CR2.2

EDI
Glacier monitoring from in-situ and remotely sensed observations

Process understanding is key to assessing the sensitivity of glacier systems to changing climate. Comprehensive glacier monitoring provides the base for large-scale assessment of glacier distribution and changes. Glaciers are observed on different spatio-temporal scales, from extensive seasonal mass-balance studies at individual glaciers to decadal assessments of glacier mass changes and repeat inventories at the scale of entire mountain ranges. Internationally coordinated glacier monitoring aims at combining in-situ measurement with remotely sensed data, and local process understanding with global coverage. We invite contributions from a variety of disciplines, from tropical to polar glaciers, addressing both in-situ and remotely sensed monitoring of past and current glacier distribution and changes, as well as related uncertainty assessments. A special focus of this year’s session shall be on (i) strengths and limitations of different types of satellite data for global and regional glacier surveys, (ii) achieving a better temporal resolution of global and regional surveys (iii) how to develop in-situ networks for real-time monitoring of glacier changes and (iv) advances in studies on local process understanding and how best to combine them with regional to global change assessments?. An additional focus this year relates to improving understanding of debris-covered glaciers from in-situ and remote sensing methods, as well as understanding their long-term dynamics with numerical models.

Convener: Ines DussaillantECSECS | Co-conveners: Lauren VargoECSECS, Bruce Raup, Fanny BrunECSECS, Evan MilesECSECS, Mohan Bahadur ChandECSECS
Presentations
| Wed, 25 May, 15:10–18:30 (CEST)
 
Room N2, Thu, 26 May, 08:30–10:00 (CEST)
 
Room 1.85/86

Presentations: Wed, 25 May | Room N2

Chairpersons: Ines Dussaillant, Bruce Raup, Fanny Brun
15:10–15:15
Glacier change observations
15:15–15:22
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EGU22-3376
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Highlight
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Virtual presentation
Isabelle Gärtner-Roer, Samuel U. Nussbaumer, Bruce Raup, Frank Paul, Ethan Welty, Ann Windnagel, Florence Fetterer, and Michael Zemp

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.

15:22–15:29
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EGU22-10073
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ECS
Gregoire Guillet and Tobias Bolch

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.

15:29–15:36
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EGU22-7501
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ECS
Luca Mondardini, Paolo Perret, Simone Gottardelli, Marco Frasca, and Fabrizio Troilo

High Alpine environments are rapidly changing in response to climate change, and understanding the evolution of small glaciers is a crucial step to investigate future water availability for populations that inhabits these areas. With an average loss of 1.6 km2 of regional glacier area every year, Aosta Valley is predicted to lose most of its glaciers before the end of the century. With this study, we present a comprehensive analysis of a small glacier’s recent mass balance evolution (1991-2020) where no specific previous mass balance data was available. To do so, we combined historical data (topographic surveys and LiDAR DEMs of the area) with newly acquired satellite stereo imagery and aerophotogrammetric surveys to reconstruct different digital elevation models of the Thoula glacier (0.52 Km2), located on the Italian side of the Mont-Blanc Massif. The ice volume loss that occurred over this period was assessed by accomplishing two GPR surveys to investigate the ice thickness and the underlying bedrock. The Thoula glacier shows a significantly lower loss of volume in comparison to other glaciers located in the Aosta Valley region as well as most of the WGMS (Word Glacier Monitoring Service) reference glaciers for Central Europe. Particular weather-climatic conditions of the Mont Blanc Massif area, generally characterized by a greater amount of snowfall, could explain the observed differences, however, the present study shows how understanding spatio-temporal local variability of small glaciers can significantly contribute to recognizing different regional patterns developing in response to climate change.

How to cite: Mondardini, L., Perret, P., Gottardelli, S., Frasca, M., and Troilo, F.: Understanding the recent evolution of a small Alpine glacier: from geodetic mass balance reconstruction (1991-2020) to local variability of glaciers retreat., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7501, https://doi.org/10.5194/egusphere-egu22-7501, 2022.

15:36–15:43
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EGU22-4377
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ECS
Nancy Alvan Romero, Gianluca Palermo, Edoardo Raparelli, Paolo Tuccella, Pino D'Aquila, Tiziano Caira, Massimo Pecci, and Frank Marzano

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.

15:43–15:53
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EGU22-8606
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solicited
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Highlight
Matthias Braun, Michael Zemp, and Fanny Brun

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.

15:53–16:00
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EGU22-8240
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Virtual presentation
Eyjólfur Magnússon, Vincent Drouin, Finnur Pálsson, Krista Hannesdóttir, Joaquín M. C. Belart, Gunnar Sigurðsson, Jan Wuite, Tómas Jóhanneson, Benedikt G. Ófeigsson, Thomas Nagler, Magnús T. Gudmundsson, Thórdís Högnadóttir, Michelle Parks, Matthew J. Roberts, and Etienne Berthier

The subglacial lake Grímsvötn, beneath Vatnajökull ice cap, has been an important study area since the first attempts to explain the physics of jökulhlaups. The lake, covered by an up to 300 m thick ice shelf, is situated within a caldera of an active central volcano. It collects meltwater produced by geothermal and volcanic activity, in addition to meltwater from the glacier surface. During most of the 20th century the period of water accumulation was typically 4-6 years, collecting 1-3 km3 of water. The jökulhlaups, as  observed in the river at the glacier terminus ~50 km south of the lake, typically reached peak discharge of 2,000-10,000 m3s-1 after approximately exponential increase over 2-3 weeks. In October 1996, 3.2 km3 of meltwater from an eruption north of Grímsvötn were collected in the lake. This resulted in hydrostatic uplift of the lake ice dam and sudden release of the accumulated water, reaching a peak flow of ~50,000 m3s-1 at the glacier terminus in less than a day. Due to damage to the lake ice dam during the 1996 jökulhlaup and further undermining from geothermal activity near the dam, the water accumulation and release has been different after this event. Between 1996 and 2018, smaller jökulhlaups typically occurred at 1-2 year intervals with the largest volume of ~0.6 km3 in 2004 and 2010. The jökulhlaup discharge still resembled an exponentially rising discharge, but faster, reaching a peak discharge at the glacier front in 3-5 days after detection of flood water in the river. In 2004 and 2010 the peak discharge was ~3,000 m3s-1. From autumn 2018 until November 2021, ~1 km3 of water accumulated in Grímsvötn. The lake level has been monitored since the 1990s, but now with increased accuracy using online GNSS stations located on the floating ice shelf and repeated glacier surface mapping using Pléiades stereo images. Around mid-November 2021 the GNSS instruments started subsiding, revealing that the lake had started draining. In 3 weeks, the discharge from the lake, estimated from the subsidence rate and the lake hypsometry, gradually increased from a few m3s-1 to a peak discharge of ~3500 m3s-1 on 4 December. A few days later, the lake had drained completely. We present the data showing the development at the lake prior to and during the jökulhlaup, and we report on: a) discharge measurements near the glacier front, which combined with the lake discharge allows for an estimate of the temporal subglacial floodwater storage, b) horizontal and vertical ice motion in the vicinity and above the subglacial flood route during the jökulhlaup, from ICEYE and Sentinel-1 radar images obtained with InSAR (24 hour repeat) analysis and amplitude offset tracking, showing the distribution of flood water and the widespread effect of the jökulhlaup on the horizontal ice motion, c) ice surface motion measured by a GNSS station located half-way between the lake and the glacier margin, spanning the entire jökulhlaup. All this provides new insight into the physical processes occurring during a slow, exponentially rising jökulhlaup from Grímsvötn.

How to cite: Magnússon, E., Drouin, V., Pálsson, F., Hannesdóttir, K., Belart, J. M. C., Sigurðsson, G., Wuite, J., Jóhanneson, T., Ófeigsson, B. G., Nagler, T., Gudmundsson, M. T., Högnadóttir, T., Parks, M., Roberts, M. J., and Berthier, E.: The jökulhlaup from the subglacial lake Grímsvötn, beneath Vatnajökull ice cap, in November-December 2021, revealing new insight in to slowly rising jökulhlaups, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8240, https://doi.org/10.5194/egusphere-egu22-8240, 2022.

16:00–16:07
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EGU22-5467
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Virtual presentation
Adina E. Racoviteanu, Neil F. Glasser, Benjamin A. Robson, Stephan Harrison, Romain Millan, Rijan B. Kayastha, and Rakesh Kayastha

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.

16:07–16:14
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EGU22-243
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ECS
Aaron Cremona, Johannes Landmann, Leo Sold, Joël Borner, and Daniel Farinotti

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.

16:14–16:21
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EGU22-6853
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ECS
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On-site presentation
Asim Ali, Paul Dunlop, Sonya Coleman, Dermot Kerr, Robert W McNabb, and Riko Noormets

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.

16:21–16:36
Coffee break
Chairpersons: Bruce Raup, Ines Dussaillant, Evan Miles
17:00–17:05
Glacier process understanding
17:05–17:12
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EGU22-10033
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ECS
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On-site presentation
Laurane Charrier, Yajing Yan, Emmanuel Trouvé, Elise Colin Koeniguer, Silvan Leinss, Jeremie Mouginot, and Romain Millan

Intra-annual glacier velocities are key parameters to study glacier basal conditions or short-term events such as glacier surges. However, intra-annual glacier velocities remain poorly understood at a global scale, especially in mountains areas. Indeed, many ice velocity maps are now available on-line or on-demand at a temporal resolution up to 2 days and a spatial sampling up to 50 m (Millan et al., 2019) all over the world. However, these products contain gaps, noise and artefacts especially where image-matching algorithms fail because of strong surface changes, surface locking, shadow casting, clouds, or feature-less regions. Moreover, this amount of data is complex to analyse since velocities span different temporal baselines, are derived from different sensor images using different algorithms. Therefore, there is a need to fuse the available multi-temporal and multi-sensor glacier velocity observations in order to study intra-annual glacier dynamics with a high temporal resolution.

The proposed approach relies on an inversion based on the temporal closure of displacement observation networks. Because the observations have different uncertainties, not necessarily known, the inversion is solved using an Iterative Reweighted Least Square. This approach results in velocity time series which have a complete temporal coverage, a uniform temporal sampling without overlapping time intervals (i.e. without redundancy) by tacking advantage of all available velocity observations without a priori on the displacement behavior. The temporal sampling of these velocity time series can be selected. To select an optimal temporal sampling based on a compromise between temporal resolution and uncertainty, we propose to minimize Root Mean Square Error (RMSE) over stable areas and maximize Velocity Vector Coherence (VVC) over fast moving areas. The proposed approach is illustrated with both mono-sensor and multi-sensor datasets, on two different glaciers: 1) Sentinel-1 velocity observations from (Round et al., 2017) over the Kyagar glacier which is a surge glacier situated in the Karakoram range 2) Sentinel-2 and Venµs velocity observations from (Millan et al., 2019) over the Fox glacier, a temperate maritime glacier with a strong seasonality, situated in Southern Alps of New Zealand. The results reveal strong intra-annual variations of velocity with a reduced uncertainty for both glaciers: RMSE over stable areas is lower for the results than for the original velocities: 1) from 22% lower for 12-days temporal sampling to 67% lower for 36-days temporal sampling over the Kyagar glacier 2) from 78% lower for 5-days temporal sampling to 40% lower for 60-days temporal sampling over the Fox glacier.

This approach is not dataset dependent and can be applied to any available velocity observations derived from any sensors.

How to cite: Charrier, L., Yan, Y., Trouvé, E., Colin Koeniguer, E., Leinss, S., Mouginot, J., and Millan, R.: Fusion of multi-sensor, multi-temporal velocity observations to study intra-annual glacier dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10033, https://doi.org/10.5194/egusphere-egu22-10033, 2022.

17:12–17:19
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EGU22-2286
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ECS
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On-site presentation
Bas Altena, Andreas Kääb, and Bert Wouters

A large amount of velocity data is now becoming available through portals, pipelines and repositories. Typically the error characterisation for these individual velocity fields or mosaics is done through sampling statistics, resulting in a proxy of precision for the whole dataset. However even within a scene pair, the appearance can change considerably, or be stable at nearby locations. For example, think of regions close to the transient snowline, or an elongated moraine band, a  crevasse train after a bump or a shear zone. Here the precision of localising an exact image match is clearly anisotropic. If such anisotropic precision estimates are taken into account, it is possible to provide a more correct error-propagation. The merit of velocity data can be found in the help for inversion for thickness estimates (as it is related to the fourth power), or shear and strain rates. Here we introduce a simple and fast methodology to generate an individual dispersion estimate, based upon the similarity surface of an image match. A linear least squares adjustment of the neighbouring similarity scores is sufficient to fit an oriented gaussian peak. This setup makes the computation fast and is easy to implement into already available processing pipelines. We demonstrate its effectiveness on two glaciers, Sermeq Kujalleq, a large outlet glacier of the Greenland icesheet, with strong shear margins and Malaspina Glacier a piedmont glacier with looped moraines. We find directionality within an image subset to be the dominant factor influencing the correlation dispersion. This stems from crevasses and moraine bands within the imagery, while a relation to differential flow, such as shear, is less pronounced. It is our hope, this methodology will narrow the integration gap between models and measurements.

How to cite: Altena, B., Kääb, A., and Wouters, B.: Precision description for remote sensing glacier velocity data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2286, https://doi.org/10.5194/egusphere-egu22-2286, 2022.

17:19–17:26
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EGU22-4654
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ECS
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On-site presentation
Anuar Togaibekov, Andrea Walpersdorf, and Florent Gimbert

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.

17:26–17:33
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EGU22-143
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ECS
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On-site presentation
William D. Harcourt, Duncan A. Robertson, David G. Macfarlane, Brice R. Rea, Matteo Spagnolo, Doug I. Benn, Michael R. James, Wojciech Gajek, Danielle Pearce, and Penelope How

The release of icebergs into the ocean through glacier calving is a major source of mass loss from tidewater glaciers across the Arctic. However, there are very few direct measurements of calving activity in Svalbard at daily to sub-daily resolution which impedes our understanding of how these processes influence ice discharge and therefore regional patterns of mass balance. Quantifying ice loss from Svalbard is important because the archipelago contains ~10% of the total Arctic glacier area and holds a sea-level equivalent of ~1.5 cm. In this contribution, we generate an 8-day time series from August 2021 of calving activity at sub-daily resolution for the Hansbreen tidewater glacier in Svalbard using a suite of state-of-the-art remote sensing instruments. Millimetre-wave radar at 94 GHz (called AVTIS2) was used to map the 3D structure of the Hansbreen frontal ice cliff, so that terminus change could be tracked and the volume of ice released through calving quantified. Millimetre-wave radar can map glacier surfaces at high angular resolution and through most weather conditions, hence is not impeded by poor weather conditions unlike instruments such as Terrestrial Laser Scanners (TLS). AVTIS2 mechanically scans across the scene of interest, measures radar backscatter along each Line of Sight (LoS) and generates 3D point clouds by calculating the range to maximum received power along each LoS. In this study, an angular area of 83° (azimuth) x 5° (elevation) was scanned which ensured the entire marine-terminating portions of the ice front were measured throughout the study period. The 3D AVTIS2 point clouds were validated using a coincident survey from a TLS (Riegl LPM-321) and a time-lapse camera deployed at the same location to provide additional validation and knowledge of environmental conditions throughout the study period. Calving events from both datasets were correlated to seismic activity recorded by two networks of geophones deployed in the vicinity of the glacier terminus. We will report on the following: (1) the calving rate of Hansbreen in August 2021, (2) the volume of ice released into the ocean through calving during the 8-day study period, (3) the capabilities of millimetre-wave radar for monitoring glacier calving fronts versus optical approaches (TLS and time-lapse camera images), and (4) calving processes at Hansbreen. This study pushes forward our understanding of frontal ablation processes in Svalbard and demonstrates new possibilities for ground-based remote sensing of ice-ocean interactions.

How to cite: Harcourt, W. D., Robertson, D. A., Macfarlane, D. G., Rea, B. R., Spagnolo, M., Benn, D. I., James, M. R., Gajek, W., Pearce, D., and How, P.: Millimetre-wave radar observations of glacier calving at Hansbreen (Svalbard) correlated with TLS, time-lapse camera images and seismic records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-143, https://doi.org/10.5194/egusphere-egu22-143, 2022.

17:33–17:40
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EGU22-7140
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ECS
Annual deformation and sliding in an alpine temperate glacier: observations and implications for ice rheology and seasonal variation
(withdrawn)
Juan Pedro Roldan Blasco, Luc Piard, Adrien Gilbert, Florent Gimbert, Christian Vincent, Olivier Gagliardini, Anuar Togaibekov, and Andrea Walpersdorf
17:40–17:47
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EGU22-13196
Heather Purdie, Peyman Zawar-Reza, Benjamin Schumacher, Marwan Katurji, and Paul Bealing

In mountain regions around the world, crevasses in glacier accumulation areas undergo cycles of burial and re-exposure between one melt season and the melt season that follows. However, climate warming is extending the length of the ablation season meaning that crevasses are now exposed at the glacier surface for longer.  An analysis of air temperature inside crevasses in the accumulation area of a maritime glacier has found that air temperature inside crevasses can at times be higher than the overlying air temperature. Here we combine measurements of air temperature and wind-speed from inside crevasses with adjacent meteorological data to demonstrate that open crevasses trap incoming shortwave radiation and have complex relationships with wind shear. Results show that crevasse morphology influences warming with the effect more pronounced at wider (more open) crevasses. This highlights the potential of crevasses to enhance glacial melt by acting as heat source through positive radiative and sensible heat feedback. Therefore we hypothesis that energy balance models that treat glacier accumulation areas as smooth surfaces will be underestimating snow melt and possibly overestimating mass balance on alpine glaciers. 

How to cite: Purdie, H., Zawar-Reza, P., Schumacher, B., Katurji, M., and Bealing, P.: Air temperature variability inside crevasses in the accumulation area of a maritime glacier in the Southern Alps, New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13196, https://doi.org/10.5194/egusphere-egu22-13196, 2022.

Snow on glaciers
17:47–17:54
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EGU22-4008
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ECS
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On-site presentation
Annelies Voordendag, Brigitta Goger, Christoph Klug, Rainer Prinz, Martin Rutzinger, and Georg Kaser

A permanent long-range terrestrial laser scanning (TLS) system is installed at Hintereisferner, Ötztal Alps, Austria to validate snow cover dynamics such as simulated by high-resolution atmospheric models.

Snow cover dynamics include several processes such as snow fall, compaction, metamorphism, snow redistribution by wind, avalanches and melt manifested in specific magnitudes and frequencies. To be able to quantify these surface changes, the smallest possible magnitude that can be measured by the TLS needs to be known.

An uncertainty analysis of the system has been conducted acquiring its limitations. It was known before that atmospheric conditions, the scanning geometry and mechanical properties contribute to the total uncertainty, but so far, these error sources and the total uncertainty had not been quantified.

It was assumed that the position of the TLS was stationary and thus, the georeferencing of the scan was automated with an unchanged transformation matrix. A case study of 29 hourly scans during 5 and 6 November 2020, with no surface changes due to external conditions, showed vertical differences between -0.62 m and +0.47 m relative to a selected reference scan. These deviations are related to ongoing minor movements of the scanner over the scope of day and result in errors of a few decimetres due to the long range acquisition.

The accuracy of the scans improves after manual georeferencing (RiSCAN PRO), resulting in smaller deviations between -0.15 and +0.04 m relative to the selected reference scan.

The total accuracy of the TLS system is ±10 cm (vertical direction) after manual georeferencing, but strongly depends on the range between target surface and TLS. This makes it possible to detect snow fall events, snow redistribution, melt, and avalanches with changes larger than one decimeter. Snow compaction and metamorphism are processes, which are over hourly to daily time steps too small to be detected by the TLS at Hintereisferner.

Over all, the determined accuracy of the TLS shows the suitability of the system setup for validating high-resolution atmospheric models that explicitly compute snow redistribution by wind and thus significantly will improve the treatment of snow cover dynamics in future glacier mass balance research.

 

How to cite: Voordendag, A., Goger, B., Klug, C., Prinz, R., Rutzinger, M., and Kaser, G.: Detection of snow cover dynamics with a long range permanent TLS system at Hintereisferner (Austria) – possibilities and limitations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4008, https://doi.org/10.5194/egusphere-egu22-4008, 2022.

17:54–18:01
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EGU22-2317
Bernhard Hynek, Anton Neureiter, Gernot Weyss, Elke Ludewig, and Wolfgang Schöner

Spatially distributed winter snow accumulation over glaciers is an important information for a lot of purposes. Typically, snow depth on glaciers is measured by manual snow probing or ground penetrating radar. The point measurements of snow depth and snow density are then used to calculate the winter mass balance of the glacier.

In the last decade remote sensing techniques such as LIDAR and structure from motion (sfm) photogrammetry in combination with unmanned aerial vehicles (UAVs) have become more frequent to reconstruct snow surfaces providing a better spatial coverage and spatial resolution. Snow depth is calculated by DEM differencing of a No-Snow surface (summer surface) and the snow surface (winter surface).

However, using DEM differencing to extract snow depth over glaciers introduces the problem, that the No-Snow surface is not constant, as (1) the glacier is moving between the survey dates and (2) the surface possibly undergoes surface lowering due to melt after the summer survey.

In this study we present measurements on two small mass balance glaciers in the Austrian Alps (Goldbergkees and Kleinfleißkees). We account for the evolution of the No-Snow surface by (1) applying a simple model of the vertical ice movement and by (2) calculating the surface lowering due to melt using a distributed mass balance model.  The effect of both corrections is then validated using a dense network of manual snow depth measurements across the glacier.

How to cite: Hynek, B., Neureiter, A., Weyss, G., Ludewig, E., and Schöner, W.: Correcting UAV derived winter snow depth on glaciers by modelling the evolution of the No-Snow glacier surface , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2317, https://doi.org/10.5194/egusphere-egu22-2317, 2022.

18:01–18:08
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EGU22-3609
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ECS
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On-site presentation
Trine Dahl-Jensen, Shfaqat Abbas Khan, Michele Citterio, Jakob Jakobsen, and Andreas Ahlstrøm

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.

18:08–18:15
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EGU22-1480
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ECS
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On-site presentation
Maurice van Tiggelen, Paul C. J. P. Smeets, Carleen H. Reijmer, Michiel R. van den Broeke, Dirk van As, Jason E. Box, and Robert S. Fausto

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.

18:15–18:30

Presentations: Thu, 26 May | Room 1.85/86

Chairpersons: Evan Miles, Fanny Brun, Ines Dussaillant
08:30–08:35
Debris covered glaciers
08:35–08:45
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EGU22-10241
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solicited
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Highlight
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Virtual presentation
Adina E. Racoviteanu

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.

08:45–08:52
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EGU22-12672
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ECS
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On-site presentation
Alexander Raphael Groos and Jérôme Messmer

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.

08:52–08:59
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EGU22-8327
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ECS
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On-site presentation
Yota Sato, Pascal Buri, Evan Miles, Marin Kneib, Sojiro Sunako, Akiko Sakai, Francesca Pellicciotti, and Koji Fujita

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.

08:59–09:06
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EGU22-6163
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ECS
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On-site presentation
Marin Kneib, Evan S. Miles, Pascal Buri, Stefan Fugger, Michael McCarthy, Chuanxi Zhao, Thomas E. Shaw, Martin Truffer, Matthew Westoby, Wei Yang, and Francesca Pellicciotti

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.

09:06–09:13
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EGU22-11134
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ECS
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On-site presentation
Gernot Seier, Jakob Abermann, Siri H. Engen, Marthe Gjerde, Thomas Scheiber, Karina Löffler, Jonathan L. Carrivick, Liss M. Andreassen, and Jacob C. Yde

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.

09:13–09:20
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EGU22-4217
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ECS
Yoni Verhaegen, Oleg Rybak, Victor Popovnin, and Philippe Huybrechts

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.

09:20–09:27
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EGU22-11904
Francesca Pellicciotti, Adria Fontrodona-Bach, David R Rounce, Catriona L. Fyffe, Mike McCarthy, Evan Miles, and Thomas E. Shaw

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.

09:27–09:34
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EGU22-10142
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ECS
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Virtual presentation
Purushottam Kumar Garg and Mohd. Farooq Azam

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.

09:34–09:41
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EGU22-11900
Darrel Swift, Andrew Jones, Matthew Westoby, Robert Bryant, and Remy Veness

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.

09:41–09:48
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EGU22-8742
Christoph Mayer and Carlo Licciulli

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.

09:48–09:55
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EGU22-10238
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ECS
James C. Ferguson, Tobias Bolch, Argha Banerjee, and Andreas Vieli

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.

09:55–10:00