ICG2022-7

On this 60^th. anniversary of Chorley’s paradigm changing paper on geomorphology and general systems theory, the application of his ideas specifically to mountain geomorphology is briefly reviewed. Five kinds of general systems are recognized: (i) morphological systems; (ii) spatio-temporal systems; (iii) water, solute and sediment cascading systems; (iv) mountain process-response systems; and (v) so-called mountain control systems that are actually “out-of-control” systems because of policy and planning failures following intensification of land use and climate change during the Anthropocene epoch. Two examples of research questions under systems categories (iii) and (v) illustrate the value of a general systems approach. The first question concerns the relation between disconnectivity and connectivity and discusses reasons for the comparative neglect of disconnectivity in the recent geomorphological literature. The second question concerns the geomorphological effects of human use of land and associated climate change and discusses reasons for the failure of many policy and planning analysts to recognize the links between human use of land, climate change and  environmental degradation.

How to cite: Slaymaker, O. and Leinberger, E.: A general systems approach to mountain geomorphology, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-4, https://doi.org/10.5194/icg2022-4, 2022.

The definition of the timing of infilling and environmental evolution of Alpine valleys is essential in the knowledge of the mountain geomorphological systems response to the climate oscillations after the Last Glacial Maximum. This assessment is necessary in the comparison of a system controlled only by natural factors, dominated by paraglacial and paraperiglacial erosion models, and the increasing role played by anthropogenic factors modifying the environment. In the Southern Swiss Alps, anthropogenic factors start playing a role since the frequentation of the valley bottoms and main Alpine passes during the Middle Mesolithic (8.0–7.0 ka BCE). This role increased significantly since the Lower Neolithic (5.4–4.3 ka BCE), with the first permanent settlements.

Radiocarbon dating in Lago di Monate (Varese, Italy) starts the deglaciation of the Lago Maggiore basin just before 19.93–18.81 ka cal BP (BE 8023.1.1, Rey et al. 2020, Clim. Past 16; cf. Kamleitner et al. 2022, Quat. Sci. Rev. 279). Complete deglaciation of the Lago Maggiore basin by no later than 16.89–16.34 ka cal BP is indicated by radiocarbon dating of an organic lacustrine deposit in the lower Riviera valley in Castione (north of Bellinzona). ¹⁰Be surface exposure dating of three erratic boulders located upslope of Claro (left side of Riviera valley) point to deglaciation slightly earlier. These chronological elements show a 70 km retreat of the Ticino glacier between Lago di Monate and Castione in 2.6 ± 1.0 ka. The deglaciation was followed by a significant debris supply from the slopes to the valley bottoms, contributing to the development of large alluvial fans. Valley bottom damming exercised by rapidly growing alluvial fans allowed the creation of a series of lake basins of increasing level upstream. Radiocarbon dating performed in Castione points out the lake formation just during the deglaciation, and its complete infilling by fluvial deposits between 12.72 and 12.76 ka cal BP, as indicated by the woods found in fluvio-deltaic deposits.

From Castione to Lago Maggiore, the progradation of the Ticino (and Moesa) river delta completely filled the valley bottom step by step. This infilling was dated: in Bellinzona (13.9 km from the actual river mouth) between 13.48 and 13.31 ka cal BP, when the Castione palaeo-lake was still present; in Giubiasco (10.6 km) between 10.70 and 10.49 ka cal BP; in Gudo (7.6 km) between 8.36–8.17 ka cal BP and 7.43–7.26 ka cal BP; in Riazzino (2.9 km) between 3.89 and 3.58 ka cal BP; and in Magadino di Sopra (1.3 km), according to historical information, between 1365 and 1518 CE (0.59–0.43 ka cal BP).

Both depositional rates in the alluvial plain and delta progradation rates follow the paraglacial erosion model from the Late Pleistocene to the beginning of the Meghalayan. During the Meghalayan, anthropogenic factors, such as deforestation and reforestation, are added to morpho-climatic factors and indicate an increasing human pressure on the erosional/depositional dynamics since the Early Bronze Age (2.20–1.55 ka BCE) and, rising significantly, since the Early Iron Age (0.90–0.45 ka BCE).

How to cite: Scapozza, C., Giacomazzi, D., Czerski, D., Kamleitner, S., Ivy-Ochs, S., Mazzaglia, D., Patocchi, N., and Antognini, M.: Timing of deglaciation and Late Glacial and Holocene infilling of the Ticino valley between Biasca and Lago Maggiore (Southern Switzerland), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-118, https://doi.org/10.5194/icg2022-118, 2022.

The Upper Garonne Basin hosted the largest glacier of the Pyrenees during Late Pleistocene glaciations. Glacial retreat started after the Last Glacial Maximum (20-19 ka) of the last glacial cycle, and by the onset of the Bølling–Allerød interstadial (B-A; 15-14 ka) ice masses were already confined within the glacial cirques and highest valleys. In the Aran Valley, headwaters of the Garonne Basin, the low glacial cirques (with maximum elevations of ~2600 m) preserve a significant variety of glacial and periglacial landforms of unknown age. This study focuses in the Locampo Cirque, where we conducted a detailed geomorphological mapping of the glacial and periglacial landforms and dated a set of 8 samples using ¹⁰Be Cosmic-Ray Exposure (CRE). This approach allowed to establish the chronology and identify the mechanisms involved in the transition from glacial to periglacial dynamics. CRE ages reveal that the external moraine closing the cirque (2210-2335 m) probably formed during the second half of the B-A at 13.7 ± 1.5 ka. Subsequently, glaciers retreated, and a rock glacier developed inside the external moraine (2210-2310 m) during the paraglacial phase. The final stabilization of this rock glacier most likely occurred during the Younger Dryas (YD)-Holocene transition, at 11.9 ± 0.7 ka. These results report the first chronology on the formation of rock glaciers in the northern slope of the Central Pyrenees and confirm the pattern observed in other mid-latitude mountains, showing that the final deglaciation occurred during the (cold but dry) YD, accompanied by the development and stabilization of rock glaciers.

How to cite: Fernandes, M., Oliva, M., Vieira, G., Fernández-Fernández, J. M., Palacios, D., García-Oteyza, J., Ventura, J., and Schimmelpfennig, I.: Glacial-periglacial transition in the northern Central Pyrenees from the Bølling–Allerød to the Younger Dryas, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-614, https://doi.org/10.5194/icg2022-614, 2022.

Deglaciation of mountain ranges promotes landslides of various scales and types, and many of them may present a major hazard. It is commonly thought that the main concentration of landslides is located in parts of the mountain ranges that have pronounced topography, high amount of precipitation and strong tectonic activity. Based on our mapping of large landslides (>1km²) over an extensively large area of Southern Patagonia (~305,000 km²), we show that the distribution of landslides can have the opposite character. The largest landslides within the limits of the former Patagonian Ice Sheet (PIS) are concentrated along its eastern margins and thus occupying lower, tectonically less active, and arid part of the Patagonian Andes. In contrast to the heavily glaciated, highest elevations of the mountain range, the peripheral regions have been glaciated only episodically. However, a combination of glaciation, weak volcanic and sedimentary rocks, sufficient relief, and presence of large glacial lakes in the past, created favourable conditions for formation of huge number of large landslides along eastern margin of PIS. We explain the scarcity of large landslides in the highest parts of the PIS by presence of strong granitic rocks and long-term glacial modification, that adjusted topography for efficient ice discharge. Our model is limited to large bedrock landslides as shallow slides and rock falls are abundant in the highest and western part of the Andes.

How to cite: Břežný, M., Pánek, T., Harrison, S., Schönfeldt, E., and Winocur, D.: Large landslides are concentrated along Patagonian Ice Sheet margin, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-141, https://doi.org/10.5194/icg2022-141, 2022.

This work explores how feedbacks between erodibility contrasts and sediment production influence the evolution of mountain rivers incising through layered rocks. Mountain rivers are key drivers of landscape response to climatic and tectonic forcing. Transient perturbations from changes in climate or tectonics are reflected in the profiles of bedrock rivers, but these signals can be challenging to unravel in lithologically complex settings. In layered rocks in particular, contrasts in erodibility cause erosion rates to vary through space and time, complicating landscape response to external forcing. Recent studies have used the detachment-limited stream power incision model to illustrate the complex variations in erosion rates that arise in layered rocks (Forte et al. 2016, Perne et al. 2017). However, these studies do not capture the effect of sediment cover on channel evolution. We use the Stream Power with Alluvium Conservation and Entrainment (SPACE) model (Shobe et al. 2017) to explore how sediment cover influences landscape evolution and modulates the topographic expression of erodibility contrasts in mixed bedrock-alluvial rivers incising through horizontally layered rocks.

Lithology influences channel evolution by setting the substrate erodibility and by producing coarse sediment. Motivated by the layered strata of the Guadalupe Mountains in Texas and New Mexico, USA, this study uses the SPACE model to simulate how relative differences in sediment grain size influence long-term landscape evolution. The influence of sediment particle size is tested by varying both the particle settling velocity and the erodibility of the alluvial layer across model runs. While the SPACE model does not resolve individual grains, varying these two parameters allows us to test the relative effects of finer vs. coarser sediment. We simulate river evolution through alternating layers of hard and soft rock over million-year timescales, with a constant uplift rate of 1 mm/year. We find that compared to the detachment-limited case, model runs with sediment cover have systematically higher channel steepness values in soft rock layers and lower channel steepness values in hard rock layers. As the relative sediment particle size is increased, the contrast in steepness between the two rock types decreases. We also find that model runs with relatively coarser sediment reach a steady average elevation more quickly than model runs with finer sediment, suggesting that sediment size exerts a strong control on landscape adjustment times. We also analyze how erosion rates across the entire model grid and sediment flux at the watershed outlet vary through time as hard and soft layers are exposed in different proportions. This work illustrates how strongly sediment cover influences channel evolution in mountains with layered stratigraphy, and demonstrates the importance of taking lithology and sediment cover into account when interpreting channel profiles.

How to cite: Guryan, G., Johnson, J., and Gasparini, N.: Modeling feedbacks between lithologic contrasts, erosion, and sediment production in layered landscapes, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-481, https://doi.org/10.5194/icg2022-481, 2022.

The Himalayas experience frequent fluvial disasters due to precipitation-driven floods, as well as events such as glacial lake outburst floods and landslide lake outburst floods. Such floods represent a major hazard, causing loss of life and damage to property and infrastructure. In steep mountain landscapes, rivers and hillslopes are often tightly linked, and interactions between these domains can strongly influence flood impacts and dynamics. Floods can erode the base of hillslopes and terraces, driving mass wasting, while hillslopes can deliver large amounts of coarse sediment, driving aggradation and potentially creating temporary dams. Data from a 2016 glacial lake outburst flood in central Nepal demonstrate that flood-induced mass wasting can be a dominant driver of damage from such an event, with at least 85 homes and many stretches of the Araniko highway destroyed by slope failures. The hillslope impacts were not confined to the event itself, as a number of hillslopes experienced longer-term destabilization, continuing to slide for years following the flood and hampering efforts to rebuild the road. While the 2016 event represents a case of flood-driven hillslope hazards, a 2021 event on the Melamchi River in central Nepal demonstrates the amplification than can occur with more complex river-hillslope feedbacks. Here, the interaction between the river and a range of hillslope inputs, including a paleo landslide dam, recent colluvial deposits, and a flood-triggered landslide dam, led to massive aggradation throughout the Melamchi River. This aggradation substantially altered the river channel, amplifying the impacts of later floods and promoting additional mass wasting, further increasing the sediment loading of the river. This perturbation of the river-hillslope system is still ongoing, and is expected to cause continued hazard over the next monsoon seasons. These cases demonstrate the importance of considering hillslopes and river channels as an integrated system rather than as distinct domains during assessment of geomorphic hazards in steep mountain landscape such as the Himalaya.

How to cite: Cook, K., Andermann, C., Puri, B., Schwanghart, W., and Adhikari, B. R.: The influence of river-hillslope interactions on fluvial hazards in the Himalaya, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-508, https://doi.org/10.5194/icg2022-508, 2022.

The ongoing retreat of glaciers in the Sikkim Himalaya as a result of climate change (Racoviteanu et al., 2015; Chowdhury et al., 2021) has far-reaching implications for the development and expansion of glacial lakes. Gurudongmar lake complex (GLC) represents a typical paternoster lake system, resembling a series of glacial lakes connected by single or braided streams with a surface or subsurface drainage system. A detailed study of the GLC evolution and outburst susceptibility assessment is required. Glacial lake volume estimation and lake outburst susceptibility assessment were carried out to reveal different characteristics for all four lakes (GL-1, GL-2, GL-3, and GL-4) from the lake complex. Each of these lakes has a moderate to very high potential to outburst. As the dam of GL-1 provides no retention capacity, there is a very high potential of a combined effect with the sudden failure of the moraine-dams of GL-2 or GL-3 located upstream. Temporal analysis of GLC using optical remote sensing data and in-field investigations revealed a rapidly increasing total lake area by ~74 ± 3%, with an expansion rate of +0.03 ± 0.002 km² a^–1 between 1962 and 2018 due to climate change and ongoing glacier retreat. The overall lake area expansion rates are dependent on climate-driven factors, and constantly increasing average air temperature is responsible for the enlargement of the lake areas. Simultaneously, changes in GLC expansion velocity are driven by changes in the total amount of precipitation. The deficit in precipitation probably triggered the initial higher rate from 1962 to 1988 during the winter and spring seasons. The post-1990s positive anomaly in precipitation might have reduced the rate of the glacial lake area expansion considerably.

How to cite: Chowdhury, A., Kroczek, T., De, S. K., Vilímek, V., Sharma, M. C., and Debnath, M.: Quantifying the Rapid Expansion and Outburst Susceptibility of Cascading Moraine-dammed lakes in the Sikkim Himalaya: The Case of Gurudongmar Lake Complex, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-20, https://doi.org/10.5194/icg2022-20, 2022.

High Mountain Asia (HMA) – the Tibetan Plateau and surrounding high Asian mountains – is now experiencing amplified climate change, glacier melt, and permafrost thaw. The rapid climate change and melting and thawing of the cryosphere are not only affecting the water cycle but also causing landscape instability and mountain hazards, potentially threatening over 2 billion people in the downstream river basins. Glacier retreat and permafrost thaw are accelerating associated with frequent rockfalls, landslides, and debris flows. Lake outburst floods from (pro)glacial- and landslide-dammed lakes have potential runout distances of hundreds of kilometers. Moreover, greater amounts of sediment are mobilized, and fluvial sediment fluxes are increasing. Such mountain landscape instability can be largely attributed to climate change and is threatening infrastructure and livelihoods. We suggest that policymakers and stakeholders in the Himalaya countries must be urgently and fundamentally aware of these increasing threats in a changing climate. Adaptation measures should be based on extensive and continual monitoring of the glaciers, permafrost, unstable paraglacial landscapes, and sediment transport, to better understand compound and cascading hazards.

How to cite: Li, D., Lu, X., Zhang, T., Walling, D., Harrison, S., Shugar, D., Koppes, M., Lane, S., and Bolch, T.: Modern landscape change in High Mountain Asia (1950-present), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-23, https://doi.org/10.5194/icg2022-23, 2022.

Rock avalanches are voluminous debris instabilities originated from a fallen portion of bedrock that suffers pervasive disintegration [1]. Tough rock avalanches are foreseen as low-frequency events, their volume (>10⁶ m³) and runout distance (kilometric scale) make them extremely hazardous processes in populated mountain settings and key contributors to landscape denudation [2]. Deciphering the timing of recurrent rock avalanches is crucial to understand the triggering factors involved in their origin (e.g., role of seismicity) and for risk assessment.

This study focuses on a rock avalanche cluster preserved in the southern flank of Sierra de la Sobia; a limestone massif located in the Cantabrian Mountains (North Spain). The rock avalanche cluster analyzed is spatially related to the Marabio Fault trace, which shows unequivocal evidence of Quaternary activity [3]. Rock avalanches in this area have been interpreted as coseismic based on the following evidence [4]: (i) boulder populations show fractal block-size distributions consistently with dynamic fragmentation; (ii) the kinematic analysis of local minor transverse and parallel faults points to a horizontal N-S compression consistent with the regional stress field; and (iii) slope stability analysis indicates that headscarps will turn unstable if ground acceleration peak rises to 0.10–0.15 g during an earthquake, which is within the values expected according to the 2013 European Seismic Hazard Map. A first attempt of numerical dating was performed through the U-Th technique on calcite cements found in the oldest rock avalanches. Results suggest multiple episodes of cementation during the last ~280 ka, but age dispersion hinders the age bracketing of instability events⁴. Here we present a collection of twenty cosmic ray exposure ages relying on the isotope Cl-36 obtained from limestone boulders sampled in the youngest accumulation bodies of the Entrago and Carrea rock avalanches. Results allow to constrain up to 5 instability events spanning the last ~22 ka and occurring at average recurrence intervals of ~3.6 ka. The youngest rock avalanche event took place 8.5 ka ago and left boulder accumulations close to the headscarp of both rock avalanches. Boulder age dispersion increases accordingly with the increase in runout distance from the headscarp, possibly due to the spatial overlapping of accumulation bodies resulting from different instability events of seismic origin. These preliminary results are promising, because if extended to other rock avalanche clusters of the Cantabrian Mountains, they could help to decipher the recurrence time of severe earthquakes in mountain settings where tectonic deformation occurs at low to moderate rates.

[1] Hermanns, R. L. Encyclopedia of Natural Hazards. vol. 2 (2013).

[2] Davies, T. Rock Avalanches. In Oxford Research Encyclopedia of Natural Hazard Science 58 (Oxford University Press, 2018). doi:10.1093/acrefore/9780199389407.013.326.

[3] Fernández, F. J., Alonso, J. L. & Pando, L. Evidence for quaternary tectonic activity in the western cantabrian Zone (Passes of Marabio, Sobia nappe). Geogaceta 64, 1–3 (2018).

[4] Fernández, F. J., Menéndez-Duarte, R., Pando, L., Rodríguez-Rodríguez, L. & Iglesias, M. Gravitational slope processes triggered by past earthquakes on the Western Cantabrian Mountains (Sierra de la Sobia, Northern Spain ). Geomorphology 390, 107867 (2021).

How to cite: Rodríguez-Rodríguez, L., Fernández-Rodríguez, F. J., Menéndez-Duarte, R., Guillou, V., Puente-Berdasco, B., Rinterknecht, V., Aumaître, G., Keddadouche, K., and Bourlès, D.: Temporal recurrence of hazardous rock avalanches in Sierra de La Sobia (Cantabrian Mountains, Spain), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-244, https://doi.org/10.5194/icg2022-244, 2022.

The system rockwall-talus slopes is very common in the high-mountain. It develops mostly due to rapid mass movements, like rockfalls and debris flows. The quantitative data about changes of slopes and sediment transfer within the system enable to get to know complexity and controls of its morphodynamics. Using data from multi-annual temporal  monitoring by terrestrial laser scanning (TLS) survey of the rockwall-talus slope systems we examine their functioning in context of cooperation of rapid mass movements. The attention is paid to showing the different pattern of sediment transfer through the system and its controls.

The study were made in the Tatra Mts. The two adjacent rockwalls and talus slopes systems at the head of the Rybi Potok valley was monitored using terrestrial laser scanning TLS during last decade (2011-2021). They extend between ~1400 and 2500 m a.s.l. Their morphometric parameters are similar, but there is small hanging glacial cirque in one of them. The data was supplemented by meteorological data from the stations located in the bottom of the cirque and at the base of talus slopes.

The rockfall events occurred on the rockwall in each of the systems, which provided few thousands or dozen thousands of loose sediments to talus slopes. It was found that rockfalls occurred in effect of coupling geological and thermal conditions of rocks, not as result of permafrost degradation. The sediment transfer mechanism differs between the systems. The material transported by rockfalls was mostly deposited at the bottom of glacial cirque, while at adjacent system was transported to the apex of talus slope. Therefore activity of two adjacent talus slopes varies. The results showed that changes in talus slopes are essentially effects of debris flows. Their final effect is building up of the talus slope, even if the debris flows moved part of the debris sediments out. The studies reveal and confirm the importance of interplay between different extreme morphogenetic processes and show the complexity of talus slope transformation. A single input of loose debris from a massive rockfall dominated the effectiveness of debris flows. The studies also demonstrated differentiation of spatiotemporal pattern of sediment transfer trough rockwall-talus slope system. Moreover, relations between rapid mass movements and extreme rainfall and temperature as a result of climate change were found.

How to cite: Rączkowska, Z., Cebulski, J., Gądek, B., and Kajdas, J.: Quantitative assessment of the rockwall-talus slope system morphodynamics using TLS monitoring data (Tatra Mts., Poland)., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-330, https://doi.org/10.5194/icg2022-330, 2022.

Stratified sedimentary rock slope are conducive to differential erosion. The retreat and settlement of weak rock strata (shale, siltstone) causes the gradual cantilevering of stronger rock strata (sandstone, greywacke), contributing to the development of tension cracks. As a result, blocks may break away from these stronger rock strata and they will eventually slide or topple on the eroding weak rock strata below. Since 1987, more than 17 500 rockfalls reaching the road have been reported by the Québec Ministry of Transport (MTQ) in northern Gaspésie (eastern Canada). Although these events are well correlated with the meteorological conditions, it is not clear if and how the weathering process affect the failure mechanism. These dynamics have been observed, but rarely studied to 1) determine the mechanical stresses and weathering conditions that promote rock cracking and 2) assess the effect of meteorological conditions on the mechanical deformations promoting rockfalls. We use the cantilever beam theory to model critical cantilever length (block size) and a frost cracking model (Rempel et al., 2016) was then used to explain the decrease of rock tensile strength over time. Meteorological instruments and crack-meters were installed on a flysch rockwall to monitored and explained mechanical deformations. In addition, rockwalls were scanned with a terrestrial laser scanner (TLS) during specific pre-targeted meteorological conditions. The results show that the areas of frost damage concentration correspond to those of maximum stress in the overhanging blocks. The gradual settling measured with the crack-meters in the shale strata causes the destabilization of the above stronger rock strata. Sandstone blocks may then slide or topple on the inclining plane. Heavy rainfall, snowmelt and freeze-thaw cycles are then responsible for most irreversible deformation in both silstone/shale strata and sandstone strata. Over a period of 18 months, 17 LiDAR surveys have allowed to identify 1287 rockfalls with a magnitude above 0.005 m³ on a scanned surface of 12 056 m² resulting in retreat rate between 2.8 to 5.4 mm/years. In winter, rockfall frequency is 12 times higher during a superficial thaw than during a cold period in which temperature remains below 0°C. In summer, rockfall frequency is 22 times higher during a heavy rainfall event than during a dry period. Superficial freeze-thaw cycle (< 50 cm) causes mostly a high frequency of small magnitude events while deeper spring thaw (> 100 cm) results in a high frequency of large magnitude events. Influence of meteorological conditions on mechanical deformations and on rockfall frequency and magnitude is crucial in order to improve risk management since large magnitude events represent higher potential hazards.

How to cite: Gauthier, F., Birien, T., and Meloche, F.: Rock slope and rockfall dynamics in flysch formation under mid-latitude cold climate, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-173, https://doi.org/10.5194/icg2022-173, 2022.

Although ice retreat is widely considered to be an important factor in landslide origin, many links between deglaciation and slope instabilities are yet to be discovered. Here we focus on the origin and chronology of exceptionally large landslides situated along the eastern margin of the former Patagonian Ice Sheet (PIS). Accumulations of the largest rock avalanches in the former PIS territory are concentrated in the Lago Pueyrredón valley at the eastern foothills of the Patagonian Andes in Argentina. Long-runout landslides have formed along the rims of sedimentary and volcanic mesetas, but also on the slopes of moraines from the Last Glacial Maximum. At least two rock avalanches have volumes greater than 1 km³ and many other landslide accumulations have volumes in the order of tens to hundreds of million m³. Using cross-cutting relationships with glacial and lacustrine sediments and using OSL and ¹⁴C dating, we found that the largest volume of landslides occurred between ~17 and ~11 ka. This period coincides with the most rapid phase of PIS retreat, the greatest intensity of glacial isostatic uplift, and the existence of a dropping glacial lake along the foothills of the Patagonian Andes. The position of paleoshorelines in the landslide bodies and, in many places, folded and thrusted lacustrine sediments at the contact with rock avalanche deposits indicate that the landslides collapsed directly into the glacial lake. Although the landslides along the former glacial lobe of Lago Pueyrredón continue today, they are at least an order of magnitude smaller than the rock and debris avalanches that occurred before the drainage of the glacial lake around 10-11 ka. Preliminary numerical modeling results indicate that large postglacial landslides may have been triggered by a combination of rapid sequential glacial lake drawdowns and seismicity due to glacial isostatic adjustment. We conclude that in addition to direct links such as glacial oversteepening, debuttressing and permafrost degradation, the retreat of ice sheets and the subsequent formation of transient large glacial lakes can fundamentally alter stability conditions, especially if the slopes are built by weak sedimentary and volcanic rocks.

How to cite: Pánek, T., Břežný, M., Schönfeldt, E., and Winocur, D.: Large landslides and glacial lakes: a new chapter of the Patagonian Ice Sheet story, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-137, https://doi.org/10.5194/icg2022-137, 2022.

Shallow planar landslides are common phenomena in the mountainous region of Rio de Janeiro, constituting natural hazards that can result in catastrophic disasters such as the landslides in January 2011 and February 2022 in the cities of Nova Friburgo, Teresópolis and Petrópolis in the state of Rio de Janeiro. The study here presented provides geochronological evidence of the recurrence of landslides in this region during the Holocene and the paleoenvironmental conditions associated with bioclimatic changes, evidencing the influence of extreme events on the evolution of this mountainous landscape. The geochronological analysis of these past events was obtained from the survey of organic paleosols interspersed in colluvial sequences. All radiocarbon ages found in colluvial deposits were calibrated using the SHCAL 20 curve and depositional chronological models were applied using the Oxcal software (version 4.4). Two depositional models were used, considering the random (P_sequence) or uniform (U_Sequence) deposition process from the crossing of sedimentological information. The geochronological results of colluvial deposits with the presence of superimposed organic paleosols indicate a progressive evolutionary behavior, marked by episodes of landslides and correlate deposits between 8,990 ± 40 to 856 ± 46 yrs BP from base to top, with recurrence intervals on the order of a few hundred years, ranging between 300 and 600 years. The analysis of carbon isotopes (δ¹³C) information together with palynological data indicate significant vegetation transformations in the area as well as the incidence of natural fires preceding the occurrence of landslides. The detonation of landslides after the occurrence of fires and burning of vegetation still occurs today, however, with recurrence intervals that can be less than 10 years in the same area.

How to cite: Facadio, A. C., Coelho Netto, A. L., Macario, K., Barth, O. M., and Ishimine, K.: Extreme rainfall induced landslides and landscape evolution in the mountainous region of Rio de Janeiro state, SE-Brazil: geochronological and paleoenvironmental evidences., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-598, https://doi.org/10.5194/icg2022-598, 2022.

Glacier retreat has increased in the European Alps during the last four decades. This affects proglacial geomorphic processes and the spatial distribution of plants. We assessed how the type and the magnitude of geomorphic disturbance control the spatial distribution of a rare alpine plant species: Trifolium saxatile All., whose main habitats are proglacial forelands and alluvial bars and banks, within the Glacier Blanc et Glacier Noir catchment area (Ecrins National Park, French Alps). Based on field observations during the summers of 2020 and 2021, we produced a map combining geomorphological deposits and presence-absence of T. saxatile to detect which geomorphological units are relevant for our study. We determined the magnitude and frequency of superficial sediment reworking between the 2020 and 2021 summers using Radio Frequency IDentification experimentation on moraines slopes and glacio-fluvial deposits on which populations of T. saxatile were observed. Abundance and functional traits (stem height, length and number of inflorescences) were also measured. To analyze the potential impacts of geomorphic disturbances on T. saxatile presence, abundance and intra-specific trait variability, generalized linear mixed models (GLMM) and factor analyses of mixed data (FAMD) were used. Results showed heterogeneity in the geographical distribution of T. saxatile within the proglacial landscape. Clovers preferentially established over three geomorphological units: (i) nearly stabilized lateral moraines, (ii) active braided floodplains and (iii) the exposed young alluvial bars. It was totally absent in purely gravitational landforms (e.g. scree, talus cones). The largest individuals of T. saxatile with many inflorescences were mostly found within the active torrential channel where geomorphic disturbances are intense and frequent but this was however balanced by a low abundance of individuals. On lateral moraines and alluvial terraces, which are almost stabilized and exhibit a lower level of geomorphic disturbances than the active braided floodplain (in terms of magnitude and frequency of movement of RFID tracked sediment particles), individuals were much more abundant, but they were smaller and with less inflorescences compared to the active torrential channel. This study shows the importance of geomorphic processes as key drivers of the spatial distribution, and potentially traits expression, of alpine species living in glaciated catchment areas.

How to cite: de Bouchard d'Aubeterre, G., Till-Bottraud, I., Roussel, E., Fort, N., Bizard, L., Tissot, N., González, E., Liébault, F., Petit, S., Pringault, J., and Corenblit, D.: Proglacial geomorphic disturbances drive the spatial distribution of the rare alpine species Trifolium Saxatile All., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-151, https://doi.org/10.5194/icg2022-151, 2022.

While the knowledge of the dynamics and internal structure of rock glaciers is well developed, a lack of understanding of their hydrological functioning is observed in the scientific literature. In particular, the origin and the quality of the water emerging from rock glaciers are not well known, together with its contribution to aquatic systems. Since rock glaciers are becoming increasingly important water sources under the influence of climate change, it is essential to improve knowledge about the modification of the hydrological regime of these high altitude debris accumulation, in particular by tracing ice melt in rock glacier outflows, and to quantify the impact of ground ice melting on the hydrochemistry of Alpine water systems. In this research, we combined isotopic and physico-chemical analyses for six rock glacier outflows in the Swiss Alps during the 2020 summer season. Chemical and isotopic analyses were also performed in sources not fed by rock glaciers at all study sites. The ionic content (SO₄^2-, Ca²⁺, Mg²⁺, NO₃^-) measured in water emerging from active rock glaciers and ice-patches was higher than that detected in sources not fed by rock glaciers. Water emerging from active rock glaciers and ice-patches was also characterized by an increase in electrical conductivity and in ionic content (SO₄^2-, Ca²⁺, Mg²⁺), and by isotopic (δ¹⁸O) enrichment during the warm season. The seasonal evolution of these physico-chemical and isotopic parameters could indicate the water supply related to ground ice melting in water emerging from active rock glaciers and ice-patches. We assume that the cryosphere stored atmospheric pollutants and other chemical elements during a colder period in the recent past (1960s-1980s) and that the current melting of rock glacier ice releases these chemical compounds in the Alpine water systems. The hydro-chemical processes taking place in active rock glaciers were summarized in a conceptual model based on the results of this study.

How to cite: Del Siro, C., Scapozza, C., Perga, M.-E., and Lambiel, C.: Water origin and quality of rock glacier springs. Case studies in the Swiss Alps., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-138, https://doi.org/10.5194/icg2022-138, 2022.

Meteorological conditions control the impact of mechanical and chemical weathering on rock wall erosion and contribute strongly to rock wall instability. The predominant role of frost weathering on rock wall erosion has been demonstrated. Three kinds of freeze-thaw cycles are commonly defined and related to rockfall frequency and magnitude: daily, seasonal and perennial (permafrost). However, the spatiotemporal distribution of freeze-thaw cycles at a fine spatial scale remains poorly studied. This study aims to further define freeze-thaw cycles, to model the freeze-thaw dynamic and to explore the respective influence of solar radiation exposure, thermal absorptivity, lithology, degree of weathering as well as climate change on freeze-thaw dynamic at a fine spatial scale. Four thermistor sensors were inserted in horizontal boreholes 3 to 5.5 meter deep in different north and south facing rock wall structure with changing geology from massive conglomerate to highly stratified and fractured sedimentary rocks. These measurements, combined with weather conditions recorded locally, provide information on the freeze-thaw dynamic and allow to validate thermodynamic simulations run with the WUFI^® software. Results show that there is a diversity of daily freeze-thaw cycles and that they can interact with the seasonal freezing front. For a north exposed rock wall, the change in solar radiation exposure to the south-west leads to 247% more surface freeze-thaw events but to a 20% decrease of these cycles at 50 cm depth. The change in lithology or in degree of weathering of the first meters of rock mainly influences the maximum depth of the freezing front, the depth of winter thaw events, as well as the rate of spring thaw. The freeze-thaw front modeled in this study reached an average depth of 420 cm for the period 1980-2009 against 208 and 111 cm respectively for the period 2070-2099 with the RCP4.5 and RCP8.5 scenarios. For these same periods, the duration of the seasonal freeze-thaw front decreases respectively from 149 days to 102 and 36 days according to the RCP4.5 and RCP8.5 scenarios. This study demonstrates the great sensitivity of freeze-thaw dynamic to the modification of topographic or climatic variables. Spatial change as rock wall exposure or temporal change as climate warming have significant repercussions on the effectiveness of frost weathering both on the periods of occurrence and on the depths concerned. Moreover, daily and seasonal freeze-thaw cycles are complex phenomena and because of their frequent interactions, they cannot be analyzed separately.

How to cite: Birien, T., Gauthier, F., and Fortier, D.: Rock wall freeze-thaw dynamic in a climate change context, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-166, https://doi.org/10.5194/icg2022-166, 2022.

Terracing is one of the most ancient agricultural practices in mountain landscapes to develop agricultural activity and it has been spread worldwide. Furthermore, a large diversity of terraces type (i.e. check-dam terraces, braided terraces, step terraces, pocket terraces) have been constructed depending on geomorphic features and their relative position to the drainage system. These structures are reshaping the geomorphology due to the slope gradient modification, creating a different geomorphic signature than natural landscapes. Moreover, anthropogenic signatures change the geomorphological organization of the landscape with direct consequences on geomorphic processes related to water and sediment fluxes connectivity. It is clear that a different slope intervention –constructing different terraces types– is necessary depending on the background conditions. Once built, terraces promote decoupling effects according to their degree of hydrological and sediment (dis)connectivity. Hence, slope length and connectivity vary according to terraces type, size, shape, slope and inter-terrace distance, being key characteristics for an effective terraces parameterization into hydrological models to assess runoff and sediment yields at catchment scale.

The aim of this study is to analyse the spatial distribution of soil conservation structures types according to geomorphic (i.e. elevation, slope, connectivity index) and anthropic (i.e. terraces parameters) characteristics in a representative Mediterranean basin (Búger River basin; 67.4 km²; Mallorca, Spain).

The physical characterisation of the different terraces type evidenced statistically significant higher values of mean elevation, slope and connectivity index in braided terraces than check dam and terraced fields. In addition, an analysis of the mean elevation and mean slope of the terraces according to their conservation state (i.e., active or abandoned terraces) illustrated that the mean elevation of active areas and the mean slope of abandoned areas significantly decreased from 1956 to 2018, as a result of forest transition. The anthropic characteristics depicted significant differences between the terraces types, where the mean length wall was longer in terraced fields (40 m) than check dam (26 m) and braided (24 m) terraces. Furthermore, the mean distance between walls was significantly larger in check dam terraces (25 m) than terraced fields (18 m) and braided terraces (15 m). Finally, braided terraces had significantly lower dry stone wall density (360 m/ha) than check dam terraces (404 m/ha) and terraced fields (443 m/ha). The interactions between physical and anthropic characteristics were assessed through a Spearman correlation matrix, which results showed how total dry-stone had strong positive correlation with mean elevation, slope and connectivity index. However, the mean length wall decreased as values of mean elevation, slope and connectivity index increased due to its depicted a significant negative correlation. The dry-stone density negatively correlated with mean distance wall and positively correlated with mean slope. Finally, the mean distance between walls negatively correlated with mean slope.

This research may allow to parametrize the heterogeneity of terraces types in order to provide a better understanding of terracing, which can be useful for a terrace parameterization into hydrological models to assess runoff and sediment yields at catchment scale under different land uses change scenarios.

How to cite: Fortesa, J., García-Comendador, J., Company, J., Ruiz, M., and Estrany, J.: Spatial distribution of agricultural terraces according to physical and anthropic characterization in a Mountainous Mediterranean catchment, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-622, https://doi.org/10.5194/icg2022-622, 2022.

The Andes Mountains stretch over about 8900 km and cross tropical, subtropical, temperate and arid latitudes. Very few, if any, of the diverse physiographic, climatic and biogeographic regions in the Andes have been preserved from human impact. Land use and management have significantly altered the magnitude and frequency of erosion events: deforestation and agricultural practices (such as soil tillage and cattle grazing) have modified erosion rates, river sediment loads and landslide occurrences.

There is an urgent need to identify which soil conservation and management practices are most effective to combat soil erosion and to mitigate the on-site and off-site effects in the Andean region. Three large groups of water-related interventions can be identified: interventions based on land use and protective land cover including (1) restoration and protection of native ecosystems, such as montane forests or grasslands and (2) forestation with native or exotic species and (3) soil and water conservation measures including crop management, conservation tillage and slow-forming terraces and the implementation of linear elements such as vegetation strips and check dams. To expand the knowledge base on natural infrastructure for erosion mitigation in the Andes, it is necessary to move beyond case-by-case empirical studies to comprehensive assessments.

This study reviews the state of evidence on the effectiveness of interventions to mitigate soil erosion by water and is based on Andean case studies. Based on a systematic review of peer-reviewed and grey literature involving more than 120 local case-studies from the Andes, this study addressed the following research questions: (1) Which erosion indicators allow us to assess the effectiveness of natural infrastructure? (2) What is the overall impact of working with natural infrastructure on on-site and off-site erosion mitigation? (3) Which locations and types of studies are needed to fill critical gaps in knowledge and research?

From the suite of physical, chemical and biological indicators commonly used in soil erosion research, two indicators were particularly relevant: soil organic carbon of topsoil and soil loss rates at plot scale. The protection and conservation of natural vegetation has the strongest effect on soil quality, with 3.01 ± 0.893 times higher soil organic carbon content in the topsoil compared to control sites. Soil quality improvements are significant but lower for forestation and soil and water conservation measures. Soil and water conservation measures reduce soil erosion to 62.1 ± 9.2 %, even though erosion mitigation is highest when natural vegetation is maintained.

The systematic review of the existing literature allowed us to identify critical gaps in knowledge and research. There is a need for future empirical work on soil quality, erosion and sediment yield before/after interventions in data-scarce regions, such as high elevations, regions with either low or high relief, and low to very low or very high precipitation. Besides, most erosion assessments are based on short-term measurements that tend to miss the impact of rare high-magnitude events. Further research is needed to evaluate whether the reported effectiveness holds during extreme events related to, for example, El Niño–Southern Oscillation.

How to cite: Vanacker, V., Molina, A., Rosas, M. A., Bonnesoeur, V., Román-Dañobeytia, F., Ochoa-Tocachi, B. F., and Buytaert, W.: The effect of natural infrastructure on water erosion mitigation in the Andes, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-529, https://doi.org/10.5194/icg2022-529, 2022.