Permafrost creep is manifested by the presence of rock glaciers in mountainous areas, which are climatically driven landforms. Under degrading permafrost conditions, these ice-rich bodies tend to slow down until deactivation through a transition phase. However, the ongoing processes and their associated geomorphic responses remain are still poorly understood. This study aims to better understand the relationship between their activity, topo-climate conditions, and associated geomorphic responses of transitional rock glaciers. The activity of 520 landforms in the French Alps was assessed through Differential Interferometry Single Aperture Radar (DInSAR). Kinematic attributes were then correlated with topo-climatic and geomorphic characteristics using statistical exploration (Multiple Correspondence Analysis, MCA) and modelling (Multinomial/Binomial Logistic Regression, MLR/BLR). Results show that 71% of rock glaciers are stabilized or slow-moving landforms, while 23% exhibit surface velocities greater than 10 cm/year. Both MCA and MLR/BLR highlight that fast-moving rock glaciers are strongly correlated with higher latitudes, high elevations, steep slopes and convex morphologies, in contrast to slow-moving rock glaciers. MLR analysis revealed further differences between slow and fast classes. Rock glaciers with velocities <1 cm/year and 1-10 cm/year are located at lower latitudes and elevations, and in regions with unfavourable permafrost conditions. However, the <1 cm/year class is still found on steep slopes, suggesting that these landforms may not contain enough ice to maintain permafrost creep. Rock glaciers with velocities between 1 and 10 cm/year are more likely on smoother slopes, but they also show high occurrence probabilities at high elevations, indicating dynamic deactivation processes. Finally, the 10-30 cm/year class is slightly more probable under unfavourable permafrost conditions, which may suggest ongoing climatic deactivation. High-speed ranges were also associated with heterogeneous and small-moving areas within rock glacier systems, suggesting the presence of restricted permafrost conditions within a deactivating system. This finding raises important questions about spatial transitions and the temporal evolution of such kinematic behaviour.

The Cordillera Blanca (Peru) is among the world’s best documented GLOF regions. Yet hazard prioritisation frameworks still focus mainly on large lakes (>0.1 km²), while the numerous small (<0.01 km²) and medium (0.01–0.1 km²) lakes remain comparatively underassessed. In Huascarán National Park, 67% of the 882 inventoried lakes are small and 26% are medium-sized. In this study, we reconstruct the 28 April 2025 Vallunaraju cascade event in the Casca valley, where a rockfall impacted two small lakes and triggered an outburst flood reaching the Huaraz–Independencia conurbation 14 km downstream. Documented impacts included two fatalities and damage to five bridges, twenty-nine houses and water infrastructure. Although the modest initial lake-water release (~42 × 103 m3), progressive channel-bed entrainment increased the total moving mixture volume by ~6–7 times to 296 × 103 m3. Depending on plausible drainage scenarios, entrained sediment accounted for ~73–84% of the total mixture volume, whereas lake water contributed ~13–15% and background discharge ∼1–5%. We interpret Vallunaraju as a sediment-amplified cascade showing that small-lake outbursts can generate severe downstream consequences where triggers, abundant erodible sediment and exposure coincide, supporting integrated assessments that include small lakes, trigger susceptibility and propagation and exposure controls.

Rock glaciers are the visible expression of mountain permafrost. The deformation of internal ice and basal horizon make them creeping downward, which allows their detection. Their geomorphological characteristics tend to evolve as a response to degrading permafrost conditions. If the internal ice is melting, the surface creeping gradually decreases until the landform stabilizes. This gradual deactivation has led to the definition of “rock glaciers in transition”. Recent studies highlighted a general trend of active rock glaciers’ increasing surface velocity in the last decades. In this context, we are asking if remaining ice in rock glaciers in transition could allow an increase of surface velocity trend similar to active rock glaciers? This study aims to describe rock glaciers in transition geomorphic settings and their present-day kinematics, and explore how their intrinsic and extrinsic characteristics can explain their activity. To answer this question, we applied remote sensing techniques from a French inventory of rock glaciers such as i) High resolution differential radar interferometry images to describe present days surface velocities for all “inactive” inventoried rock glaciers and reveal global trends at a large scale. ii) Geomorphic mapping of the rock glaciers characteristics such as their geometry, geomorphological and geological settings (rock glacier system, slope, latitude/longitude, altitude, concavities, vegetation cover, exposition, aspect and lithology of the blocks…). iii) By combining a dataset with i) and ii), we analyze correlations and dominant parameters using an MCA factorial analysis and a multimodal linear regression. Over 521 rock glaciers, 305 present displacements detectable from 30 InSAR images during summer period between 2016 and 2018. Most of them have velocities rates lower than 10 cm. yrˉ¹ (N=184), and for 1/3 (N=120) it ranges from 10 to 50 cm. yrˉ¹. Higher rates only concern 11 rock glaciers. For 80% of them (N=247), the mean surface area of displacements is lower than a half of the rock glacier surface area. The most represented geomorphic criteria are related to sagging landforms. Indeed, more than 50% of rock glaciers have a concave transversal profile matching with subsidence, whereas the others face with a high asymmetric topography. We support the hypothesis that lithology, exposition and the slope could be external factors that explains the most the heterogeneity of rock glaciers responses to a global climatic impact. The concavity/convexity index of transversal profiles, the surface slope and the vegetation cover should be the best parameters to describe the state of a transitional rock glacier in accordance with its activity. However, for many of rock glaciers with velocities ranging between 10 and 50cm. yrˉ¹ these criteria are met. Morphodynamical approaches are essential to better understand the link between external parameters and morphological settings of rock glaciers in transition, in responses to their activity. Nonetheless, the ice content and amount of water input can be essential drivers of rock glaciers activity. It is therefore important to complement such morphodynamical studies with an analysis of the subsurface in order to correlate these characteristics with the actual internal properties of rock glaciers.

ABSTRACTRock glaciers are important headwater landforms that play a key role in alpine hydrology. North American rock glaciers are estimated to contain the third largest water volume equivalent globally, and over 3800 rock glaciers have been mapped in Colorado alone. However, these features are often overlooked in alpine water budgets. In this study, we present initial results using geophysical, hydrochemical, and repeat structure from motion data to investigate the ice presence, downslope movement, and influence on stream chemistry of the Lake Agnes rock glacier in the northern Front Range, Colorado, USA. We measured an average velocity of 23 ± 4 cm year−1 in the upper 400 m of the rock glacier, with maximum velocities up to 36 ± 4 cm year−1. Rock glacier–fed streams (n = 2) near the spring remained below 2.5°C throughout the summer, mixed‐source streams (n = 3) remained below 3.5°C, and a non–rock glacier stream (n = 1) reached 13.5°C. Rock glacier streams additionally recorded elevated ion concentrations and pH relative to the mixed‐source and lake–fed streams. Geophysical surveys suggest that the rock glacier has an internal structure consisting of a ~3‐m‐thick active layer, underlain by an ice‐poor layer up to 10 m thick and by an ice‐rich layer up to 18 m thick, with total rock glacier thickness between 20 and 30 m. This study supports the presence of ice within the Lake Agnes rock glacier and documents the rock glacier's influence on basin hydrochemistry. In many basins, including Lake Agnes, the reduced climate sensitivity of rock glaciers and their sustained cold‐water input to mountain streams will likely provide a refuge for cold‐water species in a warming climate.

AbstractsThe Cordillera Blanca, located in Peru, is a mountain range with peaks exceeding 6000 meters, preserving tropical glaciers on its surface. Currently, due to global climate change resulting from both natural and anthropogenic causes, glaciers are rapidly losing surface area and volume. Over a period of 58 years, between 1962 and 2020, the Cordillera Blanca (CB) has lost 301.4 km2 of glacier surface, equivalent to 41.50% of the total area. This has led to an increased occurrence of ice and rock avalanches, triggering violent overflow events of glacial lakes and alluvial processes. In this context, the Hydrographic Unit (HU) Ranrahírca has recorded the occurrence of two extreme avalanche events originating from the North Peak of Nevado Huascarán, corresponding to the 1962 event in Ranrahírca and the 1970 event in Yungay.The objective is to identify, differentiate, categorize, and correlate unconsolidated deposits with different historical alluvial events (Paleoalluvions) of significant magnitude that occurred on the north peak of Nevado Huascarán, Cordillera Blanca. This involves a detailed grain size analysis of soils, with emphasis on lithology, dimensions, shape, and degree of weathering of the clasts in their composition, as well as their fine material content, aiding in temporally situating the origin event. The primary study area is the Yungay district, located at the lower part of Nevado Huascarán, where Quaternary material from various paleoalluvions has accumulated in a fan-shaped pattern in the lower part of the Ranrahírca HU. This area extends for several kilometers, currently encompassing the urban areas of Yungay and Ranrahírca.To achieve this, fieldwork was conducted in August 2023 in the Yungay and Ranrahírca areas. Seven (07) chronostratigraphic columns were surveyed, and thirteen (13) soil samples were collected from different cut sections of slopes. These efforts have allowed the differentiation of various paleoalluvionic events and, in some cases, evidence the transition between them.Keywords: Cordillera Blanca, rock-ice paleoavalanche, grain size analysis, chronostratigraphic column.

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.

The Cordillera Blanca, located in Peru between latitudes 8-10°S, is the most glacierized intertropical mountain range in the world, with peaks over 6,000 meters still carrying numerous glaciers today. Ongoing climate change has resulted in a 41.50% reduction in glacier extent from 1962 to 2020, increasing natural hazards such as icefall, glacial lake overflow flooding, and rock avalanches. These events mainly affect the highest reliefs, but can reach the low elevation valleys, where around 300,000 inhabitants are exposed. Since the 1950s, these hazards have caused tens of thousands of casualties, including two major disasters: rock-ice avalanches from the northern summit of Huascaran (6,757m) traveling over considerable distances and destroying populated areas such as Ranrahirca (1962) and Yungay (1970), resulting in approximately 7,000 casualties in total. In this context, our objective is to construct a comprehensive "spatio-temporal" inventory of substantial rock-ice avalanches (volume > 106 m3) within the Cordillera Blanca. Our aim is to enhance our understanding of their spatial distribution, temporal frequency, and magnitude while pinpointing potential triggering factors. Our specific focus involves investigating potential correlations between avalanche records and climatic oscillations spanning the past hundred thousand years. The primary area of interest is the Yungay site, situated directly downstream from Huascaran North, where successive debris avalanche (historical and paleo) have accumulated, forming debris cones that extend across several square kilometers. Preliminary field observations have identified numerous large boulders indicative of events surpassing the reported magnitude for historical avalanches and their associated deposits. Employing a multi-method approach that integrates fieldwork, remote sensing, geochronology, and numerical modeling, we intend to assess rock-avalanche deposits and volumes. A preliminary field mission conducted in August 2023 in Yungay facilitated the mapping and sampling of approximately 30 boulders of pluri-decametric size for surface-exposure dating (in situ 10Be on quartz). Anticipating dating results by early 2024, one of the primary expected outcomes of this study is to achieve a comprehensive reconstruction of the geomorphic response of the high Cordillera Blanca during past climate oscillations. This understanding will contribute to better anticipating the future evolution of natural hazards within the context of ongoing global climate warming, glacial retreat, and accelerated permafrost degradation. Additionally, our objective is to characterize the triggering mechanisms for low-frequency (recurrence time >100 yr) high-magnitude (volume >106 m3) events.

Constraining the timescales of sediment transport by glacier systems is important for understanding the processes controlling sediment dynamics within glacierized catchments, and because the accumulation of supraglacial sediment influences glacier response to climate change. However, glacial sediment transport can be difficult to observe; sediment can be transported englacially, subglacially, supraglacially or at the ice margins, and may be stored temporarily on headwall slopes or within moraines before being (re-)entrained and transported by glacier ice. This study is a proof of concept of the use of luminescence rock surface burial dating to establish rates of englacial sediment transport. Our novel approach combines luminescence rock surface burial dating of englacial clasts with an ice-flow model that includes Lagrangian particle tracking to quantify rates of sediment transport through the Miage Glacier catchment in the Italian Alps. Luminescence rock surface burial ages for seven samples embedded in the near-surface ice in the ablation area range from 0.0 +/- 1.0 to 4.7 +/- 0.3 ka and are consistent with the ice-flow model results. Our results show that the transport durations of individual clasts vary by an order of magnitude, implying rapid clast transport near the glacier surface and longer transport histories for clasts transported lower in the ice column. In some cases, clasts were stored on the headwalls or within ice-marginal moraines for several thousand years before being englacially transported. The results illustrate the different routes by which glaciers transport sediment and provide the first direct measurements of englacial sediment transport duration.

Rock glaciers dominate the cryosphere in mid‐latitude alpine settings, yet their activity and their histories remain challenging to constrain. We focus on the Thomas Lake rock glacier on Mt. Sopris in Colorado, USA. We measure surface velocities by feature tracking of image pairs and document Holocene 10 Be exposure ages on surface debris. The surface speeds average 0.8 m/yr and peak at 2 m/yr in a steep reach. Exposure ages range from 1.4 to 13.2 kyr and monotonically increase down‐glaciers. Ages exceeding 6 kyr occur in the bottom quarter of the landform, coinciding with sporadic tree cover. These constraints constrain a numerical model of Holocene rock glacier activity. In our model, surface velocity is entirely explained by the deformation of the ice‐rich core with the extra load of the rocky carapace. Surface mass balance is simplified to an accumulation area of ice and debris equivalent to the avalanche cone, and very low, uniform ablation in the remaining rock glacier where rock cover minimizes melt. Climate drives the activity through a history of ice accumulation in the avalanche cone. Matching the observed age and speed structure requires: (a) Early Holocene growth of the rock glacier, (b) low accumulation during the middle Holocene warm period (Hypsithermal), and (c) two Neoglacial accumulation pulses, the most recent being the Little Ice Age. Pulses travel down the valley as kinematic waves, re‐activating the landform. The headwall retreat rate of 4 mm/yr, inferred from rocky layer thickness and surface speed, far outpaces bedrock down wearing rates.

Constraining the pathways and time scales of englacial sediment transport is of primary importance for both understanding the processes that move sediment through glacierised catchments and quantifying the response of mountain glaciers to climate change. However, sediment transport through glaciers is a more complex process than ice flow and difficult to observe; clasts can be transported englacially and at the ice margins, but also deposited into moraines before being re-entrained into englacial transport. We developed a novel method taking a Lagrangian approach that combines luminescence rock surface burial dating of the time for englacial transport of individual rock debris with ice-dynamical glacier evolution modelling of glacial sediment transport to quantify rates of sediment transport through the Miage Glacier catchment in the Italian Alps. Luminescence rock surface burial dating allows determining the burial duration of rocks after they have been exposed to sunlight, but this method has not previously been applied to englacial clasts. We obtained luminescence ages for seven samples embedded in the ice in the ablation zone of Miage Glacier, with burial ages ranging from 0.2 ± 0.1 ka to 5.0 ± 1.4 ka. Samples collected in the upper part of the ablation zone yield younger ages than samples collected near the terminus. The younger luminescence ages (0.2 ± 0.1 ka and 0.3 ± 0.1 ka) are consistent with expected burial duration based on the present-day glacier velocity. In contrast, older luminescence ages obtained for samples located in the lower part of the ablation zone (1.2 ± 0.1 ka to 5.0 ± 1.4 ka) show that these samples record a longer and more complex burial history, suggesting that these samples were either stored in the headwall area or within moraines for several thousand years before being entrained in the ice. In the Miage catchment, debris could have been stored in a moraine at the junction between the Bionnassay Glacier and the Dome Glacier before being entrained in the Miage glacier. We compare the burial ages of the englacial clasts with simulations of glacial sediment transport using a Lagrangian particle tracking scheme in the glacier model iSOSIA. The model results illustrate the range of englacial and subglacial sediment flow paths through the Miage Glacier and simulate similar durations of englacial transport to those obtained for our luminescence samples.

s The Cordillera Blanca, located in Peru, is a mountain range with peaks exceeding 6000 meters, preserving tropical glaciers on its surface. Currently, due to global climate change resulting from both natural and anthropogenic causes, glaciers are rapidly losing surface area and volume. Over a period of 58 years, between 1962 and 2020, the Cordillera Blanca (CB) has lost 301.4 km2 of glacier surface, equivalent to 41.50% of the total area. This has led to an increased occurrence of ice and rock avalanches, triggering violent overflow events of glacial lakes and alluvial processes. In this context, the Hydrographic Unit (HU) Ranrahírca has recorded the occurrence of two extreme avalanche events originating from the North Peak of Nevado Huascarán, corresponding to the 1962 event in Ranrahírca and the 1970 event in Yungay. The objective is to identify, differentiate, categorize, and correlate unconsolidated deposits with different historical alluvial events (Paleoalluvions) of significant magnitude that occurred on the north peak of Nevado Huascarán, Cordillera Blanca. This involves a detailed grain size analysis of soils, with emphasis on lithology, dimensions, shape, and degree of weathering of the clasts in their composition, as well as their fine material content, aiding in temporally situating the origin event. The primary study area is the Yungay district, located at the lower part of Nevado Huascarán, where Quaternary material from various paleoalluvions has accumulated in a fan-shaped pattern in the lower part of the Ranrahírca HU. This area extends for several kilometers, currently encompassing the urban areas of Yungay and Ranrahírca. To achieve this, fieldwork was conducted in August 2023 in the Yungay and Ranrahírca areas. Seven (07) chronostratigraphic columns were surveyed, and thirteen (13) soil samples were collected from different cut sections of slopes. These efforts have allowed the differentiation of various paleoalluvionic events and, in some cases, evidence the transition between them. Keywords: Cordillera Blanca, rock-ice paleoavalanche, grain size analysis, chronostratigraphic column.

Depth-dependent luminescence in the top few millimetres of rock surface emerges as a potential tool to estimate rock surface exposure age and post-exposure erosion rate. It relies on the principle that the luminescence depth profile (LDP) propagates deeper with the time of sunlight exposure and moves to shallower depth with the erosion rate. The propagation of LDP is generally assumed to follow the first-order kinetic (FOK) model, except for a few recent studies. The FOK model predicts an exponential decay of infrared stimulated luminescence (IRSL) signal with light exposure time, which rarely corroborates experimental observation; IRSL signal decay is much slower than exponential decay. The faster decay of IRSL, predicted by the FOK model, results in faster propagation of LDP and thus always underestimates the exposure age and translates into a higher erosion rate. Interestingly, the slower-than-exponential decay of the IRSL signal can be better explained by general order kinetics (GOK). Thus, recent studies on rock surface luminescence dating have employed the GOK model. However, the GOK model is yet to be explored to predict post-exposure erosion rates. Here, we apply the GOK model and theoretically demonstrate the impact of the order of kinetics on the calibration and propagation of LDP in the presence of erosion and how the LDP's transient to steady state transition depends on the order of kinetics. We have performed a series of synthetic tests to assess the impact of selecting an incorrect model on the prediction of erosion rate. Finally, using the revised rate equation, the erosion rates are recalculated for natural samples (data available in the literature: Lehmann et al. (2019b)) and the impact of GOK on the predicted erosion rate is discussed.

The Chaos Canyon landslide, which collapsed on the afternoon of 28 June 2022 in Rocky Mountain National Park, presents an opportunity to evaluate instabilities within alpine regions faced with a warming and dynamic climate. Video documentation of the landslide was captured by several eyewitnesses and motivated a rapid field campaign. Initial estimates put the failure area at 66 630 m2, with an average elevation of 3555 m above sea level. We undertook an investigation of previous movement of this landslide, measured the volume of material involved, evaluated the potential presence of interstitial ice and snow within the failed deposit, and examined potential climatological impacts on the collapse of the slope. Satellite radar and optical measurements were used to calculate deformation of the landslide in the 5 years leading up to collapse. From 2017 to 2019, the landslide moved ∼5 m yr−1, accelerating to 17 m yr−1 in 2019. Movement took place through both internal deformation and basal sliding. Climate analysis reveals that the collapse took place during peak snowmelt, and 2022 followed 10 years of higher than average positive degree day sums. We also made use of slope stability modeling to test what factors controlled the stability of the area. Models indicate that even a small increase in the water table reduces the factor of safety to <1, leading to failure. We posit that a combination of permafrost thaw from increasing average temperatures, progressive weakening of the basal shear zone from several years of movement, and an increase in pore-fluid pressure from snowmelt led to the 28 June collapse. Material volumes were estimated using structure from motion (SfM) models incorporating photographs from two field expeditions on 8 July 2022 – 10 d after the slide. Detailed mapping and SfM models indicate that ∼1 258 000 ± 150 000 m3 of material was deposited at the slide toe and ∼1 340 000 ± 133 000 m3 of material was evacuated from the source area. The Chaos Canyon landslide may be representative of future dynamic alpine topography, wherein slope failures become more common in a warming climate.

The retreat of glaciers since the Last Glacial Maximum in the European Alps has left an imprint on topography through various erosional processes. However, few methods are currently capable of resolving these mechanisms on Late Glacial to Holocene timescales. Quantifying the relative contributions of mountain erosion, during these different climate cycles, is useful for understanding long-term landscape evolution and the links between global climate and erosion. Here, we combine three optically stimulated luminescence (OSL) exposure dating signals with 10Be surface exposure dating to constrain the post-glacier erosion rates of bedrock samples adjacent to the Gorner Glacier in the European Alps. The results reveal erosion rates of the order of 10−2 to 10−1 mm a−1, in general agreement with other studies in the region, as well as a strong negative correlation between erosion rate and elevation, suggesting that frost crack weathering is perhaps not the dominant form of post-glacier weathering. Finally, a global compilation of both subglacial and periglacial erosion rates shows that periglacial erosion rates could be greater than previously thought. Yet subglacial erosion remains higher, implying that it continues to have the stronger influence on shaping landscapes. Therefore, with a changing climate, periglacial erosion rates are likely to remain transient. These insights could lead to important implications for landscape evolution models.

Active rock glaciers are some of the most frequent cryospheric landforms in midlatitude high-elevation mountain ranges. Their activity strongly influences the hydrology and geomorphology of alpine environments over short (years to decades) and long (centuries to millennia) timescales. Being conspicuous expressions of mountain permafrost and important water reserves in the form of ground ice, rock glaciers are seen as increasingly important actors in the geomorphological and hydrological evolution of mountain systems, especially in the context of current climate change. Over geological timescales, rock glaciers both reflect paleoclimate conditions and transport rock boulders produced by headwall erosion, and they therefore participate in shaping high mountain slopes. However, the dynamics of rock glaciers and their evolution over different timescales remain under-constrained. In this study, we adopt a multi-method approach, including field observations, remote sensing, and geochronology, to investigate the rock glacier system of the Vallon de la Route (Combeynot Massif, western French Alps). Remotely sensed images and correlation techniques are used to document the displacement field of the rock glacier over timescales ranging from days to decades. Additionally, to estimate displacement over periods from centuries to millennia, we employ terrestrial cosmogenic nuclide (quartz 10Be) surface-exposure dating on rock boulder surfaces located along the central flow line of the rock glacier, targeting different longitudinal positions from the headwall to the rock glacier terminus. The remote sensing analysis demonstrates that between 1960 and 2018 the two lower units of the rock glacier were motionless, the transitional unit presented an integrated surface velocity of 0.03±0.02 m a−1, and the two upper active units above 2600 m a.s.l. showed a velocity between 0.14±0.08 and 0.15±0.05 m a−1. Our results show 10Be surface-exposure ages ranging from 13.10±0.51 to 1.88±0.14 ka. The spatial distribution of dated rock glacier boulders reveals a first-order inverse correlation between 10Be surface-exposure age and elevation and a positive correlation with horizontal distance to the headwall. These observations support the hypothesis of rock boulders falling from the headwall and remaining on the glacier surface as they are transported down valley, and they may therefore be used to estimate rock glacier surface velocity over geological timescales. Our results also suggest that the rock glacier is characterized by two major phases of activity. The first phase, starting around 12 ka, displays a 10Be age gradient with a rock glacier surface velocity of about 0.45 m a−1, following a quiescent period between ca. 6.2 and 3.4 ka before the emplacement of the present-day upper two active units. Climatic conditions have favored an integrated rock glacier motion of around 0.18 m a−1 between 3.4 ka and present day. These results allow us to quantify back-wearing rates of the headwall of between 1.0 and 2.5 mm a−1, higher than catchment-integrated denudation rates estimated over millennial timescales. This suggests that the rock glacier system promotes the maintenance of high rock wall erosion by acting as debris conveyor and allowing freshly exposed bedrock surfaces to be affected by erosion processes.

Our ability to quantify past climate conditions is crucial for understanding and predicting future climate scenarios as well as landscape evolution. One of the most drastic climatic changes in Earth’s history was the Last Glacial Maximum (LGM) where a significant area of the planet’s surface was covered in ice (Clark et al., 2009). However, most reconstructions of the Earth’s past climate rely on the use of climate proxies (e.g. Jones and Mann, 2004 for a review), which are particularly poorly preserved in terrestrial settings previously covered by ice- thus limiting the applicability of existing methods. Here, we apply feldspar thermoluminescence (TL) surface paleothermometry (Biswas et al., 2018; 2020) to better constrain the temperature history of exposed bedrock surfaces since the Last Glacial Maximum to present day. The aim of this study is to contribute towards a more detailed understanding of glacial and interglacial temperature fluctuations across the Central and Western Alps. Feldspar TL paleothermometry is a recently developed technique that exploits the dependence of trapped charge on temperature (Biswas et al., 2018). The trapped charge is sourced from feldspar’s crystalline lattice. While a TL signal can be extracted between room temperature and 450°C, traps sensitive to typical surface temperature variations (e.g.10°C) are found between 200°C and 250°C (Biswas et al., 2020). As a result, five thermometers (200°C to 250°C in 10°C intervals) can be used together as a multi-thermometer, and subsequently combined with a Bayesian inversion approach to constrain thermal histories over the last50 kyr (Biswas et al., 2020). The temperature histories of bedrock samples collected down two vertical transects adjacent to the Gorner (Switzerland) and the Mer de Glace (France) glaciers, which have been exposed progressively since the LGM, will be presented. Preliminary results suggest a temperature difference of ∼10 °C in both locations, which is promising and in agreement with past surface temperatures obtained from other studies. References: Biswas, R.H., Herman, F., King, G.E., Braun, J., 2018. Thermoluminescence of feldspar as a multi-thermochronometer to constrain the temporal variation of rock exhumation in the recent past. Earth and Planetary Science Letters, 495, 56-68. Biswas, R.H., Herman, F., King, G.E., Lehmann, B., Singhvi, A.K., 2020. Surface paleothermometry using low temperature thermoluminescence of feldspar. Climate of the Past, 16, 2075-2093. Clark, P. U., Dyke, A. S., Shakun, J. D., Carlson, A. E., Clark, J., Wohlfarth, B., Mitrovica, J. X., Hostetler, S. W., and McCabe, A. M., 2009. The Last Glacial Maximum. Science, 325 (5941), 710-714. Jones, P.D., Mann, M.E., 2004. Climate over past millennia. Reviews of Geophysics, 42, 2004.

Abstract. The retreat of glaciers since the Last Glacial Maximum (LGM) in the European Alps has left an imprint on topography through glacial and non-glacial erosional processes. However, few methods are currently capable of resolving these mechanisms on Lateglacial to Holocene timescales. Quantifying the relative contributions of mountain erosion, during these different climate cycles, is useful for understanding long-term landscape evolution and the links between global climate and erosion. Here, we combine three Optically Stimulated Luminescence (OSL) exposure dating signals with 10Be surface exposure dating to constrain the post-glacier erosion rates of bedrock samples down a vertical transect adjacent to the Gorner glacier in Zermatt, Switzerland. The results reveal erosion rates on the order of 10-2 to 10-1 mm a-1, in general agreement with other studies in the region, as well as a strong negative correlation between erosion rates and elevation. Finally, at present glacial erosion is assumed to have a greater influence on landscapes, yet a global compilation of both glacial and non-glacial erosion rates in deglaciated environments shows that erosion rates during interglacial times could be equally important.

Wave-transported boulders represent important records of storm and tsunami impact over geological timescales. Their use for hazard assessment requires chronological information on their displacement that in many cases cannot be achieved by established dating approaches. To fill this gap, this study investigated, for the first time, the potential of optically stimulated luminescence rock surface exposure dating (OSL-RSED) for estimating cliff-detachment ages of wave-transported coastal boulders. The approach was tested on calcarenite clasts at the Rabat coast, Morocco. Calibration of the OSL-RSED model was based on samples with rock surfaces exposed to sunlight for ∼ 2 years, and OSL exposure ages were evaluated against age control deduced from satellite images. Our results show that the dating precision is limited for all targeted boulders due to the local source rock lithology which has low amounts of quartz and feldspar. The dating accuracy may be affected by erosion rates on boulder surfaces of 0.02–0.18 mm yr−1. Nevertheless, we propose a robust relative chronology for boulders that are not affected by significant post-depositional erosion and that share surface angles of inclination with the calibration samples. The relative chronology indicates that (i) most boulders were detached from the cliff by storm waves; (ii) these storms lifted boulders with masses of up to ∼ 24 t; and (iii) the role of storms in the formation of boulder deposits along the Rabat coast is more significant than previously assumed. Although OSL-RSED cannot provide reliable absolute exposure ages for the coastal boulders in this study, the approach has large potential for boulder deposits composed of rocks with larger amounts of quartz or feldspar and less susceptibility to erosion.