloading at the glacier front. The coupled experiments show that steady-state conditions are highly unlikely for glaciers with the debris layer remaining on the glacier. However, a balance of the debris budget and the glacier mass flux is possible, when introducing debris removal from the glacier tongue. We focussed on an as realistic as possible representation of the snout geometry, in order to allow a physically sensible debris discharge. The results show that for some removal processes debris-covered glaciers have an inherent tendency to enter an oscillating state, where glacier mass balance and debris balance are out of phase. In specific experiments glacier advance periods end with the separation of the heavily debris-loaded lowermost glacier tongue, at time scales of decades to centuries, followed by an advance of the remaining clean glacier. In such cases we assume that long-term “mean-steady-state” conditions modulated by oscillations in glacier length exist and are independent from climatic variations. This makes it difficult to interpret short-term geometry observations of debris-covered glaciers in the context of climate impact.

How to cite: Mayer, C. and Licciulli, C.: What does steady state mean for debris-covered glaciers?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8742, https://doi.org/10.5194/egusphere-egu22-8742, 2022.

Numerical modelling studies examining the transient behaviour of debris-covered glaciers have typically varied either the equilibrium line altitude, which is a proxy for climate, or the rate of debris deposition. Since the rate of debris production from headwall erosion is believed to be an increasing function of temperature, a more faithful representation of debris-covered glacier evolution should include a coupling between debris source strength and climate.

In this study, we examine the transient response of debris-covered glaciers to the combined effect of a warming climate and a related increasing debris source using a numerical model that couples ice flow with englacially transported debris. This allows for a debris melt-out concentration in the ablation zone that varies in time and space, depending on the evolving glacier dynamics and the debris deposition history.

We find that debris-covered glaciers in a warming climate exhibit a complex transient response with aspects of both retreat and advance, though these distinct responses occur on different timescales. This suggests that the observed present-day retreat of debris-covered glaciers may be followed by an eventual advance despite a continued increase in global mean temperature.

How to cite: Ferguson, J. C., Bolch, T., Banerjee, A., and Vieli, A.: Modelling the complex transient response of debris-covered glaciers to climate change and interaction with debris production, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10238, https://doi.org/10.5194/egusphere-egu22-10238, 2022.