Displays

Permafrost peatlands cover extensive areas in subarctic regions, and store large amounts of soil organic carbon that can be remobilized as active layer deepening and thermokarst formation is expected to increase in a future warmer climate. In northern Fennoscandia peatland initiation started soon after the last deglaciation, and throughout most of the Holocene the peatlands were permafrost-free fens. Colder conditions during the Little Ice Age resulted in epigenetic permafrost aggradation (Kjellman et al., 2018; Sannel et al., 2018). Today, these ecosystems are characterized by a complex mosaic of different landscape units including elevated peat plateaus and palsas uplifted above the surrounding wetlands by frost heave, and collapse features such as fens and thermokarst lakes formed as a result of ground-ice melt. This small-scale topographic variability makes the local hydrology, and possibly also the ground thermal regime very variable. In a peat plateau complex in Tavvavuoma, northern Sweden, ground temperatures and snow depth have been monitored within six different landscape units; on a peat plateau, in a depression within a peat plateau, along a peat plateau edge (close to a thermokarst lake), at a thermokarst lake shoreline, in lake sediments and in a fen. A thermal snapshot from 2007/08 shows that permafrost is present in all three peat plateau landscape units, and the mean annual ground temperature (MAGT) at 2 m depth is around -0.3 °C. In the three low-lying and saturated landscape units taliks are present and the MAGT at 1 m depth is 1.0-2.7 °C. Small-scale topographic variability is a key parameter for ground thermal patterns in this landscape affecting both local snow depth and soil moisture. Wind redistribution of snow creates a distinctive pattern with thin snow cover on elevated landforms and thicker cover in low-lying landscape units. Permafrost is present in peat plateaus where the mean December-April snow cover is shallow (<20 cm). In a small depression on the peat plateau permafrost exists despite a 60-80 cm mean December-April snow cover, but here the maximum annual ground temperature at 0.5 m depth is 8-9 °C warmer than in the surrounding peat plateau and the active layer is deeper (100-150 cm compared to 50-55 cm). In recent years, 2006-2019, the depression has experienced continued ground subsidence as a result of permafrost thaw, and the dominant vegetation has shifted from Sphagnum sp. to Cyperaceae. This transition could be the initial stage in collapse fen or thermokarst pond formation. In the same time period extensive block erosion and shoreline retreat has occurred along sections of the peat plateau edge where the mean December-April snow cover is deep (>80 cm). In a future warmer climate, permafrost thaw will have a continued impact on landscape changes, shifts in hydrology, vegetation and carbon exchange in this dynamic and climate-sensitive environment.

References

Kjellman, S.E. et al., 2018: Holocene development of subarctic permafrost peatlands in Finnmark, northern Norway. The Holocene 28, 1855–1869, doi:10.1177/0959683618798126.

Sannel, A.B.K. et al., 2018: Holocene development and permafrost history in sub-arctic peatlands in Tavvavuoma, northern Sweden. Boreas 47, 454–468, doi:10.1111/bor.12276.

How to cite: Sannel, A. B. K.: Ground thermal variability and landscape dynamics in a northern Swedish permafrost peatland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8790, https://doi.org/10.5194/egusphere-egu2020-8790, 2020.

The Bale Mountains in the southern Ethiopian Highlands (7-8°N) are formed of multiple superimposed flood basalts and comprise Africa’s largest plateau above 4000 m. Glacial and periglacial landforms are well-preserved and facilitate the reconstruction of the paleoclimate and landscape of the afro-alpine environment. During the Late Pleistocene, an ice cap covered the central part of the plateau and outlet glaciers extended down into the northern valleys. A striking geomorphological feature on the plateau are large sorted stone stripes that consist of hardly-weathered columnar basalt and are up to 2 m deep, 15 m wide and 200 m long. The stone stripes are located between 3850 and 4050 m at gentle slopes (4-8°) of two volcanic plugs 3-5 km south of the highest peak (Tullu Dimtu, 4377 m) and in the far west of the plateau. Sorted patterned grounds of similar size are characteristic for periglacial environments of the high latitudes, but unique for tropical mountains since their formation requires permafrost and a deep active layer. While diurnal freeze-thaw cycles in tropical mountains are sufficient for the genesis of small-scale patterned grounds, the sorting of large basalt columns (length >2 m, diameter >40 cm) assumes seasonal (or multi-annual) freeze-thaw cycles and a deep active layer. When and under which climatic conditions the sorted stone stripes in the Bale Mountains formed, remains an unsolved mystery. The stone stripes might have developed during the Late Pleistocene under periglacial conditions in close proximity to the ice cap or after deglaciation (~15-14 ka). To assess the timing of the final stagnation of the stone stripes, we determined the age of six basalt columns from two different stripes using ³⁶Cl surface exposure dating. In addition, we installed temperature data logger in 2, 10 and 50 cm depth across the plateau and between the stone stripes to investigate the present thermal conditions and diurnal and seasonal temperature variations in the ground. The difference between the measured mean annual temperature and presumed average ground temperature for permafrost (≤0°C) indicates an extreme temperature depression on the plateau of ≥10°C during the formation period of the sorted stone stripes. Such a Late Pleistocene cooling would be unprecendented in the tropical mountains. Finally, we applied a simple statistical model forced with meteorological data from a nearby weather station to simulate ground temperatures and test which climatic preconditions are necessary for the formation of sporadic permafrost in the Bale Mountains.

How to cite: Groos, A. R., Niederhauser, J., Akçar, N., and Veit, H.: The enigma of large sorted stone stripes in the tropical Ethiopian Highlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5552, https://doi.org/10.5194/egusphere-egu2020-5552, 2020.

Arctic soil movement, accumulation and stability exert a first order control on the fate of permafrost carbon in the shallow subsurface and landscape response to climate change. A major component of periglacial soil motion is solifluction, in which soil moves as a result of frost heave and flow-like “gelifluction”. Because soliflucting soil is a complex granular-fluid-ice mixture, its rheology and other material properties are largely unknown. However, solifluction commonly produces distinctive spatial patterns of terraces and lobes that have yet to be explained, but may help constrain solifluction processes. Here we take a closer look at these patterns in an effort to better understand material and climatic controls on solifluction. We find that the patterns are analogous to classic instabilities found at the interface between fluids and air—for example, paint dripping down a wall or icing flowing down a cake. Inspired by classic fluid mechanics theory, we hypothesize that solifluction patterns develop due to competition between gravitational and cohesive forces, where grain-scale soil cohesion and vegetation result in a bulk effective surface tension of the soil. We show that, to first order, calculations of lobe wavelengths based on these assumptions accurately predict solifluction wavelengths in the field. We also present high resolution DEM-derived data of solifluction wavelengths and morphology from dozens of highly patterned hillslopes in Norway to explore similarities and differences between solifluction lobes and their simpler fluid counterparts. This work leads us toward quantitative predictions of the presence or absence of solifluction patterns and their response to variation in material properties (e.g., vegetation, rock type, grain size) and climatic conditions (e.g., water content, active layer depth, variability in snow cover).

How to cite: Glade, R., Fratkin, M., Rowland, J., and Nutt, M.: Solifluction patterns arising from competition between gravity and cohesion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12698, https://doi.org/10.5194/egusphere-egu2020-12698, 2020.

Forms related to nival accumulation are recorded worldwide, and the role of nivation in relief formation was studied by many scientists. In classifications used nowadays, adopted in the last two decades, protalus and sub-slope nivation and glacial forms are divide into four types: pronival ramparts, glacial moraines, rock-slope failures and protalus rock glaciers. The existence of terrain forms and sediments not corresponding to the classifications was found during geomorphological research in Tajikistan mountains.

The research, conducted in June 2019, included geomorphological mapping, GPS measurements and photographic documentation. The investigation was performed in the Fann Mountains in the Pamiro-Altay range. The research area elevation is approx. 2400 m a.m.s.l. It is a typical mountainous terrain, with steep slopes and active morphogenetic processes. The studied segment of the valley has a fluvial nature; the valley bed is filled with fluvial and fluvio-glacial sediments. Glaciation did not reach this level of valleys. The maximum range of glaciers, dated at approx. 55 ka, reached 2780 m a.m.s.l. and its distance from the studied area is 5.5 km.

Sediments of undoubted nival origin exist at the fluvial sections of the valley. The occurrence of two forms of nival moraines was recorded in the research area. Both forms of the nival moraine consist of sediments with various grain sizes, with a noticeable prevalence of sands and gravels. Stones, 5-20 cm in diameters, constitute (depending on the site) 5-50% of the sediment volume, with their percentage usually amounting to 10-20%. Larger rock blocks occur individually. The thickness of the sediments varies greatly. In some places the nival material is about a dozen cm thick, while in the place of its greatest thickness it reaches 21 metres. The sediment consists solely of local limestone forming the adjacent rock walls.

The grain size distribution of these sediments is similar to moraine deposits, but its location, relief and local material suggest its classification as a pronival rampart. According to the criteria proposed by Hedding and Sunmner, these forms fulfil three criteria of rock glaciers and four criteria of pronival ramparts. The analysis of such forms encourage authors to conclude that these are not intermediate forms between specific types, but a separate type of form not defined so far.

We suggest defining a nivation moraine as a sediment (and at the same time terrain form) originated as a result of accumulation of local material delivered to the valley bottom from surrounding rock slopes and accumulated on many-years old snow cover of small thickness. The distinguishing features of this deposit include: 1) diversified fraction of the material, typical of moraine sediments, 2) no erratics, the deposit of only local material, 3) no traces of glacial erosion, 4) close neighbourhood of talus slopes enabling nival transport of material, 5) the existence in a dry and cold climate, where the snow supply was small. 

How to cite: Kroh, P., Dolnicki, P., and Łajczak, A.: Nival moraine – unclassified dry-climate periglacial sediment. Example from Pamiro-Altay Mts. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11121, https://doi.org/10.5194/egusphere-egu2020-11121, 2020.

Recently deglaciated forelands contain a wealth of geomorphological and sedimentological data that can provide key information about glacier-climate relationships. Mountain glaciers are particularly important indicators of climate change due to their short response times, which means that their forelands provide a sub-decadal record of changes in glacier size and climate-related dynamics. In this contribution, we examine the glacial geomorphological and sedimentological record at Østre Svartisen, an Arctic plateau icefield in Norway, and discuss temporal variations in glacier dynamics and processes of sediment deposition in response to climate warming since the Little Ice Age (c.1750). We focus specifically on the northeastern sector of the icefield and include two separate cirque/valley glaciers immediately to the north. Differences in landform-sediment assemblages are apparent both within and between forelands relating to changes in topography as well as glacier dynamics. Satellite images and old aerial photographs are also used to investigate differences in the rates of glacier demise across the study area. This evidence enables links to be made between landform generation, bed morphology, glacier dynamics, and glacier response to climate change, which furthers understanding of plateau icefield and outlet glacier behaviour in a warming climate.

How to cite: Boston, C. M., Lovell, H., Weber, P., Chandler, B. M. P., Barrows, T. T., and Davies, B. J.: The response of Østre Svartisen Icefield, Norway, to 20th/21st century climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22419, https://doi.org/10.5194/egusphere-egu2020-22419, 2020.

Sediment dynamics of proglacial streams are strongly connected to meltwater contributions, supply and activation of sediments from subglacial and periglacial reservoirs. In this context, the present study investigates and compares these dynamics at two proglacial streams with respect to discharge, bedload rates, suspension, and runoff generation. The study area is the upper Solda-Sulden catchment in the Eastern Italian Alps (14 km² drainage area, 38 % of glacier cover, elevation range between 2225 and 3905 m a.s.l.).

From June to September 2017, 2018, and 2019, two proglacial streams from the Eastern Solda-Sulden glacier (almost without debris-cover) and the Western Solda-Sulden glacier (heavily debris-covered) were monitored. We performed bi-weekly to monthly sampling of bedload (by Bunte samplers), suspended sediment content (SSC), stable water isotopes (δ²H and δ¹⁸O), and electrical conductivity (EC). During each sampling event, we measured water stages and carried out discharge measurements derived from salt dilution method. Meteorological data were measured at the Madritsch automatic weather station at 2825 m a.s.l. and at a temporary weather station installed on the Western Sulden glacier at about 2625 m a.s.l..

At the Eastern Sulden proglacial stream, we collected 32 bedload samples, which correspond to about 32 kg. The discharge during sampling ranged from 0.03 m³ s^-1 to 2.1 m³ s^-1 and led to bedload rates ranging between 0.002 kg min^-1 m^-1 and 6.7 kg min^-1 m^-1 in August 2018. At the Western Sulden proglacial stream, total weight of bedload samples amounted to about 332 kg (n = 56). The minimum and maximum discharge measured were 0.27 m³ s^-1 to 4.7 m³ s^-1, respectively. Bedload rates were much higher than those at the previous stream and ranged from 2 x 10^-4 m³ s^-1 to a maximum bedload rate of 248 kg min^-1 m^-1 in July 2019. Tracer-based runoff calculations (using δ²H) estimated up to 65 % ± 12 of ice melt contribution during the highest bedload rates, indicating that bedload rates were strongly controlled by ice melt contributions. At the daily scale, we generally observed that highest discharges in the afternoon temporally coincided with highest bedload rates. A change of one order of magnitude of discharge increased the bedload rates by one or two orders of magnitude.

However, in the case of the Eastern Sulden proglacial stream, sudden cloud overcast had an immediate effect on the sediment activation while discharges remained unaffected. Longer-period trends in bedload rate are also likely correlated with air temperature and radiation, suggesting a complex climatic control of sediment transport.

These results will help to better understand the important drivers and sensitivities of sediment dynamics in proglacial streams, thus supporting water and sediment management in glacierized catchments.

How to cite: Engel, M., Coviello, V., Buter, A., Carillo, R., Miyata, S., Marchetti, G., Andreoli, A., Savi, S., Kofler, C., Scorpio, V., Nicholson, L., and Comiti, F.: Sediment dynamics in glacierized catchments: a comparison study from two proglacial streams in the Sulden catchment (Eastern Italian Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11199, https://doi.org/10.5194/egusphere-egu2020-11199, 2020.

Comprehensive mapping and the Briticechrono geochronology provides a reconstruction of the last advance and retreat of the only land-terminating ice lobe of the western British Irish Ice Sheet. The Irish Sea Glacier was fed by ice from Lake District, Irish Sea and Wales, and extended to maximum limits in the English Midlands. During ice retreat after 27 kyrs, a series of reverse bedrock slopes rendered proglacial lakes endemic in the land-system. Not resembling the more extensive definitions of the classical ‘Glacial Lake Lapworth’, these ice contact lakes were smaller time transgressive moraine- and bedrock-dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, OSL bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples, and constrained for the Irish Sea Glacier a post 30ka ice maximum advance, 26.5±1.8ka maximum extent, and 25.3±1.6 to 20.6±2.2ka retreat vacating the region. With retreat of the Irish Sea Glacier an opportunistic Welsh re-advance 19.7±2.5ka took advantage of the vacated space and rode over Irish Sea Glacier moraines. Our geomorphological chronosequence shows a glacial system forced by climate, but mediated by piracy of ice sources shared with the larger and marine terminating Irish Sea Ice Stream to the west. The Irish Sea Glacier underwent changes flow regime and fronting environments driven by stagnation and decline as the primary impetus to advance was diverted. Ultimately, the glacier of the English Midlands display complex uncoupling and realignment during deglaciation and ice margin retreat towards upland hinterlands ~17.8 kyrs (Lake District and Pennines) and asynchronous behaviour as individual adjacent ice lobes became increasingly important in driving the landform record.

How to cite: Chiverrell, R., Thomas, G., Burke, M., Medialdea, A., Smedley, R., Bateman, M., Clark, C., Duller, G., Fabel, D., Jenkins, G., Ou, X., Roberts, H., and Scourse, J.: The evolution of the terrestrial-terminating Irish Sea glacier during the last glaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9438, https://doi.org/10.5194/egusphere-egu2020-9438, 2020.

This work concerns the rock glacier flow model introduced, in its basic form, by Kannan and Rajagopal in [1]  and extended with inclusion of temperature effects by Kannan, Rajagopal, Mansutti and Urbini in [2]. This one is based on the general conservation laws (momentum, mass and energy) and takes into account the effect of shear rate, pressure and rocks and sand grains volume fraction onto viscosity, also by implementing the effects of local pressure melting point variation. Here we present the results of a sensitivity analysis of the parameters developed by shooting the location of the internal sliding occurence, induced by the presence of rocks and sand grains trapped within the interstices of the glacier, and the value of the shear velocity.  The case of the Murtel-Corvatsch glacier in Switzerland is considered for the availability of the detailed description based on measured data published by Arenson, Hoelzle and Springman in [3].
The numerical results obtained improve those ones presented in [1] and show clearly the contribution of each numerical and functional parameter of the model. They also exhibit a very good agreement with observations which makes this modelling approach very promising for general application.
[1] Kannan, K., Rajagopal, K.R.: A model for the flow of rock glaciers. Int. J. Non-lin. Mech., 48, pp. 59– 64 (2013) 
[2] Kannan, K., Mansutti, D., Rajagopal, K.R. and Urbini, S.: Mathematical modeling of rock glacier flow with temperature effects, in Mathematical Approach to Climate Change and its Impacts (P. Cannarsa, D. Mansutti and A. Provenzale, eds.), pp. 137-148, Springer-INDAM series, vol.38 (2020) 
[3] Arenson, L., Hoeltzle, M. and Springman, S.: Borehole Deformation Measurements and Internal Structure of Some Rock Glaciers in Switzerland. Permafrost and Periglacial Processes, 13, pp. 117-135 (2002).

Acknowledgements: D. Mansutti acknowledges Piano Nazionale Ricerca Antartide (PNRA) for financial support of this topic within the project ENIGMA (project PNRA$16-00121$).

How to cite: Mansutti, D., Kannan, K., and Rajagopal, K. R.: Numerical sensitivity analysis of a rock glacier flow model versus detection of an internal sliding occurrence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17850, https://doi.org/10.5194/egusphere-egu2020-17850, 2020.

Periglacial areas are very sensitive to contemporary climate change. Rate of morphogenetic processes depends on numerous factors, including the most important: warming of air and ground, increase of precipitation (extreme rainfalls in particular) and shortening of snow cover duration. The dynamics of above mentioned processes may effectively modify conventional slope development models. The paper shows structure of selected talus slopes on Fugleberget hillside based on field observations and radar (GPR) sounding. Then the results have been compared to the classical slope models. The radar survey in April and May 2014 used RAMAC CU II Malå GeoScience system equipped with 30 MHz RTA antenna (Rough Terrain Antenna). Six GPR profiles of various length have been collected along the talus axes and transversally on Fugleberget hillside and partly on Hansbreen lateral moraine. According to the radar sounding maximum thickness of the debris deposits is 2530 m. Weathered material is getting thicker towards terminal part of the screes and debris deposits overlap marine sediments. The morphometry of the talus slopes shows that their current forms differ from conventional slope models, what can result from significant acceleration of geomorphic processes due to climate change

How to cite: Dolnicki, P. and Grabiec, M.: Thickness of talus deposits on Fugleberget hillside (SW Spitsbergen) in the light of the theories of slope development in periglacial areas , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8377, https://doi.org/10.5194/egusphere-egu2020-8377, 2020.

The Arctic region is experiencing surface air temperature increase of twice the global average. To better understand Holocene Arctic climate variability, there is the need for continuous, high-resolution palaeoclimate archives. Sediment cores from proglacial lakes can provide such climate archives, and have the potential to record past environmental change in detail.       

Vatnsdalur, a valley in northern Iceland, hosts small, climatically sensitive cirque glaciers that became independent from the Iceland Ice Sheet after its retreat following the Last Glacial Maximum (c. 15 ka BP). Importantly, this region is located at the confluence of warm water and air masses from the south and cold polar water and air masses from the north, making it highly sensitive to North Atlantic and Arctic climate change. However, at present the region is highly understudied, lacking any high-resolution climate reconstructions.           

To address this, we combine geomorphological mapping with the first high-resolution analysis of proglacial lake sediments, to thoroughly examine northern Iceland Late Holocene environmental change.

Field mapping supplemented by high-resolution drone data was used to characterise catchment geomorphology, including seven Holocene moraines. A sediment core (SKD-P1-18) from proglacial lake Skeiðsvatn, Vatnsdalur, was analysed for sedimentological (dry bulk density, loss-on-ignition, grain size), geophysical (magnetic susceptibility) and geochemical (X-ray fluorescence core scan, 2 mm resolution) parameters.            
We identify three main sedimentary facies from these analyses, indicating variations in glacial input and catchment environmental conditions. Radiocarbon dating of lake macrofossils, supplemented by tephrochronology, provides a chronological framework. Catchment point samples, also analysed using the above analytical techniques, were used for sediment fingerprinting to disentangle non-glacial from glacial end-members.

Our results indicate the disappearance and reformation of small, climatically sensitive cirque glaciers in Vatnsdalur during the Holocene. We interpret the data to show an abrupt return to a glaciated catchment. Our results fill a geographical gap of high-resolution proglacial sediment studies in the Arctic-North Atlantic region.

How to cite: Nebel, K., Lane, T., Adamson, K., Barr, I., van der Bilt, W., Kirby, J., and Hennekam, R.: Late Holocene glacier and climate reconstruction from proglacial records in Vatnsdalur, northern Iceland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-809, https://doi.org/10.5194/egusphere-egu2020-809, 2020.

Pleistocene dynamics are usually associated with the formation of characteristic landforms such as moraines, dunes, or kettle holes. However, cold climate processes can also shape the landscape but not result in such prominent relief features. This is especially true for slope deposits that have been formed in periglacial regions through geli-solifluction and/or cryoturbation.  While the terms used to refer to such slope deposits may differ with the disciplines of soil science and/or geomorphology, such features are often still recognized by practicing scientists. In the US, geli-solifluction and/or cryoturbation features are subsumed with a very general term ‘colluvium’ whereas in Europe a more sophisticated number of terms is used separating sediments which formed under cold climate processes from sediments which formed due to anthropogenic induced soil erosion. Our study focuses on the stratigraphy of late Quaternary deposits and the soil formation in the northern Appalachians. The study area wasn’t glaciated during the Wisconsin glaciation; hence no MIS 5 or younger glacial deposits are reported.

To advance a common terminology between geoscientist, we examined pedons representative of Holocene and periglacial dynamics that reflect the strong role that solifluction played in pre and MIS 5landscape dynamics. Especially on foot slopes and toe slopes pedon stratigraphy is characterized by a several meter-thick par-autochthonous deposits that are rich in clasts. Clasts in deposits are aligned with the slope direction and are imbricated; on back slopes par-autochthonous deposits are also present but more shallow. Stratigraphy and OSL chronology strongly suggests that during the late Pleistocene several phases of morphodynamics shaped the landscape via solifluction followed by an eolian input of silt to the soils/sediments. Geochemistry reflects the multi-layer character of the soil profiles showing clear differences between the bedrock and deposits above. Elevated values of manganese in the surface soil indicate the importance of plant litter biocylcing during the Holocene. Hence on a landscape scale, the distribution of soils and the pedogenesis is strongly related to the par-autochthonous character of the substrate rather than the bedrock.

How to cite: Hirsch, F., Raab, T., Drohan, P., and Bonhage, A.: Late Pleistocence dynamics in central Pennsylvania (USA) – new findings on periglacial slope deposits, pedology and chronology , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5929, https://doi.org/10.5194/egusphere-egu2020-5929, 2020.

The glaciers in the Alps are currently shrinking, in some cases dramatically, due to progressive warming. At some glaciers this recession has made it possible to find tree remains and other organic material at or near the termini. At Pasterze Glacier, such findings have been made since about 1990, allowing new insights into the Holocene evolution and variability of this glacier. Initially, only relocated wood and peat boulders were collected, but around 2010 an in-situ locality became ice-free. Tree remains and other organic material from this site have mainly provided dates for a period of more than a thousand years in the middle Holocene (around 6 ka) proving a continuously smaller extent of this glacier during this period compared to today. Furthermore, a comparative interpretation of all available, some 80 radiocarbon and dendro dates suggests that Pasterze Glacier was probably at least from about 10.2 ka to about 3.5 ka continuously shorter compared to the extent around 2010 AD. For the last nearly 2800 years there is no similar evidence of comparable small glacier extents. Finally, after the early- to mid-Holocene retreat phase, a relatively delayed increase of Pasterze Glacier during the early Neoglacial (in the Alps after about 4 ka) can be deduced. Other glaciers almost reached or even exceeded the later LIA dimensions already during this period.

Moreover, Pasterze Glacier is also lagging behind the current climatic changes, i.e., its extent is not in equilibrium with the current warming. This circumstance is not only proven by the rapid recession during recent years, but also by simulations with the glacier model OGGM. The simulation results show on the one hand that Pasterze glacier has to melt back for several more kilometres to reach equilibrium with the climatic conditions of 1980-2010. On the other hand, this also documents that the recent climate conditions are already sufficient to allow a recession comparable to the early and middle Holocene stages of this glacier. Both the delayed increase in extent during the early Neoglacial and the considerably delayed current recession can be explained by the size of the glacier and the topographic conditions.

How to cite: Nicolussi, K., Dusch, M., Drescher-Schneider, R., Kellerer-Pirklbauer, A., and Maussion, F.: Always delayed? Holocene and current evolution of Pasterze Glacier, Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9317, https://doi.org/10.5194/egusphere-egu2020-9317, 2020.

The Pasterze Glacier is an approx. 16 km² large and rapidly receding glacier in the Austrian Alps. The aim of this study was to detect and quantify the rapid landscape modification of its glacial-proglacial transition zone between September 2018 and September 2019. The study is primarily based on the analysis of aerial imagery of five different acquisition dates, two in 2018 (11 September and 15 November) and three in 2019 (17 June, 13 and 21 September). The platforms used for data acquisition comprised unmanned and manned aircrafts that led to ground sampling distances (GSDs) of the aerial imagery of approx. 10 cm. These data were photogrammetrically processed to orthophotos and digital elevation models (DEMs), which are the main input for the subsequent analysis. The flight campaigns were complemented mainly with geodetic measurements for ground-truthing purposes, water level measurements and field observations in order to facilitate a better geomorphological and glaciological interpretation.

Thickness changes and horizontal displacement of the Pasterze Glacier tongue and its adjacent proglacial transition zone were detected applying DEM differencing and normalized cross-calculation (orthophotos). These analyses also included a quality assessment, which allowed to discriminate changes from unchanged subareas. By visual interpretation of the orthophotos and our in-situ measurements, we detected substantial geomorphic changes, the further evolution of the proglacial lake’s extent and water level changes.

Results show that the thickness of the investigated subarea at the glacier tongue (0.2 km²) decreased up to approx. 18 m from June 2019 to September 2019 with a mean ice thickness decrease of approx. 4.2 m. In contrast, a subarea of the studied proglacial area (0.14 km²) remained rather unchanged (mean thickness decrease of only 0.7 m). Taking into account the comparison of DEM elevation values with geodetically and thus independent elevation measurements, the vertical quality of the DEMs is described by a standard deviation of 0.14-0.16 m and a mean of 0.07 m. The Root Mean Square Errors of the GCPs are 0.08-0.13 m in planimetry and 0.10-0.16 m in heights.

Comparing the orthophotos of June 2019 and September 2019 shows a distinct expansion of the glacier lake towards the eastern part of the debris-covered glacier tongue by several meters in one summer only. The lake level shows a clear diurnal cycle of typically around 20 cm during sunny days (high irradiation) and changes in the order of half a meter over the entire summer season. Water temperatures of the lake follow a clear diurnal cycle, too with typical values between 1°C and 3°C.

We conclude that the Pasterze Glacier tongue and its adjacent proglacial area changed rapidly in terms of glacier surfaces modification and in terms of proglacial changes on an annual (September 2018 to September 2019) and sub-annual (June to September 2019) time-scale.

How to cite: Seier, G., Kellerer-Pirklbauer, A., Sulzer, W., Ziesler, C., Krisch, P., Abermann, J., and Lieb, G. K.: The rapid glacial-proglacial landscape modification at Pasterze Glacier in a one-year period as revealed by multiple aerial flight and field campaigns , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9224, https://doi.org/10.5194/egusphere-egu2020-9224, 2020.

Glacier recession into glacier bed overdeepenings commonly cause the formation of highly dynamical proglacial lakes. Such a proglacial lake at the terminus area of Pasterze Glacier, Austria’s largest glacier (approximately 16km²), sextupled during the last decade from 0.05 (2010) to 0.3km² (2019) as measured during multiannual ground-based differential global positioning surveys and terrestrial laser scanning campaigns.

Sonar measurements in September 2019 revealed a maximum lake depth of 48.2m and detected several depressions at the lake bottom. The calculated mean lake depth was quantified to be 13.4m based on 4276 individual data points (unevenly distributed over the lake) yielding a calculated water volume of 4 million m³. Five large-scale and rapid ice-breakup and ice-floating events were observed during the period September 2016 to October 2018 based on webcam images with a temporal resolution of (mostly) 5 minutes. Furthermore, three medium-sized and five smaller ice-cracking events or collapses as well as three iceberg-tiltings were observed. These events as well as the dynamics of icebergs for one specific day (16.06.2019) and for one specific iceberg (from September 2017 to its disappearance in September 2019) were quantified. For this, we either applied the Environmental Motion Tracking (EMT) software for feature tracking or we orthorectified (Erdas, Phyton) and analyzed (ArcGIS) webcam images using three comparative orthophotos from the years 2015-2018.

The icebergs at the proglacial lake of Pasterze Glacier probably formed by disintegration of glacier ice at the lake bottom or at the near-shore surface influenced by high water pressure along fractures. The breakup events demonstrate that the originally presumed pure “proglacial lake” seems to be (at least during the period of observation) to some extent a “supraglacial lake” covering glacier ice, which steadily disintegrates forming icebergs. During breakup events, such ice masses show signs of tilting, sudden disintegration and formation of icebergs, which steadily melt accompanied by further tilting events at the lake surface.

The first analytical approach using the EMT software yields meaningful results if icebergs do not modify substantially their geomorphological appearance during the event. If new objects appear at the lake or icebergs tilt, no trajectories can be calculated by EMT. The second approach yields surface extent and structure data as well as location of the icebergs at different times during for instance the ice-breakup events. With this information, the process of the ice-breakup could be divided into sub-processes partly related to each other. Detailed quantification of for instance crack evolution, tilting of debris-covered ice bodies, lake transgression or lateral ice shift were possible in high detail. Reasons for detected errors in the analyzed orthophoto imagery are changes in the lake level (order of 1m) or offset of the camera (maximum of 5 pixels).

No major ice-floating event was observed during the ablation period 2019. Furthermore, the aerial extent of icebergs in the proglacial lake decreased substantially in 2019. We therefore conclude that the process of lake-bottom ice disintegration has widely ceased and that the glacier ice at the lake bottom has mostly vanished.

How to cite: Kellerer-Pirklbauer, A., Avian, M., Bernsteiner, F., Gahleitner, H., Götz, J., Lieb, G. K., and Ziesler, C.: Quantification of ice-breakup events and iceberg dynamics in a highly dynamical proglacial lake in Austria (Pasterze Glacier), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13760, https://doi.org/10.5194/egusphere-egu2020-13760, 2020.

As the climate warms, the earths’ cryosphere melts. Among the regions with the highest sensitivity to recent climate change are the high altitudes of the European Alps. This can be seen most clearly in the melting of glacier ice. Most glaciers show a strong receding trend since the last maximum extent during the little ice age (LIA) around AD 1850. When glaciers retreat, they leave behind a characteristic paraglacial landscape in a transient state from glacial to non-glacial conditions. Dominated by large amounts of unconsolidated glacial sediments they show an extremely high geomorphic activity.

However, these proglacial areas can still hold ice even decades after the glacier has left. In a simplified manner, this can be conceptually described by two main mechanisms: i) When glaciers retreat parts of the glacier front are often decoupled from the main glacier. These so-called dead ice bodies can remain for years, especially when they are buried by a thick debris cover and thus protected from atmospheric conditions. ii) Particularly in high-elevated glacier forefields, the thermal regime can be suitable for the direct transition from a glacial to a periglacial environment, compassing the aggradation of permafrost ice in areas that have been released from the glacier.

Climate warming speeds up in recent times, related with an enhanced receding of glaciers and growing alpine proglacial areas. Ground and dead ice are among the most important drivers of geomorphic activity in these regions, though in the long-term it is most likely, that it will melt out as well. How fast this will happen and in what stage it may play a role in stabilizing these environments is not yet fully clarified. Therefore, a better knowledge on ice distribution and dynamics in alpine proglacial regions is needed. Additionally, the quantification of ice and water contents is crucial in terms of potential hazardous processes, regarding the supply of (drinking) water and hydropower.

Here we present a new (PhD-) project in close cooperation with the DFG-funded research unit SEHAG, which is at the beginning of its implementation. Focussing on ground and dead ice we aim i) to assess the current distribution, ii) to reconstruct dynamics since the LIA, iii) to reveal recent and future trends (aggradation, degradation and persistence), and iv) to quantify effects on sediment dynamics in three Central Alpine proglacial areas. We combine different geophysical techniques with a focus on electrical resistivity tomography, water isotope analysis and ground (surface) temperature measurements with high-resolution geomorphic change modelling.

How to cite: Bernsteiner, H., Götz, J., Haas, F., Heckmann, T., Sass, O., and Becht, M.: Ground and Dead Ice in Alpine Proglacial Areas – Sensitivity towards Climate Change since 1850, Recent Dynamics and Future Trends, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3310, https://doi.org/10.5194/egusphere-egu2020-3310, 2020.

Glacial and glaciofluvial sediments of the North Alpine Foreland have been subject to extensive quaternary research for more than a century. Nevertheless, a regional scale stratigraphic model has not been proposed since Penk & Brückner (1909). Since then, geological evidence were fit into local stratigraphic classifications, leading to severe inconsistencies across different countries/regions. The following study aims to solve inconsistencies by a morphostratigraphical approach, applying innovative methods utilizing new high-resolution digital elevation models, existing geodata and information from literature.

First, the abundant information from literature was reviewed to create a synopsis of commonly used terrace stratigraphic classifications. Second, geologic maps and (high-resolution) digital elevation models were compiled in a GIS database. To process this data, a new toolset was developed (using software R), fitting the requirements of morphostratigraphic analyses. These mainly involve the processing and statistic evaluation of terrace-top surfaces. Based on these analyses, we discussed fluvial, glacial and geodynamic factors, controlling the observed hypsometric parameters (concavity, slope, relative heights). To stratigraphically compare results across catchments and regions, the modern Danube and Rhine River were used as “fixed” base-levels to which tributary terrace tops were extrapolated. Terrace elevations above these base-levels were used as proxy to evaluate the rare absolute and otherwise inferred terrace ages from literature. Derived morphostratigraphic evidence provides an objective basis to discuss and harmonise the highly complex and diverging stratigraphic classification schemes across North Alpine Foreland regions.

Penck, A., & Brückner, E. (1909). Die Alpen im Eiszeitalter. Leipzig: Tauchnitz.

How to cite: Pollhammer, T., Salcher, B., Kober, F., and Deplazes, G.: GIS based morphostratigraphic evaluation of glaciofluvial terraces in the foreland of the European Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10666, https://doi.org/10.5194/egusphere-egu2020-10666, 2020.

We present findings from detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterised by striking sawtooth or hairpin planforms that are locally superimposed, giving rise to a complex spatial pattern. We recognise two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (a) submarginal deformation and squeezing of subglacial till or (b) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (a) sets of small squeeze moraines formed during melt-driven squeeze events and (b) push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed, and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin.

How to cite: Chandler, B. M. P., Chandler, S. J. P., Evans, D. J. A., Ewertowski, M. W., Lovell, H., Roberts, D. H., Schaefer, M., and Tomczyk, A. M.: Sub-annual moraine formation at an active temperate Icelandic glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13, https://doi.org/10.5194/egusphere-egu2020-13, 2020.

In the face of global climate change, and the associated melting of the modern-day ice sheets, the understanding and reconstruction of the dynamics and retreats of former ice sheets has become an increasingly valuable tool and indicator of the future behaviour of present-day ice masses. The deglacial period that followed the Last Glacial Maximum (~22-9 thousand years ago) represents the most recent major warming event, and final ice sheet decay, in Earth history, and is an important analogue for the threat of present-day ice sheet collapse. The recent availability of the 2m-resolution Swedish LiDAR based terrain model provides the opportunity to map glacial landforms and landscapes over large areas with greater accuracy than was previously possible through satellite images or aerial photographs. In combination with field observation-based ground-truthing, this LiDAR resource is employed to map the geomorphology of the Kebnekaise region of the northern Swedish mountains with the principal aim of producing a landform-driven reconstruction of the deglaciation of the remnant Scandinavian Ice Sheet during its final stage of retreat. The complex ‘palimpsest’ landscape is delineated and interpreted through the classification of landforms according to their relative age and respective origin. In particular, attention will be given to the segregation of glacial (e.g., terminal moraines, lineations), deglacial (e.g., eskers, lateral meltwater channels, glacial lake shorelines) and ‘relict’ (i.e., pre-glacial palaeosurfaces) landform assemblages, in order to demarcate those formed during the final deglaciation.   The resulting landform selections are used to delineate high-resolution ice retreat patterns, giving indication to the nature of the basal thermal regime, topographic response and final remnant location of the ice sheet. Additionally, this assay serves as an evaluation of the use of the Swedish LiDAR database as a means of efficiently and accurately mapping previously-glaciated landscapes. Our deglaciation reconstruction will finally be tested against formerly produced regional reconstructions.

How to cite: Edward, C., Blomdin, R., and Rosqvist, G.: A LiDAR-based glacial landform map of the Kebnekaise massif, northern Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21418, https://doi.org/10.5194/egusphere-egu2020-21418, 2020.

The Vastyanskiy Kon’ (VK) outcrop is the largest exposure of Quaternary sediments in the northeastern European part of the Russian Federation. The VK consists of Eemian to Weichselian marine and continental sediments that were deformed within a glaciotectonic complex of terminal moraine of the advancing Late Weichselian Kara Sea Ice Sheet. However, a few aspects of the stratigraphy and dynamic evolution of the VK glaciotectonic complex remain unresolved and ambiguous.

A particular debate concerns the structural position and age of the so-called “lower diamicton” (LD), a till-like unit, which generally occurs within the central part of the VK section. Two models on the development of the LD unit have been previously proposed. According to the first model, the LD is situated in its original stratigraphic position and reflects possible earlier Early/Middle Weichselian glaciation and is later deformed by Late Weichselian proglacial glaciotectonism. The second model suggests that the LD unit is a result of an injection of the overlying Late Weichselian lodgement till into underlying sandy units.

In our study, we performed a detailed tracing of stratigraphic units and structures utilizing classic surface mapping and 3D photogrammetric methods to access previously understudied parts of the VK. Our observations show that the architecture of the VK glaciotectonic complex represents an imbricate fan and partly support the model where the LD likely represents a till flow unit sourced from the overlying lodgement till under subglacial deformation mode. Finally, we conclude there is no evidence for postulated Early/Middle Weichselian glaciation in the study area.

How to cite: Zastrozhnov, A. and Zastrozhnov, D.: A glaciotectonic complex at the Vastyanskiy Kon’ outcrop, NE European Russia: subglacial or proglacial deformations?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10665, https://doi.org/10.5194/egusphere-egu2020-10665, 2020.

Located in the southern part of the Indian Ocean (49°S), the Kerguelen Archipelago is the largest of the sub-Antarctic islands with an area of ​​around 7,200 km². With a volcanic origin, its main island Grande Terre is partly covered by the Cook ice Cap which rises above 1000 m a.s.l. Numerous glaciers flow towards deep fjords especially from the ice cap. Their total surface area decreased by 21 % between 1963 and 2001, from 703 to 552 km² [1]. This high retreat rate was associated with an increase in air temperature and a decrease in precipitation potentially associated with a modification of the westerlies' regime. The archipelago has so far been the subject of very little geomorphological work, while thirty cosmogenic nuclide dates distributed on the archipelago allow a first insight in the deglaciation with ages between 41.9 ± 4.4 and 0.7 ± 0.37 ka [2].

Within the PALAS expedition (PAleoclimate from LAke Sediments) carried out in November and December 2019 on several lakes located between the ice cap and the Peninsula of the Société de la Géographie, we mapped the geomorphology of several valleys. Here we present the mapping results and analysis of the Guynemer basin located downstream the Guynemer Peak (1088 m a.s.l.). Located c. 10 km north of the Cook Ice Cap, its slopes mainly consist of frost-shattered debris interspersed with rocky escarpments, but the basin still contains a small glacier (<1.5 km²) at the foot of the east face of the peak. This face has several small hanging glaciers, one of which showing signs of destabilization. An upper Guynemer Lake resulting from the glacial over-deepening (0.5 km²; 245 m a.s.l.) is separated from the lower Guynemer Lake (1.5 km²; 121 m a.s.l.) by a rock step, a gorge and a wide delta incised by several channels. The mapped sector has many glacial inheritances, from the cirque which contains the upper lake to a frontal moraine that is partly damming the lower lake. Several dozens of morainic ridges have been recognized, corresponding at least to 6 or 7 main stages, from possibly early Holocene or Lateglacial to the 1960s. Surface exposure dating of moraines and erratic boulders in the coming months will supply a detailed chronology of the glacier fluctuations.

[1] Berthier et al. (2009). Journal of Geophysical Research - Earth Surface, 114: F3.

[2] Jomelli et al. (2018). Quaternary Science Reviews, 183: 110-123.

How to cite: Deline, P., Linge, H., Ravanel, L., Bakke, J., Arnaud, F., Giguet-Covex, C., and Støren, E.: Geomorphological analysis of a sub-Antarctic valley under deglaciation: the Guynemer basin, Kerguelen Archipelago (49°S), Southern Indian Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11568, https://doi.org/10.5194/egusphere-egu2020-11568, 2020.

The drivers of latitudinal variations in glacier advance/retreat in Patagonia remain a fundamental question in palaeo-glacier studies. Broader climatic influences that underpin large-scale glacial fluctuations are mediated by topographic, calving, and process-related controls. A key step in understanding the relative importance of these factors in localised glacier response is a thorough investigation of geomorphological evolution.

In southern South America, large ice-lobes associated with the eastern flanks of the former Patagonian Ice Sheet terminated in the stepparian foothills. The geomorphological records accompanying these palaeo-glaciers represent an invaluable tool for reconstructing past glacier fluctuations. In the Pico and Cisnes valleys (44-45^oS), ice-lobes underwent multiple advances, likely since the onset of the Great Patagonian Glaciation (~1.1 Myrs ago). The first account of Pico glacial geomorphology and the recognition of palaeo-lake existence was made by Caldenius (1932). Since then, only limited geomorphological investigations of the valley have been undertaken. 

Here we present a high-resolution geomorphological map of the Pico-Cisnes valleys based on mapping from satellite imagery at a 1:5000 scale, supported by ground-truthing in the field. Newly mapped ice limits, glaciolacustrine and glaciofluvial landforms are presented and include moraines, palaeo-shorelines, ice-contact fans, crag and tails, glacially-scoured bedrock, outwash plains and meltwater channels. These landforms provide new insights into landscape evolution essential in understanding the complex glacial/glaciolacustrine processes of the Cisnes and Pico valleys. Moreover, such data will underpin new geochronological frameworks, and allow fresh insights into the spatial and temporal response of these central Patagonian palaeo-glaciers to the onset of deglaciation.

How to cite: Cooper, E., Thorndycraft, V., Davies, B., Palmer, A., and García, J.: High-resolution geomorphological mapping of the Pico and Cisnes basins, Patagonia (44-45°S), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20856, https://doi.org/10.5194/egusphere-egu2020-20856, 2020.