Mountain Permafrost Research Articles

Evaluation of gas production from Qilian Mountain permafrost hydrate deposits in two-spot horizontal well system

In 2008–2009, gas hydrate deposits were confirmed to exist in the Qinghai–Tibet Plateau permafrost (QTPP) during the Scientific Drilling Project of Gas Hydrate in Qilian Mountain permafrost. Gas hydrate samples were successfully collected from three drilling sites: DK-1, DK-2, and DK-3. Based on the limited geological data from site measurements, gas was produced from the hydrate deposits of DK-2 zone in a two-spot well system through numerical simulation, and its commercial viability was evaluated. The two wells were placed on the same horizontal plane in the middle of the hydrate-bearing layer (HBL), and the depressurization and thermal stimulation methods were employed simultaneously in this system. Simulation results showed that desirable gas production performance could be obtained under suitable operation conditions when using this kind of well design. During the production process, large amount of free gas accumulated in the vicinity of the injection well until the flow channels between the two wells were gradually opened. It was found that the gas production performance was more favored with larger depressurization driving force, while the heat injection rate should be determined cautiously. Dependences of gas production performance on the various properties of hydrate deposits were also assessed.

Geochemical dynamics of the gas hydrate system in the Qilian Mountain Permafrost, Qinghai, Northwest China

The gas hydrate system in the Qilian Mountain permafrost region exists as an epigenetic hydrocarbon reservoir situated over a deep-seated potential hydrocarbon reservoir. This system is characterized by a particular series of geochemical processes and elemental behaviors, which control the origin of the gases, associated mineralization processes, and the geochemical migration and enrichment of different elements. In this study, we discuss these processes based on compositional analyses of the hydrate-bound gases, associated minerals, fracture fluid, and major, trace, and rare earth element behaviors. Most of the hydrate-bound gases are thermogenic in origin, with minor additional mixed microbial and thermogenic methane that is sourced from sapropelic kerogens in the underlying hydrocarbon reservoir. Episodes of mineralization that formed pyrite, alstonite, and ankerite along rock fractures were likely caused by decomposition of nearby gas hydrate, due to shrinkage of the gas hydrate stability zone. Major element concentration anomalies partly result from ion-precipitation that occurred in the pore and fracture fluid during hydrate formation and decomposition. Most of the anomalies in the measured trace element concentrations are interpreted to demarcate the base of the gas hydrate layer, as low-temperature hydrate has a strong sealing ability. Some of these enriched elements are shown to have migrated into the pyrite crystals, causing their anomalously high concentrations. In addition, the pyrite REE pattern varies with depth and, for pyrites with the same origin, the presence of a hydrate reservoir may be the major cause of fractionation of REE into pyrite. This study provides a new description of the geochemical dynamics of a gas hydrate system operating in a region of permafrost.

An Undercooled Scree Slope Detected by Geophysical Investigations in Sporadic Permafrost below 1000 M ASL, Central Austria

Multi-method geophysical investigations, accompanied by microclimatic measurements and vegetation mapping, were performed at an undercooled scree slope near Schladming (Austria) in the eastern Alps in order to detect, map and monitor mountain permafrost. The study site, at an elevation of 990m asl, is one of the lowest-lying examples of a cold, undercooled scree slope in the Alps. Geophysical measurements with electrical resistivity tomography, ground-penetrating radar and seismic refraction indicate the presence of several isolated areas of frozen ground over a full year, far below the regional lower limit of mountain permafrost. Frozen sediments identified at shallow depths (beneath 1-3m) were 5-20m thick and ice-rich. Near-surface temperatures at the foot of the scree slope were strongly influenced by pronounced cooling. Vegetation mapping showed a dominance of cryophilic plant species. The results suggest that the scree slope is strongly influenced by the interplay of vegetation cover, ground thermal regime and the distribution of frozen sediments. Copyright (C) 2014 John Wiley & Sons, Ltd. (Less)

The use of heat-assisted antigravity drainage method in the two horizontal wells in gas production from the Qilian Mountain permafrost hydrate deposits

Abstract The occurrence of gas hydrate deposits in the Qinghai–Tibet plateau permafrost (QTPP) were confirmed during the Scientific Drilling Project of Gas Hydrate in Qilian Mountain permafrost (QMP) in 2008–2009. A total of four test wells were completed, and gas hydrate samples were obtained from the drilling wells of DK-1, DK-2, and DK-3. The objective of this study is the analysis of gas production potential from gas hydrate-bearing zone of DK-2 using dual horizontal wells based on its geological properties at this site. In this paper, production strategies of permafrost hydrate deposits with the novel Heat-Assisted Antigravity Drainage (HAAD) method are investigated numerically. Gas production is induced in a two-well system and its influence factors are evaluated. When suitable heat injection rate and depressurization driving force are applied to the lower well and the upper well, respectively, favorable gas-to-water ratio and energy ratio can be obtained during the whole HAAD process. However, the absolute gas production rate may not be economically attractive for the production method we have employed. The sensitivity analysis indicates that the hydrate deposits with higher intrinsic permeability and larger rock porosity will show better perspective for hydrate exploitation.

Geochemistry and genesis of authigenic pyrite from gas hydrate accumulation system in the Qilian Mountain permafrost, Qinghai, northwest China

A type of authigenic pyrites that fully fill or semi-fill the rock fractures of drillholes with gas hydrate anomalies are found in the Qilian Mountain permafrost; this type of pyrite is known as “fracture-filling” pyrite. The occurrence of “fracture-filling” pyrite has a certain similarity with that of the hydrate found in this region, and the pyrite is generally concentrated in the lower part of the hydrate layer or the hydrate anomaly layer. The morphology, trace elements, rare earth elements, and sulfur isotope analyses of samples from drillhole DK-6 indicate that the “fracture-filling” pyrites are dominated by cubic ones mainly aligned in a step-like fashion along the surfaces of rock fractures and are associated with a circular structure, lower Co/Ni and Sr/Ba, lower ΣREE, higher LREE, significant Eu negative anomalies, and Δ34SCDT positive bias. In terms of the pyrites’ unique crystal morphology and geochemical characteristics and their relationship with the hydrate layers or abnormal layers, they are closely related with the accumulation system of the gas hydrate in the Qilian Mountain permafrost. As climate change is an important factor in affecting the stability of the gas hydrate, formation of fracture-filling pyrites is most likely closely related to the secondary change of the metastable gas hydrate under the regional climate warming. The distribution intensity of these pyrites indicates that when the gas hydrate stability zone (GHSZ) is narrowing, the hydrate decomposition at the bottom of the GHSZ is stronger than that at the top of the GHSZ, whereas the hydrate decomposition within the GHSZ is relatively weak. Thus, the zone between the shallowest and the deepest distribution of the fracture-filling pyrite recorded the largest possible original GHSZ.

Rock slope instability and erosion: toward improved process understanding

ABSTRACTRock slopes in a range of environments are among the landscape elements most sensitive to climate change, the latter affecting rock mass properties, altering slope boundary conditions, and changing geosystem configurations. Major climate‐dependent influences promoting destabilization include stress redistribution with changing glacial ice extents, degradation of mountain permafrost, altered slope hydrology and weathering environments, loading and unloading due to deposition and erosion, and changes in the spectrum of magnitude and frequency of driving forces. In steep bedrock terrain, erosional processes control slope morphology by modulating rates of: (i) weathering in response to climate and pre‐disposition, (ii) rock slope retreat in response to magnitude and frequency of detachment, and (iii) channel incision or valley infilling in response to variable sediment supply. Modelling landscape evolution and anticipating natural hazards in these environments thus requires deeper insights into the processes driving rock slope instability and erosion. This special issue emphasizes new understanding of rock slope processes through a collection of manuscripts at the forefront of research in the field. Copyright © 2014 John Wiley & Sons, Ltd.

Tracing variability of run‐off generation in mountainous permafrost of semi‐arid north‐eastern Mongolia

AbstractThe headwaters of mountainous, discontinuous permafrost regions in north‐eastern Mongolia are important water resources for the semi‐arid country, but little is known about hydrological processes there. Run‐off generation on south‐facing slopes, which are devoid of permafrost, has so far been neglected and is totally unknown for areas that have been affected by recent forest fires. To fill this knowledge gap, the present study applied artificial tracers on a steppe‐vegetated south‐facing and on two north‐facing slopes, burned and unburned. Combined sprinkling and dye tracer experiments were used to visualize processes of infiltration and water fluxes in the unsaturated zone. On the unburned north‐facing slope, rapid and widespread infiltration through a wet organic layer was observed down to the permafrost. On the burned profile, rapid infiltration occurred through a combusted organic and underlying mineral layer. Stained water seeped out at the bottom of both profiles suggesting a general tendency to subsurface stormflow (SSF). Ongoing SSF could directly be studied 24 h after a high‐intensity rainfall event on a 55‐m hillslope section in the burned forest. Measurements of water temperature proved the role of the permafrost layer as a base horizon for SSF. Repeated tracer injections allowed direct insights into SSF dynamics: A first injection suggested rather slow dispersive subsurface flow paths; whereas 18 h later, a second injection traced a more preferential flow system with 20 times quicker flow velocities. We speculate that these pronounced SSF dynamics are limited to burned slopes where a thermally insulating organic layer is absent. On three south‐facing soil profiles, the applied tracer remained in the uppermost 5 cm of a silt‐rich mineral soil horizon. No signs of preferential infiltration could be found, which suggested reduced biological activity under a harsh, dry and cold climate. Instead, direct observations, distributed tracers and charcoal samples provided evidence for the occurrence of overland flow. Copyright © 2014 John Wiley & Sons, Ltd.

Rock glacier outflows may adversely affect lakes: lessons from the past and present of two neighboring water bodies in a crystalline-rock watershed.

Despite the fact that rock glaciers are one of the most common geomorphological expressions of mountain permafrost, the impacts of their solute fluxes on lakes still remain largely obscure. We examined water and sediment chemistry, and biota of two neighboring water bodies with and without a rock glacier in their catchments in the European Alps. Paleolimnological techniques were applied to track long-term temporal trends in the ecotoxicological state of the water bodies and to establish their baseline conditions. We show that the active rock glacier in the mineralized catchment of Lake Rasass (RAS) represents a potent source of acid rock drainage that results in enormous concentrations of metals in water, sediment, and biota of RAS. The incidence of morphological abnormalities in the RAS population of Pseudodiamesa nivosa, a chironomid midge, is as high as that recorded in chironomid populations inhabiting sites heavily contaminated by trace metals of anthropogenic origin. The incidence of morphological deformities in P. nivosa of ∼70% persisted in RAS during the last 2.5 millennia and was ∼40% in the early Holocene. The formation of RAS at the toe of the rock glacier most probably began at the onset of acidic drainage in the freshly deglaciated area. The present adverse conditions are not unprecedented in the lake’s history and cannot be associated exclusively with enhanced thawing of the rock glacier in recent years.

A two-sided approach to estimate heat transfer processes within the active layer of the Murtèl–Corvatsch rock glacier

Abstract. The thermal regime of permafrost on scree slopes and rock glaciers is characterized by the importance of air flow driven convective and advective heat transfer processes. These processes are supposed to be part of the energy balance in the active layer of rock glaciers leading to lower subsurface temperatures than would be expected at the lower limit of discontinuous high mountain permafrost. In this study, new parametrizations were introduced in a numerical soil model (the Coup Model) to simulate permafrost temperatures observed in a borehole at the Murtèl rock glacier in the Swiss Alps in the period from 1997 to 2008. A soil heat sink and source layer was implemented within the active layer, which was parametrized experimentally to account for and quantify the contribution of air flow driven heat transfer on the measured permafrost temperatures. The experimental model calibration process yielded a value of about 28.9 Wm−2 for the heat sink during the period from mid September to mid January and one of 26 Wm−2 for the heat source in the period from June to mid September. Energy balance measurements, integrated over a 3.5 m-thick blocky surface layer, showed seasonal deviations between a zero energy balance and the calculated sum of the energy balance components of around 5.5 Wm−2 in fall/winter, −0.9 Wm−2 in winter/spring and around −9.4 Wm−2 in summer. The calculations integrate heat exchange processes including thermal radiation between adjacent blocks, turbulent heat flux and energy storage change in the blocky surface layer. Finally, it is hypothesized that these deviations approximately equal unmeasured freezing and thawing processes within the blocky surface layer.

Changing mountain permafrost from the 1970s to today - comparing two examples from Niwot Ridge, Colorado Front Range, USA

Melting mountain permafrost is reported from alpine areas around the world as a direct consequence of rising air temperatures over the past decades. However, alpine sites that offer suffi cient older data to compare with recent conditions are rare. The study site Niwot Ridge, situated at ~ 3600 m a.s.l. in the Front Range of the Rocky Mountains, Colorado, USA, offers permafrost distribution data from the early 1970s. We used four different approaches to evaluate and compare the old data with recent conditions and to discuss consequences in how the old data should be considered. (i) Air photographs and survey stakes were used to compare modern surface conditions of a solifl uction lobe with those in the past. Despite high resolution of the air photographs (0.3 m), the error of position after geo-rectifi cation was higher (1.0 m) than average displacement rates of gelifl uction lobes (10 mm * a–1), rendering this approach unsuitable. Replication of a 1963 –1967 study of soil movement from 2006 – 2009 yielded average movement rates of 11.4 mm * a–1 compared to 9.4 mm * a–1 in the 1960s. (ii) Temperature profi les of a three-year survey (2007– 2009) to depths of 7 m were compared with data from the 1970s from the same site. Modern temperature profi les document a complex annual curve that includes several weeks of unfrozen conditions, this fi nding is in contrast with the permafrost conditions reported from the 1970s. (iii) Electric resistivity profi les on a gelifl uction lobe, surveyed in different seasons during the year, show the freezing front down to 2 m depth during the early winter, the melting process during spring conditions and the complete melt of all ice lenses during the summer months. Geophysical results corroborate data from nearby temperature loggers and were used to extend the survey to other areas on Niwot Ridge. (iv) A simple 1 D-heat fl ow model was driven by the annual temperature variations of 1972 and 2008, resulting in several weeks of unfrozen conditions at various depths but with temperatures close to freezing during the 1970s. Our study documents that at present, on south facing slopes, permafrost neither exists at 2 m depth on wet sites nor at 4 m depth on dry sites as suggested during the 1970s. Our modeling approach further suggests that, except on wet gelifl uction lobes, it is likely that permafrost was not present at 3600 m during 1970, if so, permafrost degradation on south facing slopes on Niwot Ridge was not driven by recent climate change. However, north-facing slopes do cover permafrost, and certainly did in the 1970s, they are most probably affected by climate warming as already documented by a changing hydro-chemical signal in nearby streams.

Permafrost in Alpine Rock Faces from Jotunheimen and Hurrungane, Southern Norway

ABSTRACTThe warming and degradation of mountain permafrost within alpine areas is an important process influencing the stability of steep slopes and rock faces. In the mountains of southern Norway (Jotunheimen), an increase in ground temperatures has been recorded during the last 12 years, and modelling studies suggest the possible degradation of most mountain permafrost during the 21st century. To better estimate the thermal state of permafrost in steep rock walls in Norway, five temperature loggers were installed in 2009 and 2010, measuring the near‐surface rock wall temperatures in vertical rock faces. Surface temperatures in rock walls in Norway are on average higher than the ambient air temperature, by about 1 °C in shaded faces to more than 3 °C in faces with other aspects. An aspect dependency of rock wall temperatures is mainly visible during summer, with deviations of up to 4 °C between north‐ and south‐facing walls. Based on a 1D transient heat flow model, the active‐layer thickness at the study sites was estimated to be in the range of 3 m to 5 m at 2300 m asl and 1600 m asl, respectively. As a first‐order approximation, a spatial regression model based on elevation and potential incoming short‐wave radiation was used to estimate the lower limit and distribution of rock wall permafrost under present‐day conditions and for a scenario with average air temperatures increased by 2 °C. Today, the lower limit ranges from 1200–1300 m asl to 1600–1700 m asl in north‐ and south‐facing rock walls, respectively. With a warming of 2 °C, the lower limit would increase to about 1700 m and 2100 m, respectively, which corresponds to a loss of 70 per cent of the rock walls underlain by permafrost today in the study area, where more than half of the rock walls potentially containing permafrost are situated below 1800 m asl. Copyright © 2014 John Wiley & Sons, Ltd.

A spatial and temporal analysis of different periglacial materials by using geoelectrical, seismic and borehole temperature data at Murtèl–Corvatsch, Upper Engadin, Swiss Alps

Abstract. Different geophysical investigations, such as electrical resistivity tomography (ERT) and refraction seismic tomography (RST), allow for an improved characterization of subsurface conditions in mountain permafrost areas. The knowledge of the permafrost internal composition constitutes a major prerequisite for climate-related modelling studies, for detailed hazard or local infrastructure assessments. To detect the small-scale variations of permafrost characteristics and its varying sensitivity to climate influencing factors, two ERT and RST monitoring profiles were installed in 2009 at two different sites called Chastelets and Murtèl forefield located in the Murtèl–Corvatsch area, Upper Engadin, eastern Swiss Alps. The geophysical profiles extend over four existing boreholes and are characterized by strong small-scale variations of surface as well as subsurface structures such as bedrock, fine material or coarse debris. Here we present ERT measurements carried out in a bimonthly interval during the years of 2009 to 2012 and RST measurements which were performed once a year, normally in August, during the same period. Based on these data sets the so-called four-phase model, based on petrophysical relationships, was applied to determine the volumetric fractions of ice, water and air within the heterogeneous ground, resulting in a relatively precise description of the subsurface material around the existing boreholes. The observations revealed a permafrost occurrence at the Chastelets rock glacier with an estimated ice-saturated layer of at least 10 m thickness and the detection of a thawed layer with increased water content in the lower frontal part of the rock glacier within an area of fine material. In the area of the Murtèl forefield the analysis revealed strongly weathered bedrock, which is in the upper part covered by a pronounced layer of coarse debris establishing a thermal regime which is able to sustain permafrost beneath. In addition, the high temporal ERT measurements revealed a seasonal formation of ice during wintertime within the coarse- as well as the fine-grained active layer zones. It can be concluded that the combination of existing borehole temperature measurements, the ERT/RST measurements and the application of the four-phase model resulted in an in-depth view of the investigated area, which is a major prerequisite for future modelling studies allowing for a better treatment of the present small-scale spatial ground variabilities.

Source Rocks for Gases from Gas Hydrate and Their Burial Depth in the Qilian Mountain Permafrost, Qinghai: Results from Thermal Stimulation

The composition and isotope ratio of gases from gas hydrate and organic geochemistry of mudstone, oil shale, and coal within a gas hydrate-bearing interval in the Qilian Mountain permafrost suggest that gases from gas hydrate are derived from the deep, but the lithology and burial depth of source rocks for gases from gas hydrate are not yet known. In this study, samples of mudstone, oil shale, and coal were analyzed with thermal stimulation within the gas hydrate-bearing interval in the Qilian Mountain permafrost. Results showed that gas composition and carbon isotopes of hydrocarbon gases thermally stimulated from mudstone at temperatures of 350–400 °C and from oil shale at temperatures of 380–400 °C are similar to those of gases from gas hydrate, indicating that the deep mudstone and oil shale are potential source rocks for gases from gas hydrate. The gas composition of hydrocarbon gases thermally stimulated from coal was similar to that of gas hydrate, but their carbon isotope values were very differen...

Gas hydrate stability zone migration occurred in the Qilian mountain permafrost, Qinghai, Northwest China: Evidences from pyrite morphology and pyrite sulfur isotope

Fracture-filling pyrites, which semi-filled or fully filled rock fractures, were commonly found in the cores from all hydrate testing well in the Qilian mountain permafrost. The occurrence of the pyrites is very similar to the “fracture-filling” gas hydrate that occurred in this area, and whose distribution mainly concentrated below the hydrate layer or layer of hydrate associated anomaly. This paper carried out the study in morphology and sulfur isotope for the fracture-filling pyrites. The results show that fracture-filling pyrites consisted of cube form pyrite crystals, directionally spread in a step-like fashion along the fracture surface, and associated with a circular structure; the value of δ34SCDT ranges from 6.761‰ to 41.846‰, and the most positive excursion exists below the deepest layer of hydrate associated anomaly. The characters in pyrite crystal morphology, sulfur isotopic composition and spatial distribution closely related with the secondary change of metastable gas hydrate reservoir. The permafrost degeneration resulting from climate warming is the most direct cause for gas hydrate stability zone (GHSZ) migration that occurred in the Qilian mountain. The zone between the shallowest and the deepest distribution of the fracture-filling pyrite recorded the possible largest original GHSZ. The top and the bottom of GHSZ have moved downward and upward to a certain extent, respectively, further inferring that the depth of permafrost has decreased about 10m in the boreholes.

Monitoring of high alpine mass movements combining laser scanning with digital airborne photogrammetry

Airborne- and terrestrial laser scanning are used in combination with digital airborne photogrammetry to monitor surface changes between 2009 and 2011 on rock glaciers and landslides at three mountain permafrost sites (Grabengufer, Schafberg and Flüela Pass) in the Swiss Alps. 3D surface changes detected through comparison of multitemporal laser scanning data, as well as horizontal creep rates determined using laser scanning data and digital airborne photogrammetry are analyzed. The methods applied allow comprehensive quantification of mass movements and volumetric changes, which are presented in 2.5D. GPS ground truths are used as reference data at the Grabengufer site. On the basis of this, a quality estimation is developed for the sites without GPS reference data. For changes with an extent of about 25m2, a level of significance of 3cm was obtained for both horizontal and vertical displacements under optimal measurement conditions. The complex dynamics of creeping and sliding permafrost features are investigated through analysis of their surface kinematics.

Relict Talus‐Foot Rock Glaciers at Øyberget, Upper Ottadalen, Southern Norway: Schmidt Hammer Exposure Ages and Palaeoenvironmental Implications

ABSTRACTThree relict talus‐foot rock glaciers at Øyberget, upper Ottadalen, were dated using high‐precision Schmidt hammer exposure‐age dating (SHD). A SHD calibration curve was constructed for the local banded gneiss using two control points: (1) fresh bedrock in a road cutting; and (2) glacially scoured bedrock surfaces deglaciated c. 9.7 ka. Two alternative hypotheses are suggested to explain SHD ages (± 95% confidence intervals) of 10 340 ± 1280, 9920 ± 1385 and 8965 ± 1700 years obtained for the three rock glaciers located ~ 1000 m below the present lower limit of mountain permafrost, at a site covered by glacier ice throughout the Late Weichselian. First, the rock glaciers may be paraglacial features, which formed rapidly during deglaciation when enhanced debris supply may have buried residual ice bodies. If this was the case, the SHD ages are a true reflection of rock glacier age. Second, the rock glaciers may have formed during several thousand years of permafrost conditions in the Mid‐Weichselian (possibly during the Ålesund Interstadial, c. 34.5–38.2 ka) and then been preserved beneath a cold‐based ice sheet until renewed exposure during Holocene deglaciation. If the second hypothesis is true, then the true age of the rock glaciers is much older than their SHD ages, the latter failing to record the interval of burial when rock weathering would have been zero. Although evidence is currently insufficient to distinguish between these two interpretations, the paper demonstrates both the potential and limitations of high‐precision SHD in the context of rock glaciers. Copyright © 2013 John Wiley & Sons, Ltd.

Permafrost model sensitivity to seasonal climatic changes and extreme events in mountainous regions

Climate models project considerable ranges and uncertainties in future climatic changes. To assess the potential impacts of climatic changes on mountain permafrost within these ranges of uncertainty, this study presents a sensitivity analysis using a permafrost process model combined with climate input based on delta-change approaches. Delta values comprise a multitude of coupled air temperature and precipitation changes to analyse long-term, seasonal and seasonal extreme changes on a typical low-ice content mountain permafrost location in the Swiss Alps. The results show that seasonal changes in autumn (SON) have the largest impact on the near-surface permafrost thermal regime in the model, and lowest impacts in winter (DJF). For most of the variability, snow cover duration and timing are the most important factors, whereas maximum snow height only plays a secondary role unless maximum snow heights are very small. At least for the low-ice content site of this study, extreme events have only short-term effects and have less impact on permafrost than long-term air temperature trends.

Sensitivities and uncertainties of modeled ground temperatures in mountain environments

Abstract. Model evaluation is often performed at few locations due to the lack of spatially distributed data. Since the quantification of model sensitivities and uncertainties can be performed independently from ground truth measurements, these analyses are suitable to test the influence of environmental variability on model evaluation. In this study, the sensitivities and uncertainties of a physically based mountain permafrost model are quantified within an artificial topography. The setting consists of different elevations and exposures combined with six ground types characterized by porosity and hydraulic properties. The analyses are performed for a combination of all factors, that allows for quantification of the variability of model sensitivities and uncertainties within a whole modeling domain. We found that model sensitivities and uncertainties vary strongly depending on different input factors such as topography or different soil types. The analysis shows that model evaluation performed at single locations may not be representative for the whole modeling domain. For example, the sensitivity of modeled mean annual ground temperature to ground albedo ranges between 0.5 and 4 °C depending on elevation, aspect and the ground type. South-exposed inclined locations are more sensitive to changes in ground albedo than north-exposed slopes since they receive more solar radiation. The sensitivity to ground albedo increases with decreasing elevation due to shorter duration of the snow cover. The sensitivity in the hydraulic properties changes considerably for different ground types: rock or clay, for instance, are not sensitive to uncertainties in the hydraulic properties, while for gravel or peat, accurate estimates of the hydraulic properties significantly improve modeled ground temperatures. The discretization of ground, snow and time have an impact on modeled mean annual ground temperature (MAGT) that cannot be neglected (more than 1 °C for several discretization parameters). We show that the temporal resolution should be at least 1 h to ensure errors less than 0.2 °C in modeled MAGT, and the uppermost ground layer should at most be 20 mm thick. Within the topographic setting, the total parametric output uncertainties expressed as the length of the 95% uncertainty interval of the Monte Carlo simulations range from 0.5 to 1.5 °C for clay and silt, and ranges from 0.5 to around 2.4 °C for peat, sand, gravel and rock. These uncertainties are comparable to the variability of ground surface temperatures measured within 10 m × 10 m grids in Switzerland. The increased uncertainties for sand, peat and gravel are largely due to their sensitivity to the hydraulic conductivity.

Global warming accelerates the upfreezing of permafrost in arid middle Tianshan Mountains

Upfreezing is an important geomorphic process in the periglacial environment. It is a product of cold climate and thus an important part of the cryospheric processes. Based on the long-term positioning observations in the source area of the Urumqi River, this article represents an in-depth discussion of the characteristics of sorted circles and upfreezing mechanisms in the Tianshan Mountains. In the source area of the Urumqi River, the intensity of upfreezing is the highest within the top 25 cm near the surface, while targets with a diameter of 3 cm are least affected by upfreezing. There is no distinct difference between the centre with fine grains and the margin with coarse debris within the same sorted circle in terms of the intensity of upfreezing. The correlation analysis demonstrates that temperature plays an important role in upfreezing and the development of sorted circles. A long-time positioning observation of sorted circles reveals that periglacial landforms are sensitive to regional climate change and respond quickly to the temperature increase of the recent two decades. Enhanced upfreezing was found to be due to increased soil moisture content.

Modeled sensitivity of two alpine permafrost sites to RCM‐based climate scenarios

Climate change as projected by contemporary general circulation models (GCMs) and regional climate models (RCMs) will have a great impact on high latitude and high mountain permafrost. A process‐based one‐dimensional permafrost model is used to evaluate the sensitivity of two characteristic alpine permafrost sites to changes in climate for a 110 year time period starting 1991 and ending 2100 using output time series of six different GCM‐RCM model chains. Statistical analysis of the RCM climate variables and output of the impact model has been conducted to gain insight into the sensitivity of the active layer to changes in climatic conditions. Strong sensitivity to climate change was found for the active layer thickness (ALT) at Schilthorn, which increased by up to 100% before most of the models pointed to a degradation of the permafrost around the year 2020. The sensitivity of the ALT at the rock glacier site Murtèl is less pronounced; permafrost degradation is slower and sets in only around 2070. At both sites, the thermal evolution is linked to an increase in unfrozen water content within the permafrost body. Multiple linear regression analysis shows a strong model dependency of ALT on ice content and summer soil surface temperatures and to a less significant degree on snow cover timing and duration. The ALT at Schilthorn is influenced by the ALT of the preceding year, while at Murtèl, the ALT is influenced by the ALT of up to 15 preceding years.