Showing papers in "Permafrost and Periglacial Processes in 1996"

Permafrost monitoring and detection of climate change

Abstract: Ground temperature monitoring has been proposed as a means of detecting climate change in permafrost regions, although it is well known that the relationship is not simple. This paper presents a functional model of the permafrost-climate relationship, which accommodates the geographical variations of climatic, surface and soil factors that control ground thermal regime. The model is used to analyse the impacts of climate change on ground temperatures and to assess the design and interpretation of ground temperature monitoring programs. The model suggests that lithologic conditions form the primary local influence on permafrost temperatures, followed by snowcover and vegetation. Results using the model suggest that simple monitoring of active layer depth does not provide a reliable indicator of changes in permafrost temperature conditions, and that monitoring at exposed bedrock sites will produce the most direct signal of climate change on the ground thermal regime. © 1996 John Wiley & Sons, Ltd.

Origin of rock glaciers: Observations from Mellemfjord, Disko Island, Central West Greenland

Abstract: Surface and interior characteristics of a tongue-shaped rock glacier at Mellemfjord on Disko Island are described. A long natural section shows the existence of a solid ice core. The implications for the origin of ice within the rock glacier and its surface debris layer are discussed and, from this, the rock glacier age is estimated at about 550 years; that is, it was probably initiated during the initial period of the Little Ice Age. It is suggested that the climatic control on ice-cored rock glaciers in particular is more pronounced than traditionally assumed. It is suggested that although the geomorphological feature described displays many characteristics of a normal glacier, it should be classified as a true rock glacier. © 1996 John Wiley & Sons, Ltd.

Climatic warming and the degradation of warm permafrost

Abstract: Permafrost—a widespread constituent of the terrestrial environment—by definition is dependent upon the ambient temperature for its existence and properties. Thus, it is very sensitive to climatic changes. Simple relations based upon conductive heat transfer, with thawing and geothermal heat flow, are presented to predict the transient effects of surface temperature increases on the thermal state of permafrost. The results indicate that, based on the usual global warming scenarios, relatively small amounts of permafrost will disappear within 50–100 years. This is specifically shown for the most thermally sensitive cases, that is, warm or relict permafrost. © 1996 John Wiley & Sons, Ltd.

Pleistocene Permafrost of West Siberia as a Deformable Glacier Bed

Abstract: Subglacial permafrost is usually referred to as a factor impeding basal glacial processes, and the deformation of soft substrata in particular. In West Siberian, widespread glacial disturbances present in permafrost of Pleistocene age suggest that frozen sediments, if clayey and/or icy, can readily deform, thus translating basal glacial stress into sliding of the entire glacier/sediment complex along subglacial shear zones. Ductile deformations such as folds and diapirs are also widespread. The mode of deformation of frozen subglacial sediments is dependent on their lithology, ice content and temperature conditions. Signatures of former subglacial permafrost in currently thawed sediments are deduced from contrasting deformation behaviours of lithologically different sedimentary formations.

Modelling and verification of the permafrost distribution in the Bernese Alps (Western Switzerland)

Abstract: Results of a study to investigate the permafrost distribution and rock glaciers in the Bernese Alps (western Switzerland) are presented. Two different methods were applied. First, a computer model (PERM) has been developed, which allows one to calculate and map the probability of alpine permafrost occurrences by means of a digital terrain model on the basis of rules of thumb considering altitude, aspect, slope and type of ground cover. Second, an inventory of 80 rock glaciers has been established from the results of the interpretation of aerial photographs and field work. Active and inactive rock glaciers were used as indicators to verify the permafrost distribution calculated with PERM. Coincidence of rock glaciers with the simulated permafrost distribution proved to be very good, which seems to confirm the results of the permafrost modelling. However, the number of the rock glaciers — probably for climatic reasons — is too small to allow a strict statistical verification of the permafrost map produced with PERM. The interpretation of the field data suggests that the lower limit of discontinuous permafrost in the Bernese Alps probably reaches slightly further down than in the more continental central Alps.

Near‐surface brecciation of chalk, isle of thanet, south‐east England: a comparison with ice‐rich brecciated bedrocks in Canada and Spitsbergen

Abstract: Chalk on the Isle of Thanet, Kent, is brecciated to depths of a few metres beneath the ground surface. The brecciation commonly comprises (i) an undeformed layer of angular, platy blocks more or less parallel to the surface overlain by (ii) a deformed layer containing small open folds, typically with vertical axial planes. Above the brecciated chalk is an involuted layer (∼0.5 to 2.0 m thick) of chalk diamicton and brickearth. By analogy with brecciated ice-rich limestones, arkoses and shales in areas of continuous permafrost in Arctic Canada and Spitsbergen, it is suggested that brecciation of the Chalk resulted primarily from ice segregation in perennially frozen bedrock, and repeated segregation formed an ice-rich layer just beneath the former permafrost table. Subsequent thaw consolidation of this layer is thought to have formed an involuted layer through soft-sediment deformation. Three implications arise from this study: (i) near-surface brecciation of the Chalk probably took place during conditions of continuous permafrost; (ii) the growth and thaw of the ice-rich layer in chalk was probably an important element in the geomorphological evolution of the English Chalklands, heaving and brecciating the Chalk during permafrost conditions, and deforming or redepositing the overburden during periods of active-layer deepening; and (iii) repeated ice segregation near the top of permafrost may have brecciated other bedrocks in the British Isles.

Soil moisture variability in relation to diurnal frost heaving on Japanese high mountain slopes

Abstract: Frost heave, ground temperature and moisture were concurrently monitored on two alpine slopes with thin debris mantles. Electrical sensors connected to data loggers permitted automated monitoring of the three variables. Diurnal frost heave of up to 3 cm frequently took place during spring and autumn. Soil moisture contents are regarded as the primary control on the amount of frost heave, while the intensity of freezing is secondary. Heave was usually greatest just after a major rainstorm that produced high moisture contents in the near-surface soil, and decreased with soil desiccation. Rainstorms often interrupted the desiccation process and reactivated frost heaving. Despite reaching a depth of 1 m or more, seasonal frost penetration caused only small amounts to heave, because the lower part of the seasonally frozen layer was not frost-susceptible. These observations imply that the thin debris mantle and periodic precipitation during periods of freeze-thaw combine to result in the predominance of shallow frost creep, which is typical of soil movements in Japanese high mountains.

Formation of miniature sorted patterns by shallow ground freezing: A field experiment

Abstract: At an experimental site near sea level in Scotland, a miniature sorted net with cell diameters of 56–172 mm and stony borders 4–9 cm deep developed in frost-susceptible regolith over two winters. Pattern formation was evident after only 8 freeze-thaw cycles, during which the minimum surface temperature was −5.3°C and freezing extended to a maximum depth of 16–17 cm. The primary process of pattern development was repeated differential growth of near-surface needle ice, causing upcoming of a cover of coarse debris. During subsequent thaw, bending and melting of ice needles resulted in net migration of upheaved clasts towards dome margins, causing progressive concentration of clasts in stony borders surrounding finer cells. This differentiation of near-surface soil texture appears self-sustaining, promoting preferential growth of ice lenses and thus preferential heave in fine cells. The experiment suggests that miniature frost-sorted patterns are not necessarily diagnostic of present or former periglacial environments, but may develop on unvegetated soil of suitable composition in a wide range of mid- or even low-latitude environments where shallow ground freezing is accompanied by the growth of needle ice. © 1996 John Wiley & Sons, Ltd.

Active layer distortion of annual air/soil thermal orbits

Abstract: A straightforward procedure is proposed as a first order, initial approximation for assessing the character of the heat transfer process in the subsurface. Considering monthly averages of air and soil temperatures as a perpendicular superposition of simple harmonic motions, ‘phase-space’ figures can be generated to permit a rapid qualitative diagnostic of the subsurface thermal regime. It is found that for subsurface conductive regimes the shape of the interface thermal regime. It is found that for subsurface conductive regimes the shape of the interception figures is regular. For sites where an active layer and associated processes are present, the interception figures are highly irregular owing to non-conducive heat transfer. Implications for the prediction of soil temperatures and determination of climatic changes from geothermal data are discussed in this context.

Surficial characteristics associated with the occurrence of permafrost near Mayo, central Yukon Territory, Canada

Abstract: Key criteria have been isolated for predicting the location of discontinuous permafrost in central Yukon Territory. Eighteen soil, vegetation, and topographic variables were documented at 60 sites in a 2500 km2 area, and analysed to establish their association with the occurrence of permafrost. The singular features most associated with permafrost were a thick surface organic layer and a hummocky microtopography. In combination, soil moisture content and organic-layer thickness were diagnostic of permafrost occurrence. The thickness of the organic layer, a horizon of low thermal diffusivity, governs attenuation of the summer temperature wave; soil moisture content supplies water for evapotranspiration, which reduces surface temperature. Variation in these indices accounted for 95% of variation in permafrost occurrence within the 60 sites. A diagnostic system to predict permafrost occurrence was constructed with these indices, and tested against field data from 60 different sites. The occurrence of permafrost in the second data set was predicted correctly at every site. The critical soil moisture content and organic-layer thickness were 25% (gravimetric) and 11 cm, repectively. Permafrost is present where these values are exceeded. The results indicate that the occurrence of permafrost in this portion of the discontinuous zone can be determined from relatively few variables.

Sand-wedge and ventifact palaeoenvironmental indicators in North-West Saskatchewan, Canada, 11 ka to 9.9 kaBP

Abstract: Exhumed sand wedges and ventifacts in the upper Churchill watershed of north-western Saskatchewan indicate that aeolian and periglacial processes were dominant from c. 11 to c 10.5 ka BP. Nineteen sand wedges were identified that display vertical foliation, form polygonal nets, and penetrate either till, glaciolacustrine sediment or glaciofluvial diapiric sand. The sand wedges, and sand lenses within the till and glaciolacustrine sediments, indicate permafrost aggradation after glaciation and lake drainage. Ventifacts that overlie the sand wedges have preferred keel orientations that correlate with palaeo-katabatic wind directions interpreted from stabilized parabolic dune orientations. Rat-tail lineaments on faceted surfaces of coarse-grained, granitic ventifacts also indicate palaeo-wind flow direction. Strong and weakly developed lineaments on the same einkanter are explained by opposing flow from prevailing winds, katabatic winds and anticyclonic air flow from the adjacent Laurentide Ice Sheet, or by flow separation at the ventifact keel under unidirectional air flow. Two geomorphic surfaces are identified: (1) an older surface with sand wedges and weakly developed ventifacts indicative of permafrost and brief aeolian activity; and (2) a lower and younger segment of the former Lake Agassiz basin, without permafrost indicators but with well-developed ventifacts. The upper surface, developed in association with the Beaver River Moraine and glacial Lake Meadow-McMurray, is 11–10.5 ka BP in age, synchronous with the Younger Dryas cold period. The younger, lower surface was last modified beginning at 9.9 ka BP, when the north-west outlet of Lake Agassiz opened, was susceptible to greater aeolian reworking than the upper surface, and postdates the Younger Dryas. © 1996 John Wiley & Sons, Ltd.

Effects of nivation on periglacial landscape evolution in western Jutland, Denmark

Abstract: This paper briefly discusses the concept of nivation as used in modern periglacial research and presents a detailed investigation of nivation forms and sediments from western Jutland in Denmark. On a part of the Saalian glacial landscape on Skovbjerg bakkeo, nivation forms are numerous. Nivation niches, V-shaped dry valleys and associated alluvial cones consisting of accumulated nival sediments are seen as coherent and genetically linked landforms. The influence of nivation on the Weichselian periglacial transformation of the Saalian glacial landscape is demonstrated and it is further shown how nivation forms are acting as Holocene sedimentary sinks.

The occurrence of a holocene rock glacier on Mount Kenya: Some observations and comments

Abstract: The morphology of the Lenana rock glacier is briefly described from Mount Kenya. Biological activity and ground temperature data do not support contemporary rock glacier development at the site. It is suggested that the rock glacier and protalus ramparts were active during the Holocene and are indicative of a recent frozen core and perennial snowbanks above ∼4750 m ASL. © 1996 John Wiley & Sons, Ltd.

Deep‐seated creep of massive ground ice, Tuktoyaktuk, NWT, Canada

Abstract: A study of the in situ creep deformation of massive ground ice has been carried out at a field site near the village of Tuktoyaktuk, NWT. Cumulative surface displacements, accounted for by creep deformation to a depth of 25 m, vary from about 3 mm/a at the upslope site to 4 mm/a at the downslope site. While net displacements on a year to year basis were downslope, the creep pattern at both sites displays a quasi-sinusoidal fluctuation, with significant seasonal upslope movement during the late winter and early summer. This fluctuation is thought to be due to the effects of thermal contraction. © 1996 John Wiley & Sons, Ltd.

Rates of periglacial processes in the Central Tianshan, China

Abstract: The periglacial landforms of the Central Tianshan are mainly distributed above the lower boundary (3200 m ASL) of permafrost. In the eastern part of the region, there are 130 days per year when the daily average air temperature fluctuates around 0°C. The annual precipitation is 430 mm. Thus, periglacial landform development reflects the high frost-thawing frequency. By contrast, in the western part, there are only 90 days per year when the daily average air temperature fluctuates around 0°C; thus, periglacial landforms are those typical of areas with low frost-thawing fequencies, even though the annual precipitation reaches 827 mm. Based on observations from 1985 to 1989, schist (bedrock) cracks have a maximal dilatational value of 19 mm/a in the region, and gneiss cracks have a maximal dilatational value of 4 mm/a. The frost-heaving of diorite reaches 8–40 mm/a. The moving rate of rockfall talus is 1 m/a. On sunny slopes (195°SW), the talus debris has amounted to as much as 31.5 cm in the past 25 years, but on semi-shady slopes (65°NE), the debris accumulation is only 5 cm. The alluvial talus (scree) has a downward movement rate of 146 cm/a on south-facing slopes, and 73 cm/a on north-facing slopes. Block slopes have a downward movement rate of 96 mm/a on sunny or semi-sunny slopes and 72 mm/a on the shady or semi-shady slopes; the average rate is 81 mm/a in the study region. East of 86°E, the lobate rock glacier is the main type and its mean moving rate is about 6 cm/a, as deduced by debris discharge which has covered the highway over the past 25 years. Measurements from 1985 to 1986 show that the movement of lobate rock glaciers is from 1 to 49 cm/a. Rates at the higher elevation (15.5–49 cm/a) are faster than at the lower elevation. At the same elevation, the rates on the northward slopes (about 49 cm/a) are greater than on southward slopes (45 cm/a). According to lichenometry data, lobate rock glaciers formed between 3949 a BP to 180 a BP. West of 86°E, the main rock glacier type is the tongue-shaped rock glacier. The mean movement rate is 0.4 m/a. Gelifluction lobes and terraces have an average annual movement of 25 cm in the east. In the west, the average annual movement rate of gelifluction is 49 cm/a.

Monitoring the evolution of permafrost in the Tien Shan

Abstract: The extent and altitudinal range of permafrost in the Tien Shan has changed many times during the Holocene. The lower limit of permafrost has risen significantly, but from time to time it has regressed. For example, the limit of permafrost during the Little Ice Age was lower than it is now by about 300–400 m. Based on the distribution of relict permafrost features in the Tien Shan, the mean annual air temperature in the Little Ice Age was 2–3°C lower than today. During the last years, permafrost temperatures have increased 0.1 to 0.4°C.

Modalités de la cryoreptation dans les massifs du chambeyron et de la mortice, Haute‐Ubaye, Alpes Françaises du sud

Abstract: From 1975 to 1992, displacements were measured at the soil surface and at depth, at various sites of the Haute-Ubaye, southern French Alps, between 2450 m and 3150 m altitude. The mean rates of movement calculated varied from 0.5 to 5 cm/a. Frost creep predominates; it is more active between 2800 and 3150 m, in the alpine periglacial zone. The fairly elevated silt content of the slope deposits is favourable to frost creep. The evolution of different slopes to produce sorted stripes and solifluction lobes is variable; it depends on vegetation cover, water retention and slope exposure. The movement also varies, yearly, according to the intensity and distribution of precipitation. The soil solifluction is restrained because the number of freezing and thawing cycles is small, generally about 20 to 25 per annum at 5 cm depth.

Prospection électrique sur les glaciers rocheux du cirque de Sainte-Anne (Queyras, Alpes du Sud, France)

Abstract: The Sainte-Anne cirque in the Queyras area contains several active rock glaciers. The internal structure of the main two (Ste-Anne and Petite-Part) have been studied by electrical means (about 15 resistivity soundings of the Schlumberger type). The apparatus and the methodology have been tested in the Alps since 1986. The shape of the resistivity curves clearly shows the occurrence of ice in the ground. The interpretation of these curves leads us to estimate the ice content and geometry of the investigated layers. In the Sainte-Anne area, the internal structure of the rock glaciers is somewhat complex, with coexistence of rather pure ice from the upper glacierets and ice-cemented sediments of periglacial origin. The tongue of the rock glacier can be iceless (Sainte-Anne). The active terminal lobe always contains a core of poorly ice-cemented sediments. This is responsible for the measured movements (35 cm/a) and the observed ridges. This core, actually melting, is about 20 m thick at Sainte-Anne and 10 m at Petite-Part, under a few metres of ice-free sediments.

Relationship between the distribution of periglacial landforms and glaciation history, Fildes Peninsula, King George Island, Antarctica

Abstract: Three kinds of profile assemblage features show that periglacial landforms have an internal relationship in genesis. For example, where there is a rich weathering debris, the dominant landforms are talus, black slopes, mass movement features, and mega-grained sorted forms. Where the debris material is silty, fine-grained periglacial forms (for example, gelifluction steps and striated soils) dominate. Where the debris source is limited, talus only appears at the south-east side of periglacial tors and hilltops; the major periglacial forms are striated soils and muddy sorted circles. In general, periglacial landforms show a difference between stoss and leeward slopes.

Cryptogamic soil buds in the equatorial Andes of Venezuela

Abstract: Soil buds, formed by particle heaving and sorting by needle ice, were studied in a high Andean paramo. Soils were finer in buds than in adjacent trough areas, where pebbles had been concentrated by lateral sorting. Some buds were composed only of mineral grains, others were covered by a cryptogamic crust of liverworts (Marsupella spp.) or mosses (Grimmia longirostris). Particle sorting was studied by comparing the grain-size distributions of buds and troughs, and by using a numerical sorting index. Degree of sorting varied widely among bare bud sites, where it was dependent on the presence of gravel in the substrate. Sorting was pronounced in sites with cryptogamic plants, where fines (<0.05 mm) were concentrated within buds, which also contained higher amounts of organic matter than the adjacent troughs. Microscopic examination showed that cryptogamic buds were layered in three concentric bands. This resulted in a gradual increase of fines and organic matter toward the bud top, as well as in a lower pH and darker colour. The pronounced rise in silt and clay near bud surfaces is due to interception of aeolian material by plants, which can trap fines and then grow above the deposited dust, thus forming a cumulic sequence of thin crustal laminae. Vughs and vesicles formed by frost activity were common in buds, particularly in their basal layer. Field experiments showed that cryptogamic crusts increase the infiltration rates and compressive strength of soil buds. This results in a lower chance of runoff generation and in an increased resistance to detachment by various geomorphic agents. An idealized developmental sequence of cryptogamic soil buds is discussed in detail.

Albert Pissart and his role in the study of periglacial environments (Albert Pissart et son rôle dans l'étude des millieux périglaciaires)

Abstract: On the occasion of his retirement from the University of Liege, a group of colleagues summarize the main achievements and activities in periglacial research of Albert Pissart. He is one of the few periglacial geomorphologists who has (1) successfully studied both Pleistocene phenomena and present day processes, (2) undertaken palaeogeographic reconstructions, and (3) carried out numerous experimental and laboratory studies into the effects of cold climates upon rocks and landforms.