The present-day landscape of Southern Canadian Rocky Mountains is a product of the interaction among tectonics, lithologic resistance, and surface processes including erosion by rivers and glaciers. Rivers have adjusted to the orogeny-associated structures, regional tectonic uplift and growing terrain slope, and post-orogenic, extensive glaciation by modifying their channel profile and planform geometry. Understanding the relationship between fluvial and glacial erosion is crucial, as not only does it reflect the landscape’s sensitivity to the climate change, but also because it can indicate whether glacier-driven stream piracy (and basin reorganization) can cause significant downstream discharge alterations. The mechanisms of glacial headwall erosion, drainage divide migration, and resulting stream capture, still form a considerable research gap in landscape evolution studies. The Canadian Rockies provide an excellent opportunity for understanding the progression of subglacial channel network geometry and related basin reorganization. This study aims to evaluate glacial headwall erosion processes in glaciated headwaters through progressive divide lowering, lateral migration, and stream capture. We remotely analyze topographic features, corroborating them in the field. We completed the morphometric investigation using the MATLAB based TopoToolbox, Topographic Analysis Kit, and a customized DivideMigration function. We observe two unique signatures of glacial divide migration in the Canadian Rockies: (1) breached drainage divides that suggest lateral erosion by glaciated headwaters directed along weak lithologies and (2) the presence of low relief, high elevation divides without headwall preservation, possibly indicating periods of paleo-drainage capture during glaciation. Our preliminary results have implications for the role of glacial erosion in reshaping the landscape with respect to the structure, lithology, and climate.  

How to cite: Yadav, H. and Schoenbohm, L.: Controls on glacial divide migration in Southern Canadian Rocky Mountain fold and thrust belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-367, https://doi.org/10.5194/egusphere-egu24-367, 2024.

The topography and bathymetry of Scandinavia have been molded by ice across numerous glacial cycles during the Quaternary. In this study, we explore the interplay between this changing morphology and the Scandinavian Ice Sheet (SIS). Using a higher-order ice-sheet model, we simulate the SIS over a glacial cycle on three different topographies, representing different stages of Quaternary glacial landscape evolution. By subjecting these simulations to identical climate conditions, we isolate the effects of landscape morphology on the evolution and dynamics of the ice sheet. Our findings indicate that early Quaternary glaciations in Scandinavia were restricted in both extent and volume by the pre-glacial bathymetry. It was only as glacial deposits filled a depression in the North Sea and expanded the Norwegian shelf that the ice sheet could expand further. This is illustrated by our middle to late Quaternary simulation (around 0.5 million years ago), where a filled bathymetry facilitated both a faster and further southward expansion, resulting in a relative increase in both ice-sheet volume and extent. Additionally, our study highlights that the formation of The Norwegian Channel acted as a barrier to southward ice-sheet expansion. This limitation only allowed the ice sheet to advance into the southern North Sea close to glacial maxima. Notably, our experiments suggest that distinct segments of The Norwegian Channel may have formed in different stages during glacial periods after the bathymetry was sufficiently filled with glacial sediments. These results underscore the importance of considering changes in landscape morphology over time when interpreting ice-sheet history based on ice-volume proxies and when interpreting climate variability from past ice-sheet extents.

How to cite: Jungdal-Olesen, G., Andersen, J. L., Born, A., and Pedersen, V. K.: How glacial landscape evolution has impacted Scandinavian Ice Sheet dynamics and dimensions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7461, https://doi.org/10.5194/egusphere-egu24-7461, 2024.

In steep alpine environments, the succession of glacial-interglacial cycles during the Quaternary led to multiple transient geomorphological phases. These periods are induced by an imbalance between the inherited shape of the topography and the dominant geomorphological processes. In particular, post-glacial periods are key transition phases experiencing rapid geomorphic changes, characterized by intense hillslope processes where ice and permafrost have shrunk. As landslides are the main factors controlling sediment production in steep mountain environments, we approach numerically their late-glacial to interglacial dynamics and explore the associated evolution of catchment topography across a wide range of morphological signatures (i.e. from fluvial to glacial initial topographies). Using the landscape evolution model ‘Hyland’, we quantitatively assess the response of each type of catchment to landsliding. We focus on the cumulative impact of landslides, during the post-glacial phase, on catchment slope distribution, hypsometry and produced sediment volume.  Moreover, glacial topographic inheritance seems strongly sensitive to hillslope processes with a non-homogeneous spreading of landslides over the catchments, both spatially and temporarily. Our results reveal a temporal change in slope-elevation distribution associated to a general lowering in maximum catchment elevations. On the contrary, fluvial catchments show more stable topography and less intense landslide activity. Landscape evolution models appear as a suitable tool to quantitatively explore (1) the role of different internal or external parameters (e.g., bedrock cohesion, return time of landslides), and (2) the non-linear interactions between landsliding and catchment topographic evolution, which are strongly influenced by external forcing such as climatic fluctuations in mountainous settings.

How to cite: Ariagno, C., Steer, P., and Valla, P.: Investigating post-glacial transient phases as hot-moments of landscape dynamics - combining numerical modelling and topographic analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7434, https://doi.org/10.5194/egusphere-egu24-7434, 2024.

Rockwall erosion due to rockfalls is one of the most efficient erosion processes at high elevations. It is, therefore, important to quantify this erosion to understand the long-term evolution of mountain topography. This is especially crucial since rockfall frequency is increasing in high-Alpine areas, such as in the Mont-Blanc massif (MBM), due to regional scale permafrost degradation (which occurs through thickening of the active layer, the subsurface layer freezing and thawing throughout the year), a consequence of climate warming and the multiplication of heat waves.

To better understand rockfalls as a permafrost-related process, we quantify the erosion rates at different time scales by i) a short-term (  ̴ ten-year scale) quantification of the dynamics of the rock walls based on the diachronic comparison of topographic measurements carried out by terrestrial laser scanning (LiDAR) and ii) a long-term quantification (10²-10⁴ year scale) based on the ¹⁰Be concentration of sediment sampled downglacier on medial moraines. Our analysis considered that once the rockfalls have occurred, clasts are transported within the ice stream and amalgamated by ice melt in the ablation zone, forming medial moraines. The ¹⁰Be concentration is linked to the rockwall erosion rate and the time needed to transport from the glacier equilibrium line to the sampling location.

Scanned rockwalls and rockwall sources vary in elevation, aspect, slope, and area, allowing us to assess whether these factors influence the measured ¹⁰Be concentration and erosion rates. We studied rockwalls located on the French side between 2800 m and 4200 m a.s.l. and between 2500 m and 4600 m a.s.l. on the Italian side. We collected 8 (Géant basin and Vallée Blanche, France) and 10 supraglacial samples (Brouillard and Frêney glaciers, Italy), respectively.  

Our results reveal substantial variations in ¹⁰Be concentrations. On the French side of the MBM, ¹⁰Be concentrations vary from 1.2 ± 0.2 to 6.7 ± 0.4 x 10⁴ atoms g^-1, while they range from 3.0 ± 0.2 to 92.0 ± 3.2 x 10⁴ atoms g^-1 on the Italian side. These results suggest that the long-term erosion rates vary between 0.8-1.7 and 0.1-0.3 mm.yr^-1, respectively. The short-term erosion rates for the French side are 4.3 mm.yr^-1 for 2005-2014 and 39.3 for the period of 2015-2022. On the Italian side, they are 0.8 mm.yr^-1 for 2005-2011 and 6.1 for 2011-2017.

Our results show spatial differences in erosion rates on both sides of the MBM. Short-term erosion rate is lower on the Italian side, and ¹⁰Be concentrations are higher, meaning that the rock walls are more stable in this area. However, on both sides of the MBM, erosion rates have increased significantly recently, with a further acceleration during the last decade. This suggests that high-altitude rockwalls, previously unaffected by global warming, are progressively entering a state of permafrost degradation.

How to cite: Courtial-Manent, L., Mugnier, J.-L., Ravanel, L., Carcaillet, J., Vassallo, R., Lhosmot, A., and Schwing, A.: Increased erosion rates on high-Alpine rockwalls evidenced by comparison of short-term (terrestrial LiDAR) and long-term (cosmogenic nuclides) approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17419, https://doi.org/10.5194/egusphere-egu24-17419, 2024.

Rock glaciers, major cryospheric features in alpine landscapes, pose formidable challenges in extracting climatic information over recent to Holocene timescales. This presentation delves into an integrative multi-method approach, striving to replicate modern motion through feature tracking, exposure ages from 10Be concentrations, and observations of rock glacier morphology. Applying a novel numerical model for rock-glacier dynamics, our study focuses on the Holocene to modern activity of a prominent rock glacier flowing northeast from a 300-m tall headwall on the Mt. Sopris (West Elk Mountains, Colorado USA).

The Mt. Sopris rock glacier spans 2 km from its headwall avalanche source cone to a 25 m tall terminus, adorned with metric size granitic blocks exhibiting systematic variations in lichen cover and weathering. Fine-grained material fills voids between blocks in the lowermost reaches, supporting tree clusters. The ¹⁰Be-based exposure ages of block surfaces range from 1.5 to 12 kyr, with ages older than 6 kyr being compressed into the bottom quarter of the rock glacier. Modern rock-glacier surface velocities, ranging from 0.6 to 2 m/yr, can be explained by the internal deformation of a 25-m thick ice core beneath the rocky surface. However, interpreting the ¹⁰Be exposure age profile proves challenging, leading to the development of a new numerical model for rock-glacier dynamics.

Our model simplifies the mass balance to an avalanche cone accumulation zone, and the rock cover is assumed to damp melting of underlying ice over the remaining areas of the rock glacier. Climate forcing is achieved through a proposed history of the snow avalanche activity. The rock glacier velocity is calculated assuming Glen’s flow law in the interior ice and acknowledges the role of debris cover in augmenting the stress profile throughout. Preliminary modeling suggests that an avalanche cone history with two independent pulses, one in the early Holocene and the other simulating the Neoglacial, captures dominant features of the ¹⁰Be exposure age structure. The first manifestation of the rock glacier extends to approximately 1.5 km in lengths, then extends, thins, and slows over the mid-Holocene lull in input, before being overtaken and re-accelerated by the Neoglacial pulse.

This study contributes new insights into rock glacier dynamics, bridging multiple timescales and quantitatively assessing physical processes in action. Rock glaciers, key players in alpine landscape evolution, exhibit a response to climate that differs from typical glacier systems in that they never retreat, and can survive long periods of low snow input. Our numerical simulations allow investigation of dynamic responses to variations in both climate and headwall backwearing erosion. Success of our approach on the Mt. Sopris rock-glacier system suggests its utility in developing a deeper understanding of how different high mountain landscapes respond to climatic fluctuations over Holocene timescales.

How to cite: Lehmann, B., Anderson, R. S., Cusicanqui, D., and Valla, P. G.: Advancing understanding of Holocene rock glacier dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5833, https://doi.org/10.5194/egusphere-egu24-5833, 2024.

Rock glaciers serve as crucial indicators of climate change impacts, offering valuable insights into environmental consequences. Assessing the activity rate of these landforms is essential for understanding their vitality, yet recent activity remains largely undocumented, particularly across extensive regions. In this study, we present an innovative methodology for categorizing rock glacier activity, leveraging state-of-the-art remote sensing technologies and adhering to the latest guidelines established by the IPA Action Group on rock glaciers.

In this work, we use SqueeSAR^© processed Sentinel-1 data over two years (2020-2022) and digital image correlation (DIC) of repeated airborne imagery and digital elevation models using SAGA IMCORR tool to classify rock glaciers in Austria. DIC techniques were used in several local test sites to calibrate a model of SqueeSAR classification for rock glacier activity based on a threshold approach. The approach was verified using existing local rock glacier kinematic data from across the country.

Our results show that around 10% of the almost 5800 rock glaciers in Austria can be considered active, showing motion rates above a 10 cm/yr threshold within more than 40% of their total area.  Another 350 rock glaciers (6%) have been categorised a transient status characterised by low movement rates at limited parts of the landforms. Furthermore, we identified about 1100 rock glaciers relict that have been classified intact in the original inventory. This increases the number of relict rock glaciers in Austria from 60% to 77%.  Active rock glaciers are located mainly in the Ötztal, Zillertal and Hohe Tauern ranges.

This new categorisation enables to identify rock glaciers in motion that may react sensitive to increasing ground temperatures and may contribute to a local hazard potential.

How to cite: Otto, J.-C., Schroeckh, T. R., and Keuschnig, M.: Assessing rock glacier activity in the Austrian Alps using radar interferometry and image correlation techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13150, https://doi.org/10.5194/egusphere-egu24-13150, 2024.

Rock glaciers are important to monitor due to their importance (i) as indicators of permafrost distribution, (ii) as integral components of the mountain hydrological systems, (iii) as indicators of permafrost temperature and pore-water pressure reflected in their kinematic behaviour under climate change and (iv) as potential triggers for geohazards such as rockfalls, debris flows, and lake outbursts related to their destabilization. Understanding these aspects requires accurate, systematic and updated rock glacier inventories. Currently, these remain patchy over extensive areas of High Mountain Asia. In a recent study, we presented a deep-learning-based approach for mapping rock glaciers across the Tibetan Plateau based on Deeplabv3+ deep learning network, trained using visually consistent and cloud-free Planet Basemaps and multi-source rock glacier inventories from multiple regions. This resulted in 44,273 rock glaciers covering a total area of ~6,038 km², including both intact and relict types. In this work, we used the well-trained model to extend the mapping of rock glaciers over the entire Hindu-Kush Himalaya (HKH) range, resulting in an additional 46,425 rock glaciers candidates covering an area of ~5,700 km². The raw number of rock glaciers mapped is significantly higher than previous estimates based on upscaled samples. We first screened the deep learning output based on AW3D30 elevation data to remove outliers and then validated the remaining candidates over several key regions in HKH (Manaslu, Khumbu and Ladakh regions) using independent satellite data from Pléiades, SPOT etc.

The now complete inventory over the Tibetan Plateau-KHK constitutes a significant contribution to the IPA RGIK action group and serves as a benchmark dataset for modeling and monitoring the state of permafrost in a changing climate. Furthermore, this provides an important dataset for training deep learning models for global application.

How to cite: Racoviteanu, A., Sun, Z., Hu, Y., Liu, L., and Harrison, S.: Rock glacier inventorying and validation across the Hindu Kush Himalaya from deep learning and high-resolution images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16141, https://doi.org/10.5194/egusphere-egu24-16141, 2024.

Rock glaciers are periglacial landforms often observed above the timberline in alpine mountains. Their activity states can indicate the existence of permafrost. To help further explore the development and motion mechanisms of rock glaciers in semi-arid and humid transition regions, we used a manual visual interpretation of Google Earth Pro remote sensing imagery and a 7-year (2017-2023) InSAR time series analysis to provide a detailed rock glacier inventory of the Goikarla Rigyu area of the Tibetan Plateau (TP). Approximately 5057 rock glaciers were identified, covering a total area of ∼ 404.69 km2. Rock glaciers are unevenly distributed in the study area from west to east, with 80 % of them concentrated in the central region, where climatic and topographic conditions are most favorable. Under the same ground temperature conditions, increases in precipitation are conducive to rock glaciers forming at lower altitudes. Indeed, the lower limit of rock glaciers’ mean altitude decreased eastward with increasing precipitation. The LOS deformation velocities results showed that 71.3% (n=3608) of the rock glaciers were in the transitional state, including 58.4% (n=2954) of the rock glaciers with deformation rates in the range of 10-30 mm/year and 12.9% (n=654) of the rock glaciers with deformation rates in the range of 30-100 mm/year. And 28.7% (n=1449) of the rock glaciers were in the relict state. Analysis of mean annual air temperature and annual precipitation data for the period 2000-2022 in the region where the rock glaciers are located shows that the faster-moving rock glaciers are distributed in locations where the mean annual air temperature is warming significantly faster and the rate of decrease in annual precipitation is relatively low. By comparing the results of rock glacier activity discrimination based on different indicators, it is found that the method based on kinematic data is more applicable to the discrimination of transitional state rock glaciers in the region, especially for those rock glaciers whose surfaces have been covered by vegetation but are still in motion. This study contributes to the understanding of the complex response of rock glaciers to environmental and climate change in semi-arid and semi-humid climatic zones.

How to cite: Li, M., Liu, G., Hu, X., and Mohammad Javad Mirzadeh, S.: Inventory and kinematics of rock glaciers in Goikarla Rigyu, Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17330, https://doi.org/10.5194/egusphere-egu24-17330, 2024.

The present climate change is affecting geomorphic processes and landforms related to mountain permafrost in alpine areas. Impressive expressions of permafrost degradation include significant ground surface warming of rock glaciers, a general acceleration of rock-glacier surface-flow velocity, and rapid gravitational mass movements in steep terrains. In this context, the interest in mountain permafrost conditions in the Eastern Italian Alps is growing, in view of the possible consequences in terms of natural hazard assessment and mitigation, and of management of water resources. Therefore, there is a great need to assess the current and future changes of geomorphological processes and landform evolution related to degrading permafrost in this region.

Here, we present the study approach and preliminary results of the ongoing project RETURN, which is an Extended Partnership funded by the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005). Our research group is working on the current and projected impacts of climate change on the alpine cryosphere of the Eastern Italian Alps. The activities of this project, which is focussing on the area of the Province of Trento, are aimed at: i) understanding the current local and regional permafrost state and distribution, ii) modelling the distribution and state of permafrost in future warming scenarios, and iii) determining whether the ongoing permafrost degradation is causing an increase of slope instability in terms of frequency and magnitude. These aims are accomplished by using a multidisciplinary approach that comprises a) photogrammetric analyses aimed at reconstructing interannual variations and possible acceleration of rock glacier kinematics, b) geophysics aimed at estimating the volume of permafrost in active and pseudo-relict rock glaciers, c) ground-surface temperature monitoring aimed at modelling the  conditions of permafrost at local and regional scale, and d) geomorphological analyses of areas affected by landslides induced by permafrost degradation.

The results of the RETURN project are expected to contribute to a better understanding of ongoing processes and similar issues in other mountain areas affected by warming and degrading permafrost.

How to cite: Morino, C., Carturan, L., Pavoni, M., Boaga, J., Seppi, R., and Zumiani, M.: The current and future state of mountain permafrost in the Eastern Italian Alps: the RETURN project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7706, https://doi.org/10.5194/egusphere-egu24-7706, 2024.

How to cite: Duvanel, T., Lambiel, C., and Delaloye, R.: Towards a comprehensive rock glacier inventory in the Swiss Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15821, https://doi.org/10.5194/egusphere-egu24-15821, 2024.

Over the recent years, there has been focused international efforts to coordinate the development and compilation of rock glacier inventories. Nevertheless, in some contexts, identifying and characterizing rock glaciers can be challenging as complex conditions and interactions, such as glacier-rock glacier interactions, can yield landforms or landform assemblages that are beyond a straightforward interpretation and classification.

To gain a better understanding of the spatial and temporal complexity of the ongoing processes where glacier-permafrost interactions have occurred, the characterization of the subsurface is quantitively assessed using a petrophysical joint inversion (PJI) scheme (Mollaret et al., 2020), based on electrical resistivity (ERT) and refraction seismic (RST) data. Surface dynamics are assessed using both in-situ and close-range remote sensing techniques. These techniques include stationary GNSS stations to monitor daily and seasonal displacements, and biannual GNSS and UAV surveys to monitor landform-wide surface changes at high spatial resolution.

Both the geophysical data and geodetic data allowed to delineate two zones of the rock glacier: the intact permafrost zone and the complex contact zone where both permafrost and embedded surface ice are present. In the complex contact zone, resistivity values ranging up to MΩm are discernible, indicating very high ice contents (estimated up to 85%). However, in the uppermost zone, the liquid water-to-ice content ratio is greater, which probably indicates an ongoing thermal degradation (melt) of the embedded surface ice. This ongoing thermal degradation is reflected by important ice-melt induced subsidence, which ranges between -0.5 m to -0.7 m over the summer season (03.07.2023 – 07.10.2023). Yet, in winter when ground surface temperatures are below 0°C, the ice melt stops. In the intact permafrost zone of the Gruben rock glacier, the uppermost part of the section shows a distinct 5 m thick layer with low resistivity values and low velocity, which corresponds to the active layer. Right below this layer, a 30 m thick layer with high kΩm resistivity values dominates the lower section of the profile, suggesting widespread ice-saturated sediments. Surface displacement rates in this zone are typical of permafrost creep behaviour, with a gradual acceleration in late spring and a gradual deceleration in winter. Moreover, the coherent nature of the intact zone surface deformation contrasts with the back-creeping and slightly chaotic surface deformation of the complex contact zone.

Favouring a multi-method approach allowed a detailed representation of the spatial distribution of ground ice content and origin, which enabled to discriminate glacial from periglacial processes as their spatio-temporal patterns of surface change and geophysical signatures are (mostly) different.  

References

Mollaret, C., Wagner, F., Hilbich, C., Scapozza, C. and Hauck, C. 2020. Petrophysical Joint Inversion Applied to Alpine Permafrost Field Sites to Image Subsurface Ice, Water, Air, and Rock Contents, Frontiers in Earth Sciences, 8(85): 1-23. doi: 10.3389/feart.2020.00085

How to cite: Wee, J., Vivero, S., Mollaret, C., Hauck, C., Lambiel, C., and Beutel, J.: Characterizing ground ice content and origin to better understand the seasonal surface dynamics of the Gruben rock glacier (western Swiss Alps), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19785, https://doi.org/10.5194/egusphere-egu24-19785, 2024.

In the current context of climate change, intact rock glaciers represent potentially important water resources in high mountain regions, regarding the storage of both liquid and solid water. In particular, water stored in ground ice could become a valuable resource in the long term, due to slower ice melt rates occurring in rock glaciers than in surface glaciers. However, the amounts of ground ice are difficult to detect, and the related processes (i.e melting and refreezing) are complicated to monitor and therefore poorly understood. In this regard, geochemistry of water emerging from rock glaciers can help gaining more insight. In this study, morphodynamic analyses of three active rock glaciers located in the Swiss Alps were therefore combined with the physico-chemical monitoring of water emerging from these periglacial landforms. The three studied rock glaciers (Monte Prosa A, Ganoni di Schenadüi and Piancabella) are located in the Lepontine Alps (Canton of Ticino) and their ground surface temperatures and kinematics are monitored since 2009. Two of them (Monte Prosa A and Piancabella) belong to the Swiss Permafrost Monitoring Network PERMOS.

Changes in morphodynamics of the rock glaciers were investigated through repeated Unmanned Aerial Vehicle (UAV) and differential Global Navigation Satellite System (dGNSS) surveys during the warm season (i.e in early summer, late summer and early autumn). Intra-seasonal comparison between dense point clouds obtained through Structure from Motion (SfM) photogrammetry shows significant seasonal changes in elevation, especially a negative volumetric change in the rooting zone of two rock glaciers (Monte Prosa A and Ganoni di Schenadüi), with thickness losses ranging from about 0.15 to 0.55 m. Rooting zone also shows the largest seasonal horizontal displacements (up to 0.3 m) for these rock glaciers, obtained through image correlation. Furthermore, isotopic analysis (δ¹⁸O) were performed on water samples arising from rock glacier springs, precipitation, snowpack and seasonal ground ice, the latter sampled between blocks within the active layer. A seasonal increase in δ¹⁸O was observed in rock glacier springs, indicating a change in the water origin, from a supply fed mainly by snowmelt to a supply fed by a mixture of more ¹⁸O-enriched water. In addition, ion content of water samples collected from rock glacier springs and seasonal ground ice was also measured. Rock glacier springs show a seasonal increase in the solute export (e.g. SO₄^2-, Ca²⁺ and Na⁺), while high concentrations of Na⁺, K⁺ and Cl^- were found in seasonal ground ice samples. These first results show a clear seasonal pattern and indicate a probable influence of ground ice melting on both morphodynamics and chemistry of water emerging from the studied active rock glaciers.

How to cite: Del Siro, C., Crivelli, G., Gärtner-Roer, I., Lambiel, C., Delaloye, R., and Scapozza, C.: Morphodynamics of three active rock glaciers and its influence on spring hydrochemistry in the Swiss Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6056, https://doi.org/10.5194/egusphere-egu24-6056, 2024.

The aim of this study was to quantify the seasonal to daily freeze-thaw cycles of a rock glacier (RG) located in the Val d'Ursé catchment (Bernina Range, Switzerland) and their role in controlling the dynamic of the connected groundwater system. We combined digital image correlation techniques (Bickel et al., 2018) and time series analysis of discharge rates and physicochemical properties of springs and streams influenced by the RG, as well as changes in hydraulic head in nearby deep boreholes. The results indicate an acceleration of creep since 1990 due to rising temperatures, with the most active regions exhibiting horizontal velocities of ~1 m/yr. Distinct geochemical signatures of springs affected by RG discharge reflect different mixing rates with groundwater. Observed variations in discharge and dilution/enrichment cycles (based on the electrical conductivity signal) reveal an afternoon onset linked to the diurnal freeze/thaw cycle of the RG ice. This daily signal is superimposed on a seasonal trend that combines the effect of the changes in temperature and recharge/discharge dynamics of the deep groundwater system. Based on the results of a FFT-based analysis performed on the electrical conductivities and temperature signals of springs, we discuss the evolution of flow and transport mechanisms involved at the seasonal timescale. Specifically, the analysis of the phase lag between the signal of electrical conductivity with respect to the air temperature reveal key information on transport properties and timescales. Further investigations using a cryo-hydrogeological model (HEATFLOW-SMOKER code, Molson and Frind, 2019) allowed us to investigate the coupled processes governing groundwater-meltwater mixing on daily to seasonal time scales, supporting the interpretations of our field observations.

How to cite: Halloran, L., Louis, C., Molson, J., and Roques, C.: Seasonal and daily freeze-thaw dynamics of a rock glacier and their impacts on mixing and solute transport: a case study from the Val d’Ursé, Bernina Range, Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20330, https://doi.org/10.5194/egusphere-egu24-20330, 2024.

A burgeoning theme of research has focused on overflow and outburst flood events in reorganizing drainage basins, creating new fluvial landscapes and transverse drainages. Generalized conceptual ideas may not fully grasp the complexity of real proglacial and deglacial landscapes, making these landscapes important to examine. The St. Croix River valley (SCRV), MN/WI, USA, and its drainage basin contain well understood glacial geology, and the complex evolution of SCRV is largely the result of dyssynchronous advance and retreat of the Superior Lobe and Grantsburg Sublobe through the SCRV basin. Several proglacial lakes formed in and surrounding the SCRV, including Glacial Lake Duluth (GLD) in the Superior basin and Glacial Lake Grantsburg (GLG) at the margin of the Grantsburg Sublobe. Prior research identified multiple high-magnitude meltwater flood spillways that drain into the SCRV that formed between ~22–10.6 ka. However, these floods are not well constrained in terms of process, magnitude, and timing. Thus, the landscape evolution of the SCRV fluvial system remains poorly understood.
We focus on a specific reach of SCRV through which all high-magnitude meltwater discharge was routed. This reach contains numerous terraces, abandoned paleovalleys, a transverse reach and bedrock canyon, and an anomalously high and extensive terrace-like surface called the Osceola Bench (OB). We compile pre-existing data and add ground penetrating radar (GPR) data, describe sediments extracted with hand augers and a Geoprobe, date sediments with optically stimulated luminescence (OSL), and interpret sediment geochemistry using X-ray fluorescence (XRF). In addition, we map landforms using LiDAR DEMs and aerial imagery. We identify alluvial terraces and paleovalleys that step down from the OB towards the modern river. GPR results from OB and adjacent terraces reveal a horizontally continuous and shallow (<2.5 m) reflection. We interpret this to be a strath beneath alluvial sediments. Hyperbolic and inclined reflections within the alluvial sediments capping these landforms are interpreted as large clasts embedded within cross-bedded sands and gravels – supported by augering/coring that encountered large boulders within deposits of sand and gravel. These landforms were capped by a silt to sandy loam that commonly fines upward. We interpret these sediments as being deposited during waning stages of high-magnitude flows.
We hypothesize OB was formed by catastrophic outflows from GLG (sometime between 16.3-13.6 ka), released as the Grantsburg Sublobe retreated westward. Sculpted bars on OB indicate a northeastern source and likely outlet of GLG. Strath terraces and incised paleovalleys inset into the western margin of OB step down towards the river, providing evidence for a progressive westward shift in meltwater flow and valley incision that mirrored retreat of the Grantsburg Sublobe. Incision does not appear to have reached the modern river level, suggesting later flows from GLD punctuated GLG incision. GLD flows are likely the primary cause of bedrock incision across the transverse reach at St. Croix Dells (between 13.6-10.6 ka). This superimposed sequence of top-down drainage events demonstrates the complexity of drainage-basin evolution in deglacial settings and emphasizes the need for field-based investigations to develop more comprehensive models of drainage basin evolution and integration.

How to cite: Delikowski, H., Uchytil, G., Rowen, J., Fischer, A., Larson, P., Johnson, M., Faulkner, D., Running, G., Rittenour, T., Wickert, A., Brown, A., Hilgendorf, Z., and Schirmer, R.: Assessing the Role of Outburst Floods in the Formation of the Lower St. Croix River Valley, MN/WI, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4107, https://doi.org/10.5194/egusphere-egu24-4107, 2024.

Preliminary observations of three trains of dune-like landforms, just south of the shore of Lake Superior, near Christmas, MI, USA, reveal the presence of large and imbricated boulder clasts on their surface and 20–33 m deep bedrock canyons in close proximity. These characteristics suggest an ambiguous episode of high-magnitude discharge across this landscape before the modern physical geography of the Lake Superior basin was established. Understanding the formation of these landforms is important in reconstructing regional deglacial chronology, meltwater routing history, and proglacial lake-level fluctuations within the Lake Superior basin. In addition, because these landforms are similar to other landscapes where catastrophic drainage occurred, like the Camas Prairie (Missoula Floods, Montana, USA), such comparisons further our understanding of the processes that occur during these high-magnitude events. Unfortunately, little data exists from this site that can elucidate the depositional chronology and genesis of these landforms, herein named the Christmas Dunes (CD). 

We collected 20 ground penetrating radar (GPR) lines and measured 814 boulders (dimensions, strike and dip). Additionally, we collected 7 cosmogenic nuclide (CN) samples for 10Be exposure ages, 6 from imbricated sandstone boulders and 1 from a granitic boulder. Morphologic analysis was conducted using newly available LiDAR DEMs. The GPR data from a landform most proximal to a spillway contained inclined reflections that dip up-flow. It is possible dipping reflections are imbricated boulders buried within the dune because the ~23° reflection angle is similar to imbrication angles of surface boulders (21° - 59°), but no down-flow reflection indicating a potential buried boulder could be positively identified. Thus, we hypothesize these are antidune-like forms. The presence of antidunes suggests that the flows stopped abruptly because antidunes are commonly obliterated once a flow transitions from supercritical to subcritical. We hypothesize rapid lake draw-down caused abrupt spillway abandonment allowing the antidune forms to be preserved. 

Dune-like landforms further from the spillways contain inclined GPR reflections interpreted as down-flow dipping sedimentary structures and suggest a transition in flow regime beyond the most spillway-proximal landforms. Boulder B-axis diameters (0.2 - 10.7 m) decrease with distance from the spillways, supporting the interpretation of a flow and transport-regime shift. Preliminary estimates of paleodischarge suggest flows may have been 0.22 Sv (0.106 – 0.33 Sv; Breckenridge and Fisher, 2021). Given similarities between CD and sites like Camas Prairie, we hypothesize that CD formed during rapid proglacial lake draw-down across the sandstone bedrock ridge into which the spillways are incised. CD also represents a well-preserved location indicative of internal basin evolution dynamics during the rapid draining of a proglacial lake basin – inadequately understood in overflow and outburst flood literature. This event likely occurred when the easternmost outlet of the Lake Superior basin opened, abruptly rerouting southward-flowing meltwater from the Au-Train/Whitefish spillway across the CD site prior to 10.5 ka.

How to cite: Fischer, A., Susnik, C., Stafford, N., Delikowski, H., Rowen, J., Breckenridge, A., Larson, P., Seong, Y. B., Faulkner, D., Ullman, D., Wickert, A., Barefoot, E., and Brown, A.: A Sedimentologic, Morphometric, and Geochronologic Investigation of Ambiguous Dune-like Landforms: An Indicator of Proglacial Lake Drainage in the Lake Superior Basin, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4108, https://doi.org/10.5194/egusphere-egu24-4108, 2024.