Showing papers in "Permafrost and Periglacial Processes in 2006"
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TL;DR: In this article, a review paper examines thermal conditions (active layer and permafrost), internal composition (rock and ice components), kinematics and rheology of creeping perennially frozen slopes in cold mountain areas.
Abstract: This review paper examines thermal conditions (active layer and permafrost), internal composition (rock and ice components), kinematics and rheology of creeping perennially frozen slopes in cold mountain areas. The aim is to assemble current information about creep in permafrost and rock glaciers from diverse published sources into a single paper that will be useful in studies of the flow and deformation of subsurface ice and their surface manifestations not only on Earth, but also on Mars. Emphasis is placed on quantitative information from drilling, borehole measurements, geophysical soundings, photogrammetry, laboratory experiments, etc. It is evident that quantitative holistic treatment of permafrost creep and rock glaciers requires consideration of: (a) rock weathering, snow avalanches and rockfall, with grain-size sorting on scree slopes; (b) freezing processes and ice formation in scree at sub-zero temperatures containing abundant fine material as well as coarse-grained blocks; (c) coupled thermohydro-mechanical aspects of creep and failure processes in frozen rock debris; (d) kinematics of non-isotropic, heterogeneous and layered, ice-rich permafrost on slopes with long transport paths for coarse surface material from the headwall to the front and, in some cases, subsequent re-incorporation into an advancing rock glacier causing corresponding age inversion at
427 citations
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TL;DR: In this article, a review examines methods of investigation, testing techniques and the impact of freeze-thaw processes on the physical and mechanical properties of soils, especially those underlain by permafrost.
Abstract: Freeze-thaw cycling affects the geotechnical properties of soils and must be taken into account when selecting soil parameters for stability and deformation analysis of slopes, embankments and cuts in cold regions, especially those underlain by permafrost. This review examines methods of investigation, testing techniques and the impact of freeze-thaw processes on the physical and mechanical properties of soils. Copyright © 2006 John Wiley & Sons, Ltd.
268 citations
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TL;DR: In this article, the seasonal variation in the geochemical and isotopic content of the outflow of the Green Lake 5 rock glacier (RG5), located in the Green Lakes Valley of the Colorado Front Range, USA, was characterized.
Abstract: We characterize the seasonal variation in the geochemical and isotopic content of the outflow of the Green Lake 5 rock glacier (RG5), located in the Green Lakes Valley of the Colorado Front Range, USA. Between June and August, the geochemical content of rock glacier outflow does not appear to differ substantially from that of other surface waters in the Green Lakes Valley. Thus, for this alpine ecosystem at this time of year there does not appear to be large differences in water quality among rock glacier outflow, glacier and blockslope discharge, and discharge from small alpine catchments. However, in September concentrations of Mg2+ in the outflow of the rock glacier increased to more than 900 µeq L−1 compared to values of less than 40 µeq L−1 at all the other sites, concentrations of Ca2+ were greater than 4,000 µeq L−1 compared to maximum values of less than 200 µeq L−1 at all other sites, and concentrations of SO reached 7,000 µeq L−1, compared to maximum concentrations below 120 µeq L−1 at the other sites. Inverse geochemical modelling suggests that dissolution of pyrite, epidote, chlorite and minor calcite as well as the precipitation of silica and goethite best explain these elevated concentrations of solutes in the outflow of the rock glacier. Three component hydrograph separation using end–member mixing analysis shows that melted snow comprised an average of 30% of RG5 outflow, soil water 32%, and base flow 38%. Snow was the dominant source water in June, soil water was the dominant water source in July, and base flow was the dominant source in September. Enrichment of δ18O from −10‰ in the outflow of the rock glacier compared to −20‰ in snow and enrichment of deuterium excess from + 17.5‰ in rock glacier outflow compared to + 11‰ in snow, suggests that melt of internal ice that had undergone multiple melt/freeze episodes was the dominant source of base flow. Copyright © 2005 John Wiley & Sons, Ltd.
172 citations
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TL;DR: The origin and growth of numerous thermokarst lakes near Mayo, central Yukon, has been examined, using ground surveys, aerial photographs and dendrochronology as discussed by the authors.
Abstract: The origin and growth of numerous thermokarst lakes near Mayo, central Yukon, has been examined, using ground surveys, aerial photographs and dendrochronology. Many of the lakes are currently expanding, at rates of axial increment up to 1.2 m/yr. Three lakes, whose axes are currently enlarging at about 1.0 m/yr, were studied in particular detail: tree-ring analysis indicates that these lakes formed by the middle to the late part of the last century. The talik profile was determined beneath one lake, and is consistent with the Stefan solution for thawing of ice-rich soil with such an initiation date and rate of expansion. Organic-rich horizons containing logs, vegetative detritus and fresh-water ostracods have been exposed in two retrogressive thaw slumps near the lakes. These horizons have been interpreted as the bottoms of former thermokarst lakes. Radiocarbon dates of approximately 8500 BP, 3900 BP and 2300 BP have been obtained, indicating several periods of thermokarst activity during the Holocene. The results suggest that thermokarst lake development is not solely associated with changing climatic conditions in this region, since the current lakes and those that formed around 2300 BP do not appear to be directly linked to climatic warming. It is suggested that the most recent initiation of thermokarst activity is related to the effects of forest fires.
108 citations
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TL;DR: Active layer and permafrost monitoring at two sites in Northern Victoria Land, Boulder Clay (74°44′45′′S-164°01′17′′E at 205
Abstract: Active layer and permafrost monitoring at two sites in Northern Victoria Land, Boulder Clay (74°44′45′′S—164°01′17′′E at 205 m a.s.l.) and Oasi (74°42′S—164°06′E at 80 m a.s.l.), have been undertaken since 1996. Active layer monitoring was performed at Boulder Clay by probing on a 100×100 m grid following the CALM protocol, and by temperature measurements to ascertain the maximum depth of the 0°C isotherm. Automatic and year-round recording of ground temperatures and of the main climatic parameters was carried out near the grid. Since 1999, ground temperatures have been monitored in a 15.5 m borehole at Oasi. The depth of the 0°C isotherm correlates well with climate because the thermal offset is small, averaging less than 0.5°C. The large spatial and temporal variability of its depth mainly reflects the snow accumulation pattern. Future efforts to extend the monitoring network in continental Antarctica may combine annual measurements of the maximum 0°C isotherm depth with year-round monitoring of ground temperature at selected points of standardised CALM grids. Copyright © 2006 John Wiley & Sons, Ltd.
96 citations
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TL;DR: In this paper, a hydrological study of a cluster of ponds in a polar oasis of the Canadian Arctic showed the dominance of overland flow in the spring as an agent that recharged the pond storage.
Abstract: Tundra ponds are a common type of wetland in the High Arctic. Their preservation is predicated upon ample water supply and storage to overcome evaporation losses. Two years of hydrological study of a cluster of ponds in a polar oasis of the Canadian Arctic showed the dominance of overland flow in the spring as an agent that recharged the pond storage. The freshet produced by snowmelt gave rise to extensive surface flow connections between the ponds and with their surrounding areas, but such flow connectivity lasted only about 2 weeks. After that, the ponds appeared to be separated from lateral drainage. Detailed mapping of the water and frost table positions together with water balance investigation, however, indicated the presence of subsurface flows between some ponds and with their adjacent slope. The flow magnitude was small relative to the vertical processes of evaporation and rainfall. Evaporation loss was mainly responsible for storage depletion, leading to a decline in pond level and shrinkage of open water area, unless major rain events restored the storage (as in 2006). It is postulated that climate warming could increase evaporation and active layer thickness to promote greater loss in surface water storage, or geomorphic processes could breach the pond rims, leading to the demise of ponds. Copyright © 2006 John Wiley & Sons, Ltd.
89 citations
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TL;DR: In this article, a GIS-based empirical permafrost model that is calibrated with ground temperature observations, and utilises a multi-criteria approach to derive zones of permaffrost favourability based on terrain parameters and land cover information is presented.
Abstract: Lake Hovsgol is located on the southern fringe of the continuous permafrost zone in northern Mongolia. This paper describes a GIS-based empirical permafrost model that is calibrated with ground temperature observations, and utilises a multi-criteria approach to derive zones of permafrost favourability based on terrain parameters and land cover information. The scores are derived either by logistic regression or from satellite image information. The model is validated by DC resistivity tomography measurements. The overall permafrost distribution in the study area is well-described and the method appears to be a valid approach for mapping permafrost at both local and regional scales in mountain areas with low data coverage. Copyright © 2006 John Wiley & Sons, Ltd.
87 citations
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TL;DR: In this paper, the isotopic composition of ice wedges formed in alluvial and loess-like sediments generally reflects the palaeoclimate of winter conditions, and the transition to the Holocene is characterised by increases of 5'€ and 35'€ in δ18O and δD, respectively.
Abstract: Ice-rich permafrost deposits and their isotopic composition were studied at four sites in the western foreland of the Verkhoyansk Mountains, Central Yakutia. The isotopic composition of ice wedges formed in alluvial and loess-like sediments generally reflects the palaeoclimate of winter conditions. The middle Weichselian Ice Complex developed around 41 ka 14C BP during a period with colder winters than today. Similarly severe conditions are reflected in the late Weichselian Ice Complex from around 20 ka to 13 ka 14C BP. The transition to the Holocene is characterised by increases of 5‰ and 35‰ in δ18O and δD, respectively. This warming is documented in wedge ice, which grew between 8.5 and 4.5 ka BP. Towards the late Holocene and sub-recent times, a climatic deterioration is recorded, reflected by lighter isotopic composition of ice wedges, which developed between 1.2 ka and 0.7 ka 14C BP.
58 citations
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TL;DR: In this paper, a series of ground-penetrating radar (GPR) profiles at five sites from May-September, using 100, 200 and 400 MHz antennas, were acquired to investigate thaw progression over the 2004 summer season.
Abstract: Thaw depths beneath arctic streams may have significant impact on the seasonal development of hyporheic zone hydraulics. To investigate thaw progression over the 2004 summer season we acquired a series of ground-penetrating radar (GPR) profiles at five sites from May–September, using 100, 200 and 400 MHz antennas. We selected sites with the objective of including stream reaches that span a range of geomorphologic conditions on Alaska's North Slope. Thaw depths interpreted from GPR data were constrained by both recorded subsurface temperature profiles and by pressing a metal probe through the active layer to the point of refusal. We found that low-energy stream environments react much more slowly to seasonal solar input and maintain thaw thicknesses longer throughout the late season whereas thaw depths increase rapidly within high-energy streams at the beginning of the season and decrease over the late season period. Copyright © 2006 John Wiley & Sons, Ltd.
56 citations
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TL;DR: The properties, distribution patterns and thermal processes that influence the active layer and permafrost in the Transantarctic Mountains region of Antarctica, as deduced from soil investigations since 1964 and drilling investigations since 1990, are outlined in this paper.
Abstract: The properties, distribution patterns and thermal processes that influence the active layer and permafrost in the Transantarctic Mountains region of Antarctica, as deduced from our soil investigations since 1964 and drilling investigations since 1990, are outlined. The active layer depth varies from around 80 cm thick in coastal areas to <5 cm in inland and upland regions, due to the effect of the adiabatic lapse rate. Saline, ice-bonded, dry permafrost and transitional types of permafrost all occur. Ice content is highest in ice-bonded permafrost of the coastal regions and lowest in inland dry permafrost where values may be <1%. At the regional scale, ice-bonded permafrost most commonly occurs at lower elevations and beneath younger land surfaces but with increasing elevation, distance inland and land surface age, dry permafrost becomes predominant. At the local scale (<1 m) there are large variations in the depth to the permafrost table due to variations in ground surface features. Permafrost properties are largely governed by solar energy receipt, but albedo, air temperature cooling and available soil moisture strongly modulate the conversion of solar energy receipt into soil heating. These factors account for the considerable broad-scale and local variability in permafrost properties that exists. Copyright © 2006 John Wiley & Sons, Ltd.
56 citations
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TL;DR: In this paper, the authors describe the grain-size distribution, particle shape and fabric of some recent to fresh (1 day old) flow deposits, and conclude that the coarse openwork external parts of the debris-flow levees are formed during the passage of the flow surge(s).
Abstract: Debris-flow tracks are present at many sites within the French Alps. The vertical zonation (mainly between 1700 m and 2800 m altitude) of these medium-scale debris flows means that they are active within a mild periglacial environment, where the flows are triggered by high-intensity summer rainstorms.
The present paper describes the grain-size distribution, particle shape and fabric of some recent to fresh (1 day old) flow deposits. It was found that characteristic differences exist between the different parts of the levees and the terminal lobes. An interpretation of these phenomena is given with regard to processes involved in their origin.
It is concluded that the coarse openwork external parts of the debris-flow levees are formed during the passage of the flow surge(s), and that the matrix-rich, coarsening upward, channel-side parts of the levees, as well as the terminal lobes, mainly consist of material transported in the waning phases of the surges.
The existence of these sedimentologically different zones within thedeposits of a debris flow that are related to flow morphology has consequences for the recognition of debris-flow sediments within fossilized deposits. A correct interpretation is only possible if sections allow a sufficiently detailed analysis.
Des traces de laves torrentielles existent en de nombreux endroits dans les Alpes francaises. La zonation verticale (principalement entre 1700 m et 2800 m d'altitude) de ces traces de taille moyenne signifient qu'elles sont actives dans un environnement periglaciaire humide ou les ecoulements sont declenches par des pluies d'ete de forte intensite.
Le present article decrit la granulometrie, la forme des elements transportes et leur disposition individuelle au sein de quelques depǒts de lave torrentielle recents ou tres recents (anciennete un jour). II a ete decouvert que des caracteristiques differentes existent entre les differentes parties des levees et les lobes terminaux. Une interpretation de ces phenomenes est proposee en considerant les processus qui leur ont donne naissance.
Les parties externes grossieres des levees des laves torrentielles paraissent formees pendant le passage de pointes d'ecoulement tandis que la partie centrale des levees, riche en matrice fine et plus grossiere a la partie superieure, aussi bien que les lobes terminaux consistent principalement en des materiaux transportes pendant les phases decroissantes des vagues d'ecoulement.
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TL;DR: In this paper, three study sites were selected on zonal sites from north to south along a climate gradient in Arctic Alaska Air and mineral soil surface temperatures of nonsorted circles and adjacent well-vegetated tundra plots were monitored from September 2003 through September 2004, and the depths of vegetation, soil organic horizons and snow were measured.
Abstract: Three study sites were selected on zonal sites from north to south along a climate gradient in Arctic Alaska Air and mineral soil surface temperatures of nonsorted circles and adjacent well-vegetated tundra plots were monitored from September 2003 through September 2004, and the depths of vegetation, soil organic horizons and snow were measured N-factors, the ratio of ground-surface temperature to air temperature, were determined for the summer and winter seasons N-factors and thaw depths were greater for relatively barren nonsorted circles than for adjacent well-vegetated tundra Along the climate gradient, the thickness of vegetation, soil organic layer and snow increased from north to south, while n-factors and thaw depths decreased at bare circles from 143 � 002 to 074 � 001 and from 812 � 14 cm to 595 � 24 cm, respectively, and at the tundra from 099 � 002 to 017 � 001 and from 626 � 14 cm to 210 � 28 cm, respectively Copyright # 2006 John Wiley & Sons, Ltd
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TL;DR: In this paper, the main shaft of the CRREL tunnel was analyzed using an environmental scanning electron microscope (ESEM) and the micro-morphology of typical cryostructures was described.
Abstract: Cryostratigraphicmapping inthe main shaft of the CRREL tunnelindicates secondary modificationoforiginal Pleistocene-age syngenetic permafrost. Layered, lenticular-layered and micro-lenticularcryostructures within undisturbed silt characterise the syngenetic permafrost. Thawed and refrozendeposits are characterised by massive and reticulate-chaotic cryostructures. The micro-morphology oftypical cryostructures, as observed through an environmental scanning electron microscope (ESEM),is described. It is inferred that preferential cryogenic modification has occurred due to fluvio-thermalerosion operating along ice wedges. Soil and ice pseudomorphs are the manifestation of this process.Gravel, silt, ice and mixed (silt/ice) pseudomorphs occur within silt. Ice pseudomorphs are formed bythermokarst-cave ice (‘pool ice’) which filled thermokarst pits, channels and gullies. Copyright #2006 John Wiley & Sons, Ltd. KEY WORDS : permafrost; ground ice; cryostructures; thermokarst; pseudomorphs
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TL;DR: Permafrost borehole temperatures were measured in 1985, 1998, and 2004 on Barter Island near the village of Kaktovik and in the Arctic National Wildlife Refuge (Arctic NWR) north of the Brooks Range as discussed by the authors.
Abstract: Permafrost borehole temperatures were measured in 1985, 1998, and 2004 on Barter Island near the village of Kaktovik and in the Arctic National Wildlife Refuge (Arctic NWR) north of the Brooks Range These measurements indicate that the century-long warming documented for the central and western Arctic has also occurred in the region near Barter Island and in the northern Arctic NWR At Kaktovik, the warming occurred during the second quarter of the 20th century or earlier and its magnitude exceeded 08°C A more recent warming (since the mid to late 1980s) similar to that in the central and western Arctic is also occurring on Barter Island and in the northern Arctic NWR Near Kaktovik, the permafrost warmed about 2 to 3°C from 1985 to 2004 In the northern Arctic NWR, on a line extending southward from Tapkaurak Point, it warmed about 15 to 2°C from 1985 to 1998 If air temperatures warm 5°C over the next century, as predicted, some of the permafrost in the northern Arctic NWR would be expected to thaw Copyright © 2005 John Wiley & Sons, Ltd
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TL;DR: In this article, the composition of rock glaciers was sounded by a combination of conventional geophysical methods near the lower limit of mountain permafrost in the Swiss Alps P-wave velocity, direct current resistivity and year-round ground surface temperatures were measured on 32 talus-derived rock glaciers.
Abstract: The composition of rock glaciers was sounded by a combination of conventional geophysical methods near the lower limit of mountain permafrost in the Swiss Alps P-wave velocity, direct current (DC) resistivity and year-round ground surface temperatures were measured on 32 talus-derived rock glaciers Subsurface P-wave velocities differ significantly between non-vegetated (probably active/inactive) rock glaciers and vegetated (probably relict) rock glaciers DC resistivities reflect structural differences in the rock glaciers (eg bouldery or pebbly, ice-cemented or highly ice-rich) rather than thermal differences (ie frozen or unfrozen) The combination of these methods provides reliable thermal and structural information on subsurface deposits In addition, mean annual ground surface temperatures are equally good indicators of the distribution of permafrost as bottom temperatures of snow Copyright © 2006 John Wiley & Sons, Ltd
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TL;DR: In this article, winter observations were carried out on aeolian sand sheets in Western Greenland, in order to obtain insight into the occurrence and influence of niveo-aeolian sedimentation in modern cold-climate sand-sheet environments.
Abstract: Winter observations were carried out on aeolian sand sheets in Western Greenland, in order to obtain insight into the occurrence and influence of niveo-aeolian sedimentation in modern cold-climate sand-sheet environments. The alternating or simultaneous aeolian transportation of snow and sand appears to form an important factor in the sedimentation. Niveo-aeolian beds develop annually and are deposited during a period when the snow cover is thin. They are covered by clean snow when sand transport is impeded by ample snow or insufficient wind velocity.
The nature and significance of denivation features in the sedimentological record are equally poorly understood. In order to study these snow-related structures, the winter observations are compared with sections trenched in summer when no snow was left. After desiccation of the surface in summer, the sediments deriving from the niveo-aeolian beds on planar and low-angle inclined surfaces are likely to be redistributed by wind action. However, on slip faces denivation structures are frequently preserved as deformation of cross-strata and a model of their association is presented. Most of these structures resemble deformation structures previously described in wetted sand, but their association, indicating (1) collapse due to volume reduction and (2) the alternation of deformed and undeformed sedimentary units, form diagnostic indicators of cold-climate aeolian deposits.
Des observations faites en hiver sur les sables eoliens du Groenland Occidental ont ete executees afin d'ameliorer la connaissance des processus niveo-eoliens et pour preciser leur rǒle dans le developpement des couvertures sableuses en climat froid actuel. Le transport de neige et de sable, alternant ou simultane, est un facteur important de la sedimentation. Des couches sableuses niveo-eoliennes se developpent chaque annee pendant une periode ou la couverture de neige est mince. Elles sont couvertes par une couche de neige pure quand le transport de sable est supprime a la suite d'une chute de neige abondante ou parceque la vitesse du vent est insuffisante.
La nature et l'importance des phenomenes de denivation dans les sediments sont mal compris. Pour etudier les structures en relation avec la fonte de la neige, des observations faites en hiver ont ete confrontees avec des coupes creusees en ete, apres la disparition de la neige. Apres dessication de la surface en ete, les sediments des niveaux niveo-eoliens deposes sur des surfaces planes ou peu inclinees sont probablement redistribues par le vent. Par contre, les structures de denivation sont souvent conservees sur la face sous le vent des dunes, sous forme de litage oblique deforme. L'analyse aboutit a la presentation d'un modele de leur association. La plupart de ces structures ressemblent aux structures de deformation de sables humidifies mais leur association, comprenant (1) l'effondrement dǔ a une reduction de volume et (2) l'alternance d'unites sedimentaires deformees et non-deformees, est un critere diagnostique pour des depǒts eoliens de climat froid.
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TL;DR: In this article, a capacitively-coupled resistivity system (OhmMapper) operating in the kilohertz range and a standard galvanically coupled multi-electrode resistivity (SYSCAL) system operating in direct-current (DC) limit were compared in terms of permafrost detection.
Abstract: A capacitively-coupled resistivity system (OhmMapper) operating in the kilohertz range and a standard galvanically-coupled multi-electrode resistivity system (SYSCAL) operating in the direct-current (DC) limit were compared in terms of permafrost detection. The systems differ mainly in relation to operating frequency and the principle used to ensure sufficient electrical coupling between the sensors and the ground. Both were able to detect isolated permafrost in the Swiss Alps previously found by various geophysical field surveys. However, inter-year differences between results using the same system were less than differences between the two at the same time and at exactly the same location. There was good agreement between the systems at an unfrozen reference area, whereas at a mountain permafrost site, apparent electrical resistivity values with the capacitively-coupled system were approximately one quarter of those obtained with the galvanically-coupled system. As dielectric effects in resistive permafrost terrain become more important at lower frequencies (around 1 kHz) than in comparable but unfrozen environments (around 10 MHz), permafrost resistivity values obtained with the OhmMapper are generally lower than galvanically obtained values near the DC limit. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this article, the authors measured and explained the seasonal changes in soil ice content in the frost boils of Galbraith Lake, Alaska over a period of four years, and found that total heave and its distribution across the frost boil are similar between years.
Abstract: Our aim is to measure and explain the seasonal changes in soil ice content in the frost boils of Galbraith Lake, Alaska. Instruments were installed in a frost boil to monitor the ground surface position and soil state over a period of 4 years. By comparing the subsidence and thaw rates, we calculate the soil ice content as a function of depth. Measured soil temperatures, liquid water contents and bulk apparent thermal conductivities are used to estimate latent heat production and release in the soil. The frost boil heaves during freezing and settles during thaw while the surrounding tundra heaves negligibly, but subsides measurably. Despite large changes in freezing rates from year to year, total heave and its distribution across the frost boil are similar between years. Winter air temperature and snow depth influence the freezing rate and ice distribution as a function of depth, but not the overall heave. This suggests that heave is controlled by water availability rather than the rate of heat removal from the soil. Areal ground subsidence rates between 2 and 5 cm/yr are due to the disappearance of ice at the base of the active layer, raising the possibility of ongoing thermokarst expansion around Galbraith Lake.
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TL;DR: In this article, it is suggested that biological weathering may be a major destructive mechanism of the granitic lithologies, caused by wetting and drying episodes, results in the surface flaking of the rock.
Abstract: Observations on a number of nunataks of the Juneau Icefield indicate that chasmolithic algae play a major role in the breakdown of granitic rock. Expansion and contraction of the algal mucilage, caused by wetting and drying episodes, results in the surface flaking of the rock. Available data suggest that the average mass of material lost per year from 1 m2 of rock could be as high as 562 g. It is suggested that biological weathering may be a major destructive mechanism of the granitic lithologies.
Des observations sur plusieurs nunataks du glacier Juneau indiquent que des algues chasmolithiques jouent un rǒle capital dans la rupture des roches granitiques. L'expansion et la contraction du mucilage algaire, dues a des periodes de secheresse et d'humidite entrainet la detachement de plaques superficielles de roche. Les donnees disponibles suggerent que la masse de materiau perdue par an sur une surface de 1 m2 de roche peut atteindre une valeur aussi elevee que 562 g. Il est suggere que cette alteration biologique peut ětre un mecanisme de desagregation capital pour des roches granitiques.
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TL;DR: In this paper, the role of freeze-thaw action in riverbank erosion was investigated along a small mountain stream in a region with seasonal frost, and the authors found that the rate of subaerial erosion reaches a maximum during the thawing period, reinforced by increasing water content and decreasing soil hardness.
Abstract: Processes of riverbank erosion involve fluvial entrainment, mass failure and subaerial erosion. The role of freeze-thaw action in these erosion processes was investigated along a small mountain stream in a region with seasonal frost. Riverbank profiles, horizontal erosion, soil temperature, frost depth and soil water content were monitored over 20 months including two winters. Diurnal and annual freeze-thaw action directly triggers subaerial erosion and indirectly contributes to mass failure and fluvial entrainment. The rate of subaerial erosion reaches a maximum during the thawing period, reinforced by increasing water content and decreasing soil hardness. The subaerial erosion, which occurs uniformly along the riverbank and recurs every year, contributes to progressive deepening of a notch developed above the water level as both preparatory and erosive processes. The overdeepening of the notch decreases bank stability, followed by occasional mass failure immediately after the thawing period and periodic fluvial entrainment during the summer flood period. The annual amount of subaerial erosion is comparable to that of fluvial entrainment. These observations demonstrate that freeze-thaw erosion plays a fundamental role in erosion of riverbanks subject to deep seasonal frost. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this paper, the surface movement of the Muragl glacier forefield (Swiss Alps) is compared to direct current resistivity surveys for the same area, and isolated patches of frozen sediments are inferred, each about 10,000-20,000 m2 in area.
Abstract: Photogrammetric measurements of surface movement, 1981–94, on the Muragl glacier forefield (Swiss Alps) are compared to direct current resistivity surveys for the same area. At three locations isolated patches of frozen sediments were inferred, each about 10,000–20,000 m2 in area. These were deforming at surface velocities of up to 50 cm per year. The locations where creep was observed coincide well with areas where two-dimensional (2D) resistivity surveys suggest ice is present within the ground. Copyright © 2005 John Wiley & Sons, Ltd.
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TL;DR: In this article, an empirical modeling approach was applied in order to estimate the spatial distribution of ground surface temperatures, the presence of permafrost and the depth of the active layer in the Lake Hovsgol area in northern Mongolia.
Abstract: Near-surface temperature variations in different topographic settings were obtained from miniature temperature data-loggers at 17 locations over a 2-year period in the Lake Hovsgol area in northern Mongolia. These measurements were used to analyse the influence of vegetation, solar radiation, surface wetness and snow cover on the ground thermal regime. An empirical modelling approach was applied in order to estimate the spatial distribution of ground surface temperatures, the presence of permafrost and the depth of the active layer. Our study shows that spatial interpolation of ground surface temperature parameters, mainly known from previous research in the Arctic, can be feasible in the arid mountain environments of Central Asia. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this paper, thermal and geo-electrical investigations were carried out on five rock glaciers in the Argentera Massif to detect the presence of permafrost and to define its existence and activity elevation limits.
Abstract: Thermal and geo-electrical investigations were carried out on five rock glaciers in the Argentera Massif to detect the presence of permafrost and to define its existence and activity elevation limits. Ground surface temperature was monitored using digital dataloggers, and sub-surface ice occurrence was inferred from one-dimensional geo-electrical soundings. Bottom temperatures of snow cover, extracted from winter recordings, indicate possible or probable presence of permafrost for some rock glaciers. Geo-electrical soundings reveal the existence of sediments rich and super-saturated with ice for thicknesses often reaching several tens of metres. The limits for permafrost existence and for rock glacier activity can thus be fixed respectively at about 2500 m and 2600 m ASL. The results from 110 earlier geo-electrical soundings, carried out on rock glaciers in different sectors of the southwestern Alps, were processed and compared with the results of this work. A general classification of rock glaciers into active, inactive and relict was possible for the Argentera Massif. Inactive and relict rock glaciers probably originated during colder Holocene and Late-glacial periods. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this article, large-scale polygonal crop marks underlain by sand-filled wedge structures cover extensive surfaces on the West Flanders plateau (Flanders, Belgium) and are interpreted as composite-wedge pseudomorphs, formed by thermal contraction cracking in a permafrost environment.
Abstract: Large-scale polygonal crop marks underlain by sand-filled wedge structures cover extensive surfaces on the West Flanders plateau (Flanders, Belgium). Wedge structures (∼1.0 m wide, up to ≥1.6 m deep) observed at several sites are interpreted as composite-wedge pseudomorphs, formed by thermal contraction cracking in a permafrost environment. The composite infilling points to former relatively dry conditions on the plateaus. Superimposed wedge structures may indicate discrete growth stages. The structures probably formed during the Pleniglacial (comprising Marine Isotope Stages 2–4), although an older age is not excluded. The widespread occurrence of composite-wedge pseudomorphs on the plateaus conflicts with the literature suggesting that ice-wedge pseudomorphs are dominant in Flanders. As a consequence, palaeoenvironmental reconstructions may have been biased towards environmental conditions suitable for ice-wedge formation. Ice wedges probably formed mainly in depressions, whereas composite wedges may have been common on the plateaus. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this paper, a regional trend of decreasing size from west to east in the Abisko region, in the norther part of the country, was observed.Turf-banked lobes and terraces on the valley slopes and stone-banked or non-sorted lobes at summits.
Abstract: Turf-banked lobes and terraces on the valley slopes and stone-banked or non-sorted lobes at summits show a distinct regional trend of decreasing size from west to east in the Abisko region, norther ...
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TL;DR: The area around Monte Beigua is characterized by accumulations of large blocks as mentioned in this paper, and the formation of block streams is tentatively attributed to cold-climate conditions during the Pleistocene.
Abstract: The area around Monte Beigua is characterized by accumulations of large blocks. Survey indicates the occurrence of flow structures on the surfaces of the blockfields, and a pattern of long axis orientation aligned in the same direction as the local gradient. Blocks are often imbricated upslope at the front. The formation of block streams is tentatively attributed to cold-climate conditions during the Pleistocene. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this paper, a model for vertical permafrost distribution is presented and an altitude of 3500m a.s. is suggested for the lower limit of continuous permfrost.
Abstract: The areas studied display a rich periglacial geomorphology. The effects of seasonal and perennial ground frost are visible in the form of widespread solifluction phenomena, patterned ground and numerous rock glaciers. Soil and rock temperatures have been recorded, and permafrost distribution has been partly checked in selected areas with measurements of the basal snow temperature, and using geoelectrical and hammer seismic soundings.
Permafrost is widespread on northerly exposed slopes, with a thickness of several decametres at 3100m a.s.1. Below 2800 m a.s.1. patchy permafrost occurs. A model for vertical permafrost distribution is presented and an altitude of 3500 m a.s.1. is suggested for the lower limit of continuous permafrost.
As a result of aspect, soil and rock temperature fluctuations are different on northern and southern slopes. This induces differences in vegetation cover, debris production and geomorphological processes.
Cette partie des Alpes suisses est tres riche en ce qui concerne la geomorphologie periglaciaire. Les effets du gel saisonnier et permanent du sol sont visibles sous forme de phenomenes de solifluction largement repandus, de sols structures et de nombreux glaciers rocheux. Des temperatures du sol et des roches ont ete enregistrees, et la distribution du pergelisol a ete partiellement verifiee dans des regions choisies par des mesures de la temperature basale de la neige et en utilisant des sondages geoelectriques et des sondages seismiques au marteau.
Le pergelisol est tres frequent sur les pentes exposees au nord et atteint une epaisseur de plusieurs decametres a 3.100 m au dessus du niveau de la mer. Sous 2.800 m, le pergelisol est sporadique. Un modele de distribution verticale du pergelisol est presente et il est suggere que la limite du pergelisol continu se trouve a une altitude de 3.500 m au dessus du niveau de la mer.
II en resulte des fluctuations differentes de temperature du sol et des roches sur les pentes septentrionales et meridionales. Ceci induit des differences dans la couverture vegetale, la production de debris et les processus geomorphologiques.
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TL;DR: In this paper, the authors used EM38DD to locate near-surface Pleistocene frost-wedge pseudomorphs at a test site where a polygonal network was exposed.
Abstract: Electromagnetic induction was used to locate near-surface Pleistocene frost-wedge pseudomorphs at a test site where a polygonal network was exposed. The soil apparent electrical conductivity (ECa) was measured simultaneously with the EM38DD in the vertical and horizontal orientation, allowing the profile ratio (PR) to be calculated. Based on a fuzzy k-means classification the PR map was classified into two zones with a mean PR difference of 10%. A detailed drawing of the polygonal network served as a validation. A cross-tabulation yielded an overall accuracy of 81% when only wedges wider than 0.25 m wide were considered. The overall accuracy increased to 83% by introducing an uncertainty zone. Due to differences in composition between the wedge fillings and the host material, the PR was found to be a useful indicator of these phenomena. Copyright © 2006 John Wiley & Sons, Ltd.
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TL;DR: In this article, the authors reviewed the distribution and character of periglacial phenomena in New Zealand, as well as the broad factors controlling their origin and development, including topography and lithology.
Abstract: The presence of periglacial phenomena and activity in New Zealand is controlled primarily by altitude, especially as modified by topography and lithology. Thus, the alpine-type mountains that form the backbone of the South Island (Southern Alps) show little in the way of patterned ground, while the block mountains of Otago and less sharply peaked mountains in Canterbury and Marlborough display these features on varying scales. Some forms are considered to be fossil, while others are at present active. This paper reviews the distribution and character of periglacial phenomena in New Zealand, as well as the broad factors controlling their origin and development.
L'occurrence des phenomenes et de l'activite periglaciaire en Nouvelle Zelande est reglee par l'altitude, surtout modifiee par al topographie et la lithologie. Ainsi les montagnes de type alpin formant l'epine de l'ǐle du Sud (Alpes du Sud) ne montrent pas beaucoup de sols a figures geometriques, alors qu'on les trouve a plusieurs echelles dans les montagnes d'Otago et celles moins pointues de Canterbury et Marlborough. On pense que quelques unes de ces formes seraient fossiles, mais que d'autres seraient actives actuellement. Cette communication passe en revue la repartition et le caractere des phenomenes periglaciaires en Nouvelle Zelande ainsi que les facteurs generaux qui contrǒlent leurs origines et leur developpement.