Peak Flood Glacier Discharge Percolation Zone

PERIGLACIAL 827

Arctic system. Permafrost regions occupy approximately PEAK FLOOD GLACIER DISCHARGE 24% of the terrestrial surface of the Northern Hemisphere. Today, a considerable area of the Arctic is covered by per- Monohar Arora mafrost (including discontinuous permafrost). National Institute of Hydrology (NIH), Roorkee, UA, India

Sudden release of glacially impounded water causes cata- PERIGLACIAL strophic floods (sometimes called by the Icelandic term “jôkulhlaup”), known as outburst floods, and occasionally H. M. French spawn debris flow that pose significant hazards in moun- University of Ottawa (retired), North Saanich, BC, tainous areas. Commonly, the peak flow of an outburst Canada flood may substantially exceed local conventional bench- marks, such as the 100-year flood peak, but predicting the Synonyms peak discharge of these subglacial outburst floods is a very Cryogenic difficult task. Increasing human habitation and recreational use of alpine regions has significantly increased Definition the hazard posed by such floods. Outburst floods released “ ” in steep, mountainous terrain commonly entrain loose sed- Periglacial : an adjective used to refer to cold, non- iment and transform into destructive debris flows. glacial landforms, climates, geomorphic processes, or environments. “Periglaciation”: the degree or intensity to which periglacial conditions either dominate or affect a specific landscape or PERCOLATION ZONE environment.

Prem Datt Origin Research and Development Center (RDC), The term periglacial was first used by a Polish geologist, Snow and Avalanche Study Establishment, Himparisar, Walery von Łozinski, in the context of the mechanical dis- Chandigarh, India integration of sandstones in the Gorgany Range of the southern Carpathian Mountains, a region now part of The area on a glacier or ice sheet or in a snowpack where central Romania. Łozinski described the angular rock- a meltwater percolates are known as percolation zone. rubble surfaces that characterize the mountain summits In case of glaciers, the upper part of the glacier (accumula- as periglacial facies formed by the previous action of tion zone) where ice is covered by snow represents intense frost (Łozinzki, 1909). Following the XI Geologi- the percolation zone. As such water percolates through cal Congress in Stockholm in 1910 and the subsequent the snowpack because snow behaves like a porous media, field excursion to Svalbard in 1911 (Łozinzki, 1912), the while in the lower part of glacier (ablation zone) water concept of a periglacial zone was introduced to refer to flows over the ice because ice is not permeable and hardly the climatic and geomorphic conditions of areas periph- allows any percolation. This is the reason the water chan- eral to Pleistocene ice sheets and glaciers. Theoretically, nels are found in the ablation part of the glaciers where this was a tundra zone that extended as far south as the exposed ice surface is available. tree-line. In the mountains, it was a zone between timberline and snow line (Figure 1). Today, Łozinski’s original definition is regarded as unnecessarily restricting; few, if any, modern analogs exist PERENNIALLY FROZEN GROUND (French, 2000). There are two main reasons. First, frost action phenomena are known to occur at great distances Monohar Arora from both present-day and Pleistocene ice margins. In National Institute of Hydrology (NIH), Roorkee, UA, fact, frost action phenomena can be completely unrelated India to ice-marginal conditions. For example, parts of central Siberia and interior central Yukon remained unglaciated Perennially frozen ground occurs wherever the ground during the Pleistocene, yet these are regions in which frost temperatures remain continuously below 0C for 2 or action was, and is, very important. Second, although more years. Most permafrost is located in high latitudes Łozinski used the term to refer primarily to areas rather (i.e., land in close proximity to the North and South poles), than processes, the term has increasingly been understood but alpine permafrost may exist at high altitudes in much to refer to a complex of cold-dominated geomorphic pro- lower latitudes. The extent of permafrost can vary as the cesses. These include not only unique frost action and per- climate changes. Permafrost, or perennially frozen mafrost-related processes but also the range of azonal ground, is a critical component of the cryosphere and the processes, such as those associated with snow, running 828 PERIGLACIAL

X6 Ice X5 Periglacial zone

X4 Relict X3 periglacial zone

(1) Theoretical limit of (2) Pleistocene periglacial (3) Present-day periglacial zone periglacial zone, as zone, displaced includes (a) climatically determined by climate southward and induced periglacial zone and peripheral to ice sheets (b) relict periglacial zone: X1–X7 = Climate zones northern part of boreal X4 = Treeline forest zones a X6 = snowline

∗ ∗ ∗ ∗ Continuous Timberline Continuous Discontinuous (Timberline) Widespread Discontinuous Periglacial zone

Periglacial zone Patchy

Sporadic

Permafrost ∗ Snow and ice b

Periglacial, Figure 1 Schematic diagram illustrating the concept of the periglacial zone in (a) high-latitude and (b) high-altitude (alpine) areas. (From French, 2007.) water and wind, which demand neither a peripheral ice- Modern periglacial geomorphology is a branch not only marginal location nor excessive cold. Instead, they assume of mainstream geomorphology but also of permafrost sci- distinctive or extreme characteristics under cold, non- ence or geocryology (Washburn, 1979; Romanovskii, glacial (i.e., periglacial) conditions. 1980; Williams and Smith, 1989; Yershov, 1990; Zhou et al., 2000). Periglacial areas are regarded as cold-climate Historical context “zones” in which seasonal and perennial frost, snow, and Periglacial geomorphology developed in a relatively normal azonal processes are all present to greater or lesser rapid fashion in the 2 decades after 1945 as a branch of degrees (French, 2007). The reality is that many so-called a European-dominated, but somewhat unscientific, cli- periglacial landscapes inherit the imprint, in varying matic geomorphology. It was aimed largely at Late- degrees, of previous glacial conditions. Pleistocene paleo-climatic reconstruction. This changed in the latter half of the twentieth century when isotopic Extent and significance of periglacial dating techniques and the explosion of the Quaternary sci- environments ences came to dominate paleo-environmental reconstruc- Periglacial environments are restricted to areas that experi- tion. At the same time, the growth of permafrost studies ence cold, but essentially non-glacial, climates. They occur in Arctic North America and the emergence of Russian not only as tundra zones in the high latitudes, as defined geocryology liberated periglacial geomorphology from by Łozinski`s concept, but also as forested areas south of its Pleistocene heritage. tree-line and in the high-altitude (i.e., alpine) regions of PERIGLACIAL 829 mid-latitudes (Figure 2). They include (a) the polar deserts Permafrost and/or intense frost action would have charac- and semi-deserts of the High Arctic, (b) the extensive tun- terized an additional 20–25% of the earth’s land surface at dra zones of high northern latitudes, (c) the northern parts some time during the Pleistocene. of the boreal forests of North America and Eurasia, and As regards human occupance, the periglacial environ- (d) the alpine zones that lie above timberline and below ments are relatively sparsely populated. A reasonable esti- snowline in mid-latitude and low-latitude mountains. To mate is just seven to nine million people, mostly living in these must be added: (a) the ice-free areas of Antarctica, Russia, or only 0.3% of the world’s population. Thus, the (b) the high-elevation montane environments of central larger importance of periglacial environments lies not in Asia, the largest of which is the Qinghai-Xizang (Tibet) their spatial extent, their snow and ice, or their proximity Plateau of China, and (c) small oceanic islands in the high to glaciers but in their environment and their natural latitudes of both Polar Regions. resources. For example, the Precambrian basement rocks Periglacial environments occur over approximately that outcrop as huge tablelands in both Canada and Siberia one quarter of the Earth’s land surface. During the Pleisto- contain precious minerals, such as gold and diamonds, and cene glacial periods, large areas of now-temperate mid- sizable deposits of lead, zinc, and copper, while the sedi- latitude experienced reduced temperatures because of mentary basins of western Siberia, northern Alaska, and their proximity to the continental ice sheets and glaciers. the Canadian High Arctic contain large hydrocarbon

Limit of continuous permafrost Limit of discontinuous permafrost Limit of sporadic permafrost Treeline

Glaciers

Alpine periglacial zone

Subarctic- maritime periglacial zone

Subarctic- continental periglacial zone

Boreal periglacial zone

Tundra zone

Arctic frost- debris zone

High arctic frost- debris zone

0 500 1000 1500 km

Periglacial, Figure 2 Map showing the extent of the current periglacial domain in the northern hemisphere. Not included are the alpine areas of mid-latitude mountains and the high-altitude montane environment of central Asia. (From Karte and Liedtke, 1981. Reproduced in French, 2007.) 830 PERIGLACIAL reserves. In the more distant future, the exploitation of gas The surface offset reflects primarily the influence of snow hydrates that occur within permafrost and the freshwater cover and vegetation, while the thermal offset is condi- resources associated with the large northern lakes and riv- tioned largely by the physical properties of the active layer ers will become important. A second reason why (thermal conductivity and moisture content). periglacial environments are of significance is their place within the cryosphere (snow, ice, frozen ground, sea ice) and the critical role which the cryosphere plays in the Periglacial ecosystems global climate system. Periglacial environments contain a range of ecosystems. The most extensive are those of the high northern latitudes. They can be regarded as being either arctic or sub- Periglacial climates arctic in nature (Table 1). The boundary between the two Periglacial environments experience mean annual air tem- approximates the northern limit of trees, the so-called peratures of less than +3C. They can be subdivided by the tree-line. This is a zone, 30–150 km in extent, north of 2C mean annual air temperature into environments in which trees are no longer able to survive. Ecologists which frost action dominates (mean annual air tempera- refer to the barren, treeless Arctic as tundra. The tundra ture less than 2C) and those in which frost action occurs progressively changes into polar desert at extreme high but does not necessarily dominate (mean annual air tem- latitude as climate becomes increasingly colder and drier. perature between 2C and +3C). Fundamental to most The tree-line also approximates the southern boundary of periglacial environments is the freezing of water and its the zone of continuous permafrost; i.e., north of the tree- associated frost heaving and ice segregation. line, the terrain is perennially frozen and the surface thaws Based upon temperature and solar radiation charac- for a period of only 2–3 months each summer (see above). teristics, the majority of periglacial environments can be The mid-latitude alpine environments are a localized categorized as being either (1) High Arctic (polar), and specialized periglacial environment. They are domi- (2) Continental, or (3) Alpine in nature. In both High nated by both diurnal and seasonal climatic effects, by Arctic and Continental environments, temperatures are steep slopes, tundra (alpine) plants, rocky outcrops, and dominated by a seasonal rhythm; summer temperatures snow and ice. In such environments, the timberline consti- range between 10C and 30C and winter temperatures tutes the boundary between the alpine and sub-alpine. The may fall as low as 30C. Perennially frozen ground montane environments of central Asia are also distinct and (permafrost) is widespread. By contrast, the Alpine mid- consist of extensive steppe grasslands and intervening latitude environment experiences both diurnal and sea- desert-like uplands. Finally, the ice-free areas of Antarc- sonal rhythms. Permafrost may, or may not, be present. tica and northeast Greenland are essentially polar deserts Periglacial environments that do not fit the above clas- or rock-rubble surfaces. sification are (1) the extensive high-altitude montane envi- The tundra and polar desert regions of both North ronments of central Asia that experience a mix of both America and Eurasia contain a surprisingly large number seasonal and continental temperature rhythms, (2) Iceland, of plant and animal species. Plant cover varies from 5% and other smaller islands in the subarctic oceans of both in the polar deserts to over 60–75% in meadow tundra polar regions such as Jan Mayen, Kerguelen, and South terrain (Figure 4a). In the western Canadian Arctic Archi- Georgia that experience diurnal, seasonal and/or perennial pelago, the diversity of flora and vascular plants is espe- frost, and (3) the high elevations and summits of moun- cially well documented (e.g., Porsild, 1957). Large tains in South America and Africa that, lying near the mammals such as the polar bear, musk-oxen, and fox all equator, experience low annual temperature range and manage to survive in the extreme high northern latitudes. strong diurnal rhythms. The freezing and thawing condi- In the subarctic, two major ecological zones can be rec- tions experienced by these different periglacial environ- ognized. Near the tree-line is a zone of transition from ments are summarized in Figure 3. tundra to forest, consisting of either open woodland or for- In terms of periglacial landscape dynamics, ground est-tundra. Here, the trees are stunted and deformed, often temperature is probably more important than air tempera- being less than 3–4-m high (Figure 4b). Woodland cari- ture. Typically, the depth of ground freezing varies from bou and grizzly bear replace polar bear and musk-oxen. as little as 10–20 cm beneath organic materials to over This zone merges into the boreal forest, or taiga,an 500 cm in areas of exposed bedrock. It is important to immense zone of almost continuous coniferous forest stress that relatively few freeze-thaw cycles occur at extending across both North America and Eurasia. It is depths in excess of 30 cm; there, only the annual tempera- regarded as a fire climax community (Figure 4c). In North ture cycle usually occurs. It is important to differentiate America, the dominant tree is spruce (Picea glauca and between the mean annual air temperature (MAAT) and Picea mariana) and in central Siberia, both pine (Pinus the mean annual ground surface temperature (MAGST) silvestris) and tamarack (Larix dahurica) are dominant. that results in the so-called surface offset and the mean In northern Scandinavia, on account of the warm Gulf annual ground surface temperature (MAGST) and the tem- Stream, stunted birch forest (Betula nana) forms the perature at the top of permafrost (TTOP) that results in the tree-line (Figure 4d). The southern boundary of the sub- so-called thermal offset (Smith and Riseborough, 2002). arctic is less clearly defined than its northern boundary; PERIGLACIAL 831

Yakutsk, Russia Fenghuo Shan, Tibet Plateau 30 30 11

20 126 20 197 10 10 No. of days No. of days 354 42 a 0 e 0

Tuktoyaktuk, Canada Mont Blanc Station, Peru 30 30 27

108 20 20 214

337 10 10 No. of days No. of days

43 b 0 f 0

Spitsbergen Summit station, Peru 30 30

323 20 91 20 215

10 10 No. of days No. of days 42 59 c 0 g 0

Sonnblick, Alps Kerguelen Island, South Atlantic 30 30

20 35 20 20 225 267 10 10 No. of days No. of days 120 63 d 0 h 0 JDJD

Days > 0°C (a)–(c) High-latitude, low elevation (d)–(f) Low-latitude, high elevation Freeze-thaw days (g) Midlatitude, high elevation (h) Subarctic oceanic, low elevation Days < 0°C

Periglacial, Figure 3 Freezing and thawing conditions in various periglacial environments of the world. (From French, 2007.) typically, coniferous species begin to be replaced by such as bison and yak take advantage of these grasslands. others of either local or temperate distribution, such as Because these ecosystems experience deep seasonal frost, oak, hemlock, and beech, or by steppe, grassland, and they represent the outer spatial extent of the periglacial semi-arid woodland in more continental areas. Ungulates environment. 832 PERIGLACIAL

Periglacial, Table 1 Summary characteristics of high-latitude periglacial ecosystems

Arctic Antarctic Low Arctic High Arctic Continent, not Peninsula

Climate: Very cold winters, cold summers, Very cold winters, cold summers, Extremely cold, short summers, very low low precipitation, 3.5–5 months very low precipitation, 2–3 precipitation, strong winds 1 month >0C months >0C >0C Snow-free 3–4 months 1–1.5 months 1–2 months period Length of 3.5–5 months 1–2 months Negligible growing season Permafrost: Continuous: temperature is 3to Continuous: temperature is 10 to Continuous: temperature is 8to18C 4Cat10–30-m depth 14Cat10–30-m depth at 10–30-m depth Active-layer 30–50 cm in silt/clay 30–50 cm in silt/clay 30–50 cm in gravel and ablation till depth 2–5m in sand 70–120 cm in sand 1–2 m in bedrock Vascular 400–600 species 50–350 species Hair-grass, pearlwort plants: Mosses Sphagnum common Sphagnum minor 30+ types Lichens Foliose species abundant Fruticose and crustose species 125+ types common Total plant 80–100% 1–5% polar deserts <5% in most areas cover 20–100% polar semi-deserts 80–100% sedge-moss tundra Total plant 200–500 g/m² 0.5 g/m² polar deserts 0.5 g/m² in most areas production 20–50 g/m² polar semi-deserts 150–300 g/m² sedge-moss tundra Vegetation: Tundra types dominate Tundra types minor Mosses, lichens Tall shrubs, 2.4 m Polar semi-desert common Low shrubs, 0.5 m Cushion plant – moss Cottongrass tussock- Cushion plant – lichen Dwarf shrub heath Herb-moss Dwarf shrub heath wet-edge sedge Polar desert common Herb-moss Mammals: 10–15 species 8 species (1) Terrestrial: none (2) Southern Ocean: numerous marine mammals Nesting Birds: 30–60 species 10–20 species Penguins, skuas Large Barren-ground caribou, musk-oxen, Peary’s caribou, musk-oxen, Polar None herbivores: moose, Polar bear, fox, wolf bear, wolf Fishes: (lakes 4–6+ species 1–2 species (Arctic char, trout) (1) Rivers: none and rivers) (2) Southern Ocean: numerous

The harsh, climatic environments of the ice-free areas range between those in which the entire landscape is fash- of Antarctica support little life. However, these areas are ioned by permafrost and frost-action processes and those adjacent to a highly productive marine ecosystem that in which frost-action processes are subservient to others. results from the nutrients associated with upwelling of This diversity is accentuated by the fact that (1) certain water along the Antarctic Divergence. Not surprisingly, rock types are more prone to frost weathering than others a number of marine mammals (e.g., Antarctic elephant and (2) many regions currently experiencing periglacial seal, southern fur seal) and birds (e.g., penguins, wonder- conditions have only recently emerged from beneath con- ing albatross) use the ice-free areas for critical breeding tinental ice sheets and are largely glacial landscapes. For purposes. However, the terrestrial flora and fauna are example, certain areas of western Siberia and the north- few; mainly mosses and lichens. There are no land mam- western Canadian Arctic possess large bodies of relict mals in Antarctica. glacier ice, of Pleistocene age, partially preserved beneath ablation till (e.g., Astakov et al., 1996; Murton et al., 2005). It is clear that these so-called periglacial landscapes Periglacial landscapes are largely relict and that periglacial processes are slowly The geomorphic footprint of periglacial environments is modifying the landscape. not always achieved and most periglacial landscapes pos- The only periglacial landscapes that are probably in sess some degree of inherited paraglacial or proglacial geomorphic equilibrium are those that have protracted his- characteristics. The reality is that periglacial landscapes tories of cold non-glacial conditions. In the northern PERIGLACIAL 833

Periglacial, Figure 4 Examples of typical periglacial ecosystems: (a) Lowland tundra, Kellett River, southern Banks Island, Canada, showing ice-wedge polygon terrain, thaw lakes, an active-layer detachment (in foreground) and grazing muskoxen; (b) Northern boreal forest near the tree-line, just south of Inuvik, NWT, Canada, showing stunted black spruce with non-sorted circles (mud/earth hummocks); (c) A recently burned area of taiga forest, Lena River valley, central Siberia, now subject to thermokarst erosion and willow/shrub revegetation; (d) Birch trees constitute the northern boreal forest in northern Finland. hemisphere, these include (1) parts of central Alaska and Frost action and cold-climate weathering interior Yukon, (2) much of central and eastern Siberia, The weathering of bedrock in periglacial areas is generally and (3) much of the montane and steppe environments assumed to be mechanical in nature and the result of freez- on, and surrounding, the Qinghai-Xizang (Tibet) Plateau. ing and thawing of water within rock or mineral soil. Rates In the southern hemisphere, some of the ice-free areas of of cold-climate rock weathering are usually assumed to be Victoria Land are thought to have been free of ice for sev- as great, if not greater, than those in warmer environments eral million years. but this has yet to be convincingly demonstrated. In all these areas, it is clear that geological structure Rock disintegration by frost action is generally and lithology largely control the macroscale periglacial assumed to be the result of either (1) volumetric expansion landscape. For example, in areas of resistant igneous, of ice or (2) ice segregation. metamorphic and sedimentary bedrock, the higher elevations consist of structurally-controlled rock outcrops. Everywhere, the upland surfaces and upper valley-side Volumetric expansion slopes are covered by angular rock-rubble accumulations The freezing of water is accompanied by a volumetric (variously termed “mountain-top detritus,” blockfields, expansion of approximately 9%. In theory, this can gener- or kurums). Bedrock is frequently disrupted by joint and ate pressures as high as 270 MPa inside cracks in a rock fissure widening, the frost-jacking of blocks, and by brec- strong enough to withstand such pressures. While volu- ciation. Typically, uplands are bordered by low-angle, metric expansion was probably the mechanism that pediment-like surfaces. In many ways, these landscapes Łozinski envisaged when he talked of “periglacial facies,” resemble those of the hot deserts of the world. By contrast, the dominant role attributed to simple volumetric expan- areas of poorly-lithified bedrock and unconsolidated sion is probably incorrect. This is because the conditions Tertiary- and Quaternary-age sediments form more undu- necessary for frost weathering by volumetric expansion lating, poorly-drained, lowland terrain. Typically, the are somewhat unusual. Not only must the rock be water landscape is characterized by large-scale tundra polygons, saturated but also freezing must occur rapidly from all thaw lakes and depressions, and widespread mass-wasting side. On the other hand, there is no doubt that volumetric and patterned-ground phenomena. expansion of water within existing joints and other lines 834 PERIGLACIAL of weakness within bedrock outcrops can lead to bedrock Ice segregation heave and joint widening, and that near-surface frost There is increasing acceptance that the progressive growth wedging in fissile sedimentary rocks is a common occur- of ice lenses as liquid water migrates to the freezing plane rence (Figure 5a). is the most likely cause of the widespread fracture of moist A related mechanism is hydrofracturing, in which rock porous rocks (Walder and Hallet, 1986). This is because it disintegration results from pressures generated by pore- is now understood that moisture migrates within freezing water expulsion. For this to happen, the water-saturated or frozen ground. It is the result of a temperature gradi- rock must possess large interconnected pores, the expelled ent-induced suction (dPw) that affects the unfrozen water pore water is unable to drain away as quickly as it is held in capillaries and adsorbed on the surfaces of mineral expelled, and pore-water pressures must rise sufficiently particles. In theory, a temperature drop of 1C induces to deform or “hydrofracture” the rock. Rapid inward freez- a cryosuction of 1.2 MPa (12 atm). According to Williams ing is the ideal circumstance; for example, there have been and Smith (1989): occasional instances where Arctic field observations indicate that boulders or rocks on the ground surface have dPw ¼ dTl=VT (1) burst or “exploded” during periods of rapid temperature drop during midwinter. where, dT is the lowering of the freezing point, l is the A third possible mechanism relates to the breakup of latent heat of fusion, V is the specific volume of water, individual mineral particles by the wedging effect of ice and T is the absolute temperature. formed in micro-cracks or by the freezing of water within The conditions needed for ice segregation are slow gas–liquid inclusions at cryogenic (i.e., subzero) tempera- rates of freezing and sustained subzero temperatures. tures. For example, certain Russian laboratory experi- These are relatively common in most periglacial environments (e.g., Konishchev and Rogov, 1993) indicate that, ments. In frost-susceptible sedimentary bedrock, long- during repeated freeze-thaw cycles, quartz sand breaks continued ice segregation can lead to the brecciation of down more readily than feldspar and produces finer parti- bedrock to a depth of several meters (Figure 5b). Ice cles; this may also reflect the increasing brittleness of segregation and rock fracture has also been verified in quartz at very low temperatures when compared to other laboratory experiments that simulate natural uni- and minerals. bi-directional freezing; the most susceptible rock types

Periglacial, Figure 5 Examples of frost action and cold-climate rock weathering: (a) In situ bedrock disintegration and frost jacking of Devonian-age siltstone and sandstone, Rea Point, Melville Island, Arctic Canada; (b) An exposure of Late-Cretaceous shale in the wall of a drilling sump illustrates near-surface brecciation due to ice lensing, Sabine Peninsula, Melville Island, Arctic Canada; (c) Fractured, fine-grained diorite boulder lying on ablation till surface (“Younger Drift”), Simpson Crags, northern Victoria Land, Antarctica; (d) Taffoni weathering of coarse-grained monzogranite boulder, Terra Nova Bay, northern Victoria Land, Antarctica. PERIGLACIAL 835 appear to be fine-grained porous rocks such as chalk and similar to the more well-known “taffoni” of mediterranean shale (Murton et al., 2006). and tropical regions. Third, the efficacy of chemical weathering at low temperatures is unclear, despite a number of recent detailed Other mechanisms studies in northern Scandinavia (e.g., Dixon and Thorn, A number of other weathering mechanisms are also 2005), while the nature of the biological and biochemical thought to operate in periglacial environments. These are weathering processes associated with rock-colonizing briefly discussed below. organisms and the formation of phenomena such as rock First, insolation weathering, or spalling, refers to crack- varnish are extremely poorly understood (e.g., Guglielmin ing in bedrock thought to be caused by temperature-induced et al., 2005; Etienne, 2002). volume changes such as expansion and contraction. For It would appear that cold-climate weathering is com- many years these thermally-induced stresses were thought plex, frost action takes many forms, certain processes act more appropriate for rock weathering in hot arid regions alone, others in combination, and some may be physico- than for cold regions. However, laboratory studies suggest chemical in nature. the threshold value for thermal shock approximates to a rate of temperature change of 2C/min and experimental Frozen ground studies, using cold room facilities, have established that Periglacial environments experience either seasonally fro- different minerals have varying coefficients of linear ther- zen or perennially frozen ground. The latter, if it persists mal expansion in the range of +10 to 10C. These param- for more than 2 years, is termed permafrost (Muller, eters certainly apply to many periglacial environments. For 1943) (Permafrost). In areas underlain by permafrost, the example, in parts of Antarctica, field studies document active layer refers to the near-surface layer of ground daily temperature ranges of 40C42C, and rates of which thaws during summer. Where discontinuous perma- heating and cooling of 0.8C/min and of 15–20C/h. frost is present, the active layer may be separated from These measurements suggest that thermal stress, or fatigue, underlying permafrost by an unfrozen layer (tálik), or may be a viable rock-weathering process (Hall, 1999) by a residual thaw layer if permafrost is relict. If no (Figure 5c). Unfortunately, until further field, laboratory, permafrost is present, the active layer no longer exists and experimental studies are undertaken, this important and the near-surface layer is one of seasonal freezing mechanism is still largely speculative. and thawing. Second, equally perplexing is the relationship between The typical ground thermal regime of an area underlain salt, present in the snow in areas adjacent to marine envi- by permafrost is illustrated in Figure 6. Thawing begins in ronments and the granular disintegration of coarse-grained early summer and the depth of thaw reaches a maximum in igneous rocks that results in cavernous weathering in the late summer at which point, freeze-back occurs. The ice-free polar deserts of Antarctica (French and freeze-back is slower than the thaw because the release Guglielmin, 2000) (Figure 5d). These phenomena are of latent heat offsets the temperature drop. This gives rise

Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. 0.0 15.0° –15.0° –15.0° 0.5 –10.0°

10.0° Permafrost Active layers –10.0° –5.0° 1.0 –4.0° –3.0° Depth in meters 5.0° 4.0° –2.0° 5.0 1.5 –5.0° 3.0° –1.0° Depth in feet –0.5° –4.0° 2.0° 1.0° 6.5 2.0 0.5° –3.0° –2.0° 0.0° 2.5

3.0 –1.0° 3.5 –0.5° –0.5° 4.0

All temperatures are gentigrade Thermal regime of ground at Skovorodino, Siberia (1928–1930)

Periglacial, Figure 6 Diagram illustrating the typical ground thermal regime of a permafrost area, Skovorodino, Siberia, 1928–1930. (From Muller, 1943.) 836 PERIGLACIAL to the so-called zero-curtain effect, in which near isother- degradation of perennially frozen ground. Other pro- mal conditions persist in the active layer for several weeks. cesses, not necessarily restricted to periglacial environ- Both thawing and freezing are one-sided processes, from ments, are important on account of their high magnitude the surface downward. However, if permafrost was pre- or frequency in cold environments. They relate to the pres- sent, freezing is a two-sided process, occurring both ence of snow, or lake and river ice. Other azonal processes, downward from the surface and upward from the perenni- such as fluvial, eolian, and coastal processes, assume ally frozen ground. special characteristics in cold environments. The Stefan equation is sometimes used to approximate the thickness of the active layer: p Permafrost-related processes ¼ = Z 2TKt Qi (2) Permafrost-related processes include (1) the aggradation where Z = thickness of the active layer (m or cm), of permafrost and ground-ice bodies, (2) thermal contrac- T = ground surface temperature during thaw season tion cracking of frozen ground, (3) thawing of permafrost (C), K = thermal conductivity of unfrozen soil (W/m K (thermokarst), and (4) the creep of ice-rich permafrost. All or kcal/m C h), t = duration of the thawing season are intimately related to the presence of ice within permafrost. (day, h, s), and Qi = volumetric latent heat of fusion (kJ/ m³). The Stefan equation can also be used to calculate Much of our understanding of permafrost-related land- the depth of seasonal frost penetration. In this case, time forms and geomorphic processes is derived from the t is the duration of the freezing season (T < C) and K rep- 50 years of field investigations undertaken by J. R. Mackay resents the thermal conductivity of frozen soil. in the Mackenzie Delta region of the western Canadian The base of the active layer represents an unconformity Arctic (e.g., Mackay, 1963, 1998, 2000; Mackay and between frozen and unfrozen earth material. Because the Burn, 2002). annual depth of thaw may vary from year to year, Frost mounds, reflecting the growth of ground ice bod- depending upon the variability of summer climate, the ies, are aggradational permafrost features. A range of concept of the transient layer recognizes the different peri- forms exists. The largest and most dramatic is the pingo, odicities at which near-surface permafrost cycles through a perennial ice-cored mound. Pingos are of two types: 0C (Shur et al., 2005). The active-layer permafrost inter- either hydaulic (open) or hydrostatic (closed) in nature. face is commonly ice-rich. This is because, in summer, as Both cases require specific hydrologic conditions for the active layer thaws, moisture migrates downward and their formation. Pingos are relatively rare in the majority refreezes at the base while, during winter, unfrozen water of periglacial landscapes; however, the largest concentra- migrates upward in response to the colder temperatures at tion of closed-system pingos, over 1,350, occurs in the the surface. Thus, the active layer not only limits the depth Mackenzie Delta region of Canada (Figure 7a), while to which freeze-thaw action occurs but also its base acts as more isolated open-system pingos are found in central a slip plane for solifluction and other gravity-induced Yukon and interior Alaska, Svalbard, and central and near-surface movements such as active-layer detachments northern Siberia. In many subarctic areas, the preferential and for slope instability. growth of permafrost beneath organic material results Ground ice is an important component of permafrost. in the formation of peat plateaus and palsas. A number Many of the human occupance problems of periglacial of smaller frost mounds, mostly seasonal in nature, environments relate to either frost heaving of the ground also occur. or thaw subsidence (thermokarst) of ice-rich material. Pore The most widespread surface feature that is characteristic of permafrost is a network of thermal-contraction and segregated ice are the most widespread forms of ground – ice but other types include vein ice and intrusive ice. In cracks, typically 15 30 m in dimensions, which divide parts of western Siberia and the western North American the ground surface up into orthogonal or random- Arctic, massive icy bodies of either an intra-sedimental orthogonal patterns or polygons (Figure 7b). The cracks (i.e., segregated ice) or glacier-ice origin are present are caused by thermal contraction cracking of the ground (Astakov et al., 1996; Mackay and Dallimore, 1992). In during winter. In summer, the cracks fill with water from general, fine-grained materials are often ice rich and frost- snow melt that subsequently freezes to form wedge- susceptible, whereas coarse-grained materials are ice poor shaped bodies of foliated ice (Figure 7c). In lowland tundra terrain, ice-wedge ice may constitute between 10% and generally regarded as non-frost-susceptible. Typically, – the base of the active layer and the upper 1–3 m of perma- and 20% by volume of the upper 5 10 m of permafrost. frost contain the highest amounts of ice, often exceeding The thaw of ice-rich permafrost gives rise to distinct 50% by volume. Ground ice is discussed more fully under features. These, and the complex of processes associated Permafrost. with thawing permafrost, are generally termed thermokarst. For example, snowmelt-induced runoff in spring results in gully erosion along the lines of ice wedges Periglacial processes and landforms and where massive icy bodies become exposed, as along Geomorphological processes clearly unique to periglacial riverbanks and at coastal locations, retrogressive ground- environments are those related to the formation and ice slumps may develop (Figure 7d). On terrain underlain PERIGLACIAL 837

a b

Periglacial, Figure 7 Features of permafrost terrain: (a) Closed-system pingo near Tuktoyaktuk, NWT, Canada; (b) Poorly drained tundra lowland, northern Alaska, showing low-centered ice-wedge polygons; (c) Epigenetic ice wedge, southern Banks Island, Arctic Canada; (d) Ground- ice slump, northern Yukon coast, Canada. by fine-grained and ice-rich sediments, numerous shallow Azonal processes ponds or thaw lakes can develop (see Figure 4a). On gentle Mass-wasting processes are not unique to cold environ- slopes, active-layer-detachment failures may occur in ments but can assume distinctive characteristics and years of enhanced summer thaw (see Figure 4a). On bed- enhanced importance. For example, in non-permafrost rock outcrops, the thaw of ice within joints can lead to regions in summer there is slow mass wasting of the instability and enhanced rockfall activity. water-saturated thawed layer. This is termed solifluction. The creep of permafrost refers to the long-term defor- Where it occurs in permafrost regions, the process is called mation of frozen ground under the influence of gravity. gelifluction (Figure 8a). The result is heterogeneous slope Fine-grained frozen sediments, such as silt and clay, which deposits, or diamicts, that mantle gentle and lower valley- contain large unfrozen water content amounts, are espe- side slopes. These may form lobes and terraces, usually cially suitable to frozen creep deformation. Rates of move- with risers between 0.5 and 3 m in height (Figure 8b). ment are slow, usually less than 0.5 cm/year. The most More rapid movements involve rockfalls, debris flows, rapid creep deformation is recorded in rock glaciers, espe- and avalanches. These are particularly common in humid cially those that occur in mid-latitude mountains. For alpine environments where steep bedrock outcrops are example, the Muragle rock glacier in Switzerland is present. Frost-induced movements within the active layer, reported to be deforming at a rate of 50 cm/year (Kaab or in the zone of seasonal frost, leads to the formation of and Kneisel, 2006). stone nets that, as slope angle increases, turn into stone 838 PERIGLACIAL

c d

Periglacial, Figure 8 Examples of periglacial patterned-ground phenomena: (a) Oblique air view of mass wasting (non-sorted stripes) and gelifluction movement, Sachs Harbour, Banks Island, Canada; (b) Turf-banked gelifluction lobe, Holman, Victoria Island, Arctic Canada; (c) Stone stripes on low angled slopes (3–7) are separated from each other by vegetated stripes of finer material; the patterned ground is relict, Mont Jacques-Cartier, Gaspe´sie, Que´bec, Canada; (d) Small earth or frost hummocks (thufur), central Iceland. stripes (Figure 8c). Even in non-permafrost environments, parts of northwestern North America, long-continued frost action and ice segregation within the seasonally fro- mass wasting of loessic materials has led to the partial zen layer gives rise to the formation of small-scale sorted infilling of valleys with heterogenous organic-rich and and non-sorted patterned ground (circles, nets, stripes), ice-rich sediments known locally as “muck” while in frost heaving of bedrock, and the formation of small parts of central Siberia, similar mass wasting combined hummocks or frost mounds (thufurs, earth hummocks) with long-continued aggradation of alluvial sediments (Figure 8d). has created similar ice-rich sediments known locally as Wind plays an especially important geomorphic role in “Yedoma complex.” the tundra and polar desert environments (Seppala, 2004). A special characteristic of periglacial areas immedi- For example, the depth and coverage of snow is deter- ately adjacent to the Antarctic and Greenland ice sheets, mined by the prevailing wind regime. Typically, upland and to a lesser degree, the ice-marginal areas peripheral surfaces are blown clear of snow, while lee slopes and to all glaciers, is the presence of persistent and strong lower valley-side slopes are sites of snow-bank accumula- gravity-driven (katabatic) winds that flow outward from tion. In spring, the melt of snow banks promotes runoff or the ice. At extremely low temperatures, snow crystals surface wash that transports sediment down slope. Soli- become effective abrasive agents with MOH hardness fluction or gelifluction is enhanced immediately below values exceeding 4 at 40C; as a result, wind-polished snow banks because of the saturated near-surface thaw and fluted rocks and bedrock outcrops and wind-abraded layer. In some regions, preferential snow distribution cobbles (ventifacts) are common (Figure 9b). In the dry results in enhanced solifluction on lee slopes and the valleys of southern Victoria land and Antarctica, these development of asymmetrical valleys, with streams being winds promote sublimation to such an extent that peren- progressively “pushed” toward the windward (steeper) nial snow and ice is unable to form. slope. Elsewhere, localized wind erosion can occur in In spite of apparent aridity, fluvial activity is another weakly consolidated sedimentary bedrock and deflation important component of periglacial environments. This operates on fine-grained sediments. is because losses through evaporation and infiltration In the absence of vegetation, deflation assumes local are minimized by low temperatures and frozen ground, importance in many periglacial environments (Figure 9a). respectively. The result is a highly seasonal discharge In more continental periglacial environments, loess and regime, dominated by a nival (snowmelt) peak in early cover-sand deposition is widespread. For example, in spring. The fluvial dynamics are no different to other PERIGLACIAL 839

Periglacial, Figure 9 Examples of wind action in periglacial environments: (a) Deflation caused by strong winds and an absence of surface vegetation, central Iceland; (b) Wind-sculpted bedrock blocks of welded volcanic ash, Brown Bluffs, Antarctic Peninsula. environments, but high sediment loads and highly variable albedo, or reflectivity, of land or ocean surface and allows seasonal discharges lead to a dominance of braided more solar radiation to be absorbed. channels as opposed to straight, meandering, and Periglacial environments are thought to act, therefore, anastomozing patterns. In fact, the well-developed drain- as a positive feedback mechanism for climate warming. age networks and large-scale organization of periglacial Already, there is speculation that this is the cause of landscapes are not dissimilar to those elsewhere. River recent reductions in snow cover and sea-ice extent. In and lake ice persists for several months of the year; at the future, any thaw of the organic-rich upper layers of spring melt, ice jams may develop, causing flooding and permafrost, especially in the subarctic, will release damage to structures such as bridges. Where powerful significant quantities of carbon dioxide and methane, both perennial springs emerge, the freezing of discharge in of which are important greenhouse gases. Finally, the sig- the downstream direction forms tabular ice bodies (river nificance of gas hydrates, which exist frozen within icings) that may cover several square kilometers. permafrost, is still not widely recognized. Yet, their even- In the northern hemisphere, periglacial coasts experi- tual potential release to the atmosphere will lead to ence wave action for a restricted period of the year a dramatic increase in greenhouse gases and this could fur- and are often protected from erosion by an ice foot. Ice ther accelerate any climate warming. pushing is a common feature of many arctic coastlines. If climate warming proceeds as predicted, periglacial Where the coast is formed in ice-rich unconsolidated sed- environments will be among the first to be affected. iments, as along much of the Beaufort, Laptev, and East Warming will be enhanced because of (1) increased meth- Siberian Seas, wave action and thermal erosion result in ane flux due to decomposition of organic matter frozen in coastal retreat of several meters per year. The rapid forma- near-surface permafrost and release of methane hydrates tion of spits and offshore bars is characteristic. In Antarc- as permafrost bodies degrade, (2) increased biomass tica, wave action and coastal processes are relatively production and decay in tundra and taiga zones, and unimportant on account of the hard bedrock that forms (3) decreased surface albedo as snow-cover extent and the coastline and the extremely short open-water season. duration decrease. Already, there is evidence that warming of permafrost has been ongoing for over 30 years (e.g., Osterkamp, 2008; Brown and Romanovsky, 2008). This Periglacial environments, environmental may lead to long-term changes. For example, at the south- challenges, and global climate change ern (warm) limits of the discontinuous permafrost Periglacial environments constitute part of the cryosphere. zone, permafrost bodies will progressively disappear, the As such, they play a critical role in global climate change tree-line will advance northward, and the active-layer (Lemke et al., 2007). It is now understood that the hydro- thickness will increase. The latter, monitored by the logical cycle of the big northern rivers of North America CALM program of the International Permafrost Associa- and Eurasia links snowmelt and precipitation with river tion (Brown et al., 2000), will probably lead to an increase runoff, sea ice, and ocean circulation in a single system. in the frequency of active-layer detachment failures and This influences deep water formation in the Arctic basin slope instability, to changing snow-melt and hydrological and the corresponding global thermohaline circulation of regimes, and to enhanced mass wasting and landscape the oceans (Peterson et al., 2002). At the same time, any modification in high-latitude permafrost environments. reduction in the extent of sea ice or snow cover reduces In alpine periglacial environments, thawing permafrost 840 PERIGLACIAL may lead to instability of rock outcrops that could threaten French, H. M., 2000. Does Łozinzki’s periglacial realm exist today? the foundations of ski lifts and other recreational installa- A discussion relevant to modern usage of the term “periglacial”. 11 – tions at high elevation (Gruber and Haeberli, 2007; Permafrost and Periglacial Processes, ,35 42. French, H. M., 2007. The Periglacial Environment, 3rd edn. Haeberli, 1992). Chichester: Wiley, 458 pp. A number of environmental concerns relate to global cli- French, H. M., and Guglielmin, M., 2000. Cryogenic weathering of mate change and the impact of human activity in periglacial granite, Northern Victoria Land, Antarctica. Permafrost and environments. Many centre around the various problems Periglacial Processes, 11, 305–314. associated with natural resource management, exploitation, Guglielmin, M., Cannone, N., Strini, A., and Lewkowicz, A. G., and ownership (e.g., Young, 2009; Tin et al., 2009). For 2005. Biotic and abiotic processes on granite weathering landforms in a cryotic environment, Northern Victoria Land, example, the marine and terrestrial ecosystems are increas- Antarctica. Permafrost and Periglacial Processes, 16,69–85. ingly being subject to environmental stress. In the arctic, Gruber, S., and Haeberli, W., 2007. Permafrost in steep bedrock the marine food chain is linked to sea ice, nutrient availabil- slopes and its temperature-related destabilization following cli- ity, and water density. Any changes to these may induce mate change. Journal of Geophysical Research, 112, F02S18, changes to the marine ecosystem and the associated doi:10.1029/2006JF000547. biochemical cycling of essential nutrients. The terrestrial Haeberli, W., 1992. Construction, environmental problems and food chain is limited by the short growing season, low natural hazards in periglacial mountain belts. Permafrost and Periglacial Processes, 3, 111–124. temperatures, and low rates of nutrient cycling. Thus, cli- Hall, K., 1999. The role of thermal stress fatigue in the breakdown mate warming in high latitudes will change plant and ani- of rock in cold regions. Geomorphology, 31,47–63. mal communities. This will affect the hunting and Kaab, A., and Kneisel, C., 2006. Permafrost creep within a recently harvesting of animals and plants by northern indigenous deglaciated glacier forefield: Muragl, Swiss Alps. Permafrost peoples in Canada, Greenland, and northern Scandinavia. and Periglacial Processes, 17,79–85. A second environmental concern for the northern high lat- Karte, J., and Liedtke, H., 1981. The theoretical and practical definition of the term “periglacial” in its geographical and geological itudes is the recent increase in industrial air pollution from meaning. Biuletyn Peryglacjalny, 28, 123–135. mid-latitudes. Small particles, such as sulfur dioxide, are Konishchev, V. N., and Rogov, V. V., 1993. Investigations of cryo- transported by atmospheric circulation toward high lati- genic weathering in Europe and Northern Asia. Permafrost and tudes where they appear as “arctic haze.” The harsh reality Periglacial Processes, 4,49–64. is that the northern high latitudes act as an atmospheric Lemke, P., Ren, J., Alley, R. B., Allison, I., Carrasco, J., Flato, G., “sink” for industrial pollutants generated in the mid- Fujii, Y., Kaser, G., Mote, P., Thomas, R. H., and Zgang, T., 2007. Observations: changes in snow, ice and frozen ground. latitudes, especially those of northern Europe and European In Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Russia. Third, in Antarctica, the increasing number of Averyt, K. B., Tignor, M., and Miller, H. L. (eds.), Climate cruise ships and related tourism activities will soon inadver- Change 2007: The Physical Science Basis. Contribution of tently impact upon certain of the critical marine- and bird- Working Group 1 to the Fourth Assessment Report of the breeding localities in South Georgia and the Antarctic Intergovernmental Panel on Climate Change. Cambridge, UK/ New York: Cambridge University Press. Peninsula. There is also the possibility of a major marine Ł environmental disaster if a cruise ship were to hit an iceberg ozinzki, Walery von, 1909. Über die mechanische Verwitterung der Sandsteine im gemässigten klima. Bulletin International de and sink in Antarctic waters. Finally, Chinese upgrading of l’Academie des Sciences de Cracovie, Classe des Sciences the Qinghai-Xizang (Tibet) Highway in recent years and Mathematiques et Naturelles, 1,1–25. (English translation: completion of the Qinghai-Tibet Railway in 2003 has Mrozek, T., 1992. On the mechanical weathering of sandstones opened the large montane periglacial environment of the in temperate climates. In Evans, D. J. A. (ed.), Cold Climate Tibet Plateau to a potential increase in human occupancy Landforms, Chichester, UK: Wiley, pp. 119–134). Ł and economic activity with, as yet, unknown consequences. ozinzki, Walery von, 1912. Die periglaziale fazies der mechanischen Verwitterung. Comptes Rendus, XI Congrès Internationale Geologie, Stockholm 1910, 1-39-1053. Mackay, J. R., 1963. The Mackenzie Delta area. Geographical Bibliography Branch Memoir, No 8, Ottawa, 202 pp. Astakov, V. I., Kaplyanskaya, F. A., and Tarnogradski, V. D., 1996. Mackay, J. R., 1998. Pingo growth and collapse, Tuktoyaktuk Pleistocene permafrost of West Siberia as a deformable glacier Peninsula area, western Arctic coast, Canada: a long-term field bed. Permafrost and Periglacial Processes, 7, 165–191. study. Géographie physique et Quaternaire, 52, 271–323. Brown, J., and Romanovsky, V. E., 2008. Report from the Interna- Mackay, J. R., 2000. Thermally-induced movements in ice-wedge tional Permafrost Association: State of permafrost in the first polygons, western Arctic coast. Géographie physique et decade of the 21st century. Permafrost and Periglacial Pro- Quaternaire, 54,41–68. cesses, 19, 255–260. Mackay, J. R., and Burn, C. R., 2002. The first 20 years (1978-1979 Brown, J., Hinkel, K. M., and Nelson, F. E., 2000. The Circumpolar to 1998-1999) of active-layer development, Illisarvik experi- Active Layer Monitoring (CALM) program. Research design mental drained lake-site, western Arctic coast, Canada. Cana- and initial results. Polar Geography, 24, 165–258. dian Journal of Earth Sciences, 39, 1657–1674. Dixon, J. C., and Thorn, C. E., 2005. Chemical weathering and Mackay, J. R., and Dallimore, S. R., 1992. Massive ice of the landscape development in mid-latitude alpine environments. Tuktoyaktuk area, western Arctic coast, Canada. Canadian Geomorphology, 67,85–106. Journal of Earth Sciences, 29, 1235–1249. 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No 62, 136 pp. Second printing, 1945, 230 pp. (reprinted in Definition 1947, J. W. Edwards, Ann Arbor, MI, 231 pp). Murton, J. B., Peterson, R., and Ozouf, J.-C., 2006. Bedrock Permacrete is a versatile and unique resurfacing material fracture by ice segregation in cold regions. Science, 314, that can be applied to concrete, masonry, foam, steel, 1127–1129. stucco, and aggregate surfaces. Permacrete is an architec- Murton, J. B., Whiteman, C. A., Waller, R. I., Pollard, W. H., tural, chemical-concrete with twice the strength of stan- Clark, I. D., and Dallimore, S. R., 2005. Basal ice facies and dard concrete (What is Permacrete, 2009). Permacrete is supraglacial melt-out till of the Laurentide ice sheet, Tuktoyaktuk a very strong and heat-resistant material that can be used Coastlands, western Arctic Canada. Quaternary Science Reviews, 24, 681–708. in a variety of applications. Osterkamp, T. E., 2008. Thermal state of permafrost in Alaska during the fourth quarter of the Twentieth Century. In Kane, D. E., Formation and Hinkel, K. M. (eds.), Volume Two: Proceedings, Ninth Inter- national Conference on Permafrost, June 29-July 3, 2008. Fair- Permacrete is a three part, acrylic polymer cementations banks, AK: University of Alaska Fairbanks, Institute of Northern system with strength of over 6,000 PSI (pounds force Engineering, pp. 1333–1338. per square inch). These three parts include a matrix mix Peterson, B. J., Holmes, R. M., McClelland, J. W., Vorosmarty, (early-strength concrete mixture), chemical bonding addi- C. J., Lammers, R. B., Shiklomanov, A. I., Shiklomanov, I. A., tive, and a stain sealer. It is sealed and nonporous, resists and Rahmstorf, S., 2002. Increasing river discharge to the Arctic chemicals, and withstands freeze-thaw cycles as well as Ocean. Science, 298, 2171–2173. Porsild, A. E., 1957. Illustrated flora of the Canadian Arctic Archi- intense heat and ultraviolet rays (What is Permacrete, pelago. National Museum of Canada, Bulletin No 146, 209 pp. 2009; Kirk, 1998). Romanovskii, N. N., 1980. The Frozen Earth. Moscow: Moscow Thermal disturbance and exposure to solar heat consid- University Press, 188 pp (in Russian). erably affect the physical and mechanical properties of the Seppala, M., 2004. Wind as a geomorphic agent in cold climates. permafrost. Preservation of the thermal properties in the Cambridge University Press: Cambridge, 368 pp. permafrost is the major challenge in building the engineer- Shur, Y., Hinkel, K. M., and Nelson, F. E., 2005. The transient layer: implications for geocryology and climate-change science. Per- ing and construction work (Jumikis, 1983). Since the mafrost and Periglacial Processes, 16,5–18. permacrete has the high insulating and heat-resistant prop- Smith, M. W., and Riseborough, D. W., 2002. Climate and the limits erties, it is extensively used in permafrost regions to build of permafrost: a zonal analysis. Permafrost and Periglacial the residential properties (houses) and commercial proper- Processes, 13,1–15. ties (oil, gas pipelines, and tunnels) in combination of soil Tin, T., Fleming, Z. L., Hughes, K. A., Ainley, D. G., Convey, P., and ice material. Moreno, C. A., Pfeiffer, S., Scott, J., and Snape, I., 2009. Impacts of local human activities on the Antarctic environment. Antarctic The ancient form of similar material can be compared Science, 21,3–33. with use of snow by Eskimos where they used the block Walder, J. S., and Hallet, B., 1986. The physical basis of frost of ice to build the igloos for their shelters in high arctic weathering: toward a more fundamental and unified perspective. environment. The application of permacrete as building Arctic and Alpine Research, 18,27–32. material can be found when the US Army developed the Washburn, A. L., 1979. Geocryology: A Survey of Periglacial Pro- artificial aggregates by mixing silicates and aluminum- cesses and Environments. London: Edward Arnold, 406 pp. silicate with snow to form “permacrete” while performing Williams, P. J., and Smith, M. W., 1989. The Frozen Earth. Funda- mentals of Geocryology. Cambridge: Cambridge University experiments in Greenland (Kirk, 1998). Press, 306 pp. Yershov, E. D., 1990. Obshcheya Geokriologiya. Nedra, Moscow (English translation: Williams, P. J., 1998, General Geocryology, Bibliography Cambridge: Cambridge University Press, 580 pp). Kirk, R., 1998. Snow. University of Washington Press: Seattle, Young, O. R., 2009. Whether the Arctic? Conflict or cooperation in p. 150. the circumpolar north. Polar Record, 45,73–82. Jumikis, A. R., 1983. Rock Mechanics. Trans Tech: Clausthal, Zhou, Y., Dongxin, G., Guodong, C., and Shude, L., 2000. pp. 87–88. Geocryology in China. Lanzhou: Cold and Arid regions Envi- Permacrete, 2009. http://www.permacrete.com/commercial/faq.php ronmental and Engineering Research Institute (CAREERI), What is Permacrete, 2009. http://www.bulifant.com/HFBulifant/ Chinese Academy of Sciences, 450 pp (in Chinese). permacrete.htm

PERMACRETE PERMAFROST

Ashok Kumar Verma Yuri Shur1, M. Torre Jorgenson2, M. Z. Kanevskiy1 Department of Geography and Environmental Studies, 1Department of Civil and Environmental Engineering, Cold Regions Research Center, Wilfrid Laurier University of Alaska Fairbanks, Fairbanks, AK, USA University, West Waterloo, ON, Canada 2Alaska Ecoscience, Fairbanks, AK, USA

Synonyms Synonyms Duracrete Perennially cryotic ground