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The CryoGrid community model is a flexible toolbox for simulating the ground thermal regime and the ice–water balance for permafrost and glaciers, extending a well-established suite of permafrost models (CryoGrid 1, 2, and 3). The CryoGrid community model can accommodate a wide variety of application scenarios, which is achieved by fully modular structures through object-oriented programming. Different model components, characterized by their process representations and parameterizations, are realized as classes (i.e., objects) in CryoGrid. Standardized communication protocols between these classes ensure that they can be stacked vertically. For example, the CryoGrid community model features several classes with different complexity for the seasonal snow cover, which can be flexibly combined with a range of classes representing subsurface materials, each with their own set of process representations (e.g., soil with and without water balance, glacier ice). We present the CryoGrid architecture as well as the model physics and defining equations for the different model classes, focusing on one-dimensional model configurations which can also interact with external heat and water reservoirs. We illustrate the wide variety of simulation capabilities for a site on Svalbard, with point-scale permafrost simulations using, e.g., different soil freezing characteristics, drainage regimes, and snow representations, as well as simulations for glacier mass balance and a shallow water body. The CryoGrid community model is not intended as a static model framework but aims to provide developers with a flexible platform for efficient model development. In this study, we document both basic and advanced model functionalities to provide a baseline for the future development of novel cryosphere models.

Ground temperatures in coarse, blocky deposits such as mountain blockfields and rock glaciers have long been observed to be lower in comparison with other (sub)surface material. One of the reasons for this negative temperature anomaly is the lower soil moisture content in blocky terrain, which decreases the duration of the zero curtain in autumn. Here we used the CryoGrid community model to simulate the effect of drainage on the ground thermal regime and ground ice in blocky terrain permafrost at two sites in Norway. The model set-up is based on a one-dimensional model domain and features a surface energy balance, heat conduction and advection, as well as a bucket water scheme with adjustable lateral drainage. We used three idealized subsurface stratigraphies, blocks only, blocks with sediment and sediment only, which can be either drained (i.e. with strong lateral subsurface drainage) or undrained (i.e. without drainage), resulting in six scenarios. The main difference between the three stratigraphies is their ability to retain water against drainage: while the blocks only stratigraphy can only hold small amounts of water, much more water is retained within the sediment phase of the two other stratigraphies, which critically modifies the freeze–thaw behaviour. The simulation results show markedly lower ground temperatures in the blocks only, drained scenario compared to other scenarios, with a negative thermal anomaly of up to 2.2 ∘C. For this scenario, the model can in particular simulate the time evolution of ground ice, with build-up during and after snowmelt and spring and gradual lowering of the ice table in the course of the summer season. The thermal anomaly increases with larger amounts of snowfall, showing that well-drained blocky deposits are less sensitive to insulation by snow than other soils. We simulate stable permafrost conditions at the location of a rock glacier in northern Norway with a mean annual ground surface temperature of 2.0–2.5 ∘C in the blocks only, drained simulations. Finally, transient simulations since 1951 at the rock glacier site (starting with permafrost conditions for all stratigraphies) showed a complete loss of perennial ground ice in the upper 5 m of the ground in the blocks with sediment, drained run; a 1.6 m lowering of the ground ice table in the sediment only, drained run; and only 0.1 m lowering in the blocks only, drained run. The interplay between the subsurface water–ice balance and ground freezing/thawing driven by heat conduction can at least partly explain the occurrence of permafrost in coarse blocky terrain below the elevational limit of permafrost in non-blocky sediments. It is thus important to consider the subsurface water–ice balance in blocky terrain in future efforts in permafrost distribution mapping in mountainous areas. Furthermore, an accurate prediction of the evolution of the ground ice table in a future climate can have implications for slope stability, as well as water resources in arid environments.

Rock glaciers are geomorphological expressions of permafrost. Close to sea level in northernmost Norway, in the subarctic Nordkinn peninsula, we have observed several rock glaciers that appear to be active now or were active in the recent past. Active rock glaciers at this elevation have never before been described in Fennoscandia, and they are outside the climatic limits of present-day permafrost according to models. In this study, we have investigated whether or not these rock glaciers are active under the current climate situation. We made detailed geomorphological maps of three rock glacier areas in Nordkinn and investigated the regional ground dynamics using synthetic aperture radar interferometry (InSAR). One of the rock glaciers, namely the Ivarsfjorden rock glacier, was investigated in more detail by combining observations of vertical and horizontal changes from optical images acquired by airborne and terrestrial sensors and terrestrial laser scans (TLSs). The subsurface of the same rock glacier was investigated using a combination of electrical resistivity tomography (ERT) and refraction seismic tomography (RST). We also measured ground surface temperatures between 2016 and 2020, complemented by investigations using an infrared thermal camera, and a multi-decadal climatic analysis. We mapped the rock glaciers in the innermost parts of Store and Lille Skogfjorden as relict, while the more active ones are in the mouths of both fjords, fed by active talus in the upper slopes. Several of the rock glaciers cross over both the Younger Dryas shoreline (25 m a.s.l.) and the Early to Mid-Holocene shoreline at 13 m a.s.l. Both InSAR and optical remote sensing observations reveal low yearly movement rates (centimetres to millimetres per year). The ERT and RST suggest that there is no longer permafrost and ground ice in the rock glacier, while temperature observations on the front slope indicate freezing conditions also in summer. Based on the in situ temperature measurements and the interpolated regional temperature data, we show that the mean annual air temperature (MAAT) of the region has risen by 2 ∘C since the late 19th century to about 1.5 ∘C in the last decade. MAATs below 0 ∘C 100–150 years ago suggest that new rock glacier lobes may have formed at the end of the Little Ice Age (LIA). These combined results indicate that the Nordkinn rock glaciers are transitioning from active to relict stages. The study shows that transitional rock glaciers are still affected by creep, rock falls, snow avalanches, etc., and are not entirely dynamically dead features. Our contrasting results concerning permafrost presence and rock glacier activity show the importance of a multi-methodological approach when investigating slope processes in the edge zones of permafrost influence.

With the EU-funded PACE project in the turn of this century, several deep boreholes (100 m +) were drilled in European mountain sites, including mainland Norway, Svalbard and Sweden. During other projects from c. 2004 and the International Polar Year (IPY) period in 2006/07, several additional boreholes were drilled in different sites in both Norway and Iceland, measuring temperatures along both altitudinal and latitudinal gradients. At most sites, multi-temporal geophysical soundings are available using seismic and electrical resistivity tomography (ERT). Here we study the development of permafrost and ground temperatures in mainland Norway and Iceland based on these data sets. We document that permafrost in is warming at an high rate, including the development of taliks in both Norway and Iceland in response to climate change during the last 20 years. At most sites ground surface temperature (GST) is apparently increasing stronger than surface air temperature (SAT). Changing snow conditions appear to be the most important factor for the higher GST rates. Modelling exercises also indicate that the talik development can by explained both by higher air temperatures and increasing snow cover.

This research was funded by the European Space Agency Permafrost-CCI project (grant number 4000123681/18/I-NB). Rock glaciers are landforms related to permafrost creep that are sensitive to climate variability and change. Their spatial distribution and kinematic behaviour can be critical for managing water resources and geohazards in periglacial areas. Rock glaciers have been inventoried for decades worldwide, often without assessment of their kinematics. The availability of remote sensing data however makes the inclusion of kinematic information potentially feasible, but requires a common methodology in order to create homogeneous inventories. In this context, the International Permafrost Association (IPA) Action Group on rock glacier inventories and kinematics (2018-2023), with the support of the European Space Agency (ESA) Permafrost Climate Change Initiative (CCI) project, is defining standard guidelines for the inclusion of kinematic information within inventories. Here, we demonstrate the feasibility of applying common rules proposed by the Action Group in 11 regions worldwide. Spaceborne interferometric synthetic aperture radar (InSAR) was used to characterise identifiable moving areas related to rock glaciers, applying a manual and a semi-automated approach. Subsequently, these areas were used to assign kinematic information to rock glaciers in existing or newly compiled inventories. More than 5000 moving areas and more than 3600 rock glaciers were classified according to their kinematics. The method and the preliminary results were analysed. We identified drawbacks related to the intrinsic limitations of InSAR and to various applied strategies regarding the integration of non-moving rock glaciers in some investigated regions. This is the first internationally coordinated work that incorporates kinematic attributes within rock glacier inventories at a global scale. The results show the value of designing standardised inventorying procedures for periglacial geomorphology. Copyright: © 2022 Aldo Bertone et al. Publisher PDF

Blockfields remain enigmatic regarding their origin, internal structure, surface processes, and glaciological implications. In Scandinavia, blockfields are found on high-elevation, low-relief mountains (plateaus) across the Arctic and Subarctic. In this study, we present a 1D numerical model that uses near-surface temperatures measured between summer 2018 and summer 2020 to calculate frost-cracking intensities (FCI) within the ground column in three different blockfields in Norway and Svalbard. Eighty-nine miniature temperature loggers were distributed on Tron Mountain (1650 m a.s.l.) in Alvdal, Gamlemsveten (780 m a.s.l.) near Ålesund in southwestern Norway and on Platåberget (460 m a.s.l.) near Longyearbyen, Svalbard. We modelled FCI by scaling the time spent in the frost cracking window (between −3 and −8°C) with the temperature gradient and a penalty function for distance to available water. At Tron and Gamlemsveten, ground temperatures never reached the frost cracking window at one third of our sites due to insulation by a thick snow cover in depressions and on the lee sides of summits. The highest FCI (0.05–0.4 K m) are obtained where the subsurface consists of boulders and stones in a matrix of relatively fine sediment (sand, silt, gravel). In contrast, very low FCI (0.003–0.02 K m) were modelled for blocky layers with large air-filled pores because of the low water availability. On Platåberget, all sensors reached the frost-cracking window during the annual temperature cycle, but FCI are extremely low (0.0004–0.15 K m) as water availability is limited due to (i) permafrost and (ii) near-surface temperatures remaining below the frost-cracking window for 3/4 of the year. This indicates that boulder-rich blockfields with air-filled hollows are preserved in very cold climates, whereas warmer, maritime settings with higher availability of fine interstitial material place blockfields in the fast lane for frost weathering.

Ground temperatures in coarse, blocky deposits such as mountain blockfields and rock glaciers have long been observed to be lower in comparison with other (sub)surface material. One of the reasons for this negative temperature anomaly is the lower soil moisture content in blocky terrain, which decreases the duration of the zero curtain in autumn. Here we used the CryoGrid community model to simulate the effect of drainage in blocky terrain permafrost at two sites in Norway. The model setup features a surface energy balance, heat conduction and advection, as well as a bucket water scheme with adjustable lateral drainage. We used three idealized subsurface stratigraphies, denoted blocks only, blocks with sediment and sediment only and are either drained or undrained of water, resulting in six ‘scenarios’. The main difference between the three stratigraphies is their ability to retain water against drainage: while the blocks only stratigraphy can only hold small amounts of water, much more water is retained within the sediment phase of the two other stratigraphies, which critically modifies the freeze-thaw behaviour. The simulation results show markedly lower ground temperatures in the blocks only, drained scenario compared to other scenarios, with negative thermal anomaly of up to 1.8–2.2 °C. For this scenario, the model can in particular simulate the time evolution of ground ice, with build-up during and after snow melt and spring and gradual lowering of the ice table in the course of the summer season. We simulate stable permafrost conditions at the location of a rock glacier in northern Norway with a mean annual ground surface temperature of 2.0–2.5 °C in the blocks only, drained simulations. Finally, transient simulations at the rock glacier site showed a complete or partial lowering of the ground ice table since 1951 for all simulations except the blocks only, drained run. The interplay between the subsurface water/ice balance and ground freezing/thawing driven by heat conduction can at least partly explain the occurrence of permafrost in coarse blocky terrain below the assumed elevational limit of permafrost. It is thus important to consider this effect in future efforts on permafrost distribution mapping in mountainous areas. Furthermore, an accurate prediction of the evolution of the ground ice table in a future climate can have implications for slope stability, as well as water resources in arid environments.

The importance of frost weathering processes has long been discussed in the context of cold-climate landscape evolution. The 9 % volumetric expansion of in situ water when it freezes to ice was initially held responsible for generating the stresses that create and widen cracks in rocks. This theory has since been challenged by the theory of ice segregation in rocks, in which the growth of ice lenses is supplied by additional water that is drawn to the freezing front. Numerical modelling and laboratory experiments suggest that segregated ice growth can generate enough stress to cause rock damage and is most intense between approximately -8 and -3 ℃ (the precise range depends on rock properties), in the so-called frost cracking window (FCW). The two theories of weathering have different implications for landscape evolution: (1) if in situ volumetric expansion is more important, most frost weathering should occur close to the freezing point, (2) if ice lensing is more important, most frost weathering should occur in the FCW. For the latter theory, several frost weathering indices have been developed based on such factors as the time spent vulnerable to cracking within the FCW, the magnitudes of ground temperature gradients that induce water transport, and other factors that affect water availability. In this study, we model ground temperature using the ground heat flux model CryoGrid 2D (Myhra et al., 2017) and apply the one-dimensional frost weathering index proposed by Rempel et al. (2016), where frost weathering potential is assumed to be correlated with porosity changes that accompany gradients in water flux. Here, we adjust the frost weathering index so that frost weathering potential is modeled in two dimensions. Our results predict spatial and temporal patterns of frost weathering in rock walls that can be tested in the field. References Myhra, K. S., Westermann, S., & Etzelmüller, B. (2017). Modelled distribution and temporal evolution of permafrost in steep rock walls along a latitudinal transect in Norway by CryoGrid 2D. Permafrost and Periglacial Processes, 28(1), 172-182. doi: 10.1002/ppp.1884.Rempel, A. W., Marshall, J. A., & Roering, J. J. (2016). Modeling relative frost weathering rates at geomorphic scales. Earth and Planetary Science Letters, 453, 87-95. doi:10.1016/j.epsl.2016.08.019

Large unstable rock slopes (LURS) are common in formerly and present glaciated mountain environments. Many of these instabilities started moving or failed shortly after deglaciation due to debutressing. However, many LURS failed long after deglaciation or showed varying creep velocities during Holocene. This has been partly attributed to warming and thawing of permafrost, which might influence rock slope stability. This presentation reviews recent studies on the relation of permafrost distribution and rock slope stability in Norwegian mountains, summarizing new observations, models and interpretations, in cooperation with the Norwegian Geological Survey (NGU), The Norwegian Water and Energy Directorate (NVE), University College of Western Norway, Technical University in Munich (Germany), University of Tromsø and EDTYM (France).

Mountain permafrost and rock glaciers have been intensely investigated in Southern Carpathians highest ranges in the last 15 years using thermal, geophysical and remote sensing methods. However, a complete estimation of permafrost area has not been done so far. Thus, using statistical modeling we intend to offer an image of potential permafrost distribution in Southern Carpathians ranges of Făgăraș, Iezer, Parâng, Retezat, Godeanu and Țarcu. Model 1 is based on machine learning algorithms and model 2 is based on Maxent model. Both models use bottom temperature of snow (BTS) data as independent variable and land cover, altitude, slope curvature, solar radiation and snow probability as independent variables. Land cover is considered the key variable as the field methods indicated that permafrost can only be present in the talus deposits that produce negative thermal anomalies in the underground. Results indicated an area of about 45-60 km2 of potential permafrost distribution depending on the BTS threshold used for permafrost presence (-3°C, -2.5°C and -2°C). This represent about 0.01% from a total surface of about 4334 km2 of the six ranges used in this analysis being a typical sporadic mountain permafrost in a marginal periglacial environment.

Slow creeping landslides move at rates of millimeters to several meters per year. They can cause extensive damage to infrastructure and pose a major threat to human lives if failing catastrophically. Landslides can progressively weaken over time by rock mass damage processes that may occur by constant slow creep or sudden transient slips. Eventually, damage can lead to strain localization along the basal shear plane and catastrophic failure of the landslide. When observed, transient slip events, also called creep bursts, may induce short-term loading and hence can control landslide stability. These creep bursts correspond to short periods that can last several days where the displacement of a landslide accelerates and then decelerates. Here, we compiled and analyzed extensive multiphysics data series of the Åknes landslide, Norway. This landslide is moving at a slow rate of 6 cm per year and could generate a large tsunami wave in a fjord if it would rupture catastrophically. Based on the time series of an array of eight seismometers, five extensometers, seven borehole inclinometers and piezometer strings, and ten continuous GPS stations sampled with time resolutions down to 5 minutes over several years, we detected creep bursts in this landslide. These events interact with a distinct creep trend related to seasonal variations of rainfall and snowmelt. We analyze the creep bursts in regards to micro-earthquake activity and water pressure levels, to study their origin.

Warming-induced permafrost degradation is believed to be responsible for the increasing number of rock-slope instabilities, such as rockfalls or rock avalanches, over the past few decades. Relationship between permafrost degradation and geomorphological activity, is nevertheless, hard to establish because often little is known about the permafrost distribution in steep slopes. In the present study, we assess spatio-temporal changes in rock wall temperature in Norway post the Little Ice Age, using the two-dimensional ground heat flux model CryoGrid 2D. We create transects across the monitored rock walls in the Western Norway, in the high alpine range of Jotunheimen and in the Northern Norway. Our results demonstrate that rock wall temperature at 20 m depth increased by an average of 0.2 °C decade-1 since the 1980s. Therefore, if atmospheric warming rates remain similar, rock wall permafrost currently at -1 °C at 20 m depth could degrade completely at this depth by 2070. Furthermore, we show how rock wall temperature is influenced by: (1) rock wall geometry, (2) rock wall size, (3) magnitude of surface offsets due to the incoming shortwave solar radiation, (4) snow conditions above and below rock walls, (5) blockfield-covered plateaus or glaciers in their vicinity. Multi-dimensional thermal effects are smaller in Norway than in the European Alps due to the dissimilarities in mountain geometry and smaller differences in ground surface temperature between various mountainsides. Rock walls with large surface offsets arising from solar radiation might be warmer than plateaus above or talus slopes below, thus ground heat flux in such rock walls is directed towards colder plateaus or talus slopes. Furthermore, thermal conditions in blockfield-covered plateaus have impact on rock wall temperature and lead to larger warming rates at 20 m depth, whereas large glaciers decrease warming rates at the same depth. Therefore, a potential glaciers retreat would likely increase ground warming rates in the nearby parts of rock walls.

Around 10 % of unstable rock slopes in Norway are possibly underlain by widespread permafrost. Permafrost thaw and degradation may play a role in slope destabilization and more knowledge about rock wall permafrost in Norway is needed to investigate possible links between ground thermal regime, geomorphological activity and natural hazards. Here, we assess spatio-temporal permafrost variations in selected rock walls in Norway over the last 120 years. We model ground temperature using the two-dimensional ground heat flux model CryoGrid 2D along nine profiles crossing monitored rock walls in Norway. The simulation results show the distribution of sporadic to continuous permafrost along the modelled profiles. Ground temperature at 20 m depth in steep rock faces increased by 0.2 °C decade-1 on average since the 1980s. Rates of ground temperature change increase with elevation within a single rock wall section. Multi-dimensional thermal effects are in general smaller in Norway than in e.g. the European Alps due to gentler mountain topography and less aspect-related variations in ground surface temperature. Nevertheless, the steepest mountains are still sensitive to even small differences in ground surface temperature. This study further demonstrates how rock wall permafrost distribution and/or rock wall temperature increase rates are influenced by factors such as surface air temperature uncertainties, surface offsets arising from the incoming shortwave solar radiation, snow conditions in, above and below rock walls, rock wall geometry and size, adjacent blockfield-covered plateaus or glaciers.

The dependence of rock glaciers on permafrost and thus their sensitivity to climatic parameters makes the spatial distribution of these landforms very important for hydrological and climate changes reasons. Inventories of rock glaciers have been produced for decades worldwide, often without an assessment of their kinematics; the availability of remote sensing data makes the inclusion of kinematic information potentially feasible, but the absence of a common methodology makes it challenging to create homogeneous inventories. In this context, the IPA Action Group on rock glacier inventories and kinematics (2018–2023), with the support of the ESA Permafrost_CCI project, is promoting the definition of standard guidelines for the inclusion of kinematic information within inventories. Here, we test the feasibility of applying common rules proposed by the Action Group in eleven regions worldwide. Satellite interferometry is used to characterize identifiable areas with slope movements related to rock glaciers; subsequently, these areas are used to assign kinematic information to rock glaciers in existing or newly compiled inventories. More than 5,000 slope movements and more than 3,600 rock glaciers are classified according to their kinematics. The analyzes conducted on the method and on the preliminary results show small irregularities related to the detection capacity of interferometry and to lack of rock glaciers without detectable movements in some regions investigated. This is the first internationally coordinated effort of rock glacier inventories. We demonstrate the feasibility of applying common rules to implement kinematic attributes within inventories at a global scale, despite the various regions and intensive manual effort.

Microtopography can be a key driver of heterogeneity in the ground thermal and hydrological regime of permafrost landscapes. In turn, this heterogeneity can influence plant communities, methane fluxes, and the initiation of abrupt thaw processes. Here we have implemented a two-tile representation of microtopography in JULES (the Joint UK Land Environment Simulator), where tiles are representative of repeating patterns of elevation difference. Tiles are coupled by lateral flows of water, heat, and redistribution of snow, and a surface water store is added to represent ponding. Simulations are performed of two Siberian polygon sites, (Samoylov and Kytalyk) and two Scandinavian palsa sites (Stordalen and Iškoras). The model represents the observed differences between greater snow depth in hollows vs. raised areas well. The model also improves soil moisture for hollows vs. the non-tiled configuration (“standard JULES”) though the raised tile remains drier than observed. The modelled differences in snow depths and soil moisture between tiles result in the lower tile soil temperatures being warmer for palsa sites, as in reality. However, when comparing the soil temperatures for July at 20 cm depth, the difference in temperature between tiles, or “temperature splitting”, is smaller than observed (3.2 vs. 5.5 ∘C). Polygons display small (0.2 ∘C) to zero temperature splitting, in agreement with observations. Consequently, methane fluxes are near identical (+0 % to 9 %) to those for standard JULES for polygons, although they can be greater than standard JULES for palsa sites (+10 % to 49 %). Through a sensitivity analysis we quantify the relative importance of model processes with respect to soil moisture and temperatures, identifying which parameters result in the greatest uncertainty in modelled temperature. Varying the palsa elevation between 0.5 and 3 m has little effect on modelled soil temperatures, showing that using only two tiles can still be a valid representation of sites with a range of palsa elevations. Mire saturation is heavily dependent on landscape-scale drainage. Lateral conductive fluxes, while small, reduce the temperature splitting by ∼ 1 ∘C and correspond to the order of observed lateral degradation rates in peat plateau regions, indicating possible application in an area-based thaw model.

Microtopography can be a key driver of heterogeneity in the ground thermal and hydrological regime of permafrost landscapes. In turn, this heterogeneity can influence plant communities, methane fluxes and the initiation of abrupt thaw processes. Here we have implemented a two-tile representation of microtopography in JULES (the Joint UK Land Environment Simulator), where tiles are representative of repeating patterns of elevation difference. We evaluate the model against available spatially resolved observations at four sites, gauge the importance of explicitly representing microtopography for modelling methane emissions and quantify the relative importance of model processes and the model’s sensitivity its parameters. Tiles are coupled by lateral flows of water, heat and redistribution of snow. A surface water store is added to represent ponding. The model is parametrised using characteristic dimensions of landscape features at sites. Simulations are performed of two Siberian polygon sites, Samoylov and Kytalyk, and two Scandinavian palsa sites, Stordalen and Iškoras. The model represents the observed differences between greater snow depth in hollows vs raised areas well. The model also improves soil moisture for hollows vs the non-tiled configuration (‘standard JULES’) though the raised tile remains drier than observed. For the two palsa sites, it is found that drainage needs to be impeded from the lower tile, representing the non-permafrost mire, to achieve the observed soil saturation. This demonstrates the need for the landscape-scale drainage to be correctly modelled. Causes of moisture heterogeneity between tiles are decreased runoff from the low tile, differences in snowmelt, and high to low-tile water flow. Unsaturated flows between tiles are negligible, suggesting the adequacy of simpler water-table based models of lateral flow in wetland environments. The modelled differences in snow depths and soil moistures between tiles result in the lower tile soil temperatures being warmer for palsa sites. When comparing the soil temperatures for July at 20 cm depth, the difference in temperature between tiles, or ‘temperature splitting’, is smaller than observed (3.2 vs 5.5 °C). The mean temperature of the two tiles remains approximately unchanged (+0.4 °C) vs standard JULES, and lower than observations. Polygons display small (0.2 °C) to zero temperature splitting, in agreement with observations. Consequently, methane fluxes are near identical (+0 to 9 %) to those for standard JULES for polygons, though can be greater than standard JULES for palsa sites (+10 to 49 %). Through a sensitivity analysis we identify the parameters resulting in the greatest uncertainty in modelled temperature. We find that at the sites tested, varying the parameters can result in the modelled July temperature splitting being at most 0.9 or 3 °C larger than observed for palsa or polygon sites respectively. Varying the palsa elevation between 0.5 and 3 m has little effect on modelled soil temperatures, showing that having only two tiles can still be a valid representation of sites with a large variability of palsa elevations. Lateral conductive fluxes, while small, reduce the temperature splitting by ~1 °C, and correspond to the order of observed lateral degradation rates in peat plateau regions, indicating possible application in an area-based thaw model.

Permafrost is a key element of the cryosphere and an essential climate variable in the Global Climate Observing System. There is no remote-sensing method available to reliably monitor the permafrost thermal state. To estimate permafrost distribution at a hemispheric scale, we employ an equilibrium state model for the temperature at the top of the permafrost (TTOP model) for the 2000–2016 period, driven by remotely- sensed land surface temperatures, down-scaled ERA-Interim climate reanalysis data, tundra wetness classes and landcover map from the ESA Landcover Climate Change Initiative (CCI) project. Subgrid variability of ground temperatures due to snow and landcover variability is represented in the model using subpixel statistics. The results are validated against borehole measurements and reviewed regionally. The accuracy of the modelled mean annual ground temperature (MAGT) at the top of the permafrost is ±2 °C when compared to permafrost borehole data. The modelled permafrost area (MAGT 0) is around 21 × 106 km2 (22% of exposed land area), which is approximately 2 × 106 km2 less than estimated previously. Detailed comparisons at a regional scale show that the model performs well in sparsely vegetated tundra regions and mountains, but is less accurate in densely vegetated boreal spruce and larch forests.

Rock walls in high mountain areas are the expression of long–term slopes response (103–105 years) to tectonics, weathering and denudation and a major source of sediment and hazard. Controls of mountain rock walls (RW) distribution and the response to post-glacial evolution are rarely discussed in the literature at the scale of mountain ranges. Using a database of 791 RW mapped in the Romanian Carpathians, we present their distribution and morphometry in respect to lithological classes, structural features and topography and relate their exposure to post–Younger Dryas (Holocene) rock slope failure chronology. Statistical analysis results show the high significance of structural and tectonic control on RW distribution, which prevails in sedimentary units where it imposed the predominance of West and North orientations and led to the formation of RW with dimensions up to a degree higher compared to other lithologies. Morphometric data indicate that metamorphic and igneous RW (linked to a great extent to glacial valleys and cirques headwalls) are usually restricted to the highest sectors of the mountain slopes, being characterized by reduced relative heights, asymmetrically distributed, common on the North-exposed slopes and extremely rare on the South. Based on 38 in-situ produced 10Be surface exposure ages obtained on meter-sized boulders from the Southern and Eastern Carpathians, we hypothesise that metamorphic and igneous RW in the formerly glaciated Carpathian valleys were significantly shaped during Early Holocene (before 9 ka) by rock slope failures events that followed the deglaciation of the highest cirques and by intense RW permafrost degradation, which also affected some of the highest sedimentary units. We associate the long–term imprints of frost weathering to the significant North/South RW and rock glaciers distribution asymmetry, also identified in other mid-latitude mountain sites with similar topographic constraints.

Permafrost degradation in steep rock walls and associated slope destabilization have been studied increasingly in recent years. While most studies focus on mountainous and sub-Arctic regions, the occurring thermo-mechanical processes also play an important role in the high Arctic. A more precise understanding is required to assess the risk of natural hazards enhanced by permafrost warming in high-Arctic rock walls. This study presents one of the first comprehensive datasets of rock surface temperature measurements of steep rock walls in the high Arctic, comparing coastal and near-coastal settings. We applied the surface energy balance model CryoGrid3 for evaluation, including adjusted radiative forcing to account for vertical rock walls. Our measurements comprise 4years of rock surface temperature data from summer 2016 to summer 2020. Mean annual rock surface temperatures ranged from−0.6in a coastal rock wall in 2017/18 to−4.3 ∘Cin a near-coastal rock wall in 2019/20. Our measurements and model results indicate that rock surface temperatures at coastal cliffs are up to 1.5 ∘Chigher than at near-coastal rock walls when the fjord is ice-free in winter, resulting from additional energy input due to higher air temperatures at the coast and radiative warming by relatively warm seawater. An ice layer on the fjord counteracts this effect, leading to similar rock surface temperatures to those in near-coastal settings. Our results include a simulated surface energy balance with shortwave radiation as the dominant energy source during spring and summer with net average seasonal values of up to 100 W m−2and longwave radiation being the main energy loss with net seasonal averages between 16 and 39 W m−2. While sensible heat fluxes can both warm and cool the surface, latent heat fluxes are mostly insignificant. Simulations for future climate conditions result in a warming of rock surface temperatures and a deepening of active layer thickness for both coastal and near-coastal rock walls. Our field data present a unique dataset of rock surface temperatures in steep high-Arctic rock walls, while our model can contribute towards the understanding of factors influencing coastal and near-coastal settings and the associated surface energy balance.

The warming and subsequent degradation of mountain permafrost within alpine areas is an important process influencing the stability of steep slopes and rock faces. The unstable and monitored slopes of Mannen (Møre and Romsdal, southern Norway) and Gámanjunni-3 (Troms and Finnmark, northern Norway) were classified as high-risk sites by the Norwegian Geological Survey (NGU). Failure initiation has been suggested to be linked to permafrost degradation, but the detailed permafrost distribution at the sites is unknown. Rockwall (RW) temperature loggers at both sites have measured the thermal regime since 2015, showing mean rock surface temperatures between +2.5 °C and −1.6 °C depending on site and aspect. Between 2016 and 2019 we conducted 2D and 3D electrical resistivity tomography (ERT) surveys on the plateau and directly within the rock wall back scarp of the unstable slopes at both sites. In combination with geophysical laboratory analysis of rock wall samples from both sites, the ERT soundings indicate wide-spread permafrost areas, especially at Gámanjunni-3. Finally, we conducted 2D thermal modelling to evaluate the potential thermal regime. Rockwall temperatures, together with ERT measurements and modelling of the ground thermal regime strongly indicate, at least locally, the presence of permafrost. Displacement rates show a seasonality, with higher velocities during spring and early summer than the rest of the year, possibly related to snow melting.

In high‐latitude and mountain regions, local processes such as redistribution by wind, snow metamorphism and percolation of water, produce a complex spatial distribution of snow depths and snow densities. With its strong control on the ground thermal regime, this snow distribution has pronounced effects on ground temperatures at small spatial scales which are typically not resolved by land surface models (LSMs). This limits our ability to simulate the local impacts of climate change on for example vegetation and permafrost. Here, we present a tiling approach combining the CryoGrid permafrost model with snow microphysics parametrizations from the CROCUS snow scheme to account for sub‐grid lateral exchange of snow and water in a process‐based way. We demonstrate that a simple setup with three coupled tiles, each representing a different snow accumulation class with a specific topographic setting, can reproduce the observed spread of winter‐time ground surface temperatures (GST) and end‐of‐season snow distribution for a high‐Arctic site on Svalbard. For the three‐year study period, the three‐tile simulations showed substantial improvement compared to traditional single‐tile simulations which naturally cannot account for sub‐grid variability. Amongst others, the representation of the warmest and coldest 5% of the observed GST distribution was improved by 1‐2°C, while still capturing the average of the distribution. The simulations also reveal positive mean annual GSTs at the locations receiving the greatest snow cover. This could be an indication for the onset of localized permafrost degradation which would be obscured in single‐tile simulations.

On September 5, 2019, the Veslemannen unstable rock slope (54,000 m3) in Romsdalen, Western Norway, failed catastrophically after 5 years of continuous monitoring. During this period, the rock slope weakened while the precursor movements increased progressively, in particular from 2017. Measured displacement prior to the failure was around 19 m in the upper parts of the instability and 4–5 m in the toe area. The pre-failure movements were usually associated with precipitation events, where peak velocities occurred 2–12 h after maximum precipitation. This indicates that the pore-water pressure in the sliding zones had a large influence on the slope stability. The sensitivity to rainfall increased greatly from spring to autumn suggesting a thermal control on the pore-water pressure. Transient modelling of temperatures suggests near permafrost conditions, and deep seasonal frost was certainly present. We propose that a frozen surface layer prevented water percolation to the sliding zone during spring snowmelt and early summer rainfalls. A transition from possible permafrost to a seasonal frost setting of the landslide body after 2000 was modelled, which may have affected the slope stability. Repeated rapid accelerations during late summers and autumns caused a total of 16 events of the red (high) hazard level and evacuation of the hazard zone. Threshold values for velocity were used in the risk management when increasing or decreasing hazard levels. The inverse velocity method was initially of little value. However, in the final phase before the failure, the inverse velocity method was useful for forecasting the time of failure. Risk communication was important for maintaining public trust in early-warning systems, and especially critical is the communication of the difference between issuing the red hazard level and predicting a landslide.

Assessing initiation of rock-slope deformation and paleo-slip rates of rockslides is important to understand the impact of climate variability - in particular permafrost changes - on rockslide activity. Norway, with 6–6.5% permafrost cover today, continues to experience spatial and temporal variations in permafrost. We assess the timing of deformation initiation and potential late Pleistocene and Holocene sliding rates for six active gradually deforming rockslides in Norway using terrestrial cosmogenic nuclide dating. We evaluate the timing and rates of deformation considering a possible climate control by modelling the permafrost evolution since deglaciation for three rockslide locations: Mannen, Revdalsfjellet and Gamanjunni 3. Deformation at these sites started during or at the end of the Holocene Thermal Maximum (HTM), between 8 and 4.5 ka when permafrost in those regions was mostly degraded. At two low elevation sites, Oppstadhornet and Skjeringahaugane in western Norway, where permafrost remained absent during the Holocene, deformation started shortly after deglaciation. The timings suggest that the presence of permafrost in Norwegian rock slopes had a stabilizing effect over several millennia after deglaciation. Vertical transects of exposure ages along outcropping sliding surfaces indicate that pre-historical sliding rates seem to have decreased throughout the Holocene at all analysed rock-slope instabilities. However, modern measured sliding rates at four sites indicate a moderate to strong acceleration, compared to previous deformation rates. Three of these sites are located above or at the lower limit of alpine permafrost, where recent permafrost degradation may enhance slope destabilisation. The implication is that slope failures may become more frequent during accelerated warming in the Arctic and Subarctic. © 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Subarctic peatlands underlain by permafrost contain significant amounts of organic carbon and our ability to quantify the evolution of such permafrost landscapes in numerical models is critical to provide robust predictions of the environmental and climatic changes to come. Yet, the accuracy of large-scale predictions is so far hampered by small-scale physical processes that create a high spatial variability of surface ground thermal regime and thus of permafrost degradation patterns. In this regard, a better understanding of the small-scale interplay between microtopography and lateral fluxes of heat, water and snow can be achieved by field monitoring and process-based numerical modeling. Here, we quantify the topographic changes of the Šuoššjávri peat plateau (Northern Norway) over a three-years period using repeated drone-based high-resolution photogrammetry. Our results show that edge degradation is the main process through which thermal erosion occurs and represents about 80 % of measured subsidence, while most of the inner plateau surface exhibits no detectable subsidence. Based on detailed investigation of eight zones of the plateau edge, we show that this edge degradation corresponds to a volumetric loss of 0.13 ± 0.07 m3 yr−1 m−1 (cubic meter per year and per meter of plateau circumference). Using the CryoGrid land surface model, we show that these degradation patterns can be reproduced in a modeling framework that implements lateral redistribution of snow, subsurface water and heat, as well as ground subsidence due to melting of excess ice. We reproduce prolonged climate-driven edge degradation that is consistent with field observations and present a sensitivity test of the plateau degradation on snow depth over the plateau. Small snow depth variations (from 0 to 30 cm) result in highly different degradation behavior, from stability to fast degradation. These results represent a new step in the modeling of climate-driven landscape development and permafrost degradation in highly heterogeneous landscapes such as peat plateaus. Our approach provides a physically based quantification of permafrost thaw with a new level of realism, notably, regarding feedback mechanisms between the dynamical topography and the lateral fluxes through which a small modification of the snow depth result in dramatic modifications of the permafrost degradation intensity. In this regard, these results also highlight the major control of snow pack characteristics on the ground thermal regime and the potential improvement that accurate snow representation and prediction could bring to projections of permafrost degradation.

Permafrost degradation in steep rock walls and associated slope destabilization have been studied increasingly in recent years. While most studies focus on mountainous and sub-Arctic regions, the occurring thermo-mechanical processes play an important role also in the high Arctic. A more precise understanding is required to assess the risk of natural hazards enhanced by permafrost warming in high Arctic rock walls. This study presents rock surface temperature measurements of coastal and non-coastal rock walls in a high Arctic setting on Svalbard. We applied the surface energy balance model CryoGrid 3 for evaluation, including adjusted radiative forcing to account for vertical rock walls. Our measurements and model results show that rock surface temperatures at coastal cliffs are up to 1.5 °C higher than non-coastal rock walls when the fjord is ice-free in the winter season, resulting from additional energy input due to higher air temperatures at the coast and radiative warming by relatively warm seawater. An ice layer on the fjord counteracts this effect, leading to similar rock surface temperatures as in non-coastal settings. Our results include a simulated surface energy balance with short-wave radiation as the dominant energy source during spring and summer, and long-wave radiation being the main energy loss. While sensible heat fluxes can both warm and cool the surface, latent heat fluxes are mostly insignificant. Simulations for future climate conditions result in a warming of rock surface temperatures and a deepening of active layer thickness for both coastal and non-coastal rock walls. Our field data present a unique data set of rock surface temperatures in steep high Arctic rock walls, while our model can contribute towards the understanding of factors influencing coastal and non-coastal settings and the associated surface energy balance.

The presence of ground ice in Arctic soils exerts a major effect on permafrost hydrology and ecology, and factors prominently into geomorphic landform development. As most ground ice has accumulated in near-surface permafrost, it is sensitive to variations in atmospheric conditions. Typical and regionally widespread permafrost landforms such as pingos, ice-wedge polygons, and rock glaciers are closely tied to ground ice. However, under ongoing climate change, suitable environmental spaces for preserving landforms associated with ice-rich permafrost may be rapidly disappearing. We deploy a statistical ensemble approach to model, for the first time, the current and potential future environmental conditions of three typical permafrost landforms, pingos, ice-wedge polygons and rock glaciers across the Northern Hemisphere. We show that by midcentury, the landforms are projected to lose more than one-fifth of their suitable environments under a moderate climate scenario (RCP4.5) and on average around one-third under a very high baseline emission scenario (RCP8.5), even when projected new suitable areas for occurrence are considered. By 2061–2080, on average more than 50% of the recent suitable conditions can be lost (RCP8.5). In the case of pingos and ice-wedge polygons, geographical changes are mainly attributed to alterations in thawing-season precipitation and air temperatures. Rock glaciers show air temperature-induced regional changes in suitable conditions strongly constrained by topography and soil properties. The predicted losses could have important implications for Arctic hydrology, geo- and biodiversity, and to the global climate system through changes in biogeochemical cycles governed by the geomorphology of permafrost landscapes. Moreover, our projections provide insights into the circumpolar distribution of various ground ice types and help inventory permafrost landforms in unmapped regions.

Arctic earth surface systems are undergoing unprecedented changes, with permafrost thaw as one of the most striking examples. Permafrost is critical because it controls ecosystem processes, human activities, and landscape dynamics in the north. Degradation (i.e. warming and thawing) of permafrost is related to several hazards, which may pose a serious risk to humans and the environment. Thaw of ice-rich permafrost increases ground instability, landslides, and infrastructure damages. Degrading permafrost may lead to the release of significant amounts of greenhouse gases to the atmosphere and threatens also biodiversity, geodiversity and ecosystem services. Thawing permafrost may even jeopardize human health. Consequently, a deeper understanding of the hazards and risks related to the degradation of permafrost is fundamental for science and society.To address climate change effects on infrastructure and human activities, we (i) mapped circumpolar permafrost hazard areas and (ii) quantified critical engineering structures and population at risk by mid-century. We used observations of ground thermal regime, geospatial environmental data, and statistically-based ensemble methods to model the current and future near-surface permafrost extent at ca. 1 km resolution. Using the forecasts of ground temperatures, a consensus of three geohazard indices, and geospatial data we quantified the amount and proportion of infrastructure elements and population at risk owing to climate change. We show that ca. 70% of current infrastructure and population in the permafrost domain are in areas with high potential for thaw of near-surface permafrost by 2050. One-third of fundamental infrastructure is located in high hazard regions where the ground is susceptible to thaw-related ground instability. Owing to the observed data-related and methodological limitations we call for improvements in the circumpolar hazard mappings and infrastructure risk assessments.To successfully manage climate change impacts and support sustainable development in the Arctic, it is critical to (i) produce high-resolution geospatial datasets of ground conditions (e.g., content of organic material and ground ice), (ii) develop further high-resolution permafrost modelling, (iii) comprehensively map permafrost degradation-related hazards, and (iv) quantify the amount and economic value of infrastructure and natural resources at risk across the circumpolar permafrost area.

Climate change has a strong impact on periglacial regions and intensifies the degradation of mountain permafrost. This can result in instabilities of steep rock walls as rock- and ice-mechanical properties are modified. Besides altitude and the related air temperature, latitude is a crucial factor, as solar radiation has a strong impact on the energy transfer processes from the atmosphere to the ground. It can differ significantly in intensity and time over latitudinal positions and exposures of frozen rock slopes.In this project, we suggest improving the parametrization of short-wave and long-wave radiation in thermal models for permafrost degradation. To achieve this, we will analyze temperature data of surface temperature loggers from Southern Norway to Svalbard. In total, 37 loggers were installed between 2010 and 2017. The field sites display enormous latitudinal gradients as well as topographic settings. Furthermore, they provide hourly data, allowing us to set up short-stepped time series for examination of solar radiation angles at varying latitudes.The data is used to set up a transient heat-flow model (CryoGrid) to simulate the local thermal regime. The model takes into account varying input of short-wave radiation due to aspect, slope angle and time as well as long-wave radiation under different sky-view factors. Finally, the influence of solar radiation on permafrost degradation in steep rock walls is investigated.

Peat plateaus are a major type of permafrost landscape in Arctic and Siberian lowlands. They represent a substantial pool of several hundreds of petagrams of organic carbon that has the potential to contribute to the Permafrost Carbon Feedback. The thermal response of these soils to the climate signal is complex and implies the interaction of various surface and subsurface processes operating at a very small spatial scale involving water, snow and heat fluxes and surface subsidence. As these processes have the ability to generate feedbacks between each other and trigger non-linear evolutions of the landscape, they challenge our abilities to measure and model them.Peat plateaus in Northern Norway have been actively degrading over at least the last 60 years. They thus offer a precious opportunity to measure and model the degradation patterns they exhibit. We present new topographical observations derived from drone-based photogrammetry that we acquired for one site in Northern Norway. Over a period of 3 years, these Digital Elevation Models allows quantifying precisely the surface subsidence and resulting lateral degradation of the peat plateaus. In a second time, we use the land surface model CryoGrid to model the observed patterns. The model is able to (i) simulate the snow fluxes and the water and heat sub-surface fluxes within the plateau and between the plateau and the surrounding wet mire and to (ii) represent the soil surface subsidence due to excess ice melt in the soil. We implement a set up that discretize the interface between the peat plateaus and the wet mire and force the Surface Energy Balance module of the model with climatic data derived from regional atmospheric modelling.Our simulations manage to reproduce the degradation speed we observe in our topographical data. We also present a sensitivity analysis of the degradation speed to snow cover and to the geometry of the peat plateaus and show how the feedbacks between the dynamical topography and the lateral fluxes of snow and water can trigger rapid permafrost thawing and fast degradation of permafrost landscapes.

Iceland’s periglacial realm is one of the most dynamic on the planet, with active geomorphological processes and high weathering rates of young bedrock resulting in high sediment yields and ongoing mass movement. Permafrost is discontinuous in Iceland’s highlands and mountains over c. 800 m a.s.l, and sporadic in palsa mires in the central highlands. During the late Pleistocene and Holocene, Iceland’s periglacial environment varied considerably in time and space, dominated by glacial fluctuations and periglacial processes. To evaluate the dynamics of permafrost in Iceland since the last deglaciation, we use the output of a coupled climate/ice sheet model to force a transient permafrost model (CryoGRID 2) from the Last Glacial Maximum (LGM) through to the present. We find that permafrost was widespread across the deglaciated areas of western, northern and eastern Iceland after the LGM, and that up to 20% of Iceland’s terrestrial area was underlain by permafrost throughout the late Pleistocene. This influenced geomorphological processes and landform generation: the early collapse of the marine-based ice sheet together with the aggradation of permafrost in these zones initiated the formation of abundant and now relict rock glaciers across coastal margins. Permafrost degraded rapidly after the Younger Dryas, with a marked impact on slope stability. Permafrost that formed during the Little Ice Age is again thawing rapidly, and an escalation in slope failure and mass-movement might be currently underway. Our study demonstrates that large regions of Iceland have been underlain by permafrost for millennia, facilitating landform development and influencing the stability of steep slopes.

Acquiring data to analyse change in topography is often a costly endeavour requiring either extensive, potentially risky, fieldwork and/or expensive equipment or commercial data. Bringing the cost down while keeping the precision and accuracy has been a focus in geoscience in recent years. Structure from motion (SfM) photogrammetric techniques are emerging as powerful tools for surveying, with modern algorithm and large computing power allowing for the production of accurate and detailed data from low-cost, informal surveys. The high spatial and temporal resolution permits the monitoring of geomorphological features undergoing relatively rapid change, such as glaciers, moraines, or landslides. We present a method that takes advantage of light-transport flights conducting other missions to opportunistically collect imagery for geomorphological analysis. We test and validate an approach in which we attach a consumer-grade camera and a simple code-based Global Navigation Satellite System (GNSS) receiver to a helicopter to collect data when the flight path covers an area of interest. Our method is based and builds upon Welty et al. (2013), showing the ability to link GNSS data to images without a complex physical or electronic link, even with imprecise camera clocks and irregular time lapses. As a proof of concept, we conducted two test surveys, in September 2014 and 2015, over the glacier Midtre Lovénbreen and its forefield, in northwestern Svalbard. We were able to derive elevation change estimates comparable to in situ mass balance stake measurements. The accuracy and precision of our DEMs allow detection and analysis of a number of processes in the proglacial area, including the presence of thermokarst and the evolution of water channels.

The Quaternary geology of western Norway’s landscape is the result of glacial and post-glacial sedimentation and erosional processes, a significant sea-level drop and high rock-slope failure activity. All these processes are represented within a small valley section below the Mannen rock-slope instability in Romsdal valley, western Norway. Here, exposure ages, Quaternary geological mapping and geophysical investigations permit the development of a paraglacial landscape evolution model. The model contextualises at least six catastrophic rock-slope failure events within the overall sequence of fjord-valley infilling following deglaciation. A transition from a wide basin-like valley into a strongly confined valley section led to the build-up of more than 40 m thick stratified drift, which was at least partly deposited within a marine environment. The morphology of these sediments features two distinct erosional levels, which are interpreted to be connected to tidal currents during post-glacial sea-level drop. The landform evolution model illustrates the importance of catastrophic rock-slope failures and the impact of strong tidal currents on the typical sediment fill in narrow, high-relief fjord valleys.