GM7.6

Glacial outburst floods (jökulhlaups) have occurred across Earth throughout the Quaternary, often leaving a geomorphologic, sedimentological, and climatic legacy that extends far beyond the source region and can persist for millennia. Furthermore, they pose an increasing geohazard in glaciated landscapes worldwide due to climate-driven ice retreat. Iceland experiences more frequent jökulhlaups than nearly anywhere on Earth, though most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, abundant evidence also exists for non-volcanogenic floods from proglacial lakes, which may serve as a better analogue for most global jökulhlaups.

As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater lakes formed at ice margins and periodically drained in jökulhlaups. Some of the most catastrophic floods drained from ice-dammed Glacial Lake Kjölur, surging across southwestern Iceland from the interior highlands to the Atlantic Ocean. These floods left extensive geomorphologic evidence along the modern-day course of the Hvítá River, including canyon systems, scoured bedrock, boulder deposits, and Gullfoss—Iceland’s most famous waterfall. The largest events reached an estimated peak discharge on the order of 10⁵ m³ s^-1, ranking them among the largest known floods in Iceland and on Earth. Yet, all our evidence for the Kjölur jökulhlaups comes from only one publication from a quarter-century ago.

This project employs a combination of field, modelling, and laboratory methods to better constrain flood timing and dynamics at this underexplored site. This talk synthesizes geomorphologic field mapping, HEC-RAS hydraulic simulations and paleohydraulic calculations, and cosmogenic nuclide exposure dates to reconstruct Kjölur jökulhlaup routing, hydrology, and chronology. It situates these events within the context of Pleistocene-Holocene Icelandic Ice Sheet retreat and paleoenvironmental change, presenting a series of scenarios of ice margin position, glacial lake extent, and jökulhlaup drainage. Finally, it assesses the Kjölur jökulhlaups as an analogue to contemporary glacial outburst floods in other Arctic and alpine regions in terms of flood frequency, dynamics, and landscape impact.

How to cite: Wells, G., Luzzadder-Beach, S., Beach, T., Saemundsson, T., and Dugmore, A.: Geomorphology, hydrology, and chronology of Early Holocene jökulhlaups along the Hvítá River and Gullfoss waterfall, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15752, https://doi.org/10.5194/egusphere-egu21-15752, 2021.

Periglacial, paraglacial and related boulder-dominated landforms constitute a valuable, but often unexplored source of palaeoclimatic and morphodynamic information. The timing of landform formation and stabilization can be linked to past cold climatic conditions which offers the possibility to reconstruct cold climatic periods. In this study, Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated landforms (sorted stripes, blockfield, paraglacial alluvial fan, rock-slope failure) in Rondane, eastern South Norway for the first time. On the basis of an old and young control point a local calibration curve was established from which surface exposure ages of each landform were calculated. The investigation of formation, stabilization and age of the respective landforms permitted an assessment of Holocene climate variability in Rondane and its connectivity to landform evolution. The obtained SHD age estimates range from 11.15 ± 1.22 to 3.99 ± 1.52 ka which shows their general inactive and relict character. Most surface exposure ages of the sorted stripes cluster between 9.62 ± 1.36 and 9.01 ± 1.21 ka and appear to have stabilized towards the end of the ‘Erdalen Event’ or in the following warm period prior to ‘Finse Event’. The blockfield age with 8.40 ± 1.16 ka indicates landform stabilization during ‘Finse Event’, around the onset of the Holocene Thermal Maximum (~8.0–5.0 ka). The paraglacial alluvial fan with its four subsites shows age ranges from 8.51 ± 1.63 to 3.99 ± 1.52 ka. The old exposure age points to fan aggradation follow regional deglaciation due to paraglacial processes, whereas the younger ages can be explained by increasing precipitation during the onset neoglaciation at ~4.0 ka. Surface exposure age of the rock-slope failure with 7.39 ± 0.74 ka falls into a transitional climate period towards the Holocene Thermal Maximum (~8.0–5.0 ka). This indicates that climate-driven factors such as decreasing permafrost depth and/or increasing hydrological pressure negatively influence slope stability. Our obtained first surface exposure ages from boulder-dominated landforms in Rondane give important insights to better understand the palaeoclimatic variability in the Holocene.

How to cite: Marr, P., Winkler, S., Dahl, S. O., and Löffler, J.: Palaeoclimatic and morphodynamic implications of Holocene boulder-dominated periglacial and paraglacial landforms in Rondane, South Norway, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12172, https://doi.org/10.5194/egusphere-egu21-12172, 2021.

The recession of glaciers reveals a dynamic landscape exposed to high rates of hydrological and geomorphological modifications. Such deglaciation processes caused the formation of a 0.3 km² large proglacial lake (named Pasterzensee) near the terminus of Pasterze Glacier, Austria, during the last two decades. The evolution of the proglacial lake was accompanied by several buoyant calving events. The process of buoyant calving formed numerous floating dead ice bodies referred to as icebergs which covered a maximum of 7.3 % of the entire proglacial lake basin in November 2018.

Despite the existence of icebergs at some proglacial lakes in the European Alps, little is known about the evolution and life span of icebergs in proglacial lakes in the European Alps. The aim of this study was to reduce this research gap by (a) quantifying the evolution of such alpine icebergs during two different time scales and by (b) analysing the relationship between iceberg evolution and motion at the lake with meteorological conditions. At a long-term scale, one single iceberg was monitored during the period 01.09.2017-30.09.2019. At a short-term scale, all icebergs were studied during one single day (16.06.2019).

The most important data source for this study were time-lapse optical imagery from an automatic camera overlooking the entire proglacial lake (GROHAG). The used camera is a Roundshot Livecam Generation 2 (Seitz, Switzerland). Photographic imagery is captured every five minutes (during daylight) from a location 310 m above lake level and 450 m northeast of the lake margin. For the long-term analysis, a total number of 386 pictures of the lake were processed. For the short-term analysis, 97 pictures were analysed to reveal the dynamics of 84 icebergs during one single day. The oblique time-lapse images were transformed into orthorectified photos using a rectification algorithm which considers the camera properties and the lake surface geometry. Iceberg size and centroid coordinates were mapped in all generated orthophotos. In addition, meteorological data (ZAMG Vienna) was provided by a nearby automatic weather station, located at the glacier tongue of Pasterze Glacier some 1.1 km northwest of the lake margin.

Results indicate that the monitoring of one iceberg over a period of 25 months revealed highest melting rates from June to August, low melting rates from September to November and no measurable melting when the lake surface is frozen. Horizontal iceberg displacement is rising with decreasing iceberg size throughout the study period. The analysed iceberg formed during the detachment of a debris covered ice peninsula with an initial size of 7250 m² and was last identifiable at a size of 240 m². Monitoring lake-wide iceberg movement for one day shows that wind is the main influence on horizontal iceberg displacement. The existence of a strong valley wind, caused by a diurnal warming cycle, is observed. This wind system decouples the iceberg movement from the constant katabatic glacier wind, recorded by the weather station. Frequent jumps in movement rates, which are not explained by wind data, suggest that iceberg grounding is a common process influencing subaquatic lake morphology.

How to cite: Bernsteiner, F. and Kellerer-Pirklbauer, A.: Iceberg dynamics in a proglacial lake in Austria quantified by time-lapse photography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14010, https://doi.org/10.5194/egusphere-egu21-14010, 2021.

Recent permafrost degradation is detected in many cold regions of the world. This process is due to surface lowering caused by ice-rich sediments thaw and massive ice beds melt. Eastern Chukotka coastal plains polygon is one of the key sites for studying climate change's impact on permafrost conditions and human activity. This region is the habitat of indigenous people, concentrated in the coastal villages. The study site is approximately 400 km² in area and characterized by a variety of landscape, geomorphological, and permafrost conditions. Using remote sensing data, field observations, and shallow drilling results, we ranked and delineated the areas on their susceptibility to thermokarst, thermal erosion, and solifluction activation due to the further air temperature increasing and potential human disturbances. Spatial analysis on current thaw settlement rates combined with drilling data allowed us to map the areas with a high concentration of surficial massive ice beds. These studies provide a better understanding of permafrost conditions in Eastern Chukotka and its response to human impact and climate change.

How to cite: Maslakov, A., Komova, N., Egorov, E., Mikhaylyukova, P., Grishchenko, M., and Zotova, L.: Permafrost vulnerability to contemporary climate changes in Eastern Chukotka coastal plains (NE Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2196, https://doi.org/10.5194/egusphere-egu21-2196, 2021.

Ground temperatures in alpine environments are severely influenced by slope orientation (aspect), slope inclination, local topoclimatic conditions, and thermal properties of the rock material. Small differences in one of these factors may substantially impact the ground thermal regime, weathering by freeze-thaw action or the occurrence of permafrost. To improve the understanding of differences, variations, and ranges of ground temperatures at single mountain summits, we studied the ground thermal conditions at a triangle-shaped (plan view), moderately steep pyramidal peak over a two-year period (2018-2020).

We installed 18 monitoring sites with 23 sensors near the summit of Innerer Knorrkogel (2882m asl), in summer 2018 with one- and multi-channel datalogger (Geoprecision). All three mountain ridges (east-, northwest-, and southwest-facing) and flanks (northeast-, west-, and south-facing) were instrumented with one-channel dataloggers at two different elevations (2840 and 2860m asl) at each ridge/flank to monitor ground surface temperatures. Three bedrock temperature monitoring sites with shallow boreholes (40cm) equipped with three sensors per site at each of the three mountain flanks (2870m asl) were established. Additionally, two ground surface temperature monitoring sites were installed at the summit.

Results show remarkable differences in mean annual ground temperatures (MAGT) between the 23 different sensors and the two years despite the small spatial extent (0.023 km²) and elevation differences (46m). Intersite variability at the entire mountain pyramid was 3.74°C in 2018/19 (mean MAGT: -0.40°C; minimum: -1.78°C; maximum: 1.96°C;) and 3.27°C in 2019/20 (mean MAGT: 0.08°C; minimum: -1.54°C; maximum: 1,73°C;). Minimum was in both years at the northeast-facing flank, maximum at the south-facing flank. In all but three sites, the second monitoring year was warmer than the first one (mean +0.48°C) related to atmospheric differences and site-specific snow conditions. The comparison of the MAGT-values of the two years (MAGT-2018/19 minus MAGT-2019/20) revealed large thermal inhomogeneities in the mountain summit ranging from +0.65° (2018/19 warmer than 2019/20) to -1.76°C (2018/19 colder than 2019/20) at identical sensors. Temperature ranges at the three different aspects but at equal elevations were 1.7-2.2°C at ridges and 1.8-3.7°C at flanks for single years. The higher temperature range for flank-sites is related to seasonal snow cover effects combined with higher radiation at sun-exposed sites. Although the ground temperature was substantially higher in the second year, the snow cover difference between the two years was variable. Some sites experienced longer snow cover periods in the second year 2019/20 (up to +85 days) whereas at other sites the opposite was observed (up to -85 days). Other frost weathering-related indicators (diurnal freeze-thaw cycles, frost-cracking window) show also large intersite and interannual differences.

Our study shows that the thermal regime at a triangle-shaped moderately steep pyramidal peak is very heterogeneous between different aspects and landforms (ridge/flank/summit) and between two monitoring years confirming earlier monitoring and modelling results. Due to high intersite and interannual variabilities, temperature-related processes such as frost-weathering can vary largely between neighbouring sites. Our study highlights the need for systematic and long-term ground temperature monitoring in alpine terrain to improve the understanding of small- to medium-scale temperature variabilities.

How to cite: Kellerer-Pirklbauer, A. and Lieb, G. K.: Ground thermal contrasts and variability at an alpine pyramidal peak in central Austria (Innerer Knorrkogel, Venediger Mountains), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12588, https://doi.org/10.5194/egusphere-egu21-12588, 2021.

Debris-covered glaciers are fed from steep bedrock hillslopes that tower above the ice. These headwalls are eroded by rockfalls and rock avalanches, mobilizing fractured bedrock, which is subsequently deposited on the ice surface along the sides of valley glaciers and transported downglacier on and in the ice. Where glaciers join, marginal debris merges to form medial moraines. Due to the conveyor-belt-nature of glacier ablation zones, debris tends to be older downglacier and, for typical Alpine glaciers, single deposits may persist on the glacier surface for hundreds to a few thousand years.

Recent observations in high-alpine glacial environments suggest that rock walls are increasingly destabilized due to climate warming. An increase in headwall erosion and debris deposition onto glacier surfaces will modify glacial mass balances, as surface debris cover alters the rate at which underlying ice melts. Consequently, we expect that the response of debris-covered glaciers to climate change is likely also related to the response of headwalls to climate change.

In this context, we quantify headwall retreat rates by measuring the concentration of in situ-produced cosmogenic ¹⁰Be in debris samples collected from a partly debris-covered Swiss valley glacier. By systematic downglacier-sampling of two parallel medial moraines, we aim to assess changes in headwall erosion through time for small and delineated source areas. Our results indicate that indeed, nuclide concentrations along the medial moraines vary with time: downglacier and further back in time deposits have higher nuclide concentrations, whereas upglacier and more recently deposits have lower concentrations. Currently, we explore possible processes which could account for ¹⁰Be concentration changes through time, other than changes in erosion rates. These include the sensitivity of ¹⁰Be concentrations to supraglacial transport time and to temporal and spatial changes in nuclide production rates on the deglaciating headwalls. First analyses reveal, however, that neither the additional accumulation of ¹⁰Be during transport nor changes in source area production rates associated with the uncovering of formerly ice covered headwall parts alone can account for the observed trend.

How to cite: Wetterauer, K., Scherler, D., Anderson, L. S., and Wittmann, H.: Alpine headwall erosion: Insights from cosmogenic nuclide concentrations in supraglacial debris cover, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9369, https://doi.org/10.5194/egusphere-egu21-9369, 2021.

The erosion of cold bedrock hillslopes in alpine environments depends not only on rates of frost weathering and accumulated rock damage, but additionally on the removal of the weathered material from the bedrock surface. In the Mont Blanc massif, steep bedrock faces with exposure ages sometimes much older than 50,000 years sit in close proximity to actively-eroding rockwalls, suggesting a more complex relationship between temperature and erosion rates than encompassed by the proposed “frost-cracking window.” Stochastic events like rockfalls and rock avalanches, despite their rarity, contribute a non-trivial proportion of the total sediment budget in alpine permafrost regions, adding to the contribution from background “steady-state” erosion. Employing a methodology based on the combination of in-situ cosmogenic nuclides ³He -¹⁰Be-¹⁴C, we test the temperature-dependence of high-alpine erosion while taking into account erosional stochasticity.

From cosmogenic ¹⁰Be concentrations of amalgamated samples collected on the Aiguille du Midi (3842 m a.s.l.) in the Mont Blanc massif, we find an order of magnitude difference in erosion rate across the peak’s surface. Our preliminary measured erosion rates, ranging between appx. 0.03 mm yr^-1 and 1.0 mm yr^-1, correlate neither with modern temperature measurements from borehole thermistors, nor with our current estimates of bedrock cosmogenic ³He-derived paleotemperatures. The corresponding cosmogenic ¹⁴C/¹⁰Be ratios (between 1.70 and 4.0) for these erosion rates indicate that our measurements are not biased by recent stochastic rockfall events. Our current results therefore suggest that on geomorphic timescales, bedrock hillslope erosion rates are not set solely by rates of frost-cracking, but rather by the combined effects of frost-cracking and permafrost thaw-induced rockfalls. These insights are relevant both for short-term monitoring of alpine permafrost and associated geohazards under a warming climate, as well as studies of proposed “buzzsaws” operating on glacial-interglacial timescales.

How to cite: Dennis, D. P., Scherler, D., Niedermann, S., Hippe, K., Wittmann, H., Ravanel, L., Tremblay, M., Guralnik, B., and Lupker, M.: Evaluating the temperature dependence of bedrock hillslope erosion in the Mont Blanc massif using in situ cosmogenic 3He-10Be-14C, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15023, https://doi.org/10.5194/egusphere-egu21-15023, 2021.

Rock glaciers are important geomorphological structures of high mountain environments and fundamental indicators for permafrost. They consist of unconsolidated rock debris – generally derived from talus or till - held together by ice, moving slowly downslope due to the gravitation in combination with uncountable freeze-thaw-cycles in the active layer. The downslope movement of rock glaciers leads to lobate structures with depressed areas as well as ridges where the sediments tend to accumulate, creating a typical surface morphology defined as "ridges and furrows". This study focuses on the analysis of one rock glacier system located in the Pfitsch/Vizze valley (South Tyrol), in the Eastern Italian Alps.  The debris in this area comprises exclusively the granitic Central Gneiss of the Tauern window. Rock glacier sediment derives from talus, consisting essentially of more or less foliated to planar angular material, which was essentially formed by frost weathering. The size and shape of sediments present at the surface of the rock glacier system were analyzed in correlation with displacement and geomorphometry, with the hypothesis that sediments shape and size at different sites across the rock glacier might relate to its past and present dynamics. The displacement analyses were carried out to quantify rock glaciers movements during the last 20 years, and the geomorphometrical characteristics were investigated to identify specific geometrical attributes that may be linked to internal ice changes.
Clasts analysis showed how rock glacier sediments are very heterogeneous, with dimensions being mainly determined by transport distance, and sphericity and roundness by lithology. A role of sediments characteristics on displacement rate did not turn out evident. Convexities and concavities observed on the study site are apparently created respectively by the accumulation of sediments and the collapse of the structure due to the internal ice melting. Indeed, the recent, marked increase in air temperature observed in the last decades in the Alps has likely caused an accelerated ice melting in the less protected – in terms of solar radiation – rock glaciers, as is the case for our study area. Sediments here are no longer bound by ice and have become rather unstable. Therefore, the monitoring of rock glaciers is fundamental to anticipate future changes in the type and magnitude of natural hazards originating at high elevations, as thicker layers of sediments are becoming increasingly unstable.

How to cite: Minotti, F., Kofler, C., Gems, B., Mair, V., and Comiti, F.: Rock glacier sediment, kinematics and geomorphometry: a study case from the Eastern Italian Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9653, https://doi.org/10.5194/egusphere-egu21-9653, 2021.

Rock glaciers are the best visual expression of creeping mountain permafrost. Their dynamics, which largely depend on climatic forcing, provide information about the mountain permafrost and may locally pose risk to infrastructures.

The International Permafrost Association (IPA) Action Group on Rock glacier inventories and kinematics, launched in 2018, fosters the activities of a research network focused on the definition of standardized guidelines for inventorying rock glaciers, including information on rock-glacier displacement rate. The ESA Permafrost_CCI project further sustains this initiative, and proposes a standardized method to implement kinematics-based rock glacier inventories.

The proposed method exploits interferometric data from spaceborne Synthetic Aperture Radar (InSAR) to derive the kinematic information of existing or newly-compiled rock glacier inventories. In particular, areas identified as slope movements within rock glacier polygons are delineated on interferograms as “moving areas”, and are assigned a velocity class. Subsequently, a specific kinematic class is assigned to each rock glacier unit according to the velocity class and extension of the relevant moving areas.

This method is applied on two regions: the Western part of the Swiss Alps and the South-Western part of the South Tyrol (Italian Alps). Both are located at the same latitude, with rock glaciers in the Swiss part lying at slightly higher altitudes, and experiencing higher mean annual precipitation. Rock glacier polygons were drawn from existing inventories, the kinematic information was extracted exploiting InSAR data acquired between 2018 and 2019 from the Sentinel-1 constellation.

In the Swiss and Italian parts, we inventoried 660 and 783 moving areas (1443 in total). Collectively, it was possible to assign a kinematic attribute to 913 rock glaciers, providing a more objective and quantitative activity classification (compared to the qualitative active, inactive, and relict categories). In the Swiss part, 14% of the rock glaciers are moving in the magnitude order of a meter/year or faster, 43% in the magnitude order of one to several dm/yr, 36% from one to several cm/yr, the others are with unreliable movements (7%). In the Italian part, these percentages are 1% (meter/year or faster), 42% (one to several dm/yr), 39% (one to several cm/yr) and 18% (no reliable), respectively. Preliminary analyses on the Italian part are conducted on 467 additional rock glaciers recognized as geomorphologically relict: 68% are not moving or not moving fast enough to be detected, 9% have sectors moving up to several cm/yr, and the remaining 23% of relict rock glaciers have no reliable information on movement.

Preliminary results show how this approach allows to provide complementary kinematic information to the geomorphological approach, improving the knowledge on the activity status in a given time and in a given region. Since several studies have reported trends towards displacement acceleration, applying this approach over long periods will allow assessing the response of a wide selection of landforms to (warmer) climatic forcing. Furthermore, this approach is a very useful tool to help select representative rock glaciers of a region, on which to apply more accurate monitoring approaches.

How to cite: Bertone, A., Barboux, C., Brardinoni, F., Delaloye, R., Mair, V., Pellegrinon, G., Monier, T., and Strozzi, T.: A complementary kinematic approach to inventory rock glaciers applied to case studies of the Swiss and Italian Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14661, https://doi.org/10.5194/egusphere-egu21-14661, 2021.

The genesis of rock glaciers differs fundamentally from ‘normal’ glaciers and results in much older landforms that are often reaching ages of several millennia. Recent datings of rock glacier material from boreholes indicate early Holocene ages for rock glaciers and allow the derivation of age-depth profiles at the borehole location. We use here a 2-dimensional numerical modelling approach that calculates age-layers (isochrones) within the rock glacier body and that considers the accretion, melt and flow-advection of rock glacier material. We apply this model to the case of Lazaun rock glacier (Southern Ötztal Alps) for which a well dated profile from a borehole exists, with ages at the bottom older than 9000 years (Krainer et al. 2015). With our modelling we are able to reproduce the observed age-depth profiles well and are able to infer a long-term accumulation rate that is around 1 cm/yr which is an order of magnitude higher than a previous estimate that does not account for deformation. The modelling is consistent with the classic rock glacier genesis of material accretion in the upstream talus slope and confirms the dominance of deformation in the shear-zone at the bottom layer of the rock glacier.
We conclude that combining age-layer modelling with dated depth-profiles of rock glaciers allows for important new insights into our understanding of rock glacier evolution and dynamics.

REFERENCES  
Krainer, K., Bressan, D., Dietre, B., Haas, J., Hajdas, I., Lang, K. & Tonidandel, D. (2015). A 10,300-year-old permafrost core from the active rock glacier Lazaun, southern Oetztal Alps (South Tyrol, Northern Italy). Quaternary Research, 83 , 324-335. 

How to cite: Leysinger Vieli, G. J.-M. C., Vieli, A., and Cicoira, A.: Inferring rock glacier genesis and dynamics from age-layer modelling and borehole age-profile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11682, https://doi.org/10.5194/egusphere-egu21-11682, 2021.