GM10.3

The Gepatschferner in the Öztal Alps is Austria’s second largest glacier and is the subject of a monitoring campaign from 2019 onwards which was initially focussed on sedimentology and geomorphology of the forefield. Emphasis was placed on the styles and rates of sediment cannibalisation, with implications for transcription of the evidence into the deep time sedimentary record. This included the mapping of flutes, crag and tail structures, roches moutonées, fluvial sediments, till and rockfall deposits in the proglacial area. Their evolution over time is documented by repeated fieldwork and drone surveys. However, cognizant of the complexity of the subglacial environment (deforming bed areas, rigid bed areas and shifting meltwater systems) our work has expanded to ground-penetrating radar (GPR) surveys, enabling us to map subglacial conduits, englacial channels, and glacier structure. This structure involves the mapping of foliation, folds and fractures in the glacier, supported by field measurements. Repeated survey of both GPR and drones allows the 4D evolution of surficial glacier drainage, elevation, and forefield to be characterised. This work thus encompasses sedimentology, geomorphology, structural glaciology and bedrock geology. We argue that investigating the temporal and spatial landsystem-scale interactions between cryosphere (glacier and its structure), hydrosphere (meltwater pathways), and lithosphere (geomorphology, bedrock geology, sedimentology) will lead to breakthrough interpretations. These will include (i) controls on the evolution of the meltwater system, (ii) controls on the genesis of subglacial bedforms, (iii) the relationship between geology, geomorphology and glacier structure. Repeated, iterative surveys allow us to explore the teleconnections between cryosphere, hydrosphere and lithosphere, and their predictive capacity.

How to cite: Le Heron, D., Bristow, C., Davies, B., Grasemann, B., Kettler, C., and Schöpfer, M.: Teleconnections and a holistic Earth Systems approach to a retreating Alpine glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11255, https://doi.org/10.5194/egusphere-egu22-11255, 2022.

Glacial outburst floods (jökulhlaups) have significantly modified landscapes across Earth throughout the Quaternary and are a contemporary geohazard in glaciated regions worldwide. Iceland experiences more frequent jökulhlaups than nearly anywhere on Earth, though research has focused on floods triggered by subglacial volcanic eruptions. However, floods from ice-marginal lakes may be a better analogue for most global jökulhlaups because both occur during rapid global warming. As the Icelandic Ice Sheet retreated in the early Holocene, meltwater lakes accumulated at ice margins and periodically drained in jökulhlaups. One such lake formed in the Kjölur highland region and drained along the Hvítá River in southwestern Iceland, leaving behind abundant geomorphologic evidence including 50-meter-deep canyons, bedrock channels, and boulder deposits. Yet, only one previous publication has investigated these events.

This project uses a suite of field mapping, geochronological, paleohydraulic, and modeling techniques to better constrain flood timing and dynamics. It introduces new lines of geomorphologic evidence, revises drainage route maps, provides estimates of flood magnitude, and discusses ongoing cosmogenic nuclide dating analysis to reconstruct flood chronology. Finally, it interprets results to present hypothesized scenarios of ice margin position, glacial lake formation, and jökulhlaup drainage during Icelandic Ice Sheet deglaciation. The Hvítá jökulhlaups are also an excellent case study for extreme flood impacts in bedrock terrain and drainage processes from ice-marginal lakes, helping to close a research gap in Iceland and advance understanding of links between climate change, ice response, and hydrology in other Arctic and alpine regions.

How to cite: Wells, G., Luzzadder-Beach, S., Beach, T., Saemundsson, T., and Dugmore, A.: Holocene jökulhlaups along the Hvítá River, Iceland: geomorphology, chronology, and hydrology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4034, https://doi.org/10.5194/egusphere-egu22-4034, 2022.

Previous reconstructions of the glacial history of the last Fennoscandian Ice sheet (FIS) in northwest Arctic Russia are limited in scope owing to a lack of empirical geomorphological and chronological data. As a result, previous reconstructions suggest the Kola Peninsula was glaciated by either the FIS, the Ponoy Ice Cap, or the Kara Sea Ice Sheet. Utilising new databases of over 245,000 mapped glacial landforms and 209 numerical ages, we present a new time-slice reconstruction of Late Weichselian (c. 40-10 ka) FIS glaciation on the Kola Peninsula and Russian Lapland.

Subglacial bedforms are used to reconstruct ice flow geometry in the region. The relative age sequence of events demonstrates an evolving ice sheet configuration, including ice sheet build-up and retreat stages, and evidence of ice streaming. Moraines and meltwater landforms are used to reconstruct ice margin positions in the region. The Kola Interlobate Complex, stretching almost 400 km, is likely to be a time-transgressive landform assemblage, which formed at an east- and northeast-migrating junction between the warm-based White Sea lobe and cold-based ice on the Kola Peninsula, probably before the Last Glacial Maximum. Reconstructed retreat ice margin positions indicate that FIS retreat is characterised by thinning, resulting in a lobate ice margin.

This new reconstruction provides a framework into which sedimentary and chronological reconstructions can be contrasted and compared. This research also provides crucial empirical data for validating numerical model simulations of the FIS, which in turn will further our understanding of ice sheet dynamics in other Arctic, Antarctic, and Alpine regions.

How to cite: Boyes, B., Linch, L., Pearce, D., and Nash, D.: Fennoscandian Ice Sheet glaciation on the Kola Peninsula and Russian Lapland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-45, https://doi.org/10.5194/egusphere-egu22-45, 2022.

The Laurentide Ice Sheet (LIS) was the largest of the ephemeral Pleistocene ice sheets in the Northern Hemisphere, with a Last Glacial Maximum (LGM) ice volume similar to the modern Antarctic ice sheet. A recent inventory of paleo-ice streams across the LIS shows many similarities with present-day ice streaming in Antarctica, where ice streams account for approx. 90% of mass loss. However, in the Mackenzie Lowlands of the Northwest Territories, Canada, the paleo-ice stream record is enigmatic. Previous work has identified a number of large paleo-ice streams, including the Mackenzie Trough, Anderson, Bear Lake and Fort Simpson ice streams, however, their extent, configuration, temporal relationship to each other and spatial evolution over time remains poorly constrained. Consequently, their impact on the rate and style of deglaciation of the northwestern sector of the LIS is poorly understood.

Here we utilise the newly available high resolution Arctic DEM (0.5 m resolution) to re-map glacial landforms across the Mackenzie Lowlands in greater detail (area >800,000 km²). We then use this landform record to reconstruct the ice dynamics in this region following the well-established approaches of flowset mapping and the glacial inversion method. The high resolution data allow us to present a detailed reconstruction of LGM ice flow over the Mackenzie Lowlands and resolve the configuration and evolution of ice streams over time. The landform record suggests that the ice streams operated time-transgressively during deglaciation, switching on and off at different times. While ice contact landforms, such as moraines, lateral and submarginal meltwater channels and ice-contact deltas, show the overall retreat of the LIS towards the Keewatin Dome in the east, in several regions the ice retreat record is complex, suggesting interlobate ice configurations with multiple ice retreat directions.

How to cite: Dulfer, H. E., Stoker, B. J., Margold, M., Stokes, C. R., Clark, C. D., Ó Cofaigh, C., and Evans, D. J. A.: Ice stream dynamics and ice margin retreat of the last Laurentide Ice Sheet in the Northwest Territories, Canada, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4737, https://doi.org/10.5194/egusphere-egu22-4737, 2022.

Ice provenance and dynamic behaviour between the British-Irish ice sheet has been subject to controversy in recent years. Several studies of clast lithology and glacial morphology have alluded to the inland extension of the North Sea Lobe into northeast England and the Vale of York. However, the extent that the North Sea Lobe extends into the Vale of York, and its dynamic interactions with the Stainmore and Wensleydale ice masses is as yet unknown. This study aims to reconstruct the complex provenance of the Vale of York ice lobe through clast lithological and matrix geochemical analysis. Multivariate statistical methods were applied to the datasets in the form of a PCA and Cluster Analysis, to aid in the correlation of Vale of York tills to BIIS and NSL type sites. Indicator erratics for NSL (Cheviot volcanics and flint), Scottish (greywacke and metasedimentary lithologies), and Lake District (felsic tuff) provenance were found in several tills and were central to tracing till provenance. Major and trace metal, and clast lithological cluster analyses have identified at least two occasions where the NSL and Eden-Stainmore ice converges at Scorton Quarry in the north of the Vale of York. NSL ice has been traced as far south and west as Norton Mills. Deposits to the west (Marfield Quarry and Lightwater Quarry) are dominated by a local Wensleydale ice signature and lack evidence of North Sea ice.

How to cite: Jenkins, H.: A palaeo-reconstruction of Devensian ice-flow phasing in the Vale of York., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5791, https://doi.org/10.5194/egusphere-egu22-5791, 2022.

Subglacial bedforms, repetitive landforms formed at the base of an ice-sheet or glacier as a result of the movement of subglacial sediments, are abundant in areas of former glaciation where they are often used to reconstruct past-ice flow conditions. Commonly referred to as one of the following morphotypes, the formation of drumlins, subglacial ribs and mega-scale glacial lineations (MSGL), has been the subject of scientific enquiry for over a century. Understanding subglacial bedform formation has important implications for reconstructions of palaeo ice-sheets, which require assumptions to be made regarding their genesis.

One explanation envisages subglacial bedforms as the result of instabilities in the coupled flow of ice, water, and till at the ice-bed interface. Here, we evaluate the progress of this hypothesis, commonly referred to as the instability theory of subglacial bedform formation. We present numerical solutions of the current version of the instability model, exploring the simulation outcomes for various constrained parameters. In our model, subglacial ribs and drumlins commonly arise, grow to a mature state, and persist. Drumlins are always preceded by subglacial ribs, perhaps explaining their commonly observed banded arrangements in the landscape. The transition from ribs to drumlins is rapid, with transitory intermediate quasi-circular forms - this perhaps explains why they are rarely observed. This evolutionary trajectory is one-way, with no simulations showing drumlins turning into ribs. This is most likely explained by the development of preferential pathways for water and sediment between drumlin ridges as the ice-bed interface evolves. Furthermore, we find that the numerical model is unable to produce MSGL, with previously reported MSGL-like features likely to be a consequence of periodic boundary conditions. This is despite analytical solutions to the model showing features with an MSGL-like wavelength. To resolve this, either a more sophisticated numerical toolkit is required, or the model requires further development.

Using these simulations as a basis of our discussion, we argue that whether the instability theory can be regarded as the fundamental cause of subglacial bedforms likely depends upon your viewpoint. For the mathematician, linear stability analysis of the model produces bedform wavelengths consistent with observations, so perhaps the problem is solved. For a numerical modeller, producing the missing MSGL remains a challenge. For sedimentologists, the model lacks the complexity to replicate the history of processes recorded within subglacial bedforms, and necessarily generalises deformational processes. Thus, many sedimentologically-based questions remain unanswered by this model. Finally, we argue that if subglacial bedforms arise from an instability, then inverting for glaciological conditions (e.g. velocity, thickness) based on the morphology of bedforms alone may be unachievable. The nature of instabilities means that small changes to the system will alter the final bedforms produced, and similar bedforms may occur through combinations of different conditions.

How to cite: Ely, J., Stevens, D., Clark, C., and Fowler, A.: Further numerical simulations of subglacial bedform formation: Implications for interpreting palaeo-landscapes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7728, https://doi.org/10.5194/egusphere-egu22-7728, 2022.

In the Pleistocene on the territory of Ukraine palaeocryogenic processes left the most noticeable traces in the features of the structure and properties of the periglacial loess-palaeosol sequences (LPSs).

The oldest of the Quaternary palaeocryogenic stages established in Ukraine is associated with the solifluction layer (fossil active layer of the permafrost) in the loess L3 (MIS 8) overlying the Lutsk palaeosol of the regional stratigraphic scheme that corresponds to S3, MIS 9. This stage was first documented in the Boyanychi key section, thus it got the eponymous name Boyanychi. A characteristic feature of this stage is the wide development of plastic deluvial-solifluction deformations. Palaeocryogenic deformations of this stage are described in only two sections of Quaternary LPSs – Boyanychi and Korshiv on Volhynian Upland. In Boyanychi, a large ice-wedge pseudomorph with a vertical size of more than 2 m was described and sampled for engineering and geological research. This is clear evidence of the existence of permafrost at that time. The age of L3 loess in the Boyanychi section is 277±41 ka BP.

Cryogenic deformations of the Yarmolyntsi palaeocryogenic stage (early MIS 6, Yarmolyntsi subhorizon) is most pronounced directly above the Korshiv fossil soils complex (S2, MIS 7) in many sections of Volhynian, Podolian uplands and Forecarpathians. During the Yarmolyntsi palaeocryogenic stage, deluvial-solifluction plastic deformations, mainly associated with the solifluction layer (fossil active layer) overlying the Korshiv palaeosol complex, were widely developed. Ice-wedge pseudomorphs exceed 2.5 m in depth. The age of the Yarmolyntsi subhorizon within the L2 loess of the Boyanychi section is 200.4±26.1 ka BP.

The Ternopil palaeocryogenic stage is associated with the Ternopil subhorizon in L2 loess (MIS 6) and is represented mainly by structural deluvial-solifluction deformations. Occasionally there was a polygonal-vein cracking that left traces in the form of ice-wedge pseudomorphs (Velykyi Hlybochok section, etc.). The age of the Ternopil subhorizon within the L2 loess of the Korshiv section is 159±53 ka BP, 164±34 ka BP, in the Boyanychi section is 162.2±17 ka BP.

Traces of the Lanivtsi palaeocryogenic stage (upper part of MIS 6, Lanivtsi subhorizon) are more widespread in the Quaternary LPSs of Ukraine. They are associated with the upper part of the L2 loess. It is the Lanivtsi (Zbarazh?) fossil active layer of the permafrost. Its development occurred at the end of the Middle Pleistocene. In the sediments of the Lanivtsi palaeocryogenic stage gleyed loams with a well-defined semi-mesh postcryogenic structure, highlighted by films of brown ferruginization, are dominated. Structural deformations of the Lanivtsi palaeocryogenic stage are well-developed in the sections of Zbarazh and Vyshnivets on the Podolian upland. Ice-wedge pseudomorphs are filled with loess and have vertical dimensions of slightly more than 2 m.

Palaeocryogenic deformations are of great importance for the stratigraphic division of the Quaternary LPSs of Ukraine. Clear stratigraphic positions of fossil active layers, their morphological and lithological features are reliable benchmarks for the determination and justification of specific horizons.

Acknowledgements

This study was supported by the project of the National Research Foundation of Ukraine, grant number 2020.02/0165.

How to cite: Tomeniuk, O. and Bogucki, A.: The oldest palaeocryogenic stages in the Quaternary loess-palaeosol sequences of Ukraine, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5740, https://doi.org/10.5194/egusphere-egu22-5740, 2022.

Thermal contraction cracks are well-known proxies of frost action, both in recent and relict environments. A sedimentological analysis was carried out on relict sand wedges from two study sites (Kemeneshát and Mogyoród area) in Hungary, in order to investigate past periglacial processes in the Pannonian Basin. After adequate sample preparation, the grain size distribution of sand wedge infillings (N=82) was determined, and descriptive statistical analysis was carried out using GRADISTAT software. 470 quartz sand grains were examined using a scanning electron microscope (SEM). Thereby, the roundness of the grains was determined and grain surface microtextures were analysed. The results show that every sample from the Kemeneshát area exhibits poor sorting values and mainly polymodal distributions, while the Mogyoród samples are exclusively unimodal and moderately sorted. SEM investigation reinforces the abovementioned statements with Krumbein’s scale results. Most of the studied grains are angular, which refers to the short transportation time of the sediment. Crystal overgrowth was often found on the grains, which suggests sandstone or metamorphic origin for the infilling material. Intensively weathered grain surfaces mark lots of changes in the paleotemperature. Fresh, sharp edges, as well as big, unaltered conchoidal fractures and breakage blocks, indicate intensive frost weathering processes during the last damaging cycle of the sediment. These results help us to reduce the arising uncertainties in the paleoenvironmental reconstruction of the Pannonian Basin during Late Pleistocene.

How to cite: Farkas, B. and Szabó, P.: Relict sand wedge sites in Hungary – granulometry and quartz grain microfabrics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1269, https://doi.org/10.5194/egusphere-egu22-1269, 2022.

Relict sorted patterns are valuable indicators of past permafrost and climate evolution, but their detailed terrain explorations are usually challenging due to high time requirements and poor pattern visibility. Here, we test the applicability of high-resolution airborne data to map and analyse the geometry of LGM polygonal sorted patterns at one site in the Krkonoše Mts., Czech Republic. We delineated a total of 2000 sorted patterns using colour contrasts between their elevated centres and bordering troughs discernible on a LiDAR digital elevation model with a resolution of 0.5 m and on true-colour orthogonal aerial photographs with a resolution of 0.2 m. Since the patterns occupy an area of ~1.96 ha, the density of their network accounts for ~1019 cells per hectare. The patterns have a diameter of 3.59±0.95 m, a height of 0.30±0.11 m, and an estimated sorting depth of 1.00±0.26 m. The number of pattern sides ranges between three and ten, but 82 % of the patterns are pentagonal to heptagonal, and their sides mostly meet at three- or four-way intersections at an angle of 120±24°. However, isometric patterns are rather rare as a length-to-width ratio attains 1.48±0.30. Generally, the remotely-sensed pattern attributes are consistent with ground-truth data previously collected at the study site, which proves the utility of high-resolution airborne data to rapidly map and complexly analyse the geometry of large sets of relict landforms over extensive areas that could not be done by conventional terrain surveys. The sorting depth indicates that permafrost superimposed by ~1 m thick active layer occurred at the study site during the LGM, which can be further used for past permafrost and climate modelling. The dataset can also have many other applications such as for validating automated pattern mapping/delineation tools and pattern growth models or for choosing an effective sample size for future surveys.

The research is financially supported by the Czech Science Foundation, project number 21-23196S.

How to cite: Uxa, T., Křížek, M., Krause, D., and Dlabáčková, T.: Geometry of LGM polygonal sorted patterns analysed using high-resolution airborne data (Krkonoše Mountains, Czech Republic), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8172, https://doi.org/10.5194/egusphere-egu22-8172, 2022.

Boulder-dominated periglacial, paraglacial and related landforms are important elements which can help to improve our knowledge about past climatic conditions and morphodynamic processes. As the formation and stabilization of these landforms can be associated to cold or transitioning climatic conditions from cold to warm, putting them on a solid temporal basis is vital to connect their evolution to changing climatic conditions throughout the Holocene. In this study, Schmidt-hammer exposure-age dating (SHD) was performed at different landforms including sorted polygons, rock-slope failure deposits and a blockfield in and around Breheimen, South Norway. By obtaining an old and a young control point, it is possible to calculate a calibration curve, from which the respective landform ages were estimated. The SHD age estimates ranged from 8.02 ± 0.72 to 3.45 ± 0.70 ka showing their relict character. The sorted polygon ages of 6.55 ± 0.68 and 4.76 ± 0.63 ka point to a stabilization within and towards the Holocene Thermal Maximum (HTM; ~8.0–5.0 ka). Whereas the ages of the investigated rock-slope failures from 8.02 ± 0.72 to 3.45 ± 0.70 ka can be divided in two groups. The first group consists of two rock-slope failures with overlapping ages with a mean age of ~7.6 ka. This timing can be related to the onset of the HTM characterized by warmer temperatures possibly leading to slope weakening due to a variety of factors, such as permafrost degradation and increasing cleft-water pressure. Ages of the second group, with three rock-slope failures, cluster around ~3.7 ka, shortly after a cold climatic period between 4.75–3.85 ka. Therefore, we assume that the occurrences of these rock-slope failures could have been climatically induced by warmer temperatures. The blockfield age of 5.24 ± 0.79 ka is significantly younger than other dated blockfields in South Norway and indicates longer activity of the boulders at the blockfield surface. Surface exposure ages from boulder-dominated landforms stress that these landforms can be valuable elements in improving our knowledge about landform evolution and palaeoclimatic fluctuations within the Holocene in South Norway.

How to cite: Marr, P., Winkler, S., and Löffler, J.: Boulder-dominated periglacial and related landforms as palaeoclimatic and morphodynamic indicators in Breheimen, South Norway, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12371, https://doi.org/10.5194/egusphere-egu22-12371, 2022.

Warming-induced permafrost degradation is believed to be responsible for the increasing number of rock-slope instabilities, such as rockfalls or rock avalanches, over the past few decades. Relationship between permafrost degradation and geomorphological activity, is nevertheless, hard to establish because often little is known about the permafrost distribution in steep slopes. In the present study, we assess spatio-temporal changes in rock wall temperature in Norway post the Little Ice Age, using the two-dimensional ground heat flux model CryoGrid 2D. We create transects across the monitored rock walls in the Western Norway, in the high alpine range of Jotunheimen and in the Northern Norway.

               Our results demonstrate that rock wall temperature at 20 m depth increased by an average of 0.2 °C decade^-1 since the 1980s. Therefore, if atmospheric warming rates remain similar, rock wall permafrost currently at -1 °C at 20 m depth could degrade completely at this depth by 2070. Furthermore, we show how rock wall temperature is influenced by: (1) rock wall geometry, (2) rock wall size, (3) magnitude of surface offsets due to the incoming shortwave solar radiation, (4) snow conditions above and below rock walls, (5) blockfield-covered plateaus or glaciers in their vicinity. Multi-dimensional thermal effects are smaller in Norway than in the European Alps due to the dissimilarities in mountain geometry and smaller differences in ground surface temperature between various mountainsides. Rock walls with large surface offsets arising from solar radiation might be warmer than plateaus above or talus slopes below, thus ground heat flux in such rock walls is directed towards colder plateaus or talus slopes. Furthermore, thermal conditions in blockfield-covered plateaus have impact on rock wall temperature and lead to larger warming rates at 20 m depth, whereas large glaciers decrease warming rates at the same depth. Therefore, a potential glaciers retreat would likely increase ground warming rates in the nearby parts of rock walls.  

How to cite: Czekirda, J., Etzelmüller, B., Westermann, S., Isaksen, K., and Magnin, F.: Spatio-temporal variations in rock wall temperature in Norway post the Little Ice Age, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3211, https://doi.org/10.5194/egusphere-egu22-3211, 2022.

Active rock glaciers (RG) are associated with mountain permafrost occurrence, and in the last years, remote sensing has been widely used to assess their dynamics. However, the use of remote sensing in determining the dynamics of slow-moving rock glaciers, from areas with patchy permafrost, controlled by site-specific conditions still remains a significant challenge. One such area is the central part of Retezat Mountains in the Southern Carpathians, Romania.

Here we present and discuss the results obtained by using Persistent Scatterer Interferometry (PSI) on Sentinel-1 images between 15.5.2015 and 27.10.2020. The results were validated with 26 in situ measurements with a Topcon Hiper V Differential GPS connected to the ROMPOS network for real-time corrections and millimetric accuracy. Also, the spatial distribution of RG dynamics was compared with a predicted map of permafrost distribution.

The results show that the displacement rates are low, at around 10mm/year. Out of the 48 investigated RGs, only two have displacement rates between 10 and 20mm/year, 14 show displacement of up to 10mm/year, and 32 don’t show any (measurable) displacement. However, the displacement rates are found to cover only part of the RGs, with stable areas being identified on all of them. When comparing the distribution pattern of the displacement rates, there is a good overall agreement with the modelled permafrost distribution, further suggesting that rock glacier dynamics are influenced by permafrost occurrence in marginal conditions.

How to cite: Sirbu, F., Poncos, V., Strozzi, T., Onaca, A., Teleaga, D., and Birtas, D.: On the dynamics of rock glaciers in marginal mountain permafrost (Retezat Mountains, Romania)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7826, https://doi.org/10.5194/egusphere-egu22-7826, 2022.

Rock glaciers are bodies of frozen debris and ice that move under the influence of gravity in permafrost areas. They are important climatic proxies and can undergo destabilization related to flow of the frontal sectors over steep topography or acceleration related to permafrost degradation and climate change. As consequence, they evolve with complex mechanisms, mirrored by spatial heterogeneity and extremely variable displacement rates. Although a sound quantification of activity is a key component of the study of rock glaciers, only few of them can be characterized by point-like site investigations and ground-based displacement measurements. Their study is thus widely facilitated by remote sensing applications, which proved to be powerful tools for a spatially distributed and temporally continuous characterization on a regional scale

Here, we developed a novel methodology to exploit the potential of spaceborne DInSAR analyses to characterize the state of activity of 516 rock glaciers mapped by Scotti et al., (2013) over an area of approximately 1000km² in the north-eastern sector of Valtellina (Italian Central Alps) and we exploited Landsat-8 thermal imaging to explore their regional distribution according to the land surface temperature.

The original rock glacier inventory, based on orthophotos and DSM mapping, provides a morphological and a dynamic classification (active/inactive vs. relict) of the mapped landforms according to surface evidence. To integrate this dataset with information on the present-day state of activity, we developed a semi-automatic procedure in ArcGIS and Matlab ^TM combining DInSAR products, morphometric data and available permafrost extent information (APIM). To obtain a spatially distributed characterization of rock glacier activity patterns, we processed Sentinel-1 A/B images (2017-2020) with increasing temporal baselines (Bt from 12 to 120 days) and generated 124 interferograms in ascending and descending geometry to account for all the different topographic orientations. We then implemented an analysis of the interferometric phase to achieve a quantification of each rock glacier activity based on four steps: 1) correcting the phase values inside each rock glacier for the modal phase value inside a surrounding stable area; 2) stacking (median phase values) of all the selected interferograms generated with same temporal baselines; 3) extracting frequency distributions of median phase values inside each rock glacier and stable area; 4) calculating the percentage of phase values inside each rock glacier that falls outside the uncertainty ±σ range of the stable area ones. This percentage provides an “Activity Index” that allows defining four classes of rock glacier activity together with the presence (active, inactive) or absence (active debris, relict) of permafrost. Classification results based on DInSAR data at different temporal baselines allow recognizing styles of activity characterized by different ranges of displacement rates and spatial and temporal heterogeneities, possibly correlated with the underlying deformation mechanisms. The integration with land surface temperature finally provides useful insights on the distribution of rock glacier activity classes in different topographic conditions.

Our methodology can be applied to other alpine areas and datasets for a wide-area evaluation of rock glacier activity for climatic studies and possible geohazard hot-spot identification.

How to cite: Crippa, C., Codara, D., and Agliardi, F.: Regional characterization of rock glacier activity based on DInSAR phase and permafrost extent, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4668, https://doi.org/10.5194/egusphere-egu22-4668, 2022.

Active rock glaciers in Greenland have been studied since the 1980s focusing on two regions (Disko Island and Zackenberg) located north of 69°13’N. As judged from permafrost models, widespread existence of permafrost and thus active rock glaciers are also possible south of this latitude. Therefore, research on a large rock glacier on the island of Bjørneø (size: 1 km²; elevation 250-600 m a.s.l.; NNW-exposed) at 64°30’N was initiated in 2016. Research focused until 2020 on repeated differential GPS measurements at several fixed ground control points, on the analysis of the bottom temperature of the winter snow cover, and on the assessment of high-resolution orthophotos and digital terrain models based on UAV campaigns. Results up to 2020 indicate that permafrost influences a large part of the rock glacier and surface displacement takes place in the order of cm per year particularly in the central part.

Within an INTERACT research project we continued and expanded research at this rock glacier in 2021 applying two types of geophysics (electrical resistivity tomography, ground penetrating radar), differential GPS, relative surface dating, geomorphic mapping, clast form analysis, and monitoring of ground, air, and water temperatures. We find that widespread permafrost is likely along the measured geophysical profiles, that ground and water temperatures generally support the assumption of present permafrost conditions, and that the rock glacier evolved over a period of several thousand years, starting to form soon after the recession of the Greenland Ice Sheet from the coast some 10.4 to 11.4 ka BP.

In addition to fieldwork, different types of remote sensing- and modelling based research at this rock glacier were accomplished. Clast size distribution was semi-automatically quantified using a high-resolution digital terrain model. Results reveal distinct clast size-differences along a longitudinal profile of the rock glacier. Analyses of time-series of Sentinel-1 differential SAR interferograms for the period 2016 to 2021 showed minor motion in the uppermost part of the landform during a period of two months, distinct compressive flow (few cm) of two lobes of the landform after several months, and landform-wide movement over a period of 3 years. The terrain surface before the formation of the rock glacier, and thus the rock glacier volume, were reconstructed on the basis of field observations and terrain data. The volume of material relocated due to rock glacier activity was approx. 10 million m³. Finally, the present rock glacier extent and morphology were numerically reproduced as a steadily evolving and slowly moving viscous mass using a model implemented in the GIS-based open-source mass flow simulation framework r.avaflow.

Our chosen multidisciplinary approach is a significant step forward in understanding the long-term evolution and present conditions of large rock glacier systems in the low Arctic region of Greenland.

How to cite: Kellerer-Pirklbauer, A., Abermann, J., Bernsteiner, F., Langley, K., Strozzi, T., and Mergili, M.: Rock glaciers in the low Arctic of Greenland: surface and subsurface structure, permafrost conditions, long-term evolution, and present kinematics of a large rock glacier system at Bjørneø Island, SW Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3663, https://doi.org/10.5194/egusphere-egu22-3663, 2022.

Knowing the age and evolution of present-day relict rock glaciers help to decipher past landscape evolution. In an Alpine context, this is particularly relevant for the Alpine Lateglacial and early Holocene period. Relative dating of the surface of a relict rock glacier with the Schmidt-hammer exposure-age dating (SHD) approach has the advantage of a cheap, rather easy handling, and fast method in comparison to absolute age dating approaches such as for instance terrestrial cosmogenic nuclides (TCN) using ¹⁰Be. A combination of the two methods at identical sampling sites might help to reduce intrinsic uncertainties of both methods. However, there is still a lack of direct comparisons of dating results based on TCN ages to ages based on Schmidt hammer rebound values. In this study, we compared published TCN ages from 34 sampling sites of relict rock glaciers and neighboring landforms taken from Steinemann et al. (2020) with measured SHD data. The TCN-samples have been taken primarily from two rock glacier systems consisting of gneissic rocks named Tandl and Norbert in the Reißeck Mountains, Carinthia, Austria. At each site where Steinemann et al. (2020) took a sample to quantify the absolute age based on ¹⁰Be, we carried out 100 individual Schmidt-hammer rebound measurements. The results of the two methods were partly consistent but partly difficult to interpret. At the study site Tandl (n=20), a significant correlation between TCN ages and R-values has been detected. The age calibrating curve for the Tandl site, suitable to calculate absolute ages from the relative R-values, is: age[ka] = -1.128ˑx R + 55.642 with an R² of 0.803. In contrast, no significant correlation between R-values measured at the study site Norbert (n=14) in comparison to ages derived by TCN data was revealed. This might be due to a more complex transport history of the sampled boulders in terms of both glacial as well as periglacial transport elements, the influence of a more complex lithology at Norbert, elevation effects (impacting differences in weathering), block instability or exhumation and erosion effects of the sampled boulders. Furthermore, gneiss is more difficult to measure with the Schmidt-hammer approach due to its common anisotropy compared to, for example, granite, which is the lithology mostly used in previous studies where TCN and SHD was compared. Therefore, our study comprises an interesting case study of both successful and problematic direct comparisons of TCN- and SHD-derived age data.

Steinemann O, Reitner JM, Ivy-Ochs S, Christl M, Synal HA (2020) Tracking rockglacier evolution in the Eastern Alps from the Lateglacial to the early Holocene Quaternary Science Reviews 241:106424. https://doi.org/10.1016/j.quascirev.2020.106424

How to cite: Krisch, P. and Kellerer-Pirklbauer, A.: Comparing Schmidt-hammer rebound values with terrestrial cosmogenic nuclides-derived ages in the Reißeck Mountains, Hohe Tauern Range, Austria, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4080, https://doi.org/10.5194/egusphere-egu22-4080, 2022.

The Stockhorn plateau, an east-west oriented crest located at an elevation of around 3’410 m a.s.l. in the Swiss Alps, is a measurement site belonging to the Swiss Permafrost Monitoring Network (PERMOS). In this study we present a combined analysis of thermal and geophysical data by applying the so-called petrophysical joint inversion (PJI) scheme (Wagner et al., 2019). By using the PJI approach with different petrophysical relationships (Archie’s law and Resistivity Geometric Mean model) (see Mollaret et al., 2020), we attempt to quantify the ice and water content changes in the subsurface over the past 20 years and analyse their spatial heterogeneity. The results will be validated with the borehole data.

Many different data sets are available for the Stockhorn plateau and they give evidence of permafrost degradation in the past 20 years. Two boreholes were drilled in 2000 and provide temperature measurements to a depth of 17 m and 100 m, respectively. From 2002 to 2020, the active layer depth has increased by 2 m for the northern borehole and by 3.3 m for the southern borehole. A weather station provides measurements since 2002 (PERMOS, 2021). The meteorological data show an increasing air temperature trend from 2003 to 2018 (Hoelzle et al., 2020). Since 2005, annual geoelectrical surveys (ERT) have been performed with collocated seismic surveys (RST) in almost every year. The geophysical data from 2007 to 2021 show a decreasing trend for specific electrical resistivities and P-wave velocities, but a detailed interpretation of the geophysical data is however not straightforward because of heterogeneous lithology as well as the small-scale topography effects causing a complex thermal regime.

The north-south geophysical profile is hereby situated at the boundary between two different rock formations. This is visible through the occurrence of a conductive anomaly observed in the geoelectrical surveys between the two boreholes. In addition, the plateau is covered by different materials such as fine debris, blocky and fine-grained materials, and bedrock, which implies different porosity values along the geophysical profiles in the subsurface. Due to large spatial heterogeneities in the observed temperature and geophysical data, the impact of permafrost degradation on the ground properties such as water and ice content is unclear. In contrast to the formerly used four-phase model (4PM, Hauck et al., 2011), where ERT and RST inversions are computed individually and a porosity distribution had to be prescribed, the PJI scheme has the advantage of obtaining physically consistent results of water and ice content distributions in the ground by inverting the ERT and RST results simultaneously (Wagner et al., 2019). In addition to the validation of the PJI results with the borehole data, it could be possible to validate the results with the thermal model simulations using Cryogrid3 (Westermann et al., 2016).

How to cite: Morard, S., Hilbich, C., Mollaret, C., Pellet, C., Wagner, F., Westermann, S., and Hauck, C.: Analysis of the 20-year long permafrost evolution at the long-term monitoring site Stockhorn, Swiss Alps, by applying a petrophysical joint inversion and a thermal model (Cryogrid3)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6195, https://doi.org/10.5194/egusphere-egu22-6195, 2022.

Retrogressive thaw slumps (RTS) are a common thermokarst landform along Arctic coastlines and provide a large amount of material containing organic carbon to the nearshore zone. The number of RTS has strongly increased since the last century. They are characterized by rapidly changing topographical and internal structures e.g., mud flow deposits, seawater-affected sediments or permafrost bodies and are strongly influenced by gullies. Furthermore, we hypothesize that due to thermal and mechanical disturbance, large RTS preferentially develop a polycyclic behavior.

To reveal the inner structures of the RTS several electrical resistivity tomography (ERT) transects were carried out in 2011, 2012, and 2019 on the biggest RTS on Herschel Island (Qikiqtaruk, YT, Canada), a highly active and well-monitored study area. 2D ERT transects were conducted crossing the RTS longitudinal and transversal, always reaching the undisturbed tundra. Parallel to the shoreline, and crossing the main gully draining the slump, we applied 3D ERT which was first measured in 2012 and repeated in 2019. The ERT data was calibrated in the field using frost probing to detect the unfrozen-frozen transition and with bulk sediment resistivity versus temperature curves measured on samples in the laboratory.

The strong thermal and topographical disturbances by gullies developing into large erosional features like RTS, lead to long recovery rates for disturbed permafrost, probably taking more than decades. In this study we demonstrate that ERT can be used to determine long-lasting thermal and mechanical disturbances. We show that they are both likely to prime the sensitivity of RTS to a polycyclic reactivation.

How to cite: Eppinger, S., Krautblatter, M., Lantuit, H., Fritz, M., Lenz, J., and Angelopoulos, M.: Long-term destabilization of retrogressive thaw slumps (Herschel Island, Yukon, Canada), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9692, https://doi.org/10.5194/egusphere-egu22-9692, 2022.

Lakes and drained lake basins (DLB) are ubiquitous landforms in permafrost regions. The long-term dynamics of lake formation and drainage is evident in the abundance of DLBs covering 50% to 75% of arctic permafrost lowlands in parts of arctic Alaska, Russia, and Canada. Following partial or complete drainage events, DLBs evolve through time. As the basins age and ground ice enrichment occurs, the surface heaves and vegetation communities evolve, exhibiting spectral and texture differences indicative of these changing conditions. This mosaic of vegetative and geomorphic succession and the distinct differences between DLBs and surrounding areas can be discriminated and used to make a landscape-scale classification employing various indices derived from multispectral remote sensing imagery that, when combined with field sampling and peat initiation timing, can be used to scale across spatial and temporal domains. Previously published local and regional studies have demonstrated the importance of DLBs regarding carbon storage, greenhouse gas and nutrient fluxes, hydrology, geomorphology, and habitat availability. A coordinated pan-Arctic scale effort is needed to better understand the importance of DLBs in circumpolar permafrost-regions. Here we present an update of ongoing work within the Action Group on DLBs supported by the International Permafrost Association (IPA), an effort by the community to develop a first pan-Arctic drained lake basin data product. Comprehensive mapping of DLB areas across the circumpolar permafrost landscape will allow for future utilization of these data in pan-Arctic models and greatly enhance our understanding of DLBs in the context of permafrost landscapes. Utilizing remote sensing imagery (Landsat-8) and freely available DEM data sets (e.g. ArcticDEM) allows us to implement our mapping approach on a circumpolar scale. A previously published prototype of this data product covering the North Slope of Alaska forms the basis of this large-scale mapping effort. Here we present first result working towards a pan-Arctic remote sensing-based DLB data product focussing on selected areas in Canada and Siberia, Russia.

How to cite: Bergstedt, H., Jones, B., Grosse, G., Veremeeva, A., Breen, A., Liljedahl, A., Bartsch, A., Gaglioti, B., Bouchard, F., Hugelius, G., Nitze, I., Wolter, J., Hinkel, K., Farquharson, L., Fuchs, M., Kanevskyi, M., Roy-Leveillee, P., and Lantz, T.: Drained lake basins on a circumpolar scale – Updates from the IPA Action Group, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9681, https://doi.org/10.5194/egusphere-egu22-9681, 2022.