Permafrost Landforms Research Articles

Internal Structure of Open System Pingos, Adventdalen, Svalbard: The Use of Resistivity Tomography to Assess Ground-Ice Conditions

The objectives of this project were to establish the geometry and internal structure of open system pingos in Adventdalen, Svalbard using electrical resistivity tomography. A clear distinction can be made between the electrical properties of the pingos investigated, depending upon whether they are located either above (Innerhytte pingo) or below (Hytte and Longyear pingos) the maximum Holocene marine limit. The resistivity profile at Innerhytte pingo was characterised by high values of resistivity [Formula: see text], indicating either ice-rich frozen bedrock or a lens of massive ground ice. The electrical resistivity of Hytte and Longyear pingos, both developed within fine-grained, saline marine clays, is exceptionally low (predominantly [Formula: see text]) for permanently frozen ground. This is inconsistent with the presence of a body of massive ground ice, and suggests that the internal structures of Longyear and Hytte pingos do not follow the classic model of a plano-convex pingo-core of massive injection ice. Instead, the internal structure of these landforms may be dominated by segregation ice and localised pockets of massive ice within a matrix of partially frozen, fine-grained marine muds. The high salinity of the pore waters and the fine-grained nature of the sediment cause high unfrozen pore water contents, even at temperatures well below [Formula: see text], enabling electrolytic conduction and resulting in apparently anomalously low resistivity measurements. It is therefore concluded that electrical resistivity tomography must be interpreted with care when applied to the characterisation of permafrost in areas of saline marine sediments. Future field monitoring of permafrost landforms and laboratory testing of ice-rich sediments are recommended to improve geophysical interpretation of permanently frozen materials.

Collapse of permafrost mounds along a subarctic river over the last 100 years (northern Québec)

Widespread permafrost decay is currently occurring in the northern hemisphere. In subarctic Québec, most permafrost mounds are located in peatlands in the form of palsas and peat plateaus. The formation and degradation of these periglacial landforms are influenced by several regional and local factors including air temperature, depth of snow cover, and peat insulation. Mineral palsas are another type of permafrost landforms found along river shores in subarctic Canada. Due to their peculiar position near or in the river floodplain, the dynamics of these palsas are influenced by water level fluctuations. This study examines palsa dynamics along a subarctic river, the Boniface River, in northern Québec. Mapping of palsas and thermokarst ponds over a 44-year period, i.e., from 1957 (from aerial photographs) to 2001 (from field surveys) was used to evaluate changes in the distribution and area covered by permafrost landforms. Also the decay of 14 palsas was assessed using the mortality dates of black spruce trees as determined by tree-ring analysis. Between 1957 and 2001 the area occupied by palsas decreased by 23% whereas 76% of the present-day thermokarst area formed since 1957. No new palsas developed during this period. For the 14 palsas studied, degradation began at the end of the 19th century and accelerated during the 20th century. Palsa degradation was closely related to distance from the river channel. Palsas located in the river floodplain were the most affected by thawing and showed a 48% reduction in area. Degradation was less severe for palsas located 1 to 15 m from the river margin, which experienced a 19% reduction in area. The spatiotemporal distribution of palsas suggests that changes in water level are among the most important factors influencing the dynamics of riparian palsas, particularly for those palsas directly in contact with the river water.

Permafrost in Svalbard: a review of research history, climatic background and engineering challenges

This paper reviews permafrost in High Arctic Svalbard, including past and current research, climatic background, how permafrost is affected by climatic change, typical permafrost landforms and how changes in Svalbard permafrost may impact natural and human systems. Information on active layer dynamics, permafrost and ground ice characteristics and selected periglacial features is summarized from the recent literature and from unpublished data by the authors. Permafrost thickness ranges from less than 100 m near the coasts to more than 500 m in the highlands. Ground ice is present as rock glaciers, as ice-cored moraines, buried glacial ice, and in pingos and ice wedges in major valleys. Engineering problems of thaw-settlement and frost-heave are described, and the implications for road design and construction in Svalbard permafrost areas are discussed.

Localized Permafrost Peatlands in Western Canada: Definition, Distributions, and Degradation

Detailed inventory of peatlands by aerial photography shows that peatlands with climatically sensitive localized islands of permafrost cover 17,505 km2 within a broad band of occurrence in continental western Canada (Alberta, Saskatchewan, and Manitoba). Within this zone, 37.5% of the total area covered by bog, and 9.1% of total area covered by fen have localized permafrost landforms (frost mounds and/or internal lawns). Regional distribution of the presence/absence of localized permafrost peatlands relative to expansive peat plateaus (peatland completely underlain by permafrost) shows that a north to south landform gradient exists that is dominantly controlled by mean annual temperature. Percent cover of localized permafrost peatland in an area is best explained by the amount of total peatland cover that can support it. Localized permafrost is associated with collapse forms (internal lawns) throughout the range of its occurrence in western Canada. In some locations permafrost has completely melted, moving the current southern limit of permafrost north by 39 km on average, and by as much as 200 km.

Localized Permafrost Peatlands in Western Canada: Definition, Distributions, and Degradation

Detailed inventory of peatlands by aerial photography shows that peatlands with climatically sensitive localized islands of permafrost cover 17,505 km2 within a broad band of occurrence in continental western Canada (Alberta, Saskatchewan, and Manitoba). Within this zone, 37.5% of the total area covered by bog, and 9.1% of total area covered by fen have localized permafrost landforms (frost mounds and/or internal lawns). Regional distribution of the presence/absence of localized permafrost peatlands relative to expansive peat plateaus (peatland completely underlain by permafrost) shows that a north to south landform gradient exists that is dominantly controlled by mean annual temperature. Percent cover of localized permafrost peatland in an area is best explained by the amount of total peatland cover that can support it. Localized permafrost is associated with collapse forms (internal lawns) throughout the range of its occurrence in western Canada. In some locations permafrost has completely melted, moving the current southern limit of permafrost north by 39 km on average, and by as much as 200 km.

Recent Permafrost Dynamics in a Subarctic Floodplain Associated with Changing Water Levels, Québec, Canada

We have reconstructed from tree-rings the dynamics of mineral frost mounds on the floodplain of a subarctic river (Rivière Boniface, northern Québec) likely associated with snow precipitation and temperature changes during the past centuries. Due to their peculiar location in the river bed, we have postulated that the inception and decay of frost mounds (thermokarst ponds) were associated with snow-controlled water levels of the river. The periods of establishment, growth, and mortality of spruce around and in two thermokarst ponds on the shore zone were identified. The oldest tree-ring dates show that permafrost mounds formed during a period of water lowering in the 17th century, likely in a long-enduring sequence of low waters initiated around cal AD 1150 (910 yr BP), which persisted for at least 200 yr until the beginning of the 20th century. Two main periods of spruce mortality were identified, in the late 19th century and early 20th century and in the 1950s–1960s, which corresponded to a rising river level probably due to greater snow precipitation. The patterns of spruce establishment and mortality were strikingly similar in the studied sites. The first spruce to establish were all located along the pond's edges and they were also the first ones to die; most of the youngest spruce established later in the central part of each feature, i.e., in the early to mid-1850s to 1910, and died during the 1950s–1960s. The sequence of events reported here suggests an important lowering of the Rivière Boniface during the first part of the Little Ice Age (end of the 16th century–17th century) which was drier and cold. During the second part of the Little Ice Age (mainly 19th century), greater precipitation occurred and climaxed in the 20th century when climate warmed and the river stage reached its maximum level. Changes in snow precipitation were probably more instrumental than temperature changes in the rise and fall of permafrost landforms because of the snowpack's direct influence on the soil thermal regime and river level during snowmelt.

Recent Permafrost Dynamics in a Subarctic Floodplain Associated with Changing Water Levels, Quebec, Canada

We have reconstructed from tree-rings the dynamics of mineral frost mounds on the floodplain of a subarctic river (Riviere Boniface, northern Quebec) likely associated with snow precipitation and temperature changes during the past centuries. Due to their peculiar location in the river bed, we have postulated that the inception and decay of frost mounds (thermokarst ponds) were associated with snow-controlled water levels of the river. The periods of establishment, growth, and mortality of spruce around and in two thermokarst ponds on the shore zone were identified. The oldest tree-ring dates show that permafrost mounds formed during a period of water lowering in the 17th century, likely in a long-enduring sequence of low waters initiated around cal AD 1150 (910 yr BP), which persisted for at least 200 yr until the beginning of the 20th century. Two main periods of spruce mortality were identified, in the late 19th century and early 20th century and in the 1950s-1960s, which corresponded to a rising river level probably due to greater snow precipitation. The patterns of spruce establishment and mortality were strikingly similar in the studied sites. The first spruce to establish were all located along the pond's edges and they were also the first ones to die; most of the youngest spruce established later in the central part of each feature, i.e., in the early to mid-1850s to 1910, and died during the 1950s-1960s. The sequence of events reported here suggests an important lowering of the Riviere Boniface during the first part of the Little Ice Age (end of the 16th century-17th century) which was drier and cold. During the second part of the Little Ice Age (mainly 19th century), greater precipitation occurred and climaxed in the 20th century when climate warmed and the river stage reached its maximum level. Changes in snow precipitation were probably more instrumental than temperature changes in the rise and fall of permafrost landforms because of the snowpack's direct influence on the soil thermal regime and river level during snowmelt.

Cold Climate Landforms

Permafrost landforms and regional reconstructions periglacial landforms glacial and fluviglacial landforms marine and lacustrine landforms polygenetic landforms cold climate slopes rock glaciers.

Long-Term Monitoring of Permafrost Change in a Palsa Peatland in Northern Quebec, Canada: 1983-1993

Changes in the spatial distribution of permafrost in the Ouiatchouane palsa peatland (northern Quebec) were monitored from 1957 to present, using aerial photographs taken in 1957 (starting date) and three field surveys in 1973, 1983, and 1993, respectively. Between 1983 and 1993, palsa degradation occurred at about the same rate as between 1957 and 1983, although minor differences in rate of permafrost decay during the three periods (1957-1973, 1973-1983, 1983-1993) may be attributed in part to misidentification of marginal permafrost landforms. Permafrost degradation appeared to be influenced by height of individual palsas and their location within the peatland. Since 1983, thermokarst ponds have been progressively invaded by sedges and Sphagnum, a situation promoting successional peatland development and palsa formation as suggested by the presence of a small incipient palsa. Although the main geomorphic process at work is palsa degradation, permafrost aggradation is possible under present climatic conditions. 28 refs., 3 figs., 1 tab.

Chronostratigraphy of glaciations and permafrost episodes in the Cordillera of western North America

Glaciations in the Cordillera of western North America began during the Late Miocene in the St Elias Range and coastal ranges near Anchorage, Alaska. Radiometric dating of the tephra and lava flows intercalated in the succession of older tills, loesses and outwash deposits permits the reconstruction of the probable early glacial sequence along the Cordillera. No one site shows the complete sequence, but the available data suggest synchroneity of the major glacial events throughout the region. The first evidence for cold conditions at low elevations at midlatitudes is from 3.5 Ma BP. By 2.8 Ma, alpine glaciations may have occurred in the Sierra Nevada and ice wedges had formed in bedrock near Fairbanks, Alaska. Three more major glaciations complete with contemporary periglacial and permafrost landforms had occurred by 1.65 Ma, while at least six more major cold events can be recognized during the Quaternary period. Once again, expansion of permafrost conditions occurred during each event and forms an integral part of the evidence for climatic change.

FROST MOUNDS AT TOOLIK LAKE, ALASKA

Aggradation palsas and seasonal frost mounds can achieve topographic expression by localized pooling and freezing of water within the active layer. A distinction is drawn in this paper between palsas, which are permafrost landforms by definition, and seasonal frost mounds, ephemeral or oscillatory features surviving for less than 2 years. Subsurface water migration occurs in response to positive or negative pore water pressures generated during active-layer refreezing. Upward deformation results from stresses induced by the local addition of water and subsequent phase change and, in some cases, positive pore water pressures. In the absence of site instrumentation, processes associated with mound formation can be inferred by examination of massive ice cores, where a record of the aggradational event is preserved. Stratigraphic and petrographic characteristics of the core, ionic concentration patterns with respect to depth, and mound morphometric data were obtained for a large ice-cored frost mound which de...

La répartition du pergélisol dans la région du détroit de Manitounuk, côte est de la mer d'Hudson, Canada

Forty-four AC electrical resistivity soundings have been made on the Manitounuk Islands (55°30′N, east coast of Hudson Bay) as well as in post-glacial and Recent marine sediments of the supratidal zone along the east shore of Manitounuk Strait. The results indicate that permafrost, which may have a thickness of 30 m, is present within basalts and quartzites of the cuestas at elevations above 20 m. The thermal effect of the sea and the possible infiltration of sea water in the structural elements prevent the formation of permafrost at lower altitudes. Rocky sites where permafrost has been detected are windswept areas devoid of snow. Heaved bedrock landforms are numerous on those sites. Along the east coast of Manitounuk Strait permafrost is scattered in patches and the permafrost landforms are degrading. Seasonal freeze–thaw processes are responsible for many features, such as thufurs, boulder heaving, clastic dykes, mud volcanoes, and others. The processes are related to year to year variability in the temperature regime, snow depth over the land surface, groundwater movement, thermal effects of the tides, and shore ice on the tidal flat.

ANTHROPOGENIC GEOMORPHOLOGY IN NORTHERN ALASKA

Two classes of anthropogenic landforms can be recognized in the permafrost environment of northern Alaska. Primary anthropogenic landforms result from the operation of natural geomorphic processes on man-made features such as roads or gravel berms. Secondary anthropogenic forms are identical to natural geomorphic features, but evolve as indirect consequences of human actions. The first group is illustrated by a badly thermokarsted road, which has caused serious drainage disruptions likely to persist over a long time period. Secondary forms are exemplified by fields of palsa-like features, which are common where pipeline-related construction activities or structures cause shallow ponding. Because they evolve rapidly, anthropogenic permafrost landforms can provide great insight into the development of natural periglacial features.

Distribution of active glaciers and rock glaciers compared to the distribution of permafrost landforms, based on freezing and thawing indices

Climatic stations near glacial termini and equilibrium lines show a distribution of freezing and thawing indices that does not conform to the boundaries derived from data for stations in areas of continuous and discontinuous permafrost. Active tongue-shaped rock glaciers have similar limits of freezing and thawing indices to the equilibrium lines of glaciers, while active lobate rock glaciers have limits paralleling the limit for stations in the zone of continuous permafrost.This difference between the distributions of lobate and tongue-shaped rock glaciers explains why the active tongue-shaped rock glaciers can be used for indicating the limits of the permafrost areas in the Alps (a maritime regime), but cannot be used in that way in continental climates, e.g., Alberta, interior Yukon, and the Northwest Territories.

Distribution of zonal permafrost landforms with freezing and thawing indices

Distribution of zonal permafrost landforms with freezing and thawing indices

The evolution of permafrost in the taiga and in the forest–tundra, western Quebec–Labrador Peninsula

Major permafrost landforms of the discontinuous permafrost zone of Hudson Bay and James Bay, Quebec–Labrador Peninsula, are described and interpreted within an ecological perspective. These landforms are not fossil permafrost bodies; they are presently evolving under aggrading and degrading developmental stages. Permafrost peat complexes and permafrost mineral complexes are differentially distributed in the midtaiga, the forest–tundra, and the shrub–tundra zones of the study area. The wooded palsa complex is the most obvious permafrost complex in the midtaiga, and the palsa complex in the forest–tundra: The wooded palsa complex is related to the forest chronosequence, whereas the palsa complex, farther north, occurs where there is a suitable macroclimate for permafrost aggradation without the influence of cool forest microclimate. The wooded cryogenic mound complex in mineral landform is mainly distributed in the southern section of the forest–tundra and near the Hudson Bay shore; the cryogenic mineral mound complex is found in the northern section. The latitudinal shift of the northern complex is necessary for permafrost initiation in open sites. Degrading stages associated with thermokarst activity are similar for all these landforms and it is suggested that palsa complex is made of incipient, mature, and residual palsas whether they belong to palsa mounds or to peat plateaus. Similar conclusions are valid for cryogenic mineral mound complex.