bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of thermokarst lakes during the holocene at sites near Mayo, Yukon territory
Authors: Burn C. R. , Smith M. W.
Published: February 2007

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.
Soil and rock temperatures in discontinuous permafrost: Gornergrat and unterrothorn, wallis, swiss alps
Authors: King Lorenz
Published: February 2007

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.
Cryogenic physico‐chemical precipitations: Iron, silica, calcium carbonate
Authors: Vogt Thea
Published: February 2007

In Quaternary and present‐day alluvial deposits, secondary mineral accumulations are common. Previous theoretical and experimental studies have shown the occurrence of frost‐related iron and calcium carbonate precipitations. Microscopic and ultramicroscopic observations of alluvial materials from Quaternary cold periods allow the recognition of diagnostic features of cryogenic calcite crystallizations. Some iron and silica concentrations also suggest frost control, although further laboratory experiments are needed to obtain a satisfactory understanding of the mechanisms concerning these precipitations.

Nevertheless, it can be suggested that the migration of minerals under frost action is probably more important than previously taken into account.
Permafrost in the arid mountains of middle asia—the eastern pamirs, USSR
Authors: Gorbunov A. P.
Published: February 2007

Soil moisture conditions obviously play a crucial role in the distribution and structure of cryogenic forms in (ultra‐arid) alpina deserts.
Secondary sorting of sorted patterned ground
Authors: Warburton Jeff
Published: February 2007

The arrangement of small sorted patterns within the central fine domain of a larger sorted circle (herein called 'secondary sorting') was observed at two patterned ground sites: Arikaree Cirque, Colorado Front Range, USA, and Kapp Linné, Western Spitzbergen. Large polygons do not appear to be randomly filled by smaller ones of all sizes. The size of the inset polygons seems to be related to the dimensions of the larger form. Preliminary field survey suggests that large forms are filled by smaller polygon sizes in a width ratio of approximately 1:2.5‐3. Subdivision of the fine centres occurs in 77% of the sorted polygons at the Colorado site (n = 100) but only 42% of patterns at Kapp Linné (n = 31). Possible explanations of the scaling of the secondary polygons include pore water and/or soil convection and desiccation cracking. Desiccation crack systems simulated in a laboratory experiment are similar to those observed in the field.
Quaternary fan and river terrace deposits, glen orchy, East Cape Drakensberg, South Africa
Authors: Lewis Colin A. , Hanvey Patricia M.
Published: February 2007

The processes responsible for the formation of fans and river terraces is deduced from sedimentological evidence. The older fans are a result of solifluction and may have formed between 24000 and ± 12000 yearsBP. A younger fan is predominantly composed of colluvium and accumulated in at least three phases, the most recent of which post‐dates ± 2440 yearsBP. The lower of the two solifluction fans has been partially reworked by fluvial action: some of the eroded debris has been redeposited and now forms a river terrace.
Global solar radiation, soil temperature and permafrost in the Central Andes, Argentina: A progress report
Authors: Schrott Lothar
Published: February 2007

During various expeditions to the High Andes of Argentina at latitudes 30º and 33º south, extensive geomorphological investigations have been carried out. The subtropical semiarid climate is characterized by intense global radiation with peaks of more than 1400 W/m2 and daily sums of >39 MJ/m2. The daily amplitudes of the soil temperatures (≤25 cm depth) correlate with incoming radiation. Diurnal ranges of soil surface temperature (1 cm) usually exceed 45ºC, with maximum values of 55ºC at 4150 m a.s.l. Active rock glaciers exist above 4000 m a.s.l. and the thickness of the active layer varies from 1.4 to 2.5 m between 4000 and 4700 m a.s.l. Periglacial features (rock glaciers, thermokarst, gelifluction, etc.) are widespread. They are used as edaphic indicators for the lower limit of discontinuous permafrost, which is thought to be at an elevation of 4000 ± 200 m a.s.l.
Chronostratigraphic correlations of cryogenic and glacigenic episodes in central andes with patagonia
Authors: Corte Arturo E.
Published: February 2007

The stratigraphy of cryogenic and glacigenic episodes recorded in Central Andes at latitude 33º south is compared with the magnetostratigraphy of five (I‐V) main Patagonian glaciations. Most of the Central Andes cold episodes are relatively dated. A much older event (≈ 2.3 × 106 years BP) is needed to explain the oldest and largest Central Andes glaciation, the sediments of which are tectonically deformed. This is the beginning of climatic change in the Central Andes. Ice‐wedge casts in till formed 3.5 × 106 years BP in southern Patagonia are related to an even older cold episode.
Absence of frost sorting at an experimental site, green lakes valley, colorado front range, usa
Authors: Warburton Jeff
Published: February 2007

A field experiment at 3,350 m.a.s.l. in the Colorado Alpine was initiated in 1959, to investigate frost sorting. Four plots, of varying grain‐size composition, were used to test whether sorting by freeze‐thaw activity could be related to the percentage of soil particles finer than 0.074 mm and whether there was a characteristic grain size at which lateral and/or vertical sorting could be expected. Re‐examination of the site in 1984 indicated that macrofabrics, microfabrics, soil physical properties and surface clast distributions showed no evidence of large‐scale sorting. Critical conditions for the onset of pore water convection, as a mechanism for the initiation of sorting, could occur in only two of the test soils (A and B), and permeability in the third (C) was too low to allow instability. Soil convection is also unlikely, owing to the coarse, freely drained nature of the test soils.
Alpine permafrost temperature zonality, northern trans‐Baikal region, U.S.S.R.
Authors: Romanovskiy N. N. , Zaitsev V. N. , Volchenkov S. Yu. , Zagryazkin D. D. , Sergeyev D. O.
Published: February 2007

Changes of mean annual ground temperature at the depth of zero annual amplitude (tan) with elevation is well known for regions of high latitude and alpine permafrost. However, this phenomenon is not sufficiently studied in the intracontinental regions of Siberia. The authors analyse the altitudinal zonality of mean annual ground temperatures (tan) in the Udokan Ridge, Northern Trans‐Baikal. Measurements were obtained from 321 boreholes situated on different relief elements with altitudes ranging from 830 m a.s.l. to 2170 m a.s.l. A mean integral temperature (t*an), as well as the range of tan variations, was determined for every 200 m altitudinal interval. The results of large‐scale geocryological mapping were used to determine t*an, which allowed one to consider the spatial distribution of landscape types characteristic of certain tan values. It is established that with increasing altitude, t*an values uniformly decrease with a gradient of ‐0.3 °C/100 m. The difference in tan between ‘cold’ and ‘warm’ landscapes changes from 2°C to 5°C for the altitudinal intervals.
Rock moisture data from the juneau icefield (alaska) and its significance for mechanical weathering studies
Authors: Hall Kevin
Published: February 2007

Information was obtained regarding rock moisture content from nunataks along a west to east transect across the Juneau Icefield in Alaska. The data, together with rock temperatures and general climatic information, were collected for east‐, west‐, north‐ and south‐facing samples. For one day data were collected every hour. The resulting information indicates the spatial and temporal variability that can exist over both short distances and short time‐spans. It is suggested that this variability can have important repercussions with respect to weathering processes. The number of wetting and drying cycles monitored greatly depends upon the level of sample saturation that is considered significant. Available information suggests that wetting and drying can be operating at more than one level within the rock and that this will result in different weathering products. Wetting and drying may be more important than has been previously thought, both in terms of a weathering agent in its own right and as one that interacts with other processes, thereby speeding up their effect upon the rock.
The contribution of W. R. B. battle to mechanical weathering studies
Authors: Brian Whalley W. , McGreevy J. P.
Published: February 2007

W. R. B. Battle had started to make important contributions to the study of the mechanical weathering of rock in relation to the 'bergschrund hypothesis' of corrie erosion when he died. As well as temperature observations in bergschrunds, he made measurements on the reduction in strength (as Young's Modulus) for beams of rock in the laboratory. A summary of his work is given, together with the graph which was used to suggest a critical rate of cooling of 0.1 ºC/min for porous rocks.
Micro‐relief on a rock glacier, Dalton range, Yukon, Canada
Authors: Johnson P. G.
Published: February 2007

The micro‐relief on the surface of a rock glacier in the Dalton Range of the southwest Yukon provides evidence of processes occurring during and after development of the rock glacier. Ridges, mounds and flow lobes are interpreted as indicators of either the continuing deformation or reactivation of an ice‐core, solifluction of the surface deposits or changes in the internal hydrological system of the rock glacier. A glacial rather than periglacial origin for the ice core is preferred.
Distribution of mountain permafrost and climate
Authors: Guodong Cheng , Dramis Francesco
Published: February 2007

The relationship between mountain permafrost and climate is still relatively unknown. The implications of zonation (latitude, continentality), the various climatic parameters (MAAT; freezing and thawing indices; basal snow temperature, BTS; solar radiation; and surface heat balance) and climate change are outlined for mountain permafrost. Some research priorities are suggested.
Monitoring of periglacial phenomena in the furggentälti Swiss Alps
Authors: Krummenacher Bernhard , Budmiger Klaus
Published: February 2007

A monitoring system for periglacial phenomena has been installed in the Furggentälti (Gemmi) Swiss Alps in the framework of geomorphological field studies aimed at the instruction of students. Various periglacial landforms and processes can be observed in an area of about 1 km2. The research layout includes a survey station for soil and air temperatures, a geodetic surveying triangulation network of a solifluction lobe, and photogrammetric analysis of the soil frost pattern dynamics (stone rings) and a small rock glacier. Geophysical explorations (geoelectric and seismic refraction) and BTS measurements are undertaken on the rock glacier; these measurements have ascertained the presence of permafrost. The temperature survey station records values at levels between 1 m beneath the surface and 1.5 m above the surface; this allows correlation between displacement values of the solifluction lobe and the soil temperatures.
Creep of alpine permafrost, investigated on the murtel rock glacier
Authors: Wagner Stephan
Published: February 2007

Borehole and surface deformation measurements from an active rock glacier in the eastern Swiss Alps are presented and analysed. Borehole deformation was measured by slope indicator and magnetic rings. Analysis of these measurements reveal two layers which behave quite differently. The upper, highly supersaturated (i.e. ice) layer undergoes steady‐state creep (corresponds to a surface velocity of 5.5 to 6.0 cm/yr), overriding a non‐deforming lower layer of saturated (structured) permafrost. Seventy‐five per cent of the deformation takes place in a weak transitional zone, in the middle of the permafrost. Geodetic surveying shows, in contrast to the borehole measurements, a velocity variation in time by a factor of two. A constitutive law (Glen's flow law) was applied and the viscosity ratio between the upper ice layer and the weak transition zone was determined.
Observations on the rock glaciers of Monte Emilius (valle d'Aosta, Italy)
Authors: Smiraglia Claudio
Published: February 2007

Monte Emilius (3559 m a.s.l.) is a small mountain massif situated on the southern slope of Valle d'Aosta (Italy). Twenty‐six rock glaciers have been identified by use of aerial photographs. They are classified on the basis of their activity and subdivided into valley‐wall forms, cirque‐floor forms and valley‐floor forms. The mean altitude of the fronts of the active rock glaciers is 2849 m a.s.l., whereas that of the inactive rock glaciers is 2453 m a.s.l. Utilizing data from six meterological stations in Valle d'Aosta, the large‐scale climatological boundary conditions at the lower limits of the active rock glaciers were defined by calculating the thermal gradient (0.58 °C/100 m) and total annual precipitation. The MAAT at the mean altitude of the active rock glaciers fronts proved to be −2.1 °C. This altitude should represent therefore the lower boundary of discontinuous permafrost.
10 year surficial velocities on a rock glacier (Laurichard, French Alps)
Authors: Francou Bernard , Reynaud Louis
Published: February 2007

A survey of painted lines on the top and frontal zone of a talus rock glacier allows one to present a longitudinal profile of the surficial velocity distribution. Measurements were taken over a 8–12 year period at regular intervals and the results now provide information on the variability of displacements. In the upper zone a recent slowing of movement coincides with negative mass balance of local glaciers. Discussion focuses on the variations in velocity of the rock glaciers over the short time‐scale.
Rock glaciers in Svalbard and Norway
Authors: Sollid Johan Ludvig , Sørbel Leif
Published: February 2007

Rock glaciers made by talus creep are common landforms in Svalbard. This area has continuous permafrost with thicknesses varying from about 150 m to 500 m. Most rock glaciers are located in coastal areas at altitudes just above sea level, often situated below the escarpment which delimits the inner part of the strandflat. Most rock glaciers are active (at one rock glacier, annual movement rates of 3–10 cm were measured), but inactive rock glaciers with no movement in their frontal parts also exist in many areas. Their stagnation is due to topography and not to climate.

In Norway relic rock glaciers are found in coastal areas in the northern part of the country. Together with other relic permafrost features such as tundra polygons and ice‐cored moraines, the distribution of relic rock glaciers indicates that coastal areas in northern Norway had continuous permafrost during the Younger Dryas and earlier phases of the deglaciation.
Perigiacial climatic conditions and vertical form associations in Quebrada Benjamin Matienzo, Mendoza, Argentina
Authors: Ahumada Ana Lia
Published: February 2007

This paper describes the vertical zonation of cryogenic forms and their climatic significance in a region of the Central Andes near Mendoza, Argentina.
Permafrost environment of the Daisetsu Mountains, Hokkaido, Japan
Authors: Sone Toshio
Published: February 2007

The distribution of permafrost in the Daisetsu Mountains is discussed on the basis of freezing and thawing indices and the pattern of winter snow distribution. Mean annual air temperature at an altitude of 2000 m a.s.l. is estimated to be −3.6 °C in normal years. Alpine permafrost is distributed mainly on windward bare ground. The windward bare ground extends to summit areas, where most snow is removed from the ground surface by strong prevailing wind. The lower limit of permafrost is considered to be about 1650 m a.s.l. Some active periglacial processes, such as palsa formation and frost cracking, are explained by the present climate of the Daisetsu Mountains.
A note on ground thermal regimes and global solar radiation at 4720 m a.s.l., High Andes of Argentina
Authors: Happoldt Hans , Schrott Lothar
Published: February 2007

The near‐surface ground thermal regime at 4720 m a.s.l. is described and assessed in terms of its daily and annual fluctuations (frost cycles, freezing and thawing depths, etc.). Correlation between solar radiation and soil temperature in the uppermost parts of the soil is caused by intense radiation (mean annual value of 22.3 MJ m−2 d−1). Surface soil temperatures show an enormous amplitude (>50 °C in a depth of O.1 m) and frost cycles occur almost throughout the year. The seasonally frozen ground extends to only 1.5 m in depth.
Perennial névés and the hydrology of rock glaciers
Authors: Tenthorey Geneviève
Published: February 2007

From 1986 to 1990 water tracing was carried out in three rock glaciers in the Upper Val de Réchy. Results indicate different patterns of circulation depending on the size and degree of activity of the rock glaciers. Two rock glaciers show rapid superficial flow and one has slow interstitial flow. This is analogous to supra‐ and subglacial flow. Intra‐flow is also seen in one rock glacier. The importance of perennial névés at the roots of rock glaciers is demonstrated. Meltwater supplies the risings and, by refreezing, probably also increases the ice mass of the rock glaciers.
Southern limit of relict rock glaciers, Central Apennines, Italy
Authors: Dramis Francesco , Kotarba Adam
Published: February 2007

Relict rock glaciers have been identified in the Maiella Mountain massif, Central Apennines (42° N). They are located at elevations of 2500–2300 m a.s.l. and probably mark the uppermost and southernmost limit of Pleistocene discontinuous alpine permafrost in the Apennine peninsula.
A statistical analysis of the spatial distribution of rock glaciers, Spanish Central Pyrenees
Authors: Chueca J.
Published: February 2007

One hundred and seventy rock glaciers have been identified by use of aerial photographs in the southern Central Pyrenees. Through the use of statistical techniques (quadrat analysis, Poisson distribution analysis and variance‐mean ratio test), differences in lithology and fracturing density are shown to be important controls over their distribution.
The fractal geometry of thermal and chemical time series from the active layer, Alaska
Authors: Outcalt Samuel I. , Hinkel Kenneth M.
Published: February 2007

Two data sets were used to examine the fractal geometry of constituent time series. Soil temperature and soil water ionic concentration observations were collected in August 1991 at proximal sites at the Caribou‐Poker Creeks Research Watershed near Fairbanks, Alaska. The second data set contains thermal records of the 1984 active layer freezeback from Toolik Lake. Following Fourier transformation, log (variance) was plotted as a function of log (wavelength) and three parameters were generated: the exponent (S) of the power law fit to the variance spectrum, the Hausdorff‐Besicovitch Dimension (Dhb) and the Coefficient of Determination (R2). This procedure measures both the degree of roughness of a time series (Dhb) and the degree to which the time series approaches a ‘pure’ fractal condition (R2 = 1.0). The Caribou‐Poker Creeks data set demonstrates that time series from different microenvironments can be discriminated in (R2, S) space. The thermal records from Toolik Lake show that, during formation of the isothermal ‘zero curtain’ layer, heat transfer is accomplished primarily by non‐conductive processes. The zero‐curtain effect is characterized by a ‘pink noise’ spectrum with strong cyclic elements, an increase in Dhb and a corresponding decrease in R2. The methods were applied here to a single probe, but confirm previous analyses employing apparent thermal diffusivity calculations and spectral comparisons requiring data from multiple levels.
Pleistocene periglacial structures and landforms in Western Czechoslovakia
Authors: Czudek Tadeáš
Published: February 2007

The paper describes periglacial structures and landforms developed under Pleistocene coldclimate conditions in western Czechoslovakia. The thickness of Upper Pleistocene permafrost in this territory may have been between 50 and 250 m. Climatically controlled valley asymmetry developed because of different cryogenic processes on opposite valley sides and lateral stream migration (mainly due to thermal erosion). In some cases cryopediment‐like foot‐slopes developed due to down‐wearing of river terraces and/or to the combined effect of down‐wearing and back‐wearing.
Climate warming and the carbon cycle in the permafrost zone of the former Soviet Union
Authors: Kolchugina Tatyana P. , Vinson Ted S.
Published: February 2007

The continuous permafrost zone of the former Soviet Union (FSU) occupies 5% of the land surface area of the earth and stores a significant amount of carbon. Climate warming could disrupt the balance between carbon (C) accumulation and decomposition processes within the permafrost zone. Increased temperatures may accelerate the rate of organic matter decomposition. At the same time, the productivity of vegetation may increase in response to warming. To assess the future carbon cycle within the permafrost zone under a climate‐warming scenario, it is necessary to quantify present carbon pools and fluxes. The present carbon cycle was assessed on the basis of an ecosystem/ecoregion approach. Under the present climate, the phytomass carbon pool was estimated at 17.0 Gt (109 t). The mortmass (coarse woody debris) carbon pool was estimated at 16.1 Gt. The soil carbon pool, including peat‐lands, was 139.4 Gt. The present rate of carbon turnover was 1.6 Gt/yr. Under a warming climate 0.46–0.72 Gt C/yr may be gradually released to the atmosphere, mainly due to the increase in mortmass and litter decomposition. The increased efflux may be concurrently balanced by carbon uptake by vegetation as a result of enhanced productivity and forest migration to the north. However, the possibility exists that a lag between increased carbon efflux and uptake by vegetation may occur. The equilibrium of the carbon cycle may be reestablished, but at a higher rate of carbon turnover. Climate warming may not influence the depth of the active layer in peatlands. The depth of the active layer in mineral soils was comparable with the depth of the organic layer. Consequently, degradation of permafrost may not have a substantial influence on future carbon emissions.
Données Nouvelles sur la Présence d'un Pergélisol en Aquitaine au cours des Dernières Glaciations
Authors: Texier J. P. , Bertran P.
Published: February 2007

Les formes cryergiques identifiées en Aquitaine montrent que cette région de France a vraisemblablement été affectée par le développement d'un pergélisol. Celui‐ci se serait manifesté au cours de deux épisodes climatiques distincts: l'un daterait de la partie supérieure du dernier Pléniglaciaire (Dryas ancien); l'autre, plus hypothétique, se situerait dans la deuxième moitié de l'avant dernier Glaciaire. Le type de ces pergélisols ne peut être défini avec une totale certitude. Par rapport à l'actuel, la baisse de température moyenne annuelle de l'air peut être estimée entre 13 et 19°C.
Description and origin of some talus‐foot debris accumulations, Aghla Mountains, Co. Donegal, Ireland
Authors: Wilson Peter
Published: February 2007

The morphology and site characteristics of talus‐foot debris accumulations in the Aghla Mountains, Ireland, suggest that these landforms are fossil protalus ramparts and talus‐derived rock glaciers. The ramparts are linear or arcuate ridges or benches located within 45 m of the talus foot. The rock glaciers comprise several transverse ridges and depressions, interpreted as flow structures, and extend further from the talus foot than the ramparts. At least one rock glacier developed from a rampart. The ramparts indicate the former existence of perennia snowbeds and the rock glaciers are considered to result from the deformation and creep of interstitial ice (permafrost). There is no clear evidence of large scale‐slope failures or glacier ice having influenced debris accumulation. The landforms are probably of Nahanagan Stadial age (c. 11‐10 ka BP) and testify to the susceptibility of well‐jointed quartzite cliffs and talus to significant modification under the severe climatic regime of the stadial.
A low‐angle slushflow in the Kirgiz Range, Kirgizstan
Authors: Elder K. , Kattelmann R.
Published: February 2007

A rare observation of a slushflow that released on a low‐angle slope was made on 16 May 1992 in the West Karakol Valley, southern Kirgiz Range, Kirgizstan. The slushflow released on a short slope of 6° and travelled a distance of 140 m over a slope with a mean angle of 3° with a mean channel width of about 4 m. Total volume of snow and slush transported by the slide was more than 200 m3 with an estimated mass of 200,000 kg. Estimated velocity of the flow was 5 ms−1. Meteorological conditions preceding the event included heavy cloud cover and clear skies with warm temperatures. Rain fell for about six hours during the day before the event. Mixed rain and snow precipitation continued through the preceding night accompanied by steady high winds. The day of the release was warm with overcast skies and light rain. The snowpack was generally saturated to the surface at the time of the release, and water was flowing over the snow surface in the path of the slushflow.
Notes on open‐system pingo ice, Adventdalen, Spitsbergen
Authors: Yoshikawa Kenji
Published: February 2007

Analysis of open‐system pingo ice in Adventdalen, Spitsbergen, reveals its growth process. Ice and water sampled from edge to centre and from top to bottom of open‐system pingos are analysed. The results suggest that, after the underground water supply stopped, pingo ice extended downward. This downward extension seems to lower the level of underground water. The growth of open‐system pingo ice is supported by injecting and/or segregating ice originated from underground water. Sea level and climate changes probably influence the underground water level. This is especially the case for pingos formed on the coastal plain.
Gravimetrical investigation of ice‐rich permafrost within the rock glacier Murtèl‐Corvatsch (upper Engadin, swiss alps)
Authors: Vonder Mühll Daniel S. , Klingelé Emile E.
Published: February 2007

A gravimetrical study was carried out in the area of the Murtèl‐Corvatsch rock glacier in order to check the applicability of this method in alpine permafrost. The residual anomaly observed after removal of the linear regional trend is up to −1.5 mgal. Cores of borehole 2/1987 through this rock glacier showed a very high ice content in the uppermost 30 m. Borehole geophysical measurements furnished the density distribution with depth at the drill site showing values of less than 1000 kg m−3. According to the core stratigraphy and the density log at the drill site four layers were distinguished: an active layer to 3 m depth; massive ice (3–20 m); an ice‐silt‐sand layer (20–30 m); and a layer with ice‐saturated blocks (30–50 m). The extension of the four distinguished layers is modelled in three dimensions for the entire rock glacier according to the gravity data. The bedrock underneath the creeping permafrost is bowl‐shaped.
Rheological models of active rock glaciers: Evaluation, critique and a possible test
Authors: Whalley W. Brian , Azizi Fethi
Published: February 2007

Rheological properties of ice and ice/rock‐fragment mixtures relating to rock glaciers are examined. The basic criteria for flow (neglecting sliding components) are discussed with reference to published work. Even if the internal composition of a rock glacier is very variable, ranging from pure ice to an ice/rock mixture, then similar surface velocities are likely to be measured and accounted for by at least two rheological models. Under some circumstances, even when there is ice in excess of the rock debris voids ratio, flow of the frozen material may not be possible. Uncertainty in the ice/debris composition in rock glaciers allows a wide variety of temperature, density, shear strength and creep properties to account for measured velocities. Ice lenses (segregation ice) must interconnect within a surrounding mass of stronger material for substantial deformation to occur. It is suggested that a glacier ice origin can account for the measured surface flow velocities of rock glaciers as long as the ice body is thin, generally <50m. It is usually considered that low flow velocities of rock glaciers are distinctive; however, previous conditions may have shown much greater surface velocities than at present. A test for the origin of rock glaciers is given based upon flow mechanical properties. If a rock glacier had its origin as a glacier then past velocities would have been higher than at present; if as a permafrost body, then there should not have been a major decrease. Evidence is presented to show that the latter may be the case in some instances.
Periglacial landforms at Giant'S Castle, Natal Drakensberg, South Africa
Authors: Boelhouwers Jan C.
Published: February 2007

Active and inactive periglacial landforms are described for a small, south‐facing mountain catchment at Giant's Castle, 3140–3300 m A.S.L. Natal Drakensberg, South Africa. Micro‐patterned ground is found at the water divide and indicates marginal present‐day frost activity with soil frost penetration to a depth of 0.1–0.2 m. Downslope, thin stone‐banked sheets migrate over larger, inactive, stone‐banked lobe complexes. Block fields, suggested to be of a gelifluction origin, occupy the central part of the valley and gelifluction sheets cover the lower valley slopes. All are inactive. The range of inactive periglacial slope deposits suggests the presence of severe seasonal frost in the past.
Evidence for a cyclic variation of permafrost temperatures in northern alaska
Authors: Osterkamp T. E. , Zhang T. , Romanovsky V. E.
Published: February 2007

Observations of permafrost temperatures in shallow drill holes in northern Alaska near the Beaufort Sea coast show that these temperatures have cycled during the decade from 1983 to 1993. The two sites nearest the coast indicate a period of about 10 years and an amplitude at the permafrost surface of about 2°C. The two sites farthest from the coast have similar periods but reduced amplitudes of about 0.6°C. Changes in air temperatures, snowfall, length of sea ice season, solar effects, and other factors could, in principle, produce the observed temperature changes. Barrow air temperatures have a periodicity of 10.1 years but currently lead the sunspot cycle. Snowfall also shows evidence for a periodicity near 10 years. Near Prudhoe Bay, the length of the sea ice season increased about one week from 1979 to 1986 which could have caused a decrease in coastal air temperatures. The sunspot cycle (10–11 year period) leads temperatures at the 30 m depth by two to three years which is about the expected lead. During the descending part of the last solar cycle, satellite measurements of the solar total irradiance showed a decrease of about 3W m−2, which is about four times the calculated mean energy flux at the permafrost table (0.6 to 0.7 W m−2) required to produce the observed temperature changes.
Glaciological constraints on protalus rampart development
Authors: Ballantyne Colin K. , Benn Douglas I.
Published: February 2007

The growth of protalus ramparts is self‐limiting, as progressive thickening of a firn field will increase basal shear stress, encouraging creep of ice and basal sliding, and thus cause the transformation of stationary firn into a small glacier with consequent destruction or modification of the rampart. Modelling of the threshold conditions under which significant movement of the firn field begins indicates that the maximum distance between the rampart crest and the talus foot upslope cannot exceed c. 30–70 m, the limiting value being dependent on the gradient of the firn field. This finding implies that ridges or ramps of debris lying at greater distances from the talus foot cannot be [true] protalus ramparts formed by debris descending an essentially stationary firn field, and hence that many landforms previously described as protalus ramparts have been misinterpreted. Modelling of the limiting conditions for gravitational transport of debris suggests that clasts may continue to reach the front of a steep incipient glacier even after ice movement has been initiated, at least until the toe of the ice reaches a position 85–125 m from the talus foot. This implies the possible existence of [protalus moraines] whose form is influenced by moving ice, yet which continue to receive a supply of debris by direct gravitational transport across the ice surface.
Protalus ramparts and related features along the niagara escarpment, niagara peninsula, ontario
Authors: Tinkler K. J. , Pengelly J. W.
Published: February 2007

Talus foot ridges interpreted as protalus ramparts have been identified along 17 out of 42 km of the Niagara Escarpment within the Niagara Peninsula. They are distinguished from various types of slope form (rotational slumps, debris slides, quarries, dumps, moraines, raised shorelines and bedrock ledges) by their regular linear nature and their restriction to slopes facing between north‐east and north‐west. Morphologies range from a simple terrace with a flat top and a steep rocky outer slope, to compound ridges with closed depressions between. Maximum widths from rampart crest to main talus foot average 25 metres. Ramparts are characteristically extremely bouldery and include angular blocks of Thorold and Grimsby Sandstones weathered from the Escarpment slope, Ironde‐quoit Limestone and Lockport Dolomite blocks with metre dimensions transported to the outer slopes of the ramparts from the upper edge of the Escarpment, and clay from the weathering of Escarpment shales and from Wisconsinan diamictons. Associated firn field dimensions probably fluctuated dramatically in size during the year, and the palaeoclimatic implication is that there existed substantial late‐lying to perennial firn fields following local deglaciation at 12.5 ka BP. Independent confirmation of an early postglacial tundra climate is provided by the basal portions of pollen stratigraphies obtained nearby. The latest period when the firn fields might have existed is during the Younger Dryas chronozone (11 ka to 10.0 ka BP) when regional climatic cooling may have allowed the re‐establishment of a tundra‐like climate, especially in areas with severe microclimates.
Changes in hydrogeologic regimes in permafrost regions due to climatic change
Authors: Michel Frederick A. , Van Everdingen Robert O.
Published: February 2007

The general and specific effects of predicted climate change on groundwater systems in permafrost regions are summarized. Besides a general decrease in the thickness and areal distribution of permafrost, a large unfrozen near‐surface aquifer with perennial groundwater flow might develop. Recharge and discharge would become more active and increased groundwater discharge would affect the baseflow of many rivers and the chemistry of their waters.
Identification of heat‐transfer processes during soil cooling, freezing, and thaw in central alaska
Authors: Hinkel Kenneth M. , Outcalt Samuel I.
Published: February 2007

Hourly time series of temperature and a surrogate measure of the soil water ionic (solute) concentration were obtained in the upper 50 cm of soil from two adjacent sites in central Alaska from August 1991 to May 1992. One site is located in a ground water seepage zone and is characterized by seasonal freezing of the upper soil. The other site is located over a body of permafrost. The time series, used simultaneously, display a unique signature diagnostic of the operative conductive and non‐conductive heat‐transfer process. During soil cooling in autumn, internal distillation (concurrent evaporation, vertical transport, and condensation of water vapour in soil column) moderates heat transfer in the active layer. A [zero curtain] develops in winter and persists for three months; maintenance of this isothermal layer is associated with water advection and internal distillation within the unfrozen zone. Conductive heat transfer is not possible in the isothermal layer during this period but dominates during late winter following soil freezing and closure of the zero curtain. Warming of the active layer in spring occurs nearly instantaneously and results from infiltration of snow cover meltwater and downward vapour migration. In contrast, water saturation of pore space at the seepage site inhibits vertical migration of vapour and water.
Sublimation as a geomorphic process: A review
Authors: Law Jane , Van Dijk Deanna
Published: February 2007

Ice and snow sublimation is a naturally occurring process in which the solid ice changes state to become a vapour without passing through the usual liquid stage. The sublimation of blowing snow can be critical in areas which rely on melting snow as an important source of moisture. In blowing snow, the sublimation process is influenced by air temperature, relative humidity, wind speed, net radiation and particle surface area. When pore ice sublimation occurs in an ice/sediment mixture, the process is complicated by the presence of the particles of sediment. The sublimation of frozen moisture from sediments has implications for dust production, for human safety in permafrost tunnels, and for the aeolian movement of sediments in cold environments. A limited number of studies have considered sublimation from frozen sediments and a very few of these have been done under field conditions. The variables of air temperature, relative humidity, sediment moisture content and wind speed influence the amount and rate of pore ice sublimation, but there is some disagreement as to the relative importance of these variables.
Snow depth controls palsa growth
Authors: Seppälä Matti
Published: February 2007

When a young palsa has risen sufficiently above a mire (bog) and has developed steep sides, drifting snow collects against these sides and inhibits freezing of adjacent ground. Measurement of the temperature regime on the top surface, and at the foot, of the northern edge of a 2.6 m high palsa in Utsjoki, Finland supports this hypothesis. The minimum temperature recorded in the winter of 1992–93 on the uncovered palsa summit was −23.4°C. After snowfall, the temperature stayed at +0.1°C at the foot of the palsa for over six months, until 20 June 1993. At the edge of the palsa, thick snow cover prevents the establishment of permafrost.
Systématique du Remplissage en Eau des Fentes de Gel: Les Résultats d'une Étude Oxygène‐18 et Deutérium
Authors: Lauriol B. , Duchesne C. , Clark I. D.
Published: February 2007

Une douzaine de coins de glace le long de la rivière Porcupine (Yukon) ont été échantillonnés pour identifier leur période de croissance et pour déterminer l'origine de l'eau qui les a formés. Les datations au radiocarbone des sédiments qui les contiennent limitent leur période de croissance aux 4 derniers millénaires. Les isotopes stables montrent une homogénéité entre les centres et les bordures des coins, indiquant une stabilité climatique durant cette période. Le δ18O/δ2H est enrichi par rapport aux précipitations hivernales et se situe au‐dessous de la ligne des eaux météoriques ce qui laisse penser que les fentes de gel sont remplies durant les derniers moments de la fonte.
Ventifacts as palaeo‐wind indicators in southern Scandinavia
Authors: Schlyter Peter
Published: February 2007

Systematic transect and grid surveys of ventifact presence/absence were made in order to assess palaeo‐ventifact abundance/distribution through Denmark and southern Sweden. The transects reveal a continuous ventifact distribution from western Denmark to south‐central Sweden giving evidence for the existence of significant palaeo‐wind action in extensive areas previously thought lacking in such evidence. Based on ice recession dates and vegetation development, ventifact formation is interpreted as having occurred mainly contemporaneously with the receeding Weichselian ice‐sheet. A grid survey in Scania, southern Sweden, demonstrates a continuous ventifact distribution irrespective of surface materials and topography. The ventifact occurrence outside areas with sandy soils indicates that suspended particles were effective abrading agents. Stable ventifacts confirm previous observations of easterly wind abrasion in Scania and exhibit an extremely small directional variability within, and between, sites. Ventifacts in southern Scandinavia are probably more indicative of transitory paraglacial conditions than periglacial conditions as such.
Ice‐wedge formation in northern Asia during the Holocene
Authors: Vasil'chuk Yurij K. , Vasil'chuk Alla C.
Published: February 2007

The cryostratigraphy of Holocene ice wedges is described from Western Siberia, Yakutia and the Trans‐Baikal region. 14C dating and oxygen isotope determinations suggest that some of these wedges grew syngenetically during the Holocene climatic optimum. Inferred mean winter and mean January air temperatures for this period are presented.
Laboratory simulation of periglacial solifluction: Significance of porewater pressures, moisture contents and undrained shear strengths during soil thawing
Authors: Harris Charles , Davies Michael C. R. , Coutard Jean‐Pierre
Published: February 2007

Laboratory simulation of periglacial solifluction in two natural soils, one a sandy silt, the other a gravelly silty sand, was undertaken on a 12° slope in a thermally controlled 5 m square chamber. Soil freezing and thawing took place from the top downwards in an open hydraulic system. Frost heaving and surface downslope movements were much greater in the silt‐rich soil than in the sandy soil. In both cases, solifluction took place during the thaw period. At any given depth, porewater pressures rose rapidly immediately following soil thaw, and were generally positive for several days, though not in excess of hydrostatic pressure. Soil moisture contents following thaw exceeded the liquid limit and measured in situ undrained shear strengths were low, ranging between 0.8 kPa near the surface and 9.0 kPa at depth. Conventional slope stability analyses based on total stress and effective stress conditions indicated that the thawing slope was not susceptible to rapid failure. It was concluded that the observed soil displacements represent post‐thaw strain when soil moisture contents were high and Theological properties were intermediate between those of a viscous fluid and a plastic creeping solid.
Interannual variations of the thermal regime of the active layer and near‐surface permafrost in northern Alaska
Authors: Romanovsky V. E. , Osterkamp T. E.
Published: February 2007

Air, ground surface, active layer and permafrost temperature measurements were made every four hours from 1986 through 1992 near Prudhoe Bay West Dock (WD), Deadhorse Airport (DH) and Franklin Bluffs (FB). Mean annual air temperatures (MAAT) were nearly identical (−12.6 °C at WD, −12.9°C at DH, −12.5°C at FB) while the amplitudes increased from the coast inland (17.2°C at WD, 18.4°C at DH, 20.8°C at FB). Interannual variations were similar (3.2°C at WD, 2.9°C at DH and FB). Mean annual ground surface temperatures (MAGST) were similar at FB (−5.8°C) and DH (−6.2°C) and much colder at WD (−8.8°C) with amplitudes of 14.5°C at WD, 13.5°C at DH and 15.2°C at FB. Interannual variations were about the same at WD (3.8°C) and DH (3.9°C) and much smaller at FB (1.4°C). Differences between MAGST and MAAT were about the same at FB (6.8°C) and DH (6.7°C) and much smaller at WD (3.9°C). The results suggest that the snow cover was thinner at WD and/or its properties were significantly different compared with the inland sites. Mean annual permafrost surface temperatures (MAPST) were the same at FB and DH (−6.8°C) and much colder at WD (−9.1°C) with interannual variations of 2.7°C at WD, 3.0°C at DH and 1.8°C at FB. Thermal offset (MAPST − MAGST) was about the same at WD (−0.7°C) and DH (−0.67°C) and larger at FB (−1.03°C). Generally, thawing at the ground surface began earlier at FB than at DH and WD. Average duration of thawing (99 days at WD, 104 days at DH, 107 days at FB) and dates of the start of ground freezing (16 September at WD, 18 September at DH, 17 September at FB) were similar at all three sites. Average durations for freezing the active layer were similar at FB (62.5 days) and DH (68 days) and much less at WD (42 days). Active layer thicknesses increased from the coast inland (range of 0.21 m to 0.46 m at WD, 0.42 m to 0.69 m at DH, 0.57 m to 0.72 m at FB) and showed systematic temporal variations. These variations in active layer thicknesses may have significant temporal and spatial effects on the carbon balance of the tundra.
Rockslide processes on the north slope of popocatepetl Volcano, Mexico
Authors: Palacios David
Published: February 2007

This paper analyses the geomorphology of the north face of Popocatepetl Volcano (5450 m). The surface of the slope was covered earlier by the northern Popocatepetl Glacier and gradually exposed during the current century. The glacier formed at the time of the last great eruption of Popocatepetl in the seventeenth century, and reached its maximum extension at the end of the nineteenth century, at the peak of the Little Ice Age. A ramp formed at the snout of the glacier, composed primarily of ash dating from the last eruption. The material was mixed with large boulders that have been bulldozed into place by the glacier snout. As the glacier retreated, deep gorges formed on the ramp and glacial hollows appeared at the base of the steep sides of the volanic cone. Today, large‐scale rockslide processes occur on the north face. Layers of snow form a lubricating layer. The ash slides easily over the snow, covering it and later preventing it from melting and sublimation. Blocks fall from the present‐day glacial snout and pile up on the snow. Later, they slide over the snow and infill the hollows and gorges.