bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ploughing blocks of the Tien Shan
Authors: Gorbunov A. P. 
Published: February 2007

AbstractPloughing blocks (boulders) consist of three elements, namely, a rock fragment, a mound and an elongate depression. The movement of a block downslope leads to the formation of a pressure mound ahead of the block, while in its rear there is a furrow. In the Tien Shan mountains the size of the largest ploughing block is ≈11 m3, the height of the largest mound is about 1.0 m and the most elongated furrow is ≈37 m long.Seasonally frozen ground below the blocks or in their immediate vicinity gives rise to their movement. Seasonal freezing is the key factor that dictates a high ice content and ground moisture beneath the block which causes the gliding downslope. The block movement velocity is not regular and reaches its maximum in the second half of spring. Velocity varies also from year to year: in certain years it is nil and sometimes it is high as 7‐10 cm a year.
Age of growth of two pingos, Sarqaq Dalen, West Central Greenland
Authors: Yoshikawa Kenji 
Published: February 2007

AbstractThe aim of this note is to identify the beginnings of growth of two pingos located in Sarqaq Dalen, west‐central Greenland. One is located at the toe of an alluvial fan, and seems to be active; the other is on a river bed, and already collapsed. Marine sand covers the pingos and indicates that the Holocene transgression predates their growth. The pingos are located approximately 2 km from the present coastline. Pollen analysis of the overlying sediments of the two pingos leads to the following conclusions: (1) although the study area had already emerged from the sea at Post Fjord stage (7800 years BP), it was submerged again sometime between 7000‐5000 years BP; (2) one pingo started its growth approximately 4500 years BP; (3) the other pingo started its growth approximately 6000‐5500 years BP.
Changes to the permafrost environment after forest fire, Da Xi'an Ridge, Gu Lian Mining Area, China
Authors: Lin‐Heng Liang , You‐Wu Zhou , Jia‐Cheng Wang 
Published: February 2007

AbstractPermafrost field investigations in the Gu Lian Mining area of Great Xi'an Ridge (in Chinese: DA HINGAN LING) was undertaken in the second year following a forest fire. It was found that after the fire air temperature, ground temperature, evaporation (measured by pan) and wind velocity increased but humidity, ground ice and water content decreased. These changes led to an increase in seasonal thaw depths. These results illustrate that the permafrost environment is changed greatly by forest fire.
Permafrost and ground ice conditions reported during recent geotechnical investigations in the Mayo district, Yukon territory
Authors: Burn C. R. 
Published: February 2007

AbstractThe Mayo District, Yukon Territory, lies in the widespread discontinuous permafrost zone. Permafrost thicknesses of up to 40 m have been measured in valleys, and of 135 m at higher elevations. Many observations of ground ice have been made by placer miners, but generally these are unrecorded. Recently, over 200 shallow geotechnical boreholes have been drilled in the area in association with municipal or highway construction. Ground ice is usually encountered at undisturbed sites within 4 m of the surface. In the main valleys at elevations below 1100 m a.s.l. coarse, clastic, outwash materials, sand dunes and slopes with southerly aspect are usually frost‐free. Stripping of vegetation for construction or placer mining leads to permafrost degradation, but permafrost can re‐establish as vegetation regenerates. Ground temperatures at Mayo and Keno Hill indicate a geothermal flux of over 0.1 W/m2.
A model of the rate of frost shattering: Application to field data from Japan, Svalbard and Antarctica
Authors: Matsuoka Norikazu 
Published: February 2007

AbstractAn empirical model of the rate of bedrock frost shattering (Matsuoka, 1990b) was applied to field data obtained from four different environments: Japanese lowland and alpine regions, Svalbard and Antarctica. The model indicates that the annual frost shattering rate is a function of freeze‐thaw frequency per year, degree of saturation and bedrock tensile strength. Field measurements of these parameters were carried out for 1‐6 years on rockwalls in the four study areas. Despite the differences in thermal and moisture conditions, the model agreed fairly well with the field data, with the exception of those from Antarctica and part of Svalbard, where moisture is insufficient for frost shattering. The model predicts the weathering rates of bedrock situated in environments where frost shattering prevails.Un modèle empirique de la vitesse de désagrégation par le gel (Matsuoka, 1990b) a été appliqué aux données de terrain obtenues dans 4 environnements différents, à savoir: les basses terres et les régions alpines du Japon, Svalbard et l'Antarctique. Le modèle indique que la vitesse annuelle de désagrégation est fonction de la fréquence annuelle des cycles gel/dégel, du degré de saturation des roches et de la limite élastique à la traction. Des mesures de ces paramètres ont été réalisées pendant des durées variant de 1 à 6 ans sur des faces rocheuses dans les 4 régions étudiées. Bien que des différences existent dans les conditions thermiques et les conditions d'humidité, le modèle cadre bien avec les données de terrain, sauf dans l'Antarctique et une partie de Svalbard où l'humidité est insuffisante pour provoquer la désagrégation par le gel. Le modèle prédit les vitesses de gélivation du bedrock dans des enrionnements où la désagrégation par le gel est prépondérante.
Frost heave mechanism in welded tuff
Authors: Akagawa Satoshi , Fukuda Masami 
Published: February 2007

AbstractSegregation freezing, one of the heave mechanisms in freezing soils, is shown to be responsible for the breakdown of freezing welded tuff. Frost heave tests of welded tuff have proved that segregation freezing occurs in rock by revealing ice lens growth, pore water flow and the existence of hydraulic gradient driving water to the freezing front.The physical characteristics of the tuff, such as pore microstructure, mineral composition, unfrozen water conditions, permeability, and so forth, are similar to those of frost‐susceptible soils.An empirical equation, derived from the tuffs water retention curve and unfrozen water content measurements with pulsed NMR, relates the segregation freezing temperature and frost heave pressure. This equation is discussed in the context of the governing thermodynamics. We suggest that the segregation freezing concept is generally applicable to common rocks.La formation de glace de ségrégation, processus bien connu dans le gel des sols est responsable de la fracturation par le gel des tuffs cimentés à chaud. La formation de la glace de ségrégation est démontrée par la croissance de lentilles de glace, l'écoulement de l'eau des pores et l'existence d'un gradient hydraulique amenant l'eau au front de gel.
Rock Properties as Controls on Free‐face Debris Fall Activity
Authors: Douglas George R. , Whalley W. Brian , McGreevy James P. 
Published: February 2007

AbstractA free face composed of basalt flows showed, over a 72 week observation period, considerable variation in yield (kg or m3) of fallen material. Yield peaks in spring and autumn were recorded but small contributions were made from all flows throughout the year. The incidence of frost action cannot account for all of the yield peaks. An explanation of free‐face weathering can best be given by taking the microcrack crack system into account in relation to some simple rock properties. Although there are several factors involved, microcrack density and coefficient of loosening are useful indicators of flow behaviour. An explanation of rock removal which takes material properties into account as well as environmental or climatic conditions is to be preferred and can be applied as a general model for all climates.
Evidence for enhanced mechanical weathering associated with seasonally late‐lying and perennial snow patches, Jotunheimen, Norway
Authors: Berrisford Mark S. 
Published: February 2007

AbstractAt two snow patch sites in Jotunheimen, Norway, direct evidence of surface fracturing and splitting of boulders was collected to quantify spatial variations in the amounts of mechanical weathering associated with snow patches. Transects between external control and internal sites display a 3‐5‐fold increase in the percentage of clasts affected by mechanically induced fracture processes. Up to 50% of clasts within the internal areas of the snow patches exhibit either surface flaking or more severe fracturing; this contrasts with up to 15% of clasts exhibiting evidence of mechanical weathering at the snow patch peripheries. The results indicate that the snow patches significantly enhance mechanical weathering processes and that maximum mechanical weathering is associated with the average annual retreat position of the snow margin.
Hydrogen and oxygen isotopes and the origin of the ice in peat plateaus
Authors: Harris Stuart A. , Schmidt Irena H. , Krouse H. Roy 
Published: February 2007

Abstractδ18O and δD values (% SMOW) were measured on 159 samples from the active layer and permafrost on peat plateaus and from the adjacent fen at sites about 50 km north of Tuchitua along the Robert Campbell Highway in southeastern Yukon Territory. The regression lines for the samples from the active layer and the permafrost were very similar, which suggests that they both contained mainly water from meteoric sources. The water samples from the fen produced results which gave a noticeably different regression line, so that it appears that the icy core of the peat plateaus is the result of downward penetration of precipitation into permafrost rather than freezing water migrating from the surrounding fen. These relationships appear to be constant throughout the study area, and there is no evidence of the ice being from an earlier, colder period. The precipitation in this area of the Yukon Territory shows a δD versus δ18O behaviour somewhat like that reported for Whitehorse in the literature.
La gélivation des parois rocheuses dans une glacière du jura neuchǎtelois
Authors: Pancza André 
Published: February 2007

AbstractL'enregistrement de la température et les mesures de l'humidité de la roche dans la glacière de Monlési ont révélé les conditions microclimatiques très particulières dans lesquelles s'effectue la gélivation de cette cavité souterraine. La très grande efficacité du gel est en apparente contradiction avec les quelques cycles de gels‐dégels annuels enregistrés. Cette intense gélivation des parois et du plafond de la glacière s'explique par le fait, que le gel agit dans une roche imbibée, voire saturée d'eau.Vu la rareté des glacières, leur impact sur l'évolution morphologique jurassienne est insignifinate. Cependant, au cours du Quaternaire, au début et à la fin des époques glaciaires, il n'est pas exclu que la plupart des cavités karstiques di Jura aient abrité une lentille de glcae. Si l'intensité de la gélivation fur celle que nous constatons aujourd'hui, ces dépressions karstiques s'avèrent ětre des formes mixtes, dues à la dissolution mais aussi à la gélivation.
Holocene periglacial processes and environmental changes in Daqingshan mountains, inner Mongolia, China
Authors: Zhijiu Cut , Changqing Song 
Published: February 2007

AbstractPeriglacial phenomena and palaeobotany evidence of environmental changes are present in the Daqingshan area, northern China. This arid‐semiarid area is sensitive to climatic change. There were four climatic periods during the Holocene. During the Hypsithermal, the annual mean temperature was 1–2 °C higher than today. On the other hand, the annual mean temperature was 2.0–2.5 °C lower during recent glaciation and about 7 °C lower at the end of the Late Pleistocene. The fluctuation of vertical vegetation belts was about 200–600 m during the Holocene.Des phénomènes périglaciaires et des observations paléobotaniques démontrent l'existence de changements de l'environnement dans la région de Daqingshan, au nord de la Chine. Cette région aride ou semi‐aride est très sensible aux changements climatiques. Quatre périodes climatiques ont été reconnues pendant l'Holocène. Pendant l'Hypsithermal, la température moyenne annuelle était 1 á 2 °C plus élevée qu'aujourd'hui. D'autre part, la température moyenne annuelle était 2,0 a 2,5 °C plus basse pendant la glaciation récente et environ 7 °C plus élevée à la fin du Pléistocène. Les modifications des limites verticales de la végétation pendant l'Holocène ont été comprises approximativement entre 200 et 600 m.
Vertical movements of boulders in a subnival boulder pavement at 2800 m a.s.l. in the Alps (France)
Authors: Pissart A. , Francou B. 
Published: February 2007

AbstractVertical movements of boulders within a subnival boulder pavement were measured at 2800 m a.s.l. in the Alps over a period of 10 years. It was demonstrated that some boulders are undergoing sinking and others upheaving. The upheaving occurs in autumn during ground freezing, while the sinking of boulders probably occurs in springtime when the ground temperature is below 0 °C under the snow patch.
Recent microweathering phenomena in southern and central Sweden
Authors: Swantesson Jan O. H. 
Published: February 2007

AbstractMore than 200 weathering sites, in southern and central Sweden, representing different rock types and environments have been investigated. Field studies were complemented by thin‐section examination and laboratory simulation experiments. Research results in a classification of weathering forms in crystalline rocks in cool temperate climates. Special attention is paid to Holocene microweathering, facilitated because glaciation removed most old weathered material. Only minor forms, including surface colorations, mineral weathering, pitting and flaking, have been produced entirely during the Holocene. Where recent breakdown is observed, the primary reason must be sought in the geological history of rock. Holocene microweathering a few cm in depth is caused by a complex interaction between different weathering processes. Salt crystallization, however, seems important in areas that have experienced seashore conditions. Often the forms produced are as much the result of rock properties as of actual weathering processes.
Periglacial phenomena and pleistocene environmental conditions in the Netherlands—An overview
Authors: Vandenberghe J. 
Published: February 2007

AbstractDuring the IGU/IPA Symposium entitled ‘Periglacial Environments in relation to Climate’ (3–6 May 1991) prominent aspects of modern periglacial research in the Netherlands were presented in a field excursion. This paper highlights the Dutch Pleistocene periglacial environments within the framework of palaeoclimatology, sedimentology and geomorphology.
Freeze‐thaw activity and some of its geomorphic implications in the abisko mountains, Swedish Lappland
Authors: Nyberg Rolf 
Published: February 2007

AbstractFreeze‐thaw activity was studied at two mountain sites in Swedish Lappland, a debris‐mantled slope with small rockwalls at 1200 m altitude and a solifluction slope at 1050 m altitude. During the snow‐free period, there was a low intensity of short‐term frost cycles at the rockwall site, implying that current frost shattering of bedrock is mainly due to the annual freeze cycle. At the solifluction site, during a period with net surficial soil movements of up to 3 cm, short‐term frost cycles were absent below 0.1 m depth in the ground, suggesting a dominance of pure solifluction over frost creep. A considerable variability in near‐ground temperatures implies that in situ measurements, rather than meteorological screen data, are essential in assessments of frost action in high mountain terrain.
An approach to determine the origin and age of massive ice blockages in two arctic caves
Authors: Lauriol Bernard , Clark Ian D. 
Published: February 2007

AbstractMassive ice formations found blocking karst cave passages in alpine and permafrost regions are not uncommon, although their origin and age are not readily apparent. With two examples from northern Yukon, we present an approach to elucidate the mode of formation, using stable isotopes, ice fabric and the time of formation by the radiocarbon activity of cryogenic powder found in such ice. These data are supported by 14C dates on associated animal and plant remains.Ice formation is sensitive to seasonal air circulation patterns, with condensation from warm humid air flowing inward along the cave roof in summer, and sublimation by cold dry air penetrating along the cave floor in winter. Massive ice blocking the two caves is shown to form by gradual accumulation of floor ice from below, and accretion of hexagonal ice growing down from the cave roof.
Determination of pollen accumulation rates in frozen sediments
Authors: Wang Xia‐Cheng , Geurts Marie‐Anne 
Published: February 2007

AbstractPollen accumulation rates (PAR) of 48 samples from a permafrost core were calibrated to assess the influence of ice lensing on the calculations. Results show that permafrost formation can radically change PAR values. Accumulation of segregated ice is a major source of error, while the 9% volumetric expansion of pore water upon freezing must also be considered. The basic result of these influences is the exaggeration of sedimentation rates and sample volumes.
Climate and permafrost
Authors: Gavrilova M. K. 
Published: February 2007

AbstractData from Yakutia, Siberia, indicate that permafrost has been generally stable for the last 300,000 years. Historic records indicate climatic variability in the last 150 years and predict that, in comparison with the 1980s, winters will be colder and summers warmer in the early part of the twenty‐first century. Predicted man‐induced climate warming, superimposed upon these natural trends, will offset the winter cooling, while summers will be even warmer. Changes in mean annual air temperatures for the mid twenty‐first century are calculated as being half the sum of the winter and summer temperature changes. Permafrost will be preserved in mountainous regions and in the eastern polar and subarctic plains. In western Siberia and subarctic eastern and southern Siberia considerable permafrost thawing will occur and near‐surface ground temperatures will rise.
Thermokarst involutions, summer island, pleistocene mackenzie delta, Western Canadian arctic
Authors: Murton Julian B. , French Hugh M. 
Published: February 2007

AbstractThermokarst involutions form primarily by loading, buoyancy and water‐escape during the degradation of ice‐rich permafrost. In the Summer Island area of the Pleistocene Mackenzie Delta, they are formed mainly by loading and buoyancy, and occur within a Late Wisconsinan‐Early Holocene thaw layer. Involutions formed by water‐escape (fluidization) occur within slump‐floor deposits.To form thermokarst involutions, ice‐rich permafrost must thaw, drainage conditions must be poor and sediments must vary in texture or composition. In addition, the sediments should be susceptible to fluidization, liquefaction or hydroplastic deformation. Thermokarst involutions formed by loading and buoyancy require a reverse density gradient; those formed by fluidization require open‐system groundwater conditions or associated water‐saturated sediments susceptible to liquefaction.
Rock moisture data from Livingston Island (maritime antarctic) and implications for weathering processes
Authors: Hall Kevin 
Published: February 2007

AbstractRock moisture content was determined for rock samples on different aspects of rock outcrops on Livingston Island during a summer season. As a result of the dominant rainbearing northerly winds the southern aspect usually has rock moisture levels lower than the northern. The southern aspect, however, experiences high rock moisture levels during periods of snowmelt; snow accumulates on the southern, lee‐side of the rock outcrops. Wetting and drying events are more frequent on the northern exposure, although not as common as at a site open through the full 360°, while the southern aspect tends to experience continuous, low moisture levels with infrequent dry events. Contrary to earlier suggestions, freeze–thaw weathering does not appear to be a major factor during the summer. Although rock moisture levels are conducive to freeze–thaw, rock temperatures rarely go below 0°C. Rather, it appears that weathering due to wetting and drying may be more common on the northern aspects than was previously thought while chemical weathering is active on southerly aspects. Rock moisture levels may support rock damage due to segregation ice during the winter freeze when the rate of freezing is slowed by the overlying snow cover.Contrairement a ce qui a été suggéré précédemment, l'altération par gel‐dégel ne semble pas ětre, l'été, un facteur de désagrégation principal. Quoique les niveaux d'humidité soient favorables aux actions de gel‐dégel, les températures des roches y descendent rarement sous 0°C. Au contraire, il apparaǐt que l'altération due aux alternances sèchage / humidification doit ětre plus fréquente sur les versants exposés au nord, tandis que l'altération chimique serait surtout active sur les versants exposés au sud. Les niveaux d'humidité des roches peuvent engendrer une désagrégation due à la formation de glace de ségrégation pendant l'hiver parce que la vitesse de gel est ralentie par la couverture de neige.
Devensian thermal contraction networks and cracks at Somersham, Cambridgeshire, UK
Authors: West R. G. 
Published: February 2007

AbstractMiddle and Late Devensian thermal contraction networks and cracks are described from the southern Fenland, Cambridgeshire. They are associated with gravel aggradations of low terraces of the River Great Ouse. Two networks are described, one set younger than the other. Three types of contraction crack are described. Type 1 occurs within the gravel aggradation of a c. 3 m OD terrace; type 2 penetrates this gravel and is filled with a complex of sediments, including primary, secondary and trough fillings; type 3 penetrates younger lacustrine sediments and gravels associated with Lake Sparks, the lake formed by the damming of Fenland by Late Devensian ice at the Wash. The networks are related to type 2 and type 3 cracks. The relation of permafrost periods to the stratigraphy and landscape development is described, together with the chronology. Periods of sand‐loess and cover sand deposition are identified. A period of permafrost degradation may be associated with change of climate and/or the development and proximity of Lake Sparks. A major period of permafrost in the area is correlated with the Weichselian Late Pleniglacial major permafrost event in the Netherlands (24 ka to 17 ka BP) and a similar major event in Poland (22 ka to 19/20 ka BP). This appears to be, broadly, the period leading up to and associated with the advance of the Late Devensian (Weichselian) ice in Britain and on the continent.