Search

Permafrost in circum‐polar regions has been recently undergoing thawing, with severe environmental consequences, including the release of greenhouse gases and amplification of global warming. Although highly important, direct methods of tracking thawing hardly exist. In a research study conducted at Adventdalen, Svalbard, we identified a permafrost radioisotope fingerprint, and show that it can be used to track thawing. Ratios of long‐ to the shorter‐lived radium isotopes are higher in ground ice than in active layer water, which we attribute to the permafrost closed system and possibly to the long residence time of ground ice in the permafrost. Also, daughter–parent 224Ra/228Ra ratios are lower in permafrost than in the active layer. These fingerprints were also identified in a local stream, confirming the applicability of this tool to tracing thawed permafrost in periglacial watersheds. A combination of radium isotope ratios and 3H allowed the identification of recent intra‐permafrost segregation processes. The permafrost radium fingerprint should be applicable to other permafrost areas, which could assist in regional quantification of the extent of permafrost thawing and carbon emissions to the atmosphere.

A morphological model for estimating ground‐ice contents of various landscape units is presented to address the gap between large‐scale, general studies and small‐scale, site‐specific case histories. The model considers different ground‐ice types and cryostratigraphic relations between ice bodies within a terrain unit. Input parameters needed for the model are described. Derived variables and algorithms used to determine the quantity of each ground‐ice type within a terrain unit are presented. Examples of the application of the model are provided for the Yukon Coastal Plain, northwest Canada. The uncertainties and limiting assumptions of the model are discussed. Copyright © 2017 Natural Resources Canada. Permafrost and Periglacial Processes © 2017 John Wiley & Sons, Ltd.

The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analysed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterised as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments. Copyright © 2017 John Wiley & Sons, Ltd.

The rapid warming of the Arctic may not only alter species’ abundances and distributions, but likely also the trophic interactions within and between ecosystems. On the high‐arctic tundra, extreme warm spells and associated rain‐on‐snow events in winter can encapsulate the vegetation entirely in ground‐ice (i.e., basal ice) and directly or indirectly affect plants, herbivores, and carnivores. However, the implications of such extreme events for trophic interactions and food‐web ecology are generally far from understood. Here, we show that wild Svalbard reindeer populations increasingly isolated by lack of sea‐ice respond to rain‐on‐snow and ice‐locked pastures by increased kelp consumption. Based on annual population surveys in late winters 2006–2015, the proportion of individual reindeer feeding along the shoreline increased the icier the winter. Stable isotope values (δ34S, δ13C, δ15N) of plants, washed‐ashore kelp, and fresh reindeer feces collected along coast‐inland gradients, confirmed ingestion of marine biomass by the reindeer in the shoreline habitat. Thus, even on remote islands and peninsulas increasingly isolated by sea‐ice loss, effects of climate change may be buffered in part by behavioral plasticity and increased use of resource subsidies. This marine dimension of a terrestrial herbivore's realized foraging niche adds to evidence that global warming significantly alters trophic interactions as well as meta‐ecosystem processes. © 2019 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

The Las Liebres rock glacier is a large (~2.2 km long) Andean rock glacier whose internal composition and kinematics are known from previous studies. We investigate its development by posing and testing the following null hypothesis: the rock glacier has developed from a constant supply of debris and ground ice in periglacial conditions and resulting creep of the ice-rock mixture. A rheological model was formulated based on recent advances in the study of ice-rock mixture rheology, and calibrated on the known surface velocities and internal composition of the rock glacier. We show that the rock glacier viscosity is inversely related to both water and debris fractions, in agreement with recent field and theoretical studies of ice-rock mixture rheology. Taking into account the possible variations in water fraction, the model was used to estimate the time spans of development (0.91–7.11 ka), rates of rock wall retreat (0.44–4.18 mm/a), and rates of ground ice formation (0.004–0.026 m/a) for the rock glacier. These results support the null hypothesis of a periglacial origin of the Las Liebres rock glacier. Copyright © 2016 John Wiley & Sons, Ltd.

This review focuses on advances in applications of geophysical methods to permafrost terrain that have emerged in 2007–12. Improvements in the four main geophysical techniques presently used in permafrost research (i.e. electric, electromagnetic, seismic and radar methods) and new or resurrected methods for permafrost applications are discussed. Advances in geophysical monitoring and quantitative interpretation of geophysical survey results are presented, especially for ground ice and water content. Electrical resistivity is now used operationally for long-term monitoring of ice content, as well as for short-term process studies. Quantitative approaches to determine realistic ice and liquid water content values and their spatial and temporal variability exist, but need to be further refined to be widely applicable for geotechnical and numerical modelling purposes. Copyright © 2013 John Wiley & Sons, Ltd.

This paper reviews contributions to permafrost isotope geochemistry published between 2007 and 2012 and proposes future research directions. It focuses on: (1) the origin and age of ground ice; (2) geochemistry and water movement in the active and transient layers; and (3) geochemistry and water movement in deep permafrost. The use of isotope geochemistry to study permafrost-related processes has grown significantly over the last few years. These processes have been elucidated by combining geochemical and isotope measurements from different components of permafrost. Such combination has yielded new insights, for example, into the water source and transfer processes that lead to the formation of ground ice, as well as groundwater movement and residence time in permafrost. Permafrost isotope geochemistry has a promising future and should provide valuable tools for the study of a rapidly changing permafrost environment. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of the δD and δ18O composition of ice is commonly used to provide insight into the origin of ice bodies. However, studies have questioned the use of the co-isotope relationship to differentiate ground ice types. This study reviews the principles of fractionations affecting δD, δ18O and deuterium excess (d) in meteoric precipitation and during equilibrium freezing of water under changing freezing rates. Traditionally, regression slope values (SD-18O) between δD and δ18O of less than 6 have been used to suggest that ground ice was formed by freezing of liquid water but here it is shown that SD-18O values of less than 7.3 can be suggestive of freezing under equilibrium conditions. This maximum freezing SD-18O value falls within the range of many local meteoric water lines at sites in the Arctic, which can complicate proper identification of subsurface ice types. Many studies are starting to use the calculation of d to infer the origin of subsurface ice. However, d values do not provide much information on the origin of subsurface ice, as d is dependent on freezing conditions. To make proper use of d, its relation with D needs to be investigated, with no relation reflecting meteoric precipitation and a negative relation indicative of freezing. In all cases, it is recommended that stable O-H isotope measurements be supported by additional distinguishing tools (i.e. entrapped gases) when attempting to infer subsurface ice types. Copyright © 2011 John Wiley & Sons, Ltd.

Permafrost along the Qinghai-Tibet railway is featured by abundant ground ice and high ground temperature. Under the influence of climate warming and engineering activities, the permafrost is under degradation process. The main difficulty in railway roadbed construction is how to prevent thawing settlement caused by degradation of permafrost Therefore the proactively cooling methods based on controlling solar radiation, heat conductivity and heat convection were adopted instead of the traditional passive methods, which is simply increasing thermal resistance. The cooling methods used in the Qinghai-Tibet railway construction include sunshine-shielding roadbeds, crushed rock based roadbeds, roadbeds with rock revetments, duct-ventilated roadbeds, thermosyphon installed roadbeds and land bridges. The field monitored data show that the cooling methods are effective in protecting the underlying permafrost, the permafrost table was uplifted under the embankments and therefore the roadbed stability was guaranteed.

The inversion and interpretation of electrical resistivity tomography (ERT) data from coarse blocky and ice-rich permafrost sites are challenging due to strong resistivity contrasts and high contact resistances. To assess temporal changes during ERT monitoring (ERTM), corresponding inversion artefacts have to be separated from true subsurface changes. Appraisal techniques serve to analyse an ERTM data set from a rockglacier, including synthetic modelling, the depth of investigation index technique and the so-called resolution matrix approach. The application of these methods led step by step to the identification of unreliable model regions and thus to the improvement in interpretation of temporal resistivity changes. An important result is that resistivity values of model regions with strong resistivity contrasts and highly resistive features are generally of critical reliability, and resistivity changes within or below the ice core of a rockglacier should therefore not be interpreted as a permafrost signal. Conversely, long-term degradation phenomena in terms of warming of massive ground ice at the permafrost table are detectable by ERTM.

Subsurface ice in cold hyperarid conditions retreats by sublimation and diffusion through the overlying soil layer. Here, it is shown that percolating meltwater, if present, can counterbalance sublimation loss effectively and thus increase the persistence time of subsurface ice. Time averaging of transport equations is used to evaluate the significance of percolation in an otherwise complex dynamical system. The reduction in sublimation loss is approximately given by the amount of meltwater multiplied by the percolation depth and divided by the depth to the ice table. It is plausible that percolation is even more effective during a warmer, wetter climate. Copyright © 2009 John Wiley & Sons, Ltd.

Permafrost and geohydrological investigations in a small basin in northeast China indicate that permafrost affects both the depth at which groundwater occurs and its artesian pressure. Artesian flow in the basin is common, and artesian head may be as much as 10 m above ground surface. The thickness of permafrost bears a close relationship to groundwater discharge (i.e. artesian flow rate), since a number of boreholes indicate that the greater the discharge, the thinner the permafrost. Over time the average rate of artesian flow from the boreholes decreases. The duration of flow depends on the rate of artesian flow, and permafrost temperature and thickness. Long-term observations in areas where the permafrost is 70 m thick and has a mean annual ground temperature of −2.5°C indicate that if flow rate is larger than 0.8 l/s, flow continues for an indefinite period of time, but that if flow is less than 0.6 l/s, flow stops shortly. The difference in permafrost thickness, caused by the differential development of fractures and associated artesian head, may be as great as 50 m. Massive ground ice, with a thickness of more than 20 m, occurs in some boreholes at depth and is probably intrusive in nature. Des recherches se rapportant au pergelisol et a l'hydrogeologie dans un petit bassin du nord-est de la Chine indiquent que le pergelisol intervient pour determiner a la fois la profondeur a laquelle de l'eau existe dans le sol et sa pression artesienne. Des ecoulements artesiens sont connus dans le bassin etudie et la pression artesienne peut atteindre l'equivalent de la pression d'une colonne d'eau s'elevant 10 m au-dessus de la surface du sol. L'epaisseur du pergelisol est en relation etroite avec le debit d'eau du sol (c'est-a-dire avec la vitesse d'ecoulement artesienne) puisque de nombreux sondages indiquent que plus le debit est eleve, plus le pergelisol est mince. Avec le temps, le debit moyen artesien observe dans les sondages diminue. La duree de l'ecoulement depend de l'importance du debit artesien, de la temperature du pergelisol et de son epaisseur. Des observations a long terme dans des regions ou le pergelisol a 70 m d'epaisseur et se trouve a une temperature moyenne annuelle de −2,5 °C indiquent que si le debit est superieur a 0,8 l/s, l'ecoulement se poursuit pendant une periode indefinie. Par contre, si le debit est inferieur a 0,6 l/s, l'ecoulement s'arrěte rapidement. La difference d'epaisseur du pergelisol causee par le developpement differentiel de fractures et de la pression artesienne associee peut atteindre 50 m. De la glace du sol massive avec une epaisseur de plus de 20 m a ete trouvee en profondeur dans quelques sondages et est probablement d'origine intrusive.

Ice wedges are normally classified into two main types: epigenetic and syngenetic. Epigenetic wedges grow wider rather than higher or deeper. Syngenetic wedges grow both wider and higher more or less simultaneously with the deposition of material at the growth site. Field studies show that there is a third type, an anti-syngenetic wedge, which grows downward on receding slopes in a direction normal to the slope. The downward growth rate is a function of the rate of ice-veinlet growth and slope recession. The downward growth of an anti-syngenetic wedge at a site with a net removal of material is thus opposite to that of the upward growth of a syngenetic wedge at a site with a net addition of material. The deformation of epigenetic, syngenetic and anti-syngenetic wedges by shear and creep may complicate attempts at age-dating the wedges by ice petrofabrics, stable isotopes and other methods. Les fentes de gel a remplissage de glace sont d'habitude classees en deux types principaux, a savoir les fentes de gel epigenetiques et syngenetiques. Les fentes en coin epigenetiques grandissent en largeur plutǒt qu'en hauteur ou en profondeur. Les fentes en coin syngenetiques grandissent a peu pres en měme temps a la fois en largeur et en hauteur au fur et a mesure que s'accumulent des materiaux a la surface. Des etudes de terrain montrent qu'un troisieme type existe que nous appellerons ‘fentes de gel anti-syngenetiques’ qui grandissent vers le bas sur des pentes reculant parallelement a elles-měmes. La vitesse de croissance vers le bas est fonction a la fois de la vitesse de croissance de la fente de glace et de la vitesse de recul du versant. La croissance vers le bas d'un coin anti-syngenetique a un endroit ou se produit l'ablation de materiaux s'oppose donc a la croissance vers le haut d'un coin syngenetique qui apparaǐt quand des materiaux s'accumulent a la surface du sol. Les deformations par cisaillement et creep des fentes en coin epigenetiques, syngenetiques et anti-syngenetiques peuvent compliquer les essais de datation des coins de glace, realises par l'etude des caracteres de la glace, la determination des isotopes stables de celle-ci, ou encore par d'autres methodes.

The relationship between explosive volcanic eruptions and permafrost aggradation is discussed at a regional (Hekla volcano, Iceland, 63°59′N 19°40′W) and a global scale. During the most recent Hekla eruption in winter 2000, tephra buried the adjacent winter snow cover. Observations of denivation landforms, excavated sections and active-layer thickness were carried out 15 to 77 months after the eruption. Results show that the combination of climate that favours permafrost and a thin layer of tephra is sufficient to reduce the sub-tephra snow ablation substantially, possibly even to zero, causing aggradation of the surface and preserving massive ground ice and permafrost. Based on these observations, a conceptual model for permafrost aggradation related to tephra accumulation was developed. On a global scale, about one third of all active volcanoes seems to be located in permafrost-favourable areas, suggesting that explosive volcanic eruptions may be significant for permafrost aggradation. Copyright © 2007 John Wiley & Sons, Ltd.

The McMurdo Dry Valleys (MDVs) constitute the largest ice-free area (6700 km2) in Antarctica. Permafrost is ubiquitous in the region and is present as ground ice or buried ice, ice-cemented permafrost and dry-frozen permafrost. Using a combined dataset that includes more than 800 shallow (

We are testing the idea of Squyres et al. (1992) that rampart craters on Mars may have formed over a significant time period and therefore the onset diameter (minimum diameter of a rampart crater) only reflects the ground ice depth at a given time. We measured crater size frequencies on the layered ejecta of rampart craters in three equatorial regions to derive absolute model ages and to constrain the regional volatile history. Nearly all rampart craters in the Xanthe Terra region are ~3.8 Gyr old. This corresponds to the Noachian fluvial activity that region. Rampart crater formation declines in the Hesperian, whereas onset diameters (minimum diameter) increase. No new rampart craters formed after the end of the Hesperian (~3 Gyr). This indicates a lowering of the ground ice table with time in the Xanthe Terra region. Most rampart craters in the Valles Marineris region are around 3.6 Gyr old. Only one large, probably Amazonian-aged (~2.5 Gyr), rampart crater exists. These ages indicate a volatile-rich period in the Early Hesperian and a lowering of the ground ice table with time in the Valles Marineris study region. Rampart craters in southern Chryse Planitia,which are partly eroded by fluvial activity, show ages around 3.9 Gyr. Rampart craters superposed on channels have ages between ~1.5 and ~0.6 Gyr. The onset diameter (3 km at ~1.5 Gyr) in this region may indicate a relatively shallow ground ice table. Loss of volatiles due to diffusion and sublimation might have lowered the ground ice table even in the southern Chryse Planitia region afterwards. In general, our study implies a formation of the smallest rampart craters within and/or shortly after periods of fluvial activity and a subsequent lowering of the ground ice table indicated by increasing onset diameter to the present. These results question the method to derive present equatorial ground ice depths from the onset diameter of rampart craters without information about their formation time.

Cryostratigraphicmapping inthe main shaft of the CRREL tunnelindicates secondary modificationoforiginal Pleistocene-age syngenetic permafrost. Layered, lenticular-layered and micro-lenticularcryostructures within undisturbed silt characterise the syngenetic permafrost. Thawed and refrozendeposits are characterised by massive and reticulate-chaotic cryostructures. The micro-morphology oftypical cryostructures, as observed through an environmental scanning electron microscope (ESEM),is described. It is inferred that preferential cryogenic modification has occurred due to fluvio-thermalerosion operating along ice wedges. Soil and ice pseudomorphs are the manifestation of this process.Gravel, silt, ice and mixed (silt/ice) pseudomorphs occur within silt. Ice pseudomorphs are formed bythermokarst-cave ice (‘pool ice’) which filled thermokarst pits, channels and gullies. Copyright #2006 John Wiley & Sons, Ltd. KEY WORDS : permafrost; ground ice; cryostructures; thermokarst; pseudomorphs

Three geophysical methods have been applied to delineate the altitudinal limit of permafrost at Juvvasshoe/Jotunheimen in southern Norway. By using each method in a complementary way according to its applicability, the permafrost distribution could be analysed on both large and small scales. In addition, temperature-based methods such as the BTS method (bottom temperature of snow cover) were used to validate the results. On a large scale, electromagnetic induction profiling with the EM-31 was used to detect the location of the transition area between frozen and unfrozen ground. Within this area direct-current (DC) resistivity and refraction seismic tomography were also applied to further characterize and visualize the permafrost transition. The large scale surveys revealed a sharp increase in conductivity, indicating an increase in unfrozen water content, near 1400 m a.s.l., with a possible transition zone between 1500 m a.s.l. and 1380 m a.s.l. The small scale investigation delineated the altitudinal limit of permafrost between 1470 m a.s.l. and 1410 m a.s.l., with sporadic ground ice occurrences and temperatures near the freezing point. Copyright © 2004 John Wiley & Sons, Ltd.

The use of tomographic geoelectrical measurements for the detection of ground ice occurrences in mountainous regions is evaluated. Because isolated ground ice occurrences in a warming climate may be subject to rapid thawing, they present a future hazard in the context of thawing-permafrost-induced landslides and rockfalls. Isolated permafrost occurrences are difficult to detect with commonly used one-dimensional sounding techniques, as plane-layer approximations for the inversion are often invalid. Therefore, recently developed two-dimensional tomographic inversion schemes are used to yield realistic near-surface geological models. The method is applied to various types of permafrost occurrences in the European Alps. The influence of topography, measurement geometry and different inversion parameters are discussed. In addition, complimentary seismic survey results are used to exclude the possibility of air-filled cavities, which exhibit similarly high resistivities as ground ice occurrences. The results show a large variety of influencing parameters which have to be considered in resistivity inversion and interpretation. Copyright © 2003 John Wiley & Sons, Ltd.

The formation of cement (pore) and intrusive ice in the frozen rocks of the central part of the Yakutian diamond-bearing province is considered. Cement ice is best developed in the sedimentary rocks and kimberlite pipes. Intrusive ice is formed only in areas of considerable tectonic disturbance. The geochemistry of the ground ice is the result of cryogenic processes that cause salt differentiation during water freezing, together with natural solute concentration and cryogenic mineral formation. Copyright © 2002 John Wiley & Sons, Ltd.

Cryostratigraphy involves the recognition of discontinuities in the ice contained within frozen ground. It is supplemented by analyses of the petrography and hydrochemistry of the ice. Direct cryostratigraphic evidence includes cryostructures, thaw unconformities and truncated ice bodies. Cryostratigraphy can be used to infer permafrost and terrain conditions, Quaternary histories and regional climate changes. In the western Canadian Arctic, the utility of the cryostratigraphic approach is illustrated with reference to the occurrence of (1) an early Holocene thaw unconformity and (2) massive ground ice bodies. © 1998 John Wiley & Sons, Ltd. La cryostratigraphie comprend la reconnaissance des discontinuites que presente la glace contenue dans le sol gele. Elle est aidee par des analyses de la petrographie et de la chimie de la glace. Des evidences directes de cryostratigraphie sont donnees par des cryostructures, des discontinuites de degel et des corps de glace tronques. La cryostratigraphie peut etre employee pour reconnaitre des conditions de terrain et de pergelisol, l'histoire du Quaternaire et des changements climatiques regionaux. Dans l'Arctique canadien occidental, l'utilite de l'approche cryostratigraphique est illustree en faisant reference a l'existence 1) d'une discontinuite due a un degel au debut de l'Holocene et 2) a des corps de glace massifs qui se trouvent dans le sol. Copyright © 1998 John Wiley & Sons, Ltd.

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.

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.

Perennially frozen lacustrine deposits in the Bolivian Altiplano are discussed. They are situated between 21°38′S and 23°13′S at an elevation of 4117–4730 m ASL. It is hypothesized that these ice-rich lacustrine deposits formed as the result of subaquatic freezing of sediments in the Late Pleistocene to Early Holocene. The permafrost bodies are represented today by flat-topped ridges and mounds which are the remnants of the original lake plains destroyed by thermokarst processes.

A variety of active periglacial microforms have been identified in the vicinity of Tlaeeng Pass (3275 m a.s.l.) in the Lesotho Highlands. These include thufa (both earth and stone-cored varieties), terracettes, stone polygons and patterned ground. Ground ice within the saturated zone of soil profiles is clearly evident during the winter season, and pebbles perched on needle ice up to 5 cm in length are common. Although possible relict periglacial landforms (such as nivation hollows and protalus ramparts) have been recorded in the area, their identification and, hence, associated climatic inferences is problematic. The presence of active features clearly indicates present-day periglacial activity, with the variety of forms resulting from diurnal or seasonal freeze-thaw cycles. Considering a widely accepted global decrease in temperature during the Quaternary, a severity of temperatures greater than what is experienced under present marginal periglacial conditions can be projected for the Lesotho Highlands. However, past moisture regimes are more difficult to project from present-day features, and this problem is exacerbated by the general paucity of clearly defined diagnostic relict forms. Une variete de microformes periglaciaires actives ont ete identifiees au voisinage de Tlaeeng Pass (a 3275 m d'altitude) dans les regions elevees du Lesotho. Il s'agit de thufa (varietes a noyau de terre et a noyau de pierre), de terrassettes, de polygones de pierres et de sols structures. La presence de glace, lorsque les sols sont satures en eau, est evidente pendant l'hiver et des cailloux perches sur des aiguilles de glace plus grandes que 5 cm, ne sont pas rares. Bien que des formes periglaciaires reliques (comme des creux de nivation et des ‘protalus ramparts’) aient ete signalees dans la region, leur identification et aussi leur signification paleoclimatique restent problematiques. La presence des phenomenes periglaciaires actifs indique clairement l'action des cycles de gel/degel diurnes et saisonniers. En considerant la diminution globale de la temperature pendant le Quaternaire, une plus grande severite des conditions periglaciaires peut ětre supposee pour ces

The 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. Le district Mayo, territoire du Yukon, se trouve dans la zone du pergelisol discontinu mais largement repandu. Des epaisseurs de pergelisol de plus de 40 m ont ete observees dans des vallees et de 135 m aux plus hautes altitudes. De nombreuses observations de glace du sol ont ete faites par des mineurs exploitant des placers mais ces observations n'ont generalement pas ete enregistrees. R°Cemment plus de 200 sondages geotechniques peu profonds ont ete realises dans la region en association avec des constructions municipales et des routes. De la glace du sol a ete habituellement trouvee a moins de 4 m de la surface dans des sites non perturbes. Dans les vallees principals, a des altitudes inferieures a 1100 m a.s.l., les materiaux grossiers de desagregation, de plaines de lavage glaciaire, de sables de dunes ainsi que les pentes exposees au sud sont habituellement libres de glace. L'enlevement de la vegetation pour realiser des constructions ou exploiter des placers entraǐne generalement la degradation du pergelisol, mais celui-ci se retablit lorsque la vegetation se reconstitue. Les temperatures du sol a Mayo et a Keno Hill indiquent l'existence d'un flux geothermique superieur a 0.1 W/m2.