Displays

CR4.1

Glacial landscapes are constantly transforming in response to past and present climate and environmental conditions, e.g. available debris. Especially due to past and present global warming, rapid changes in these landscapes are observed. These changes are associated with transitions from different processual states : glacial – periglacial – paraglacial, and associated morphologies and landforms, including debris- covered glaciers and rock glaciers which are less understood. To unravel and quantify these past and present evolutions, controls and feedbacks, a broad spectrum of methods are available, including geomorphological mapping, dating, remote sensing, geophysics, numerical modelling, climate reconstruction, field observations and more. This session welcomes contributions related to all these methods, concepts and approaches used to investigate glacial-periglacial-paraglacial landscape evolution, controls and feedbacks. We seek abstracts on topics such as:
• conceptual frameworks of the evolution of glaciated landscapes;
• processual studies of glacial, paraglacial and periglacial landscapes across all temporal and spatial scales;
• transitions of glacial to periglacial or paraglacial landforms, and the role of debris cover within these glacier land systems
• geomorphometry of past and presently glaciated landscapes, debris-covered glaciers and rock glaciers.
• Interaction between debris-covered glaciers and the wider land system, for example, in terms of geohazards, erosion, sediment transport, and deposition.

Public information:
CR 4.1 Evolution of glacial-periglacial-paraglacial landscapes and debris-covered glaciers
Co-organized by GM7
Convener: Johannes BuckelECS | Co-conveners: Adina Racoviteanu, Evan MilesECS, Lindsey Nicholson, Tobias Bolch, Anne VoigtländerECS, Jasper Knight, Darren Jones

General structure:
- Please note that the order and number of presentations has been changed as some authors could not attend under the circumstances. At first all authors will present the abstracts with displays, afterwards the abstract without displays will be discussed. Please check the adjusted display schedule in the session description or in the uploaded session material.
- We will try to stick to the schedule and make sure the session doesn’t end in some chaos!
- Convener will introduce the presenter by display #. Presenter who should then briefly introduce their display in a couple of sentences or bullet points. Thereafter, the stage is open for discussion. When the time is up we will move to the next presenter. Please consider using the comment function at the display pages for further discussion until the end of May.

First part of our session (Wednesday, 6 May 2020, 08:30–10:15 CEST)
Chairpersons: Johannes Buckel, Anne Voigtländer

We have 10 displays and 8 abstracts to discuss, respectively. The display will be presented first because a fixed attendance is confirmed by the authors.
We have 6 min per display including chat discussion

RUNNING ORDER OF DISPLAYS

RUNNING ORDER OF DISPLAYS (6 Min per display)
08:30 – 08:34
Sign in and introduction to the session

08:35 – 08:41 solicited display
D2497 | EGU2020-19935
Geomorphic feedbacks on the moraine record
Leif Anderson and Dirk Scherler

08:41 – 08:47
D2498 | EGU2020-18360
Post-glacial dynamics of alpine Little Ice Age glacitectonized frozen landforms (Swiss Alps)
Julie Wee, Reynald Delaloye, and Chloé Barboux


08:47 – 08:53
D2499 | EGU2020-9509
Paraglacial adjustment of sediment-mantled slopes through landslide processes in the vicinity of the Austre Lovénbreen glacier (Ny-Ålesund, Svalbard)
Erik Kuschel, Christian Zangerl, Alexander Prokop, Eric Bernard, Florian Tolle, and Jean-Michel Friedt

08:53 – 08:59
D2502 | EGU2020-9201
Use of Convolution Neural Networks and Object Based Image Analysis for Automated Rock Glacier Mapping
Benjamin Aubrey Robson, Tobias Bolch, Shelley MacDonell, Daniel Hölbling, Philip Rastner, and Nicole Schaffer

08:59 – 09:05
D2507 | EGU2020-976
Structure and englacial debris content of a Himalayan debris-covered glacier revealed by an optical televiewer
Katie Miles, Bryn Hubbard, Duncan Quincey, Evan Miles, and Ann Rowan

09:05 – 09:11
D2509 | EGU2020-5057
Satellite remote sensing of ice cliff migration
Bas Altena and Andreas Kääb

09:11 – 09:17
D2511 | EGU2020-17912
Geomorphological mapping of an alpine rock glacier with multi-temporal UAV-based high density point cloud comparison
Francesca Bearzot, Roberto Garzonio, Biagio Di Mauro, Umberto Morra Di Cella, Edoardo Cremonese, Paolo Pogliotti, Paolo Frattini, Giovanni B. Crosta, Roberto Colombo, and Micol Rossini

09:17 – 09:23
D2512 | EGU2020-10373
60 years of rock glacier displacements and fluxes changes over Laurichard Rock glacier, French Alps.
Diego Cusicanqui, Antoine Rabatel, and Xavier Bodin

09:23 – 09:29
D2513 | EGU2020-1605
Creating a rock glacier inventory of the northern Nyainqêntanglha range (Tibetan Plateau) based on InSAR time-series analysis
Eike Reinosch, Johannes Buckel, Markus Gerke, Jussi Baade, and Björn Riedel

09:29 – 09:35
D2514 | EGU2020-8159
Pushing the limits of electrical resistivity tomography measurements on a rock glacier at 5500 m a.s.l. on the Tibetan Plateau: Successes and Challenges
Nora Krebs, Anne Voigtländer, Matthias Bücker, Andreas Hördt, Ruben Schroeckh, and Johannes Buckel

09:35 – 09:40
D2515 | EGU2020-7266
What makes a rock glacier? Insights into the structure and dynamics of an active rock glacier on the Tibetan Plateau
Johannes Buckel, Eike Reinosch, Nora Krebs, Anne Voigtländer, Michael Dietze, Ruben Schroeckh, Matthias Bücker, and Andreas Hördt


RUNNING ORDER OF ABSTRACTS (5 Min per display)

09:40 – 09:45
D2501 | EGU2020-1065
Reconstruction of Early Holocene jokulhlaups along the Hvita River and Gullfoss waterfall, Iceland
Greta Wells, Þorsteinn Sæmundsson, Sheryl Luzzadder-Beach, Timothy Beach, and Andrew Dugmore

09:45 – 09:50
D2503 | EGU2020-12571
A landsystems approach to understanding the evolution of ice-cored topography and distribution of retrogressive thaw slumps, western Canadian Arctic
Peter Morse, Stephen Wolfe, and Steve Kokelj

09:50 – 09:55
D2504 | EGU2020-17710
Quantifying contemporary debris supply in a debris-covered glacier catchment using high-resolution repeat terrestrial LiDAR
Rebecca Stewart, Matthew Westoby, Stuart Dunning, Francesca Pellicciotti, and John Woodward

09:50 – 09:55
D2505 | EGU2020-382
Debris cover growth, ensuing changes in morphology and impact on glacier processes at Pensilungpa Glacier, western Himalaya, India
Purushottam Kumar Garg, Aparna Shukla, Vinit Kumar, and Manish Mehta

09:55 – 10:00
D2506 | EGU2020-10593
A comparison of the drainage systems of two High Asian debris-covered glaciers
Catriona Fyffe, Evan Miles, Marin Kneib, Reeju Shrestha, Rebecca Stewart, Stefan Fugger, Matthew Westoby, Thomas Shaw, Wei Yang, and Francesca Pellicciotti

10:00 – 10:05
D2508 | EGU2020-20006
Characteristics and interannual changes of ice cliffs on the debris-covered glaciers of HMA
Marin Kneib, Evan Miles, Pascal Buri, and Francesca Pellicciotti

10:05 – 10:10
D2510 | EGU2020-8475
Improving geomorphological process understanding of complex glacier surfaces using aerial robotics
Matt Westoby, David Rounce, Thomas Shaw, Catriona Fyffe, Peter Moore, Rebecca Stewart, and Ben Brock

10:10 – 10:15 Summary and open discussion





Second part (Wednesday, 6 May 2020, 10:45 – 12:30 CEST)
Chairperson: Adina E. Racoviteanu

We will discuss 9 displays and 8 abstracts.

RUNNING ORDER OF DISPLAYS (6 Min per display)

10:45 – 10:49
Sign in and introduction

10:49 – 10:55
D2516 | EGU2020-19637
Occurrence and characteristics of ice-debris landforms in Poiqu basin (central Himalaya)
Tobias Bolch, Philipp Rastner, Jan Bouke Pronk, Atanu Bhattacharya, Lin Liu, Yan Hu, Guoqing Zhang, and Tandong Yao

10:55 – 11:01
D2519 | EGU2020-5050
Pore water pressure dynamics in a rock slope adjacent to a retreating valley glacier
Marc Hugentobler, Simon Loew, and Clément Roques

11:01 – 11:07
D2521 | EGU2020-21253
Bedload dynamics in the rapidly changing paraglacial zone of a high alpine catchment
Clemens Hiller, Kay Helfricht, Gabriele Schwaizer, Severin Hohensinner, Kerstin Wegner, Florian Haas, and Stefan Achleitner

11:07 – 11:12
D2523 | EGU2020-19854
Ice thickness measurements of the debris covered Ngozumpa glacier, Nepal
Lindsey Nicholson, Fabien Maussion, Christoph Mayer, Hamish Pritchard, Astrid Lambrecht, Anna Wirbel, and Christoph Klug

11:12 – 11:18
D2525 | EGU2020-5954
The geomorphology of debris-covered Ponkar Glacier, Nepal
Neil Glasser, Adina Racoviteanu, Stephan Harrison, Matthew Peacey, Rakesh Kayastha, and Rijan Bhakta Kayastha

11:18 – 11:24
D2526 | EGU2020-22638
The debris cover surface of Ponkar glacier: a laboratory for learning
Adina E. Racoviteanu, Neil F. Glasser, Smriti Basnett, Rakesh Kayastha, and Stephan Harrison

11:24 – 11:30
D2528 | EGU2020-20062
Glaciological controls on the spatial variability of supraglacial debris extent and thickness in the eastern Himalayas
Karla Boxall and Ian Willis


11:30 – 11:36
D2532 | EGU2020-11290
Estimating the style and duration of former glaciation in the mountains of Britain and Ireland
Iestyn Barr, Jeremy Ely, Matteo Spagnolo, Ian Evans, and Matt Tomkins

11:36 – 11:42
D2534 | EGU2020-11220
Inland dune field and deposits at Dviete: evidences of the late Pleistocene aeolian morphogenesis and landscape evolution during transition from glacial to post-glacial conditions in South-eastern Latvia
Juris Soms and Zane Egle

RUNNING ORDER OF ABSTRACTS (5 Min per display)

11:42 – 11:47
D2517 | EGU2020-8967
Post-Little Ice Age retreat of glaciers triggered rapid paraglacial landscape transformation in Sørkapp Land (Spitsbergen)
Justyna Dudek and Mateusz Czesław Strzelecki

11:47 – 11:52
D2518 | EGU2020-17195
Paraglacial Cirque Headwall Instability - Regional Scale Assessment Of Preconditioning Factors
Andreas Ewald and Jan-Christoph Otto

11:52 – 11:57
D2522 | EGU2020-685
Linking glacial lake expansion with glacier dynamics: An assessment of the South Lhonak lake, Sikkim Himalaya
Saurabh Kaushik, Pawan Kumar Joshi, Tejpal Singh, and Anshuman Bhardwaj

11:57 – 12:02
D2527 | EGU2020-16328
The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing
Anna Wirbel, Lindsey Nicholson, Christoph Mayer, and Astrid Lambrecht

12:02 – 12:07
D2529 | EGU2020-6650
Spatial distribution of debris cover and its impacts in the Hunza River Basin
Yong Zhang, Shiyin Liu, and Xin Wang

12:07 – 12:12
D2530 | EGU2020-11588
Carbon gas cycling in supraglacial debris covers
Ben Brock, Grace Brown, Paul Mann, and Stuart Dunning

12:12 – 12:17
D2531 | EGU2020-10825
A catastrophic Late Pleistocene debris flow sourced in the glaciated High Atlas of Morocco
Madeleine Hann, Jamie Woodward, Philip Hughes, and Edward Rhodes

12:17 – 12:22
D2533 | EGU2020-13381
Coastal morphodynamics in an Arctic fluvial-tidal transition zone in the deglaciated Dicksonfjord, Svalbard
Dohyeong Kim, Joohee Jo, and Kyungsik Choi

12:22 – 12:30
Open discussion / session summary

Share:
Co-organized by GM7
Convener: Johannes BuckelECSECS | Co-conveners: Adina Racoviteanu, Evan MilesECSECS, Lindsey Nicholson, Tobias Bolch, Anne VoigtländerECSECS, Jasper Knight, Darren Jones
Displays
| Wed, 06 May, 08:30–12:30 (CEST)

Files for download

Session materials Download all presentations (247MB)

Chat time: Wednesday, 6 May 2020, 08:30–10:15

Chairperson: Johannes Buckel, Anne Voigtländer
D2497 |
EGU2020-19935
Leif Anderson and Dirk Scherler

Glacial moraines represent one of the most spatially diverse climate archives on earth. Moraine dating and numerical modeling are used to effectively reconstruct past climate from mountain ranges at the global scale. But because moraines are often located downvalley from steep mountain headwalls, it is possible that debris-covered glaciers emplaced many moraines preserved in the landscape today.

Before we can understand the effect of debris cover on the moraine recored we need to understand how debris modulates glacier response to climate change. To help address this need, we developed a numerical model that links feedbacks between mountain glaciers, climate change, hillslope erosion, and landscape evolution. Our model uses parameters meant to represent glaciers in the Khumbu region of Nepal, though the model physics are relevant for mountain glaciers elsewhere.

We compare simulated debris-covered and debris-free glaciers and their length evolution. We explore the effect of climate-dependent hillslope erosion. We also allow temperature change to control frost cracking and permafrost in the headwall above simulated glaciers. Including these effects holds special implications for glacial evolution during deglaciation and the long-term evolution of mountain landscapes.

Because debris cover suppresses melt, debris-covered glaciers can advance independent of climate change. When debris cover is present during cold periods, moraine emplacement can lag debris-free glacier moraine emplacement by hundreds of years. We develop a suite of tools to help determine whether individual moraines were formed by debris-covered glaciers. Our analyses also point to how we might interpret moraine ages and estimate past climate states from debris-perturbed settings.

D2498 |
EGU2020-18360
Julie Wee, Reynald Delaloye, and Chloé Barboux

Glaciers and frozen debris landforms have coexisted and episodically interacted throughout the Holocene, the former having altered the development, spatial distribution and thermal regime of the latter. In the Alps, the apogee of last interaction phase occurred during the Little Ice Age (LIA). Since then, due to glacier shrinkage, interactions between glaciers and LIA pre-existing frozen debris have gradually diminished and are leaning towards being non-existent. Post-LIA glacier forefields in permafrost environments, including associated glacitectonized frozen landforms (GFL) have shifted from a thermal and mechanical glacier dominant regime towards a periglacial or even post-periglacial regime. GFL are undergoing thermal and mechanical readjustments in response to both the longer-term glacier recession and the more recent drastic climatic warming. They can be expressed by a combination of mass-wasting processes and thaw-induced subsidence.

 

In various regions of the Swiss Alps, slope movements occurring in a periglacial context have been inventoried in previous works using differential SAR interferometry (DInSAR) (Barboux et al., 2014). In the scope of this study, and focusing solely on mass-wasting GFL, the former inventory allowed the identification of the latter under various spatial configurations within LIA glacier forefields. While most observed GFL are disconnected from the associated glacier, some are still connected. Additionally, ground ice occurs as interstitial or massive (buried) glacier ice. This potentially infers the ongoing of non-uniform morphodynamical readjustments.

 

To understand the site-specific behaviour of GFL, the analysis of long-term time-series of permafrost monitoring and multi-temporal high-resolution Digital Elevation Models will allow the assessment of the recent evolution of the Aget and Ritord/Challand LIA glacier forefields (46°00’32’’ N, 7°14’20’’ E and 45°57’10’’ N, 7°14’52’’ E, respectively) and their associated GFL (i.e. push-moraines). Both glacier forefields present a contrasting spatial configuration, making their morphodynamical evolution to differ partly from one another. The Aget push-moraine is a back-creeping GFL, which has been disconnected from the Aget glacier since the 1940s at latest. For the last two decades, surface displacement velocities have decelerated in comparison to the accelerating regional trend (PERMOS, 2019). Additionally, a 30% decrease of the electrical resistivity of the frozen ground, combined with locally observed thaw-induced subsidence of up to 10 cm/year suggest an advanced permafrost degradation. The Ritord/Challand system presents a push-moraine disconnected from its glacier as well as several push-moraines connected to a still existing debris-covered glacier. Between 2016 and 2019, surface lowering up to 10 m attesting massive ice melt has been locally detected in the former where buried glacier ice was visually observed. Whereas in the latter, subtle surface displacements ranging from 10 to 30 cm/year occur. This confirms the heterogeneity of the morphodynamical processes occurring in GFL, expressed as a function of both their spatial configuration and ground ice properties.

 

Barboux, C., Delaloye R. and Lambiel, C. (2014). Inventorying slope movements in an Alpine environment using DInSAR. Earth Surface Processes and Landforms, 39/15, 2087-2099.

PERMOS 2019. Permafrost in Switzerland 2014/2015 to 2017/2018. Noetzli, J., Pellet, C., and Staub, B. (eds.), Glaciological Report (Permafrost) No. 16-19 of the Cryospheric Commission of the Swiss Academy of Sciences, 104.

D2499 |
EGU2020-9509
Erik Kuschel, Christian Zangerl, Alexander Prokop, Eric Bernard, Florian Tolle, and Jean-Michel Friedt

The climate-induced changes in the high arctic environment influence a wide range of processes, which are rapidly altering the landscape (e.g. glacier retreat, landslide activity). Numerous recent studies are focusing on spatio-temporal characteristics of glacier retreat in the high arctic. However, an exact identification and quantification of landslide processes modifying sediment-mantled slopes in the vicinity of retreating glaciers is in many cases not possible due to the lack of long-term high-resolution spatio-temporal terrain data.

The aim of this study is to investigate terrain changes of sediment-mantled slopes through landslide processes. It focuses on i) the quantitative and spatiotemporal identification of shallow translational debris slides, ii) the failure mechanisms and interaction with a retreating glacier in a high-arctic environment, and iii) the impact of meteorological factors on their formation. The Austre Lovénbreen glacier basin located on the Brøggerhalvøya, Svalbard at 79°N has been chosen to perform these investigations.

Landscape modifications within the basin have been investigated based on: I) high-resolution multi-temporal terrestrial laser scan data (TLS) measured annually from 2012 to 2018; II) images from stationary cameras taken between 2011 and 2018 monitoring the entire basin and; III) two geological field surveys in 2017 and 2018. During the observation period more than 100 distinctive landslide events, with a total volume of approx. 74000 m³ including 84 shallow translational debris slides were identified.

Results clearly show that landslides were the dominant process modifying sediment-mantled slopes during the observation period. Furthermore, deformation and mass waste of these slopes led to the formation of distinctive ice-cored lobate landslide deposits on the glacier. All observed translational debris slides were formed on a distinctive failure surface located at the contact zone between the talus deposits and a subsurface ice layer. Due to the sliding processes, the ice layer was uncovered locally and thus a spatial extension of up to 150 m in elevation above the present-day surface of the Austre Lovénbreen glacier could be verified.

A significant increase in the annual debris slide activity could be observed during the observation period and the data indicates that meteorological factors (e.g. rainfall duration and intensity during the summer, mean annual summer air temperatures and thawing degree days) are the driving factor for landslide activity in the Austre Lovénbreen glacier basin. The impact of these factors is however dependent on the location and exposition of the slopes within the basin. The results presented in this study contribute to a better understanding of adaptation processes of the highly dynamic arctic environments to changing meteorological conditions.

D2500 |
EGU2020-2157
Daniel Draebing, Till Mayer, Benjamin Jacobs, and Samuel McColl

Rockfall is characteristic of deglaciated alpine rockwalls. Small (<5 km²) to very small (<0.5 km²) alpine glaciers are located at altitudes where periglacial and paraglacial processes jointly influence rockfall processes. In this study, we (i) reconstruct glacier retreat history, (ii) quantify rock fracture damage, (iii) model permafrost distribution, (iv) model patterns of frost weathering, and (v) assess how these may combine to influence rockfall processes around a small alpine glacier in the Hungerli Valley (Swiss Alps). To achieve this, we use geomorphic, geophysical, geotechnical and remote sensing techniques on three rockwalls (RW1-3) with different glacial retreat history and elevation.

(i) Glacier retreat is reconstructed based on existing LGM ice extent models, mapping of moraines and analysis of historic photos. The resulting retreat history is used as an upper age limit for the calculation of paraglacial rockwall retreat rates.

(ii) Rockwall fracture damage is quantified in the field using laboratory-calibrated seismic refraction tomography and our results demonstrate that rockwall fracture density increases with proximity to the glacier. This relationship suggests that rockwalls in proximity to the glacier are still experiencing paraglacial stress-release jointing and that rockfall is yet to remove these fractured blocks.

(iii) Local permafrost modelling based on temperature logger data indicates that areas with likely permafrost occurrence (<-3°C) are limited to the peaks and upper cirque walls (>3000 m). Areas of ’possible’ permafrost (<0°C) extend to elevations as low as 2700 m.

(iv) We determined rock strength properties in the lab (Draebing and Krautblatter, 2019) and monitored rock temperature in the field for three years. These data were applied to the physical-based frost cracking model by Rempel et al. (2016).  Model simulations show that frost cracking is highly sensitive to lithology and increases with altitude due to decreasing rock temperatures.

(v) We applied terrestrial laserscanning of the rockwalls to quantify rockfall activity. Rockfall volumes demonstrate a typical frequency-magnitude distribution. Applying a space-for-time substitution using glacier retreat history reveals that rockwall retreat rates are increased in proximity to the glacier where rockwalls experience permafrost and a high frost cracking intensity.

In conclusion, our data suggest a synergy of paraglacial processes, frost cracking and permafrost thaw in preparing and triggering rockfalls. This synergy follows an altitudinal gradient that moves upwards with glacier retreat, permafrost thaw and frost cracking trajectories.

 

Draebing, D., & Krautblatter, M.: The Efficacy of Frost Weathering Processes in Alpine Rockwalls. Geophysical Research Letters, 46(12), 6516-6524, 2019.

Rempel, A. W., Marshall, J. A., & Roering, J. J.: Modeling relative frost weathering rates at geomorphic scales. Earth and Planetary Science Letters, 453, 87-95, 2016.

D2501 |
EGU2020-1065
Greta Wells, Þorsteinn Sæmundsson, Sheryl Luzzadder-Beach, Timothy Beach, and Andrew Dugmore

Glacial lake outburst floods (GLOFs) have occurred across the planet throughout the Quaternary and are a significant geohazard in Arctic and alpine regions today. Iceland experiences more frequent GLOFs—known in Icelandic as jökulhlaups—than nearly anywhere on Earth, yet most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, floods from proglacial lakes may be a better analogue to most global GLOFs.

As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater pooled at ice margins and periodically drained in jökulhlaups. Some of the most catastrophic floods drained from ice-dammed Glacial Lake Kjölur, surging across southwestern Iceland from the interior highlands to the Atlantic Ocean. These floods left extensive geomorphologic evidence along the modern-day course of the Hvítá River, including canyons, scoured bedrock, boulder deposits, and Gullfoss—Iceland’s most famous waterfall. The largest events reached an estimated maximum peak discharge of 300,000 m3 s-1, ranking them among the largest known floods in Iceland and on Earth.

Yet, all our evidence for the Kjölur jökulhlaups comes from only one publication to date (Tómasson, 1993). My research employs new methods to better constrain flood timing, routing, magnitude, and recurrence interval at this underexplored site. This talk presents new and synthesized jökulhlaup geomorphologic evidence; HEC-RAS hydraulic modeling results of flow magnitude and routing; and ongoing geochronological analyses using cosmogenic nuclide exposure dating and tephrochronology. It also situates these events within Icelandic Ice Sheet deglaciation chronology and environmental change at the Pleistocene-Holocene transition. Finally, it examines the Kjölur floods as an analogue to contemporary ice sheet response, proglacial lake formation, and jökulhlaup processes and landscape evolution in Arctic and alpine regions worldwide, where GLOFs pose an increasing risk to downstream communities due to climate-driven meltwater lake expansion.  

Citation: Tómasson, H., 1993. Jökulstífluð vötn á Kili og hamfarahlaup í Hvítá í Árnessýslu. Náttúrufræðingurinn 62, 77-98.

D2502 |
EGU2020-9201
Benjamin Aubrey Robson, Tobias Bolch, Shelley MacDonell, Daniel Hölbling, Philip Rastner, and Nicole Schaffer

Rock glaciers are an important, but often overlooked, component of the cryosphere and are one of the few visible manifestations of permafrost. In certain parts of the world, rock glaciers can contribute up to 30% of catchment streamflow. Remote sensing has permitted the creation of rock glacier inventories for large regions, however, due to the spectral similarity between rock glaciers and the surrounding material, the creation of such inventories is typically conducted based on manual interpretation of remote sensing data which is both time consuming and subjective. Here, we present a method that combines deep learning (convolutional neural networks or CNNs) and object-based image analysis (OBIA) into one workflow based on freely available Sentinel-2 imagery, Sentinel-1 interferometric coherence, and a Digital Elevation Model. CNNs work by identifying recurring patterns and textures and produce a heatmap where each pixel indicates the probability that it belongs to a rock glacier or not. By using OBIA we can segment the datasets and classify objects based on their heatmap value as well as morphological and spatial characteristics and convert the raw probability heatmap generated by the deeo learning into rock glacier polygons. We analysed two distinct catchments, the La Laguna catchment in the Chilean semi-arid Andes and the Poiqu catchment on the Tibetan Plateau. In total, our method mapped 72% of the rock glaciers across both catchments, although many of the individual rock glacier polygons contained false positives that are texturally similar, such as debris-flows, avalanche deposits, or fluvial material causing the user’s accuracy to be moderate (64-69%) even if the producer’s accuracy was higher (75%). We repeated our method on very-high resolution Pléiades satellite imagery (resampled to 2 m resolution) for a subset of the Poiqu catchment to ascertain what difference the image resolution makes. We found that working at a higher spatial resolution has little influence on the user’s accuracy (an increase of 3%) yet as smaller landforms were mapped, the producer’s accuracy rose by 13% to 88%. By running all the processing within an object-based analysis it was possible to both generate the deep learning heatmap and automate some of the post-processing through image segmentation and object reshaping. Given the difficulties in differentiating rock glaciers using image spectra, deep learning offers a feasible method for automated mapping of rock glaciers over large regional scales.

D2503 |
EGU2020-12571
Peter Morse, Stephen Wolfe, and Steve Kokelj

The landscape of the Tuktoyaktuk Coastlands, western Canadian Arctic is dominated by glacial and geocryological processes that have modified, imprinted and sculpted the surface, depositing surficial materials upon underlying bedrock. Climate warming continues in this region at a rate that is twice the global average, and retrogressive thaw slump (RTS) activity is increasing. Recently, RTS distribution was associated with glacial limits reached by the Laurentide Ice Sheet and corresponding morainal deposits, but RTS are common in other local terrain units. In this glacial-marginal region, permafrost existed pre-glacially, and non-glacial geomorphic processes occurred throughout the Late Quaternary. Superimposed on these conditions are the effects of thermokarst during the Holocene climatic optimum, followed by a period of cooling. Collectively, these processes and associated forms and deposits have contributed variously to preservation, development, or degradation of permafrost and ground ice. The multifaceted Late Quaternary history in this region has impeded understanding of the distributions of ice-cored topography and RTS. For example, rather than glaciogenic ice, the long reigning regional model for ice-cored topography is according to post-glacial development of intrasedimental segregation-intrusion ice. Toward better understanding the evolution of the whole landscape and the distribution of climate-sensitive terrain, we use a landsystems approach as a means to understand how the ice-cored topography developed where RTS form, through analysing the cryostratigraphy. To this end, we identify 6 RTS representing a suite of ice-cored topographic settings, including: (i) preserved basal glacial ice facies within clayey diamict that has been thrusted and folded by glacial push representing morainal deposits of the Sitidgi Stade; (ii) ice contact outwash sediments associated with the Sitidgi Stade, overlying a thermo-erosional contact with underlying basal glacial icy diamict of the Toker Point Stade; (iii) deformed basal glacial ice, eroded down by meltwater-deposited outwash sands some time between the Toker Point and Sitidgi Stades (could be ca. 12.9 kyr BP); (iv) massive, undeformed segregation-intrusion basal ice, likely formed subglacially by freezing of intrasedimental water in pre-existing Pleistocene sands into the base of the glacier, overlain by glacial diamicton;  (v) deformed basal ice facies of intermediate Toker Point – Sitidgi Stades, with an upper layer that may be supra-glacial melt-out till into which segregated ice formed; and (vi) segregation ice that formed as permafrost aggraded into glaciolacustrine clays deposited in proglacial or glacially dammed basins, that was subsequently eroded down by glaciofluvial outwash (Sitidgi Stade). To summarize, the distribution of RTS reflects primarily the distribution of icy basal glacial diamict preserved in moraines, but also basal ice and icy basal diamict that are preserved beneath glaciofluvial deposits, segregation ice in glaciolacustrine deposits, and massive segregation-intrusion ice in Pleistocene sands beneath a till plain.

D2504 |
EGU2020-17710
Rebecca Stewart, Matthew Westoby, Stuart Dunning, Francesca Pellicciotti, and John Woodward

Glacial debris cover is increasing at a global scale in response to increasing temperatures and negative glacier mass balance. The last decade or so has seen an abundance of research which focuses on debris-covered glacier dynamics and supraglacial processes, such as ice-cliff back wasting and the development of supraglacial ponds. However, far fewer studies have focussed on improving understanding of debris supply to these systems over short- (months-years) or long (centennial-millennial) timescales. Existing work has attempted to quantify headwall erosion by calculating the ratio of supraglacial debris flux (the product of debris thickness and supraglacial velocity) to the headwall catchment area. Whilst these studies provide estimates of headwall erosion rates over long timescales, they are unable to capture subtle (or extreme) spatial and temporal variations in debris supply that operate over shorter timescales. Capturing this variation is important because it will allow predictions of the spatial distribution and volume of debris layers on debris-covered glaciers, which in turn will increase the accuracy of ablation modelling and future melt predictions for these systems. To quantify such variability, we conducted terrestrial LiDAR surveys of potential debris slopes at Miage Glacier, Italy, between July – September 2019. We acquired > 1.8 billion 3D points per catchment survey covering an approximate slope area of 7.7 km2, which supplies debris to ~33% of the glacierised area. Sequential 3D point clouds were co-registered using iterative closest point adjustment. Vegetated surfaces were automatically detected using the CloudCompare plugin CANUPO and removed from further analysis. The M3C2 change detection algorithm was used to calculate 3D change normal to the surface plane, and a 95th percentile confidence interval was applied to eliminate non-significant change. Connected components analysis was used to identify discrete rockfall events, estimate their dimensions, explore their magnitude-frequency and quantify their spatial distribution. We find at least one large failure which developed over a period of two weeks (validated by in situ time-lapse footage) and comprised an estimated volume of around 1 x 106 m3. This particular failure occurred from a recently (<10 years) deglaciated slope, lending support to the theory that large-scale slope response to glacial erosion can be rapid.

D2505 |
EGU2020-382
Purushottam Kumar Garg, Aparna Shukla, Vinit Kumar, and Manish Mehta

Supraglacial debris affects the melting processes and overall response of glaciers to climate change. The present study investigates the temporal variation in debris cover and its influence on the overall state of the Pensilungpa glacier (14.67 ±0.29 km2), western Himalaya, India, which has extensive debris on its lower ablation zone (LAZ). For this, multiple parameters namely length, area, debris extent/thickness, snowline altitude (SLA), surface ice velocity (SIV), surface elevation changes and ice-cliffs were determined using field measurements (2016-2018), GoogleEarth images (2013-2017) and satellite data (Landsat-TM/ETM+/OLI (1993-2017), SRTM (2000) and Terra-ASTER (2017)) to comprehend the past and present status of the glacier. Results show a moderate terminus retreat (6.62 ±2.11 m/y) and area loss (0.11 ±0.03%/y) but a marked slowdown (~50%) in the glacier supported by significant SLA upshift (~6 m/y) during 1993-2017. Geodetic measurements reveal a prominent downwasting of −0.88 ±0.04 m/y during 2000-2017 which is corroborated with ablation-stake measurements that show average annual melting of −0.88 m during 2016-2017 and −1.54 m during 2017-2018. The glacier moved with a slow velocity of 13.94 ±3.94 m/y in 1993/94 and its velocity further slowed-down to 9.33 ±2.76 m/y in 1999/2000 and to 7.63 ±3.87 m/y in 2016/17 revealing a slow-down of 1.97%/y. Notably, the magnitude of change in most glacier parameters was lower in the recent period (2000-2017) as compared to the previous one (1993-2000). The observed SLA upshift (180 m), area loss (0.17 ±0.24%/y) and slowdown rates (4.73%/y) were much higher during 1993-2000. Contrarily, the glacier experienced a low area loss (0.09 ±0.09%/y), slowdown (1.14%/y) and even descend in SLA (43 m) between 2000 and 2017. The overall glacier depletion has resulted in substantial debris cover increase of 2.86 ±0.29%/y during the study period (1993-2017). Following the glacier depletion trend, the debris growth rate was also much higher (6.67 ±0.41%/y) during 1993-2000 and reduced (to 0.81 ±0.12%/y) subsequently (2000-2017). The most recent estimate (2016) shows a total debris cover of 17.35% on the Pensilungpa glacier and field measurements show that the debris tends to be thicker towards the margins. Such a setting probably insulated the glacier margins which, coupled with steady slowdown, has caused the stagnation of the LAZ up to 2 km upstream, which is reflected in SIV results and temporal GoogleEarth images. Also, the debris thickness distribution on glacier is such that it is thicker near the snout (>40 cm) and gradually decreases upstream (<2 cm at ~2.5 km). This has caused differential melting by insulating-effect and albedo lowering-effect and has promoted slope inversion, contributing further to stagnation. Stagnation of the LAZ has caused bulging in the dynamically active upper ablation zone and favored the development of supraglacial lakes (5 in 2017) and numerous ice-cliffs (79 in 2017). In view of insulated margins, back-wasting of ice-cliffs dominates the ablation process which is evident by rapid expansion in their number (48%), perimeter (31%) and area (41%) during 2013-2017. To conclude, the debris cover has significantly altered multiple glacier processes and has largely controlled the glacier evolution.

D2506 |
EGU2020-10593
Catriona Fyffe, Evan Miles, Marin Kneib, Reeju Shrestha, Rebecca Stewart, Stefan Fugger, Matthew Westoby, Thomas Shaw, Wei Yang, and Francesca Pellicciotti

Debris-covered glaciers are a crucial source of runoff for downstream communities in High Mountain Asia (HMA), especially in dry periods, and knowledge of runoff patterns is important for irrigation and hydropower. However, very few studies have investigated the hydrology of debris-covered glaciers, especially in HMA. Here, debris-covered ice represents about 30% of the total ice mass and is located in the lower reaches where melt dominates. There is increasing evidence that supraglacial debris influences the structure and efficiency of the hydrological system, but dye-tracing studies are rare (only three in HMA) and only one of those attempted repeat traces at different times in the season. Furthermore, previous studies have not sought to examine each of the hydrological components systematically, which is necessary given the unique components of debris-covered glacier drainage systems (e.g. within-debris flow and interlinked pond systems) which are not present on clean glaciers. Finally, there are differences between debris-covered glaciers which may influence their hydrological systems (such as their climate, debris thickness and surface topography), but a lack of consistency between studies hampers clear comparisons. 

This study investigates the hydrological systems of two High Asian debris-covered glaciers with contrasting debris and climate characteristics in both the pre-and post-monsoon. Langtang Glacier in Nepal (visited in May and November 2019) has a very hummocky surface topography covered in metre thick debris, while 24K Glacier, in the SE Tibetan Plateau (visited in June and October 2019) has thinner debris and a particularly wet climate. Our aim was to determine the structure, efficiency and evolution of each part of their hydrological systems. Dye tracing was used to investigate the characteristics of the supraglacial, englacial and subglacial network, and the influence of this drainage network on the resulting runoff was studied using analysis of the proglacial discharge.

The thick debris was an important component of the hydrological system on Langtang Glacier, acting as a source of water in the pre-monsoon and sink of water in the post-monsoon. The supraglacial hydrology of both glaciers had similar characteristics, with clear evidence of hydrological links between supraglacial ponds, composed of flow paths that could cross surface topographical barriers by following englacial or intra-debris routes. On Langtang Glacier the supraglacial hydrology in the post-monsoon became restricted to isolated ponds and streams emanating from ice-cliffs, whereas on 24K Glacier the linked ponds composing the main supraglacial network evolved into a more coherent stream system. Initial analysis suggests that the englacial/subglacial network of Langtang Glacier was inefficient compared to clean alpine glaciers (mean velocity 0.08 ms-1), whereas fast, peaked breakthrough curves on 24K Glacier (mean velocity of 0.5 ms-1 from repeat traces into one moulin) suggest a more efficient system. Debris-covered glaciers therefore share some distinct aspects of their hydrological system (e.g. the occurrence of interlinked ponds), but the englacial/subglacial system efficiency can be altered by the debris thickness, topography and degree of snowcover of the input catchments.

D2507 |
EGU2020-976
Katie Miles, Bryn Hubbard, Duncan Quincey, Evan Miles, and Ann Rowan

Himalayan debris-covered glaciers contribute to the discharge of some of Earth’s largest river systems, shaping the seasonal water supply to millions of people. The supraglacial debris layer heavily influences the pattern of surface melt, producing a range of unique surface features that make it challenging to collect any data, particularly from the interior of such glaciers. Models of debris-covered glaciers therefore lack calibration and validation data, which are needed for accurate predictions of future glacier geometric change and contributions to river discharge, water resources and ultimately sea level. In 2017 and 2018, we logged four boreholes drilled using pressurised hot water into the debris-covered Khumbu Glacier, Nepal Himalaya, with a high-resolution optical televiewer. The boreholes were located at four sites across the lower glacier’s debris-covered area, down-flow of the Khumbu Icefall. The resulting logs, ranging in length from 22–150 m, produced a 360° geometrically-accurate full-colour image of each borehole at ~1 mm vertical and ~0.22 mm (1,440 pixel) horizontal resolution. The logs reveal three material facies: i) steeply-dipping ice layers, some including debris; ii) steeply-dipping sediment-rich layers; and iii) clusters of sediment and debris dispersed through the ice. On the basis of these facies, we present reconstructions of the glacier’s structure and historical flow paths and the first measurements of the englacial debris concentration of a Himalayan debris-covered glacier. From the latter, we additionally infer both the sources of this englacial debris and of the supraglacial debris layer present across much of the lower ablation area of Khumbu Glacier.

D2508 |
EGU2020-20006
Marin Kneib, Evan Miles, Pascal Buri, and Francesca Pellicciotti

Ice cliffs have been shown to be key contributors to the mass balance of debris-covered glaciers in High Mountain Asia. They are zones of enhanced energy inputs and contribute to glacier melt 3 to 15 times more than the surrounding debris, with backwasting rates of up to 10 cm/day. Field observations have shown that these features can evolve quickly, extending by 50% of their area or being entirely reburied by debris within the course of one monsoon season, while others remain stable over several years. They can also appear suddenly via abrupt events such as englacial conduit collapse, crevasse opening or slope destabilization by supraglacial streams or ponds. These mechanisms and evolution patterns have never been quantified nor even observed at the scale of a glacier, mainly because very few repeat datasets of appropriate temporal resolution exist.

Here we combine one existing and new multi-temporal datasets of cliff outlines derived manually or semi-automatically, from debris-covered glaciers in four regions of HMA with varying topography, debris-cover and climatic regimes. We use a tracking algorithm to automatically detect the evolution of these features over several years, focusing on their formation rates and the evolution of their shapes and sizes obtained from high resolution digital elevation models. Surface velocity maps, debris thickness measurements and outlines of ponds and the main supraglacial streams are used to relate the evolution patterns to glacier dynamics and supraglacial hydrology.

We follow and analyze the inter-annual evolution of more than one thousand cliffs along with the nearby ponds. These results allow us to propose a classification of ice cliffs based on the mechanisms governing their genesis and evolution. Finally, we use this classification to map and quantify the different genesis mechanisms dominant at each of the four sites. By considering the evolution of each cliff independently, this study bridges the gap between large-scale statistical studies of cliff populations and detailed field observations focusing on a few features of specific glaciers. In addition to improving our general understanding of ice-cliff evolution, this study provides the first consistent and regional dataset of cliff characteristics, changes and patterns to support modeling of ice cliffs at a large scale.

D2509 |
EGU2020-5057
Bas Altena and Andreas Kääb

Ablation patterns on debris-covered glaciers are highly complex and spatially variable, while accessibility is complicated due to steep topography and loose surface debris material. One of the main ablation components on debris-covered glaciers is ice melt on steep ice cliffs and associated cliff migration. When using measurement techniques that operate in absolute coordinates, a main challenge is to separate cliff retreat from the underlying ice movement. In-situ measurements are spatially limited, while giving highly detailed understanding of processes occurring on individual ice cliffs. Drones can extent such detailed measurements to a whole glacier tongue, but are still limited to a few glaciers and measurement times. Here we show how measurements of cliff migration rates towards a regional scale are possible with spaceborne optical instruments. For this study we focus on the Mt. Everest region, specifically the Khumbu Glacier and other glaciers in the surrounding. We use Venμs, a French-Israeli multi-spectral satellite, that provides images at high temporal resolution (a two day repeat), and at high spatial resolution (5m), at this spatial resolution it provides sufficient detail to investigate individual ice cliffs.

Migration of ice cliffs can have a dominant direction, but their shape evolves over time, complicating pattern matching. Similar challenges occur for velocity extraction of the underlying glacier ice, where the shadow casted by ice cliffs is a dominant feature on glacier imagery, thus instead of debris patterns, the velocity estimates have ice cliff migration patterns within. Hence, in order to reduce the interference between both processes we reduce the influence of shadow within the imagery and extract bulk glacier ice velocity. While specific ice cliff features are isolated and tracked. Thus different image tracking techniques are deployed, in order to distinguish one displacement from the other.

The ice-cliff migration can be separated from the general glacier velocity, which results in a regional estimate of ice cliff back wasting, and thus a proxy for clean ice mass-balance of debris-covered glaciers from space. Venμs is a demonstrator satellite, with a limited lifetime and acquisition strategy, but our automatic methodology is generic and can be transferred to, for example, the 10m imagery from Sentinel-2, making regional analysis feasible.

D2510 |
EGU2020-8475
Matt Westoby, David Rounce, Thomas Shaw, Catriona Fyffe, Peter Moore, Rebecca Stewart, and Ben Brock

In the last decade or so, improvements in unpiloted aerial systems (UAS) technology and the emergence of low-cost digital photogrammetry have democratised access to accurate, high-resolution topographic data products, particularly in remote, glacial environments. One such application of these tools has been for advancing understanding of debris-covered glaciers (DCG) which are an important component of the high-mountain cryosphere, but also where detailed, ground-based process analysis is challenging. In this work, we seek to improve meso-scale (<km) geomorphological understanding of DCG surface evolution over multi-annual timescales by quantifying how debris moves around on the surface of these glaciers, and how debris transport is reconciled with wider patterns and mechanisms of ice mass loss. We applied annual UAS-photogrammetry and DEM differencing alongside debris thickness and debris stability modelling to unravel the evolution of a 0.2 km2 sub-region of the debris-covered Miage Glacier, Italy, between June 2015 and July 2018. Following corrections for glacier flow, DEM differencing revealed widespread surface lowering (mean 4.1 ± 1.0 m a-1; maximum 13.3 m a-1). We combined DEMs of difference with local meteorological data and a sub-debris melt model to produce high resolution (metre-scale) maps of debris thickness. Median debris thicknesses ranged from 0.12 – 0.17 m and were highly spatially variable. Debris thickness differencing revealed localised debris thinning across ice cliff faces, except those which were decaying, where debris thickened, as well as ingestion of debris by a newly exposed englacial conduit. Debris stability mapping showed that 18.2 - 26.4% of the survey area was theoretically subject to debris remobilisation in a given year. By linking changes in stability to changes in debris thickness, we observed a net debris thinning signal across slopes which become newly unstable, and a net thickening signal across those which stabilise between years. Finally, we linked morphometric descriptors of the glacier surface with debris thickness change data to derive empirical relationships which describe observed rates of downslope debris thickening as a function of slope-distance and slope angle. These UAS-enabled data provide new insight into mechanisms and rates of debris redistribution on glacier surfaces over sub-decadal timescales, and open avenues for future research to explore patterns of debris remobilisation and the morphological evolution of glacier surfaces at much larger spatiotemporal scales.

D2511 |
EGU2020-17912
Francesca Bearzot, Roberto Garzonio, Biagio Di Mauro, Umberto Morra Di Cella, Edoardo Cremonese, Paolo Pogliotti, Paolo Frattini, Giovanni B. Crosta, Roberto Colombo, and Micol Rossini

The acquisition of high-resolution topographic data is a widely used tool for studies related to the processes and dynamics of the Earth's surface. In this work, we present the results of the repeated acquisition of photogrammetric data by Unmanned Aerial Vehicle (UAV) in order to detect the topographic evolution of an alpine rock glaciers located in Valtournenche (AO, Italy). Field monitoring conducted in recent years has shown significant variations in the behaviour of these landforms, with an increasing trend of their dynamism, raising questions about their stability in changing climatic conditions.

 

The photogrammetric shots were taken with a DJ Phantom 4 UAV equipped with a compact RGB digital camera. The acquisitions were performed yearly from 2012 up to 2019 with a ground sampling distance never exceeding 5 cm/px. Contemporary to the acquisitions, approximately 20 Ground Control Points were placed on the rock glacier and on the surrounding areas and their coordinates were measured with a differential GPS (dGPS) for georeferencing UAV images. Moreover, in 2014, 2015 and 2019 geophysical campaigns were carried out for the detection of ice lenses under the debris cover of the rock glacier.

 

Structure-from-motion techniques were applied on overlapping images to create high-density point clouds, than converted in orthophotos and digital surface models of the Earth’s surface.

The point clouds were analysed using the M3C2 (Multiscale Model to Model Cloud Comparison) plug-in, freely available in the CloudCompare software. Maps of surface changes between acquisition pairs in the period from 2015-2019 have been created. The comparison allowed the identification of "material supply" and "material removal" zones, slightly variable from one year to the next. The major accumulation zones are concentrated along the frontal sector of the rock glacier, more focused on the western sector (black lobe) and secondly on the right side of the rock glacier (white lobe). The removal of material is mainly concentrated on the higher altitude of the body but also in correspondence to the systems of crevasses and scarps and on the central part of the black lobe.

The surface displacement analysis of the rock glacier was also performed selecting manually several clearly identifiable features on the orthomosaics collected. Blocks and ridges-and-furrows complex were marked on the 2019 orthomosaic and found them on the 2015 orthomosaic. This approach allows improving and quantifying the dynamics of the different portions of the individual apparatus.

The velocity fields’ patterns highlight non-homogeneous displacements between the West (black lobe) and East part (white lobe) of the whole rock glacier. Specifically, the black lobe showed an average horizontal displacement of around 1 m/y while the white lobe moved significantly slower than the previous one (approximately 0.5 m/y). Overall, the rock glacier moved downslope at an average horizontal velocity of 0.60 m/y in the frontal tongue, 0.48 m/y in the central portion and 0.30 m/y in the upper zone.

D2512 |
EGU2020-10373
Diego Cusicanqui, Antoine Rabatel, and Xavier Bodin

Recent acceleration of rock glaciers has been largely documented in the European Alps, hence highlighting an increase in flow speed of stable rock glaciers and some anomalous behaviors called destabilization (development of landslides-like features on the rock glacier surface).  In this study, we focus on Laurichard active rock glacier, 225 m long, up to 75 m wide, which covers an area of 0.084 km2 and has the longest measurement time-series in the French Alps. Here we aim to understand the causes of the changes in ice velocity of Laurichard rock glacier. We investigate the changes in the fluxes of ice masses across longitudinal and transversal profiles in order to be able to analyze in details the differences between the upper part and the front of the glacier. Using a combination of remote sensing data from 1952 (historical aerial images) until 2018 (Pléiades high-resolution satellite images), we documented the three-dimensional evolution of the Laurichard rock glacier during the last 60 years. We calculated the surface flow velocity between 1952 and 2018 using a feature-tracking algorithm at a resolution of 1 m and a precision of 0.5 m. Digital elevation models were assembled using the SfM techniques for aerial images, and the AMES stereo pipeline for Pléiades data. In addition, we made the analysis using in-situ annual velocities and temperatures data allowing to understand better which factors mostly explain the kinematic behavior.  We reconstructed a time series of changes in surface elevation by systematically co-registering and differencing DEMs between 1952 and 2018, with an average precision of 1 m. We first observed that the average annual horizontal velocity measured had increased progressively from 0.65 m yr-1 to 1.1 m yr-1 to 1.5 m yr-1 for the periods 1952-1960, 1994-2003 and 2013-2018, respectively. On the other hand, the surface mass changes and long term monitoring of mass transport show for all analyzed periods a clear negative surface elevation change of 2 m on average, between 1952 and 2018. The area with most of the elevation changes is the frontal part of the glacier, which is consistent with the increase in speed, which represents a mass exchange from the upper part to the front. We conclude that the rates of rock glacier mass transport have increased during the last 20 years and hypothetize, for this rock glacier, a transition state controlled mainly by local topographical factors which will eventually lead to high speed rock glacier or rock glacier destabilization.

D2513 |
EGU2020-1605
Eike Reinosch, Johannes Buckel, Markus Gerke, Jussi Baade, and Björn Riedel

The northern Nyainqêntanglha range on the southern Tibetan Plateau reaches an elevation of 7150 m and is mainly characterized by a periglacial landscape. A monsoonal climate, with a wet period during the summers and arid conditions during the rest of the year governs the landscape processes. Large parts of the mountain range are considered permafrost due to the high altitude and the associated low air temperature. Rock glaciers, which are bodies of ice-rich debris, are a typical landform. The recently published IPCC report on the cryospheres of high mountain areas highlights the sensitivity of rock glaciers to climate warming and emphasizes the importance of their study.

We study the distribution of rock glaciers of the northern Nyainqêntanglha range and our aim is to produce an inventory of active rock glaciers based on their surface motion characteristics. The lack of higher order vegetation and the relatively low winter precipitation enable us to employ Interferometric Synthetic Aperture Radar (InSAR) time-series techniques to study both seasonal and multi-annual surface displacement patterns. InSAR is a powerful microwave remote sensing technique, which makes it possible to study displacement from a few millimeters to centimeters and decimeters per year. It is thus suitable to detect sliding and creeping processes related to periglacial landscapes and permafrost conditions on the Earth’s surface. We use both Sentinel-1 (2015-2019) and TerraSAR-X ScanSAR data (2017-2019) for our analysis.

In this study we differentiate rock glaciers from the surrounding seasonally sliding slopes by their significantly higher surface creeping rates with mean velocities of 5–20 cm yr-1. We also observe that the velocity of rock glaciers is less dependent on the summer monsoon, which allows us to further differentiate between rock glaciers and other landforms. This method could potentially be used to create rock glacier inventories in other remote regions, as long as the snow cover in winter is thin enough to allow continuous InSAR time-series analysis. These rock glacier inventories are necessary to assess the effects of climate change on vulnerable high mountain regions.

D2514 |
EGU2020-8159
Nora Krebs, Anne Voigtländer, Matthias Bücker, Andreas Hördt, Ruben Schroeckh, and Johannes Buckel

Geophysical methods provide a powerful tool to understand the internal structure of active rock glaciers. We applied Electrical Resistivity Tomography (ERT) to a rock glacier at an elevation of 5500 m a.s.l. in the semi-arid Nyainqêntanglha mountain range on the Tibetan plateau, China.  The investigations comprised three transects across the rock glacier and its catchment, each spanning over a distance of 296 m up to 396 m, equipped with 75 up to 100 electrodes respectively. Our measurements were successful in revealing internal structures of the rock glacier, but were also accompanied by challenges.

We successfully detected first-order permafrost structures, such as a shallow about 4 m thick active layer of low electrical resistivity values that was underlain by potentially ice rich zones of high resistivity. Further high-resistivity zones were found and interpreted as dense bed rock of adjacent slopes that undergird the loose rock glacier debris.

Challenges, we faced in the application of ERT, were mainly posed by the morphology and internal structure of the rock glacier itself. Coarse debris created a rough surface that prevented a uniform setup with accurate 4 m spacing. The presence of loosely nested blocks of pebble size up to boulders with large interspaces resulted in high contact resistances. The consequent low injection current densities and possible noisy voltage readings downgraded part of the data, causing low data density and resolution. Coupling was partly improved by attaching salt-watered sponges to the electrodes and adding more conductive fine-grained materials to the electrodes. The detected high resistivity ice layer impeded deep penetration of electrical currents, which caused that the lower limit of the permanently frozen zone could not be defined.

Despite these challenges, the captured ERT profiles are an indispensable contribution to the sparse field data on the internal structure of rock glaciers on the Tibetan plateau. Our results contribute to a better understanding of the prospective evolution of rock glaciers in dry, high mountain ranges under a changing climate.

D2515 |
EGU2020-7266
Johannes Buckel, Eike Reinosch, Nora Krebs, Anne Voigtländer, Michael Dietze, Ruben Schroeckh, Matthias Bücker, and Andreas Hördt

Rock glaciers are typically regarded as periglacial features and their dynamics are supposed to be driven by ice content. Under ongoing global warming we expect these structures and dynamics to change and at least decay. This would be especially the case of rock glaciers in climate-sensitive high mountains of the Tibetan plateau, like in the Nyainqêntanglha range. Despite the similar past and present periglacial climatic conditions in this region, rock glaciers are only formed in a few, specific valleys. With this study, we aim to provide insights into the environmental conditions under which rock glaciers are formed and maintained, to be able to better understand how they will respond to changing boundary conditions, imposed by global warming.

To assess “what makes a rock glacier?” we studied such a feature in the Qugaqie basin, at 5500 m a.s.l. To describe the structure and the dynamics of this active rock glacier we applied several methods (geomorphological mapping, geophysics, remote sensing) and we incorporated catchment area properties such as geology, water and sediment sources. Mapping of the geomorphology, the geology and surface material properties characterizes the external structure of the rock glacier. The internal structure, like the active layer zone and the existence of ice, is described by electrical resistivity tomography (ERT). To investigate the surface dynamics of the rock glaciers, we quantify displacement rates using Interferometric Synthetic Aperture Radar (InSAR) time-series analysis. To gain insight to internal deformation dynamics we use environmental seismology, allowing for detection and location of crack signals within the rock glacier. The seismic network also allows tracking rock falls at the head scarp and continuously monitoring glaciofluvial patterns. We find that the singularity of the presence of the studied rock glacier is most likely related to a specific melange of the geological structures, former glaciation of the valley, catchment size and shape and especially water availability.

Chat time: Wednesday, 6 May 2020, 10:45–12:30

Chairperson: Adina E. Racoviteanu
D2516 |
EGU2020-19637
Tobias Bolch, Philipp Rastner, Jan Bouke Pronk, Atanu Bhattacharya, Lin Liu, Yan Hu, Guoqing Zhang, and Tandong Yao

Rock glaciers and other ice-debris landforms (I-DLs) are an important part of the debris-transport system in high mountains and their internal ice could provide a relevant contribution to water supply especially in dry regions. Recent research has shown that I-DLs are abundant in High Mountain Asia, but knowledge about their occurrence and characteristics is still limited.

We are therefore investigating I-DLs in the Poiqu basin (~28°17´N, 85°58´E) – central Himalaya/southern Tibetan Plateau using remote sensing aided by field observations. We use very high-resolution stereo Pleiades data from the contemporary period and stereo Corona and Hexagon data from the 1970s to generate digital elevation models, applied satellite radar interferometry based on ALOS-1 PALSAR and Sentinel-1 SAR data and feature tracking using Sentinel-2 and the Pleiades data. Generated DEMs allowed us to create a hillshade to support identification, to derive their topographical parameters and to investigate surface elevation changes. I-DLs were identified and classified based on their characteristic shape, their surface structure and surface movement. Field observationssupported the identification of the landforms.

We found abundant occurrence of rock glaciers (with typical characteristics like lobate-shaped forms, ridges and furrows as well as steep fronts) but also significant movements of both former lateral moraines and debris-slopes in permafrost area. Preliminary results revealed the occurrence of more than 350 rock glaciers covering an area of about 21 km2. About 150 of them are active. The largest rock glacier has an area of 0.5 km2 and three have an area of more than 0.3 km2. The rock glaciers are located between ~3715 m and ~5850 m with a mean altitude of ~5075 m a.s.l.. The mean slope of all rock glaciers is close to 17.5° (min. 6.8°, max. 37.6°). Most of the rock glaciers face towards the Northeast (19%) and West (18.5%). Surface elevation changes between the 1970s and 2018 show no significant changes but indicate slight elevation gain at the front of active rock glaciers caused by their downward movements.

Work will be continued to generate an inventory of all I-DLs in the study area including information about their activity and surface elevation changes.

D2517 |
EGU2020-8967
Justyna Dudek and Mateusz Czesław Strzelecki

Contemporary climate warming in the Arctic affects the dynamics of the entire environment, including components of the cryosphere: permafrost and glacier systems. The change in the structure of the polar landscape since the termination of the Little Ice Age (ca. 1900) was expressed by widespread retreat of glaciers, progressive exposure of glacial landforms at ice margins and opening ice marginal zones to increasing paraglacial and periglacial processes operating synchronously in adjacent areas.

The main aim of the presented study was to determine the course and spatial diversity of landscape transformation in the Sørkapp Land peninsula (Spitsbergen) as a result of glacier recession in the periods 1961-1990-2010 based on existing remote sensing data. Using photogrammetric methods of data processing combined with GIS techniques, the rates of proglacial and ice-marginal terrain change following deglaciation have been determined.

For the mentioned research period, the area of the marginal zones almost doubled from 53 km² to 99 km². The dynamics of landscape transformation in these zones manifested in rapid reduction in the surface elevation of ice-cored moraines (with mean decrease of 0,18-0,22 m per year) and the forms underlain by the dead-ice. This process was enhanced by mass movements and debris flows. Within marginal zones, the area of subglacial landforms and sediments increased by 31 km² from 8 km² in 1961 to 39 km² in 2010.

Larger volume of proglacial waters and associated intensification of denudation, transport and accumulation of sediments entailed area increase of sandurs and proglacial riverbeds (which almost tripled from 3,5 km² to over 10 km²). Further redeposition and remobilization of material in some places also promoted enhanced sediment aggradation in coastal environment forming new beaches and spit systems.

D2518 |
EGU2020-17195
Andreas Ewald and Jan-Christoph Otto

Cirques are characteristic landforms in high alpine environments with flat cirque floors flanked by steep headwalls. From a rock-mechanical perspective, rock walls are assumed to adjust over time according to their internal rock mass strength, which is determined by a number of factors including e. g. intact rock strength and fracture system characteristics. However, temperatures permanently below freezing as well as glacier coverage keep cirque headwalls stabilised so that slope inclination can evolve during glaciation that is far beyond strength equilibrium. When cirque headwalls deglaciate, the relative importance of rock mass properties increases drastically as they precondition rock slope instability. Cataclinal headwalls, where major fracture sets dip out of the slope, are rated as unstable and usually respond rapidly to glacier retreat. Anaclinal headwalls with in-dipping fracture sets in contrast respond delayed and probably less drastically. To date, a systematic assessment of the predisposition of cirque headwalls for rock slope instability following deglaciation is lacking. We aim to tackle this lacking by a systematic regional analysis of predisposition factors using GIS tools.

 

For the central Hohe Tauern Range, Austria, regional datasets are available for the most important preconditioning factors including topography (digital elevation model), geology (digital geological map), glacier extent (digital glacier inventory), and permafrost distribution (PERMAKART 3.0). We combined geomorphometric analyses with geotechnical data to locate and evaluate the sensitivity of glacier headwalls to rock slope instability using GIS and object-based analysis techniques.

 

Our results show that a vast majority of the headwalls identified can be divided by a significant convexity in the slope profile curvature into a larger, upper and a lower, steeper headwall section (> 60°). The lower limit of the steeper section is marked by a significant concavity in the slope profile curvature, which is commonly known as the schrundline. Assuming that the convex transition between steeper and flatter headwall section constitutes the upper limit of enhanced headwall retreat e. g. by periglacial weathering inside the bergschrund, we further address this headwall section as the schrundwall.

 

Geotechnical data (foliation dip and direction) has been digitalised and interpolated in a yet oversimplified manner, to distinguish  headwalls into cataclinal, anaclinal and orthoclinal slopes. Slope inclination and foliation dip has been interrelated to identify e. g. particularly sensitive overdip slopes. First results show that anaclinal and orthoclinal as well as cataclinal headwalls are quite common features in the study area. However, overdip slopes with steeply (30°-60°) outdipping foliation are almost exclusively found in schrundwall sections.

 

The persistence of steep overdip schrundwalls may be related to permafrost occurrence, which is subject to further analysis. Our approach, applied to modeled subglacial topography, may be of great value to anticipate future paraglacial instabilities in glacier headwalls.

D2519 |
EGU2020-5050
Marc Hugentobler, Simon Loew, and Clément Roques

Rock slope instabilities normally form through long-term strength degradation of initially stable slopes. The rate of progressive damage accumulation in the rock slope is expected to vary over time depending on the current environmental conditions. It is often assumed that glacial retreat, with its increased dynamics in the thermal and hydraulic boundary conditions in combination with mechanical ice unloading induce stresses that cause increased rock mass damage in adjacent slopes. However, direct field measurements to understand these dynamics and to quantify damage are rare.

In this contribution we present new data of a continuous borehole monitoring system installed in a stable rock slope beside the retreating glacier tongue of the Great Aletsch Glacier (Swiss Alps). Special focus lies on the pore water pressure evolution in order to better understand the origin of the presumably hydro-mechanically forced deformation measured in the study area. We compare data of two borehole pressure sensors installed at 50 m depth in the fractured crystalline rock, pressure fluctuations measured in a sink hole on the glacier close to our study site, and glacial melt water discharge measurements. These data show that the pore pressure variability in the slope is driven by annual snowmelt infiltration cycles, rainfall events, and the connection to the englacial water of the temperate valley glacier. We show that our in-situ measurements provide critical data to improve the understanding of the effects of a retreating valley glacier on the boundary conditions and eventually the stability of an adjacent rock slope.

D2520 |
EGU2020-10159
Lucia Felbauer, Martin Mergili, and Andrea Fischer

Glaciers are retreating at an historically unprecedented pace. Climate-determined processes are changing markedly. As a result, proglacial areas are expanding. Paraglacial dynamics are expected to further increase in significance, controlling sediment supply and landscape change in mid- to high latitudes for the next few hundred years. Paraglacial adjustment in proglacial areas has not been fully explored to date and there is an urgent need to monitor and understand these systems in more detail.

We present first insights into a planned project called glacier2go aiming to investigate changes in the paraglacial system in the highly variable and sensitive areas determined by rapid glacier retreat at two Austrian glaciers. The project aims at the development of a new holistic monitoring system, where remote sensing and field work data are combined and integrated to achieve a deeper understanding of the different stages of evolution of the paraglacial system, and to detect changes through classification approaches. The project glacier2go will fill a research gap by developing an automatic land cover classification model with very high spatial and temporal resolution for monitoring geomorphic changes. glacier2go will capture surface changes through contrasting geomorphic-classification maps.

The proposed survey will be conducted on selected glacier forefields in the Austrian Alps with Jamtalferner (Tyrol, Silvretta) and Pasterze (Carinthia, Glockner range) as the main study sites. glacier2go will be executed as a dissertation project hosted at the Interdisciplinary Institute of Mountain Research (IGF) in Innsbruck, Austria. International cooperation partners in the field of geomorphology, photogrammetry and geoinformation are on board to realize this project.

At the current stage first data comparisons are shown, emphasising the needed research on the interlinkage of geomorphology and the methodical development of new monitoring systems. Setting these first insights into the framework of paraglacial geomorphology leads to the emergence of new research questions. The associated challenges and first approaches for their solution are presented at the conference.

D2521 |
EGU2020-21253
Clemens Hiller, Kay Helfricht, Gabriele Schwaizer, Severin Hohensinner, Kerstin Wegner, Florian Haas, and Stefan Achleitner

High mountain environments have been confronted with rising temperatures and geomorphological changes over the past 150 years, with the considerable retreat of glaciers constituting one of the most pronounced impacts in the Alps. Concurrent degradation of permafrost in headwalls exposed from the downwasting ice and in periglacial hillslopes alongside glaciers causes increasing sediment flux onto glacier surfaces. The accumulation of supraglacial debris at the current glacier tongue promotes water-storage in debris-covered ice bodies and is assessed as an important source of sediment in the proglacial zone, since a close connection to the fluvial channel network can be assumed. The evolution of mountain streams, the degree of connectivity and conditional sedimentation-erosion effects significantly determine the dynamics in a generally unstable paraglacial landscape in which retreating glaciers provide high stream discharges while sediment is widely unconsolidated.

In the recent scientific debate, the anticipated progressive shift from supply-limitation (fluvial transport overcapacity) to transport-limitation (abundance of sediment) in high alpine catchment areas is discussed. Thus, this study intends to contribute by investigating the connection of coarse sediment including supraglacial debris from the proglacial transition zone to downstream fluvial transport. Key aspect is the feedback between increasing debris cover and a shifting runoff regime due to a changing composition of glacier melt, snow melt and heavy rainfall events. In that respect, the focus will be on the dynamics of bedload transport and the proglacial coarse sediment budget.

This study is part of the Hidden.Ice project and conducts in-depth monitoring of the connectivity, runoff measurements and geomorphological surveys at the LTER site Jamtalferner, Silvretta Range, Austria. Hydraulic modelling of the potential transport capacity supported by bedload trap measurements, the analysis of grain size distribution in the proglacial area and sediment volume changes calculated from UAV-based photogrammetry are aimed at raising knowledge on hydrological and geomorphological dynamics.

D2522 |
EGU2020-685
Saurabh Kaushik, Pawan Kumar Joshi, Tejpal Singh, and Anshuman Bhardwaj

The Himalayan Cryosphere is imperative to the people of south and central Asia owing to its water availability, hydropower generation, environmental services, eco-tourism, and influences on overall economic development of the region. Additionally, this influences the energy balance of the earth and contributes significantly to the sea level rise. Therefore Himalayan Cryosphere remains center of attraction for scientific community.  Glacier dynamics, seasonal snow and glacial lakes are studied at various scales using a combination of remote sensing and field observations. The existing literature reveals heterogeneous behavior of Himalayan glaciers which is largely influenced by climate change, debris cover and presence of glacial lake at the terminus. There are very limited studies that attempt to comprehend glacier dynamics and lake expansion in the Eastern Himalayan region. Therefore the present study aims to demonstrate link between glacier dynamics and lake expansion of South Lhonak glacier which is situated in the northern Sikkim. Multitemporal remote sensing data (Landsat, 1979-2019) and climate data (1990-2017) observed at Gangtok meteorological station are used in the study. The results reveal that the lake has expanded with a rate of 0.026 km2 yr-1 during the last four decades. The preliminary results show strongly imbalanced state of glacier, as glacier has deglaciated (area and length), and surface flow velocity and ice thickness have reduced significantly. The statistical analysis (Mann Kendall and Sens slope) of climate data measured at Gangtok meteorological station shows an accelerated trend of mean maximum (0.031°C yr-1) and mean minimum (0.043°C yr-1) temperatures (95% confidence interval). Whereas, no significant trend in total annual precipitation was observed. Inference can be drawn from study that glacier slow down and retreat contribute significantly to the glacial lake expansion under the influence of climate change, such lake expansion pose anticipated risk of glacial lake outburst in the region.

D2523 |
EGU2020-19854
Lindsey Nicholson, Fabien Maussion, Christoph Mayer, Hamish Pritchard, Astrid Lambrecht, Anna Wirbel, and Christoph Klug

The presence of extensive debris cover on glaciers in parts of High Mountain Asia increases the certainty about the present day amount of ice, its ongoing rate of change and resultant impact on global sea level rise, regional water and local hazards

Here we use ground penetrating radar measurements of ice thickness for the Ngozumpa glacier, a large debris-covered glacier in Nepal, to explore the challenges of using such data to calculate glacier volume, and to compare how these field measurements compare to the modelled glacier thickness for this glacier generated by the four models used in the global consensus glacier ice thickness dataset, which suggested the region holds 27% less ice than previous estimates (Farinotti and others, 2019). We also compare the ice thickness measured at Ngozumpa glacier to existing data from the smaller neighboring Khumbu glacier and evaluate the maximum volume of a possible moraine dammed lake at this site.

D2524 |
EGU2020-20639
Francesca Pellicciotti, Adria Fontrodona-Bach, David Rounce, and Lindsey Nicholson

Many mountain ranges across the globe support abundant debris-covered glaciers, and the proportion of glacierised area covered by debris is expected to increase under continuing negative mass balance. Within the activities of a newly established IACS Working Group (WG) on debris-covered glaciers, we have been carrying out an intercomparison of melt models for debris-covered ice, to identify the level of model complexity required to estimate sub-debris melt. This is a first necessary step to advance understanding of how debris impacts glacier response to climate at the local, regional, and global scale and accurately represent debris-covered glaciers in models of regional runoff and sea-level change projections.

We compare ice melt rates simulated by 15 models of different complexity, forced at the point scale using data from nine automatic weather stations in distinct climatic regimes across the globe. We include energy-balance models with a variety of structural choices and model components as well as a range of simplified approaches. Empirical models are run twice: with values from literature and after recalibration at the sites. We then calculate uncertainty bounds for all simulations by prescribing a range of plausible parameters and varying them in a Monte Carlo framework. We restrict the comparison to the melt season and exclude conditions as few current models have the capability to account for them.

Model results vary across sites considerably, with some sites where most models show a consistently good performance (e.g. in the Alps) which is also similar for energy-balance and empirical models, and sites where models diverge widely and the performance is overall poorer (e.g. in New Zealand and the Caucasus). It is also evident that with a few exceptions, most of the simpler, more empirical models have poor performance without recalibration. A few of the energy-balance models consistently give results different to the others, and we investigate structural differences, the impact of temporal resolution on the calculations (hourly versus daily) and the calculation of turbulent fluxes in particular.    

We provide a final assessment of model performance under different climate forcing, and evaluate models strengths and limitations against independent validation data from the same sites. We also provide suggestions for future model improvements and identify missing model components and crucial knowledge gaps and which require further attention by the debris-covered glacier community.

D2525 |
EGU2020-5954
Neil Glasser, Adina Racoviteanu, Stephan Harrison, Matthew Peacey, Rakesh Kayastha, and Rijan Bhakta Kayastha

Understanding the evolution of debris-covered glaciers in High Mountain Asia is important for making informed projections of climate change impacts and associated water security and hazard-related issues.  Here we describe the geomorphology of Ponkar Glacier, a debris-covered glacier in Nepal using high-resolution images from 2017 and 2019 based on Unmanned Aerial Vehicle (UAV) flights collected over the glacier and surrounding area in the field. These are used to describe the overall glacier morphology and its ice-surface geomorphology.  The key features of the glacier and its ice-surface morphology are described, including size and extent of tributary glaciers; changes in % of debris cover, lakes, ponds, ice cliffs, crevasses, and vegetation. Geomorphological mapping is used to describe the proglacial geomorphology, outwash plains and proglacial streams, the development of new ice-marginal ponds and changes in vegetation. We use these data to make inferences about the processes of moraine formation in this area. 

D2526 |
EGU2020-22638
Adina E. Racoviteanu, Neil F. Glasser, Smriti Basnett, Rakesh Kayastha, and Stephan Harrison

Understanding the evolution of debris-covered glaciers, including their evolution over time, the distribution of surface features such as exposed ice walls and supraglacial lakes, and their contributions to glacier ice melt and to glacier-related hazards such as Glacier Lake Outburst Flood (GLOF) events requires an interdisciplinary approach, with a combination of remote sensing methods and collaborative fieldwork.

Since 2017, the IGCP 672 /UNESCO project led has been focussing on the transfer of scientific knowledge on monitoring debris-covered glaciers to local partner institutions in high Asia through trainings, workshops and field collaborations. Our long-term goal is to disseminate methodologies developed under this project to local institutions in high Asia and to embed scientific knowledge into local communities. Here we report on recent capacity building activities held within the context of this new project involved local participants from universities in Nepal and Sikkim. The training included remote sensing/GIS modules, temperature measurements, sediment logging and drone surveys of the ablation zone, which will allow us to better quantify the surface features and their evolution.

 

D2527 |
EGU2020-16328
Anna Wirbel, Lindsey Nicholson, Christoph Mayer, and Astrid Lambrecht

The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing

Debris-covered glaciers are a feature of many mountain ranges around the world and their proportion is expected to increase under continued climate warming.

The impact of debris cover on glacier behavior, via its profound modification of the glacier ablation regime, causes debris-covered glaciers to respond to the same climate forcing in a markedly different way to clean ice glaciers. In order to better understand how debris cover impacts the glacier’s response to climate forcing, we revisit the concept of steady state and examine it for a debris-covered glacier system. We present simple modeling results to explore how the development and evolution of debris cover affects the potential for steady-state and how feedbacks instigated by supraglacial debris cover complicate the glacier’s response to a prescribed steady climate. These investigations highlight the non-stationarity induced by the presence of debris and as a result, that debris cannot be considered as a static component, as it is a highly dynamic component which affects the glacier system in different ways.



D2528 |
EGU2020-20062
Karla Boxall and Ian Willis

Debris cover is particularly prevalent in High Mountain Asia, with SW Asia alone containing 3,264 km2 of debris-covered ice (Scherler et al., 2018), which is increasing over time (Thakuri et al., 2014). The presence of supraglacial debris alters the energy balance by either enhancing or inhibiting ablation, depending on its thickness (Östrem, 1959). Therefore, debris cover is fundamental to the response of Himalayan glaciers to climate change. However, there remains a need to understand the glaciological characteristics that control the spatial pattern of debris cover and thus how it may evolve in the future.

Previous research has explored some controls of the spatial distribution of debris cover on a glacier scale (Gibson et al., 2017; Nicholson et al, 2018), but this research will take place on a regional scale. The chosen area is a ~9300 km2 region in the eastern Himalayas that encompasses both Ngozumpa and Lirung glaciers.

The GAMDAM glacier inventory (Sakai et al. 2019) will be used to delineate the glaciers. Within each glacier, the debris extent and thickness will be determined. Extent will be estimated through the supervised classification of optical imagery, using training data obtained from high-resolution Google Earth imagery. Thickness will be calculated through the derivation of a relationship between thermal satellite data (redistributed to a finer spatial resolution) and debris thickness measurements of Lirung glacier (McCarthy et al., 2017) and of Ngozumpa glacier (Nicholson et al., 2018).

An 8m DEM (from NSIDC) will be used to calculate slope, aspect and curvature over each glacier and repeat-pass SAR acquisitions will be used to calculate the velocity field for each glacier. The statistical relationship between debris extent and thickness with each of the aforementioned glacier characteristics is the intended output. Sensitivity tests will subsequently be carried out to determine the relative influence of each glaciological characteristic.

D2529 |
EGU2020-6650
Yong Zhang, Shiyin Liu, and Xin Wang

Hunza River is an important tributary of the Indus River, which contributes ~12% of the total runoff in the upper Indus River. 25% of Hunza River basin is covered by glaciers. The Karakoram Highway (KKH) connecting Pakistan and China goes from the Khunjerab Pass and down to the Gilgit, which is an important section of the Pakistan-China Economic Corridor in the high mountains. Many glaciers in this region are extensively covered by supraglacial debris, which strongly influences glacier melting and its spatial pattern. Changes in these glaciers may threaten the stability of the highway subgrade through meltwater floods, unpredictable behaviors of glacier terminals as well as potential outburst floods of glacier lakes near glaciers. Therefore, predicting runoff, response to climate change and risk of outburst floods of debris-covered glaciers requires different treatment to that of clean glaciers in the Hunza River Basin. In this study, we estimate the thermal resistance of the debris layer for the whole basin based on ASTER images. Our results reveal that debris-covered glaciers account for 69% and 30% of the total number and area in the basin. Using a physically-based debris-cover effect assessment model, we find different debris-cover effects on different glaciers, with important implications for the morphology and evolution of glacier hydrological system and associated hazards.

D2530 |
EGU2020-11588
Ben Brock, Grace Brown, Paul Mann, and Stuart Dunning

Debris-covered glaciers extend over 4000 km2 in the high Asian Mountains and are significant and expanding features of most of the World’s glacierized mountain ranges. Within supraglacial debris covers, a combination of fresh mechanically-weathered rock and an abundance of water and energy during melt seasons provides an ideal environment for chemical rock weathering and microbial activity. These processes involve exchange of carbon dioxide CO2 and methane CH4 with the atmosphere, while daytime heating of debris leads to evaporation of meltwater from the debris matrix. Debris-covered glaciers may therefore play an important role in regional and global cycling of major greenhous gases. This new project aims to address 2 key questions: (i) What are the important chemical and microbiological processes affecting carbon gas exchange within supraglacial debris covers? (ii) What are the rates and controls on gas exchange and how do these rates vary in time and space? Initial direct measurements of CO2 flux have been made using an eddy covariance (EC) and gas analyser system installed over debris cover at Miage glacier in the Italian Alps, during the melt season. Under fine weather conditions, there is a strong daily cycle in downwardly-directed CO2 flux, closely linked to variation in energy input to the debris, driven by the flux of shortwave radiation. In contrast, rainfall is associated with short pulses of upwardly-directed CO2 flux to the atmosphere. In common with previously published findings, these data indicate that supraglacial debris covers are a strong summer sink of CO2. At Miage glacier the mean summer (June-August) flux is almost 0.5 g carbon per day per square metre of debris, more than 2 orders of magnitude higher than reported fluxes over cryoconite. Current gas flux data are limited to a few points and this project will extend measurements to varying lithologies, elevations and glaciers in different climatic environments using portable greenhouse gas analysers in conjunction with the EC system. Direct flux measurements will be supported by in-field analysis of debris strucure and composition and subsequent laboratory analysis to determine the minerals, carbon content and microbial communities present in debris covers to uncover controlling processes and determine the relative roles of chemical weathering and microbial activity in carbon gas cycling.

D2531 |
EGU2020-10825
Madeleine Hann, Jamie Woodward, Philip Hughes, and Edward Rhodes

Catastrophic events such as debris flows and big floods are important agents of landscape change in steepland mountain environments. These events can be prominent in paraglacial settings as well as those that are tectonically active.   Since such catastrophic events pose  a significant natural hazard in deglaciating modern settings (e.g. Haeberli et al. 2017), it is useful to better understand analogous events in the recent geological past.

The Tamatert Valley, near the village of Imlil, on the northern slopes of Jebel Toubkal (4167 m a.s.l.) in the High Atlas, holds a valuable record of Quaternary landscape change.  The steepland Tamatert Valley was glaciated during the Pleistocene (Hughes et al. 2018)  and lies on the major Tizi n’Test Fault Zone.

More than 200 well rounded basalt mega-boulders (>2m b axis) have been mapped in the Tamatert Valley catchment (9 km2). Many of the boulders are larger than 5 m (b axis). The mega-boulders are found in the active channel of the Tamatert River, stranded above the modern channel, and embedded in valley-fill deposits. A preliminary chronological framework, combining cosmogenic exposure and luminescence dating, points to deposition of these boulders in the Late Pleistocene. The boulders are porphyritic basalt and lithologically distinct from the local diorite/granite bedrock.  They were transported by a catastrophic flood or debris flow over a distance of more than 3 km from the glaciated basalt source area.

Serendipitously, a debris flow producing a similarly extensive deposit of boulders (up to 3 m b axis) occurred in the neighbouring Mizane Valley in September 2019. Mapping of this modern deposit allows direct comparison with the Late Pleistocene event. Together, these provide valuable insights into the geomorphological significance of high magnitude, large boulder transit events in glaciated, steepland river catchments in the High Atlas. 

Haeberli, W., Schaub, Y. & Huggel, C. 2017. Increasing risks related to landslides from degrading permafrost into new lakes in de-glaciating mountain ranges. Geomorphology, 293, 405–417
Hughes, P.D., Fink, D., Rodés, Á., Fenton, C.R. & Fujioka, T. 2018. Timing of Pleistocene glaciations in the High Atlas, Morocco: New10Be and36Cl exposure ages. Quaternary Science Reviews, 180, 193–213

D2532 |
EGU2020-11290
Iestyn Barr, Jeremy Ely, Matteo Spagnolo, Ian Evans, and Matt Tomkins

With a view to better understanding landscape evolution, we model the style and duration of former mountain glaciation in Britain and Ireland during the Quaternary (i.e., the past 2.6 Ma). We use a simple mass balance model, driven by published temperature depression data from the Greenland Ice Core Project (for the past 120 ka), and from a benthic δ18O stack (for the Quaternary as a whole). Though there are limitations to this approach, results provide first-order estimates and indicate that during the Quaternary as a whole, the mountains of Britain and Ireland were glacier-free for 1.1 ± 0.5 Ma; occupied by small (cirque) glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. During the most recent glacial cycle specifically (i.e., the last 120 ka), these areas were glacier-free for an average of 52.0 ± 21.2 ka; occupied by small (cirque) glaciers for 16.2 ± 9.9 ka; and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka. Here, we investigate some of the regional variability in these estimates, and consider implications for long-term landscape evolution.

D2533 |
EGU2020-13381
Dohyeong Kim, Joohee Jo, and Kyungsik Choi

Pronounced morphologic changes such as coastal retreat and delta progradation occur widely along the Arctic coastal regions in response to increased sediment flux, freshwater runoff, and wave activity caused by climate changes. Compared to open coast and large-scale deltas in the Arctic region, the coastal morphodynamics and associated sediment transport in the Arctic fluvial-tidal transition zone (FTTZ) are less well understood. A series of recurved spits are developed on the upper intertidal zone of microtidal flats in the FTTZ of deglaciated Dicksonfjorden, Svalbard. The morphodynamics and sediment fluxes of the spit complexes were quantified using unmanned aerial vehicle (UAV)-assisted photogrammetry and Real-Time Kinematic GPS. Repeated annual survey indicates that the spits have elongated at 22 m yr-1 and have migrated landward at 4.3 m yr-1 over the last four years. The growth and migration rate of the spits increases seaward, where coastal cliffs consisting of an unconsolidated mixture of angular gravels and muds retreats at 0.2 m yr-1 with net erosion rate of 0.02 m yr-1 and provides local sediment source for the spits. In contrast, isolated gravel ridges, i.e., cheniers, on the tidal flats in the further landward did not migrate during the survey period. Archives of aerial photographs indicate that the cheniers had remained stationary since the 1930s, when a shoreline was located near the cheniers. The present study demonstrates that wave-induced overwash and longshore drift of coarse-grained sediments originated from the retreating cliffs are vital to the annual spit morphodynamics even in the innermost part of the fjord. Tidal flat progradation accelerated since the Little Ice Age with global warming trends by increased runoff from snow-fed rivers and alluvial fans, controls the centennial spit morphodynamics and distribution of wave-built morphology in the FTTZ of glacier-free Dicksonfjorden by regulating episodic sediment delivery via a seaward-shift in the locus of wave shoaling.

D2534 |
EGU2020-11220
Juris Soms and Zane Egle

In the south-western part of Jersika Plain (SE Latvia), the late Pleistocene aeolian sediments form the inland dune field located at Dviete village. This dune field with surface >112 km2 represents the evidence of aeolian activity and landscape evolution during the transition from glacial to post-glacial conditions in this region. The dunes have developed on the surface of glaciolacustrine plain, where subaqueous sedimentation in the Nīcgale ice-dammed lake took place during the retreat of glacier, the Pomeranian phase of the last glaciation.

Here, we focus on reconstructing paleoenvironmental conditions in this region, as inferred from landforms morphology, aeolian sand granulometry and geochemistry, and efficient wind directions derived from DEM. It will contribute to better understanding the processes of landscape evolution conditioned by last deglaciation in SE Latvia.

Results indicate that single parabolic dunes typically have U-shaped configuration in planar view. Aeolian landforms also link and override each other, presenting clustered groups. GIS analysis reveals that the dominating wind directions during the development of dunes would have been westerly to easterly. Previously published dates on OSL chronology for this dune field indicate the initial phase of aeolian activity at around 15.5 Ka and 14.5 Ka. Hence, when the studied landforms formed in presumably paraglacial landscape, the Scandinavian Ice Sheet (SIS) was still present, and most likely atmospheric circulation in this region was affected by anticyclone over the SIS.

The mean grain size Mz of the aeolian deposits forming inland dune field ranges between 143 μm and 256 μm. Hence aeolian landforms are composed mainly of fine-grained sands. It indicates the dominance of saltation and a balance between sand particles and comparatively low energy of local wind power during the aeolian processes. The sediments demonstrate well and moderately well sorting with σ values between 0.473 and 0.707 phi. Granulometry elucidates symmetrical distribution of particles of different fraction with small both negative and positive skewness Sk values ranging from -0.048 to 0.112 phi. For the values of kurtosis KG, results showed that sand is mainly mesokurtic.

Geochemical analysis points out that elemental composition is rather typical for aeolian sediments, determined by the dominance of quartz and K-silicates. Among REE elements, only Y un Nb were identified in detectable concentrations. Similar geochemical signatures across the dune field suggest the provenance of sediments from one main source, possibly associated with glaciofluvial sediment transportation by extra-glacial waters draining from the already ice-free parts of adjoining uplands to the glacial lake.

As apparent from the limited number of paleosoils, aeolian deposition seems to nearly instantly follow the drainage of the Nīcgale ice-dammed lake. It is most likely that cold and dry climate in conjunction with low groundwater tables during the late Pleistocene – beginning of Holocene were among the main controlling factors which prevented development of vegetation cover in this region and delayed stabilisation of the dunes. In turn, it facilitates the action of wind over glaciolacustrine plain as the main driving process of aeolian morphogenesis during the initial evolution of metastable post-glacial landscape.