Permafrost Body Research Articles

Rapid degradation of ground ice in a ventilated talus slope: Flüela Pass, Swiss Alps

AbstractThe degradation of ground ice in talus deposits, which are important forms of debris storage in mountain environments, can cause mass movements, subsidence or instability of mountain infrastructure. Two 20 m deep boreholes instrumented with thermistors and located in a talus slope at 2400 m asl above a lake at Flüela Pass in the eastern Swiss Alps allow the analysis of the evolution of ground temperature and permafrost thickness between 2003 and 2008. The occurrence of intra‐talus ventilation can be discerned due to thermal anomalies within a layer of coarse blocks with large voids at around 15 m depth near the base of the slope and at 10 m depth mid‐slope. Intra‐talus ventilation is particularly effective in winter when subzero air temperatures coincide with snow depths less than 50 cm and reverses to a gravity discharge of intra‐talus air when air temperatures become positive. Despite the lack of annual variability in active layer depth, rapid permafrost degradation and thinning of ground ice (from 7 m thickness to 3.5 m in 4 years) is currently occurring. It is attributed to latent heat transfer from the moving air stream, caused by the flux of vapour from the relatively warm lake water table at 20 m depth and its condensation at the base of the permafrost body. Copyright © 2009 John Wiley & Sons, Ltd.

Mapping vertical profile of discontinuous permafrost with ground penetrating radar at Nalaikh depression, Mongolia

Ground-penetrating radar (GPR) has become an important geophysical tool which can provide a wealth of interpretive information about the vertical profile of discontinuous permafrost. A GPR investigation was conducted in October 2006 at the Nalaikh site at the southern boundary of the Siberian discontinuous permafrost region in Mongolia. GPR data were collected along four 100-m-long profiles to identify the location of the permafrost body, which included an in situ drilling borehole and analysis of temperature observations and soil water content measurements from boreholes. The GPR interpretation results indicated that the thickness of discontinuous permafrost at the study site was only 1.9–3.0 m and the permafrost is vulnerable to climate change. The soil temperature and soil water content data demonstrate the precision of GPR image interpretation. This case demonstrated that GPR is well suited for mapping the internal structure of discontinuous permafrost with relatively low soil water content.

Internal structure and the thermal and hydrological regime of a typical lithalsa: significance for permafrost growth and decay

This study presents new knowledge about the ice segregation and frost-heave processes taking place in a typical lithalsa. A tomodensitometric scanner was used to produce high-resolution computer images of ice lenses, soil layers, faults, sedimentary structures, and gas bubbles. Scan-image analysis allowed the interpretation of the ice lenses and soil cryostructures resulting from permafrost aggradation. It also provided an accurate estimation of volumetric contents of ice and gas present in the permafrost. Isotopic analyses on the various phases of the permafrost (i.e., ice, gas, and soil) provided supplementary information. 18O, deuterium, and tritium analyses were undertaken on ground ice and on surface water. Monitoring of the thermal regime of the lithalsa provided clues relative to gradients that drive groundwater movements and ice-lens growth. Compilation and interpretation of the data in a three-dimensional and temporal context suggest that the lithalsa under study grew under climate conditions slightly colder than those of the 20th century. However, post-aggradational water penetrated into the permafrost of the lithalsa. Ground temperatures increased since 2000, most likely because of underground warming owing to groundwater flow around the permafrost body. As a result, the mound has started to settle down, and an incipient thermokarst pond became conspicuous in 2003.

Permafrost Distribution in Peatlands of West-Central Canada During the Holocene Warm Period 6000 Years BP

The extent and distribution of permafrost in peatlands 6000 years ago was investigated in the present discontinuous and continuous permafrost zones of west-central Canada. Permafrost peatlands were cored at 161 locations and the floristic composition of the peat was determined from macrofossil analysis. The reconstructed paleoenvironments were used to indicate the presence or absence of permafrost at the time of peat formation. Chronological control was provided by radiocarbon dating of substantial changes in the peat sequences and by dates of basal peat deposits. Peatland formation began after glacial ice disappeared from the land surface of west-central Canada. Macrofossils indicate that most peatlands were fens without permafrost at 6 ka, except in the far north. Permafrost was already present in many areas of the Arctic, and peat accumulation occurred under permafrost conditions. In the southern area, permafrost development in peatlands began about 4 ka as the middle Holocene warm period came to a close. Permafrost development in the fens was associated with the development of a Sphagnum-dominated surface on the fens, caused by the onset of a cooler and moister climate. The insulation provided by the surface peat layer and by the associated tree cover initiated permafrost development in small lenses that coalesced into large permafrost bodies according to the prevailing climatic conditions. At the target date, 6 ka, permafrost was present in some peatlands, but the distribution zones shifted 300 to 500 km to the north, relative to the present zonation. It is estimated that this corresponds to a mean annual temperature that was about 5°C warmer than at present.

Electrical resistivity tomography monitoring of permafrost in solid rock walls

This article describes the first attempt to conduct electrical resistivity tomography (ERT) in solid permafrost‐affected rock faces. Electrode design, instrument settings, and processing routines capable of measuring under relevant conditions were developed. Four transects, with NW, NE, east (E) and south (S) aspects, were installed in solid rock faces between Matter Valley and Turtmann Valley, Switzerland, at 3070–3150 m above sea level. DC resistivity in the transects was measured repeatedly during the summer and compared by applying a time‐lapse inversion routine. Resistivity values were calibrated using observed rock surface conditions of thawed, damp rocks (1–8 kΩ m), deeply frozen rocks (18–80 kΩ m), and the transition from damp thawed to frozen rocks (8–18 kΩ m). Mean surface layer resistivities of transects respond to air temperatures below 0°C with a rapid increase by a factor of 1.4 to 2.9 from values of 12–15 kΩ m to values of 22–31 kΩ m. Rock layers at depths of 2–6 m display a general trend of resistivity decrease in summer, corresponding to a persistent thawing process. Their response to anomalously cool August temperatures occurs with a time lag of 2 to 4 weeks. Only transects E, NE and NW display persistent, high‐resistivity permafrost bodies (>50 kΩ m) mostly at depths of 6–10 m. The maximum thaw depth of a continuous thawing front above permafrost is 6 m. However, the ERT results emphasize the role of heat transfer by deep‐reaching cleft water systems. Thus permafrost occurs in lenses rather than layers. ERT provides rapid detection of ice and water distribution in permafrost‐affected bedrock.

Avalanche‐derived rock glaciers in Svalbard

AbstractVisual year‐round observations have shown that snow avalanches are driving the formation of rock glaciers near the glacier Larsbreen in central Svalbard. Here, avalanches are important suppliers of fresh rock debris, but they also represent the means by which ice is added to the rock glacier interior. During the winter, 1–5 m avalanche snow containing rock debris accumulates, ablating during the following summer, but a gradually accumulating surface layer of released rock debris increasingly reduces the ablation rate. Refreezing of percolating surface water during the ablation season enhances the metamorphosis from avalanche snow into solid ice, assisted by low permafrost temperatures below the avalanche snow. At the end of each summer, a 0–100 cm thick layer consisting of remnant avalanche snow covered by a surface debris layer has been added to the rock glacier permafrost body along the initiation line. Depending upon thickness, slope, relative ice content and temperature, deformation of such thickening layered avalanche deposits eventually leads to the formation of a rock glacier in the run‐out zones of snow avalanches in permafrost regions. Avalanche‐nourished rock glaciers are expected to exhibit a regional downwind preferred orientation. Copyright © 2007 John Wiley & Sons, Ltd.

Permafrost in the Gruve-7 mine, Adventdalen, Svalbard

Bedrock temperatures were measured over a 12-month period (June 2003–July 2004) at six sites within the Gruve-7 coal mine in the Adventdalen valley, near Longyearbyen (78°N), Svalbard. One site lies 290 m beneath the Foxfonna ice cap, where stable near 0°C conditions were recorded throughout the year. This site is close to the inferred base of permafrost. Other sites at bedrock depths between 35 m and 235 m beneath both glacier-covered and ice-free terrain have mean annual values between −1.2°C and −4.9°C, and annual amplitudes between 0.5°C and 4.5°C. The lowest mean annual ground temperatures (MAGT) of −5.8°C is measured at a depth of c.6 m from the ground surface, and this site is thought to be close to the base of the bedrock active layer. The 3-dimensional nature of the permafrost body is indicated by the fact that the higher permafrost temperatures occur at deeper locations within the massif below the Foxfonna ice cap and glacier, while the lowest temperatures occur where the mine extends beneath ice-free terrain.

Permafrost and Little Ice Age glacier relationships, Posets Massif, Central Pyrenees, Spain

AbstractThis paper contributes to the study of permafrost in the Pyrenees by reporting geoelectrical investigations and thermal measurement on the Little Ice Age (LIA) forefields of two glaciers. The aim was to assess the internal composition of sedimentary bodies (debris rock glaciers and moraine deposits) located in this proglacial environment. Ground ice was prospected using two DC resistivity techniques: vertical electrical soundings and resistivity mapping at a fixed pseudo‐depth. Extreme specific resistivities ranging between 1 and 25 MΩ m were detected under a thin (1–2 m) unfrozen layer, indicating the presence of a massive ice layer, certainly buried glacier ice. This ice of glacial origin probably covers former permafrost bodies, i.e. a much thicker layer of perennially frozen sediments. Low subsurface temperatures measured on the deposits indicate that buried glacier ice could have been preserved on top of permafrost since the end of the LIA or earlier Holocene glacier advances. This stratigraphy demonstrates that glaciers and pre‐existing perennially frozen sediments (permafrost) were in contact during the LIA. Copyright © 2004 John Wiley & Sons, Ltd.

Temperatures in two boreholes at Flüela Pass, Eastern Swiss Alps: the effect of snow redistribution on permafrost distribution patterns in high mountain areas

AbstractSnow cover distribution strongly affects soil temperatures and, thus, plays a decisive role in determining permafrost distribution patterns. Redistribution of snow by avalanches and snow drift significantly affects the snow‐melt pattern and soil temperatures in steep avalanche slopes of high mountain areas. At Flüela Pass, 2380 m a.s.l., eastern Swiss Alps, the presence and origin of permafrost that occurs at the base of an avalanche‐affected slope below the regional lower limit of discontinuous permafrost was studied by field investigations and numerical simulations. Local permafrost distribution has been determined in former studies by applying geophysical methods and this was confirmed with two boreholes drilled at the slope base and in the avalanche starting zone. Temperature measurements confirm the presence of a 10 m thick permafrost body with temperatures close to the freezing point at the slope base. Numerical simulations of different snow‐cover scenarios for 2002/03 demonstrate the particular effect on soil temperatures of high snow drift accompanying intense snow falls in early winter, controlling the duration of constant zero temperatures at the base of the snow pack at the beginning of the snow period. Copyright © 2004 John Wiley & Sons, Ltd.

An Old Relict Glacier Body Preserved in Permafrost Environment: The Foscagno Rock Glacier Ice Core (Upper Valtellina, Italian Central Alps)

This paper shows the results of chemical and crystallographic analyses carried out on a core drilled within the frontal part of the Foscagno rock glacier in the Italian Alps. We use 58 vertical thin sections spaced along the massive ice core, found between depths of 2.5 and 7.65 m, to describe the ice fabric of the core. We also discuss the results of chemical analyses of more than 50 samples. The lower part of the massive ice core between 4 and 7.65 m shows a mean crystal size of 1.5 cm and a crystal shape predominantly elongated along the horizontal plane with c-axes. These characteristics are similar to those of firn ice. In contrast, the upper core between 2.5 and 4 m displays vertical elongation of large bubbles, indicating superimposed ice and the influence of melting and refreezing processes. The presence of a seasonal signal in sulfate distribution and the strong correlation between sodium and chloride in the lower part of the core confirm cold firnification without appreciable phase changes. This well-preserved glacier ice body is probably younger than 2200 ± 60 yr B.P., a minimum age for the rock glacier as indicated by the 14C age of a buried paleosoil, although the possibility that it may be older age cannot be excluded. The glacier ice body seems to be a relict of a former glacier preserved within a larger permafrost body that characterizes almost all of the rock glacier and also occurs beneath the massive ice. This finding points out that different types of ice can be preserved within a single rock glacier, reflecting a complex geological and paleoclimatic history.

Permafrost degradation on the Qinghai-Tibet Plateau and its environmental impacts

An increase of mean annual air temperature (MAAT) of about 0.2‐0.48C on the Qinghai‐Tibet Plateau as compared with the 1970s, and especially winter warming, has resulted in extensive permafrost degradation. An increase of 0.1‐0.58C in the mean annual ground temperature (MAGT) has been observed. Discontinuous permafrost bodies and thawed nuclei have been widely detected. The lower altitudinal limit of permafrost has risen 40‐80 m on the Qinghai‐ Tibet Plateau. The total permafrost area on the Plateau has shrunk about 10 5 km 2 . Permafrost degradation has caused environmental deterioration, including the destabilization of buildings, impacted upon cold regions hydrology and water resources, and accelerated desertification. Copyright # 2000 John Wiley & Sons, Ltd.

Subglacial water‐escape structures and till structures, sléttjökull, Iceland

Beyond Slettjokull, the north part of the ice cap Mýrdalsjokull, south Iceland, an undulating till plain is dissected by meltwater streams. Throughout a transect from the ice margin to the 1900 ice-marginal moraine, a distance of about 1.2 km, finely laminated wedge-shaped water-escape structures (WES) are present, originating in the till and disappearing down-ice into the underlying sands and fine gravels. A second set of much smaller and deformed black WES occurring within the till has been produced by upward injection into the till as a response to stiffening of the till after dewatering by the downward developing WES. At present the toe of the glacier is frozen to its bed and the frozen bed material is more than 2 m thick. During the relatively cold period around the turn of the century and until the late 1920s, a similar submarginal body of permafrost must have existed. The sequence reveals that subglacial meltwater, attributed to drainage following the 1918 Katla eruption, was blocked by a frozen glacier toe, causing the formation of water-escape structures. Subsequently, glacier flow deformed the substratum and produced the threefold division of the till bed. The study has important implications for theories envisaging subglacial floods because it demonstrates that it is very difficult for temperate glaciers with a temporary frozen bed in the toe region to retain subglacial meltwater. Copyright © 1999 John Wiley & Sons, Ltd.

Electromagnetic and geological transect across permafrost terrain, Mackenzie River delta, Canada

The time‐domain electromagnetic (TDEM) method provides a surface geophysical technique suitable for interpreting deep permafrost conditions. This paper describes profiles collected in early spring in a transitional area of the Mackenzie Delta, Arctic Canada, with differing permafrost conditions and surficial geology. These data augment previously published profiles and allow the construction of a 30-km-long TDEM transect from the Holocene‐age Mackenzie Delta in the southwest to the Pleistocene‐age Tuktoyaktuk Coastlands in the northeast. The geoelectric section produced from the TDEM data is interpreted in terms of permafrost distribution. This interpretation provided a basis for inferring lithologic changes. Unconsolidated, non‐ice‐bonded (unfrozen) sediment has resistivities less than 10 ohm-m. Partially ice‐bonded sediment ranges in resistivity from 10 to 40 ohm-m. Ice‐bonded (frozen) sediment has resistivities from 30 to 300 ohm-m. Bedrock has low resistivities (from 5 to 15 ohm-m). Interpretation of the geoelectric section derived from both the shallow (<200 m) and deep (>500 m) TDEM data suggests that the main body of permafrost increases in thickness from 50 to 500 m over a few kilometers. A horizontally persistent unfrozen zone (talik) is situated from 50 to 100 m in depth within the main body of permafrost. Ice‐bonding models derived from the TDEM surveys provide constraints on the geologic history of the Mackenzie Delta.

Detection of heat-mass transfer regime transitions in the active layer using fractal geometric parameters

Hourly time series of temperature and a surrogate measure of the soil water ionic (solute) concentration were obtained in the upper 50 cm at a site in central Alaska from August 1991 through May 1992. The site is located over a body of permafrost. A strong “zero curtain” develops in winter and persists for three months; maintenance of this isothermal layer is associated with water advection and vapor movement within the unfrozen zone. Warming of the active layer in spring occurs nearly instantaneously and results from infiltration of snowpack meltwater. Analysis of the time series is facilitated by use of spectral techniques. Fourier transform yields variance spectra from which fractal geometric parameters are calculated. Variations in the time- and depth-dependent fractal parameters are related to dominant heat-transfer regimes determined from previous analyses. The time series were also analyzed using Hurst rescaling. Rescaled trace minima and maxima, taken from the top, middle, and base of the active layer, self-model transitions in seasonal heat-mass transfer mechanisms. The Hurst Exponent, calculated from thermal and solute time series, exhibits process-dependent patterns. In theory, the fractal dimension and Hurst Exponent are linearly related. However, when the fractal dimension is calculated using the variance spectra method, the relationship is not linear as anticipated.

Identification of heat‐transfer processes during soil cooling, freezing, and thaw in central alaska

AbstractHourly 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.

Rheological models of active rock glaciers: Evaluation, critique and a possible test

AbstractRheological 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.

Permafrost distribution and rock glaciers in the livigno area (Northern Italy)

AbstractGeophysical investigations were undertaken in the Livigno area (Sondrio, northern Italy) during 1991–92 at a number of sites where permafrost had been suggested through the application of other techniques, such as geomorphological studies, measurements of bottom temperature of winter snow cover (BTS), measurement of ground temperature in summertime (STG), and temperature of spring waters. Geoelectrical surveys confirm and characterize these permafrost occurrences. Furthermore, they indicate that, outside the rock glaciers, permafrost is also present in some gelifluction lobes. The permafrost bodies differ with regard to parameters such as resistivity, depth and thickness. Resistivity ranges from 18,000 to 560,000 ωm (ohm metres), depth varies between 8 and 21.1 m, and the active layer is 2 to 4.7 m thick in those bodies that can be considered active on the basis of morphological features.

Origin of permafrost lake deposits in the Central Andes

AbstractPerennially 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.

The thermal regime of intertidal permafrost, George River estuary, Ungava Bay, Quebec

Permafrost in tidal-marsh sediments was studied along the estuary of George River, Ungava Bay, northern Quebec. In this macrotidal environment, wide tidal flats and marshes lie in bays along the shoreline. Discontinuous permafrost bodies occur in the silty sediments underlying the marshes in the upper part of the intertidal zone, where submersions by large tides and storm surges are rare and where the icefoot freezes to the ground in winter. The permafrost is about 5 m thick, saline, and ice poor. According to logged thermal data, a freezing-point depression of 0.9 °C is estimated for the intertidal sediments. Tidal submersions during the ice-free season have a transient warming effect on the soil profile due to water percolation in the active layer and delay freeze back at the beginning of winter. Observations in shallow drill holes and along a thermistor cable indicate that the intertidal permafrost degraded at the Kangiqsualujjuaq observation site from 1984 to 1987. From 1987 to 1990, observations and logged data clearly show aggradation and cooling of the permafrost. Those changes in ground thermal regime are the result of recent climatic variations.

The thermal regime of a permafrost body at Mont du Lac des Cygnes, Quebec

A low peat plateau in the alpine forest–tundra at Mont du Lac des Cygnes, 100 km northeast of Québec City, contains a permafrost body 2 m thick. At an elevation of 960 m, this is the southernmost known occurrence of alpine permafrost in eastern Canada. The terrain over the permafrost is windblown and bears a very thin and discontinuous snow cover. One year of continuous temperature records indicates that the mean annual air temperature at this site is about −1.3 °C. The permafrost remains at temperatures very near the freezing point for most of the year.