Geography
Periglacial Processes
Periglacial processes refer to the geological and geomorphological activities that occur in regions near the edges of glaciers or in areas that were formerly glaciated. These processes are characterized by freeze-thaw cycles, frost action, and the movement of frozen ground. Periglacial environments often exhibit unique landforms such as patterned ground, pingos, and ice wedges due to the effects of these processes.
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12 Key excerpts on "Periglacial Processes"
eBook - PDFGeomorphology: The Research Frontier and Beyond
Proceedings of the 24th Binghamton Symposium in Geomorphology, August 25, 1993
- J.D. Vitek, J.R. Giardino(Authors)
- 2013(Publication Date)
- Elsevier Science(Publisher)
This is an areal concept, which comprises all studies on geomorphic processes and land-forms in a special zone or belt. It is accepted, even if Washburn, the grand old man of peri-glacial geomorphology describes the perigla-cial concept in general as sufficiently broad and unprecise to defy (climatic) quantifica-tion (Washburn, 1979, p. 2). For Washburn (1979,p.4), PERIGLACIAL GEOMORPHOLOGY IN THE 21 ST CENTURY 143 the term periglacial designates primarily terrestrial, non-glacial processes and features of cold climates character-ized by intense frost action, regardless of age or proximity to glaciers. French (1987, p. 5) accepts this generally adopted definition as he writes: Periglacial geomorphology seeks to explain the geo-morphic processes and landforms of cold non-glaciated environments... There are two criteria which identify per-iglacial regions. These are ( 1 ) the existence of intense freezing and thawing of the ground, either on a seasonal or daily basis, and (2) the formation and preservation of perennially frozen ground or permafrost. This definition represents the same um-brella as the other definitions, even if the first critérium for identifying periglacial regions is extremely unprecise: The intensity of freezing and thawing can be given by the (daily or an-nual) number of freeze-thaw cycles related to ground or air temperatures, by the intensity of the freezing using mean minimum ground or air temperatures, etc. None of the given possi-bilities is really convincing as a general critérium. In a recent paper, Thorn (1992) tries to avoid these uncertainties, defines periglacial geomorphology as follows (Thorn, 1992, pp. 1,24): Periglacial geomorphology is that part of geomorphol-ogy which has as its primary object physically based ex-planations of the past, present, and future impacts of diurnal, seasonal, and perennial ground ice on landform initiation and development.
eBook - PDF- Vijay K. Sharma(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
209 8 Periglacial Processes and Landforms Lozinski first used the term periglacial in 1909 to explain the distribution of frost-shattered debris about the cold ice-free margins of Pleistocene glaciers (Embleton and King, 1968). As frost activity is not exclusive to the proximity of either former or present-day glaciers, the term periglacial nowadays is used for cold region pro-cesses and their landforms (Price, 1972; Washburn, 1979; Thorn, 1992). Washburn (1979) adopted the term geocryology for processes and landforms of cold environ-ments, but periglacial term has come to stay in the literature, and is widely used for the purpose. IDENTIFICATION A periglacial environment is characteristic of subfreezing air temperature and a fro-zen ground to certain depth in the subsoil. This relationship between the air tempera-ture and frozen ground is central to the identification of a periglacial environment. Peltier (1950) defined a periglacial environment by a mean annual air temperature between −15 and −1°C and a mean annual precipitation of 125 to 1400 mm, mostly in the subarctic zone of tundra vegetation. Periglacial regions have also been identi-fied with a subfreezing air temperature for at least two consecutive summers and the intervening winter season (Brown and Kupsch, 1974), and with a below freezing subsoil temperature for two consecutive years (Washburn, 1979). Observations, how-ever, suggest that even a slight snow cover effectively insulates the ground beneath from the effect of air temperature fluctuation (Harris, 1974; Embleton, 1980; Harris, 1982; Harris and Brown, 1982; Ødegård et al., 1995; Carey and Ming-ko, 1998). Therefore, periglacial regions are simply identified with perennially and seasonally frozen ground characteristic of a certain magnitude of subfreezing mean annual tem-perature range.
eBook - PDF- Mateo Gutierrez(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
15 PERIGLACIAL GEOMORPHOLOGY 1. The periglacial environment 2. Periglacial landforms 3. Applied geomorphology in periglacial regions 15.1 The periglacial environment 15.1.1 Introduction The Polish geomorphologist W. von Lozinski introduced the term ‘periglacial’ in 1909 to describe climatic conditions and geomorphic features of areas peripheral to Pleistocene ice- sheets in the Carpathians. The term was later extended to include processes and landforms characteristic of cold climates regardless of their proximity to glaciers or glaciated areas. Per- iglacial activity predominates in vast zones that are unrelated to glacial areas such as eastern Siberia (Jahn, 1975). The term periglacial has been used broadly because of its imprecise definition. The word ‘geocryology,’ which is commonly used by Russian researchers, has been suggested as an alternative term (Washburn, 1979). Geocryology is commonly defined as the study of terrestrial materials that have temperatures below 0°C, in other words permanently or seasonally frozen ground (Tricart, 1967; Washburn, 1979; French, 1996, 2007). Periglacial environments are characterized by freeze- thaw cycles and permafrost or permanently frozen ground. Either or both occur within the periglacial environment although some periglacial landforms are not associated with the presence of permafrost. The periglacial environment is present in polar areas and in middle and low latitude alpine areas of cordilleras throughout the world (Harris, 1986). Today the periglacial domain covers about one-fifth of the global land surface; periglacial conditions covered an addi- tional 20 percent of the Earth’s surface during the Pleistocene cold periods (French and Karte, 1988). Paleoclimatologists recognize the importance of periglacial phenomena in paleoclimatic reconstructions and of permafrost (Isarin, 1997).
eBook - ePub- Michael A. Summerfield(Author)
- 2014(Publication Date)
- Routledge(Publisher)
Arctic and Alpine Research, in addition to other journals which publish papers on geomorphology generally. Useful annual reviews of periglacial geomorphology are to be found in Progress in Physical Geography.- Harris (1986 ) provides a detailed discussion of the nature and formation of permafrost, while the pioneer work by Taber (1929 , 1930 , 1943 ) on frost action is still worth consulting. Thorn (1979 ) presents some intriguing data on the occurrence of freeze-thaw cycles and the efficacy of frost shattering in the alpine environment of the Colorado Rockies, and White (1976 ) compares the role of frost shattering and hydration shattering. Both field and laboratory investigations of frost shattering are reviewed by McGreevy (1981 ), and Pavlik (1980 ) provides a brief discussion of the factors controlling ground ice formation. Salt weathering in relation to tor formation is considered by Selby (1972 ).
- Mass movement processes are covered by Harris (1987 ) and Rapp (1986 ), and also in the more general texts, especially Washburn (1979 ). Benedict (1976 ) gives a useful review of frost creep and gelifluction and also provides a detailed discussion on mass movement mechanisms in alpine environments (Benedict, 1970 ). Fluvial processes in specific periglacial environments are discussed in Church (1972 ) and McCann et al. (1972 ), while Scott (1979 ) provides a comprehensive annotated bibliography on this topic. Embleton and King (1975 ) and Thorn and Hall (1980 ) discuss nivation, while Embleton (1979 ) and Thorn (1978
eBook - PDF- David Huddart, Tim A. Stott(Authors)
- 2019(Publication Date)
- Wiley-Blackwell(Publisher)
This work hints at the potential for glaciovolcanic environments to be associated with more extensive glaciolacustrine sediment assemblages. The importance of glacial processes has been emphasized by Bennett et al. (2008) in an exploration of the glaciovolcanic sequences of the Brekknafjöll‐Jarlhettur ridge in central Iceland (Figure 20.74) adjacent to the east- ern margin of the Langjøkull ice cap, which not only contains a complex assemblage of glaciovolcanic products but is associated with deposits of glaciola- custrine diamict that are in places deformed to cre- ate large‐scale glaciotectonic structures. 605 Earth Environments, Second Edition. David Huddart and Tim A. Stott. © 2020 John Wiley & Sons Ltd. Published 2020 by John Wiley & Sons Ltd. Companion Website: www.wiley.com/go/huddart/earth-environments Pingo degradation and melting ice wedge polygons near Tuktoyaktuk, North West Territories, Canada. Photo: Emma Pike, Wikipedia Commons 21 Periglacial Processes and Landform‐Sediment Assemblages 606 21.1 Introduction to the Term ‘Periglacial’ ‘Periglacial’ is a term which has had many connota- tions since it was first used by Lozinski (1909, 1912). A periglacial zone was originally defined as periph- eral to Pleistocene glaciers and was cold, mountain- ous, proglacial, or ice‐marginal, sparsely vegetated and mid‐latitude in nature. Such a periglacial zone is a specific and limiting type of periglacial environ- ment, which is difficult to recognize in modern analogues today and not typical of the majority of present‐day periglacial environments. Nor was it necessarily typical of Pleistocene periglacial envi- ronment to the south of the large continental ice‐sheets either. The landscape was dominated by frost processes, but frost action also influences land- scapes that were not at the margins of Pleistocene glaciers. For this reason, a broader definition of ‘periglacial’ is needed.
eBook - PDFGlacial Geology
An Introduction for Engineers and Earth Scientists
- N. Eyles(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER 5 Landforms and Sediments Resulting From Former Periglacial Climates N. Eylesand M. A. Paul INTRODUCTION Large tracts of the mid-latitudes south of the limit of glaciation (Fig. 1.1) are recognized as containing relict landscapes and soils resulting from former cold, periglacial climates. The purpose of this chapter is to provide a check list of sediments (engineering soils) and ground conditions of particular significance to applied studies. The general distribution of many of these features in mid-latitude areas such as Britain and North American can be depicted and their typical geometries identified at the scale of individual site investigations. The term periglacial is used elsewhere in this chapter as an umbrella-term 'for a wide variety of non-glacial processes and features of cold climates characterized by intense frost action regardless of age or proximity to glaciers' (Washburn, 1980). This is an important statement for it should be noted that the meaning of periglacial, as used elsewhere in the literature, is ambiguous. In some cases it is reserved solely for those conditions where permanently frozen ground (permafrost) is present. The term is also employed to describe a fringing zone around modern or Pleistocene ice caps. Similarly, reference to a 'periglacial climate' is unsatisfactory unless a particular climate is specified for there is a wide range of periglacial conditions with latitude and altitude. Periglacial environments range between the extremes of dry continental interiors with excessive seasonal extremes of temperature, to mountain zones in the mid and low latitudes where diurnal temperature changes are more marked and where mechanical break-up of rock masses by freeze-thaw cycles is at an optimum. It must also be pointed out that many soils and landforms identified as 'periglacial'form under conditions other than those of cold climates per se.
eBook - ePubLandscape Processes
An Introduction to Geomorphology
- Darrell and Valerie Weyman(Author)
- 2020(Publication Date)
- Routledge(Publisher)
Periglacial regions are those areas in high latitudes where average air temperatures are below freezing point but ice does not actually accumulate on the surface owing to summer melting when air temperatures are above freezing for several months. In periglacial regions, much of the denudation occurs by the processes associated with river systems, although some variations occur. On hillslopes, weathering tends to be dominated by freeze-thaw action, although chemical weathering is by no means entirely excluded. Transport processes on hillslopes include scree and debris flow, but solifluction (see below) is important. Water on hillslopes and in rivers is frozen for much of the year, but may be very effective in erosion terms during the spring and summer months, when most of the annual discharge is released as meltwater. The rivers of periglacial areas are typically braided and carry a large and coarse bedload.Figure 62 Solifluction on a periglacial hillslope.The most characteristic feature of periglacial area, however, is the existence of permafrost. This is the ground beneath the surface that is permanently frozen and it reaches a maximum depth of 400 m in parts of Northern Siberia. This permafrost layer is continuous in areas north of 70° but becomes discontinuous southwards. South of about 60 °N, permafrost is only sporadic; that is lenses of permanently frozen ground occur in an otherwise unfrozen area. In all permafrost areas, the top layers of soil thaw in summer. The depth of this active layer varies, being up to 4 m in the region of 50–60°N in Siberia but decreasing northwards into colder environments.The effect of permafrost is most noticeable on slopes. When the surface layers thaw in summer, the meltwater cannot percolate vertically into the underlying still-frozen ground and the active layer becomes saturated. Under these conditions, the active layer may move downhill as an accelerated form of soil creep called solifluction
eBook - PDFGeomorphology
The Mechanics and Chemistry of Landscapes
- Robert S. Anderson, Suzanne P. Anderson(Authors)
- 2010(Publication Date)
- Cambridge University Press(Publisher)
Summary Permafrost underlies nearly one quarter of Earth’s present landmass, and was significantly more extensive during the glacial cycles of the Plio-Pleistocene. The geomorphology of these landscapes is dictated by transfers of heat and water within the materials of the subsurface. A formal understanding of these transfers again requires that we craft balances of heat and water. The depth of permafrost, which can be hundreds of meters thick, is dictated by the mean annual temperature, the thermal conductivity of near-surface materials, and the geothermal heat flux. The thickness of the active layer, on which all ecological systems of periglacial landscapes depends, and on which all human infrastructure is placed, is dictated by the annual cycle of ground surface temperature, and by the surface energy balance. Here water content is crucial, as this stalls the pene-tration of the cold wave by requiring latent heat of fusion to be conducted away. When a porous material freezes, more interesting things happen than simple freezing of water in pores. Water migrates in thin films at temperatures well below the bulk freezing point in fine-grained (especially silty) substrates. This results in growth of segregation ice, or discrete ice lenses in frost-sus-ceptible soils. Some soil lenses are just a few millimeters thick. But massive ground ice many meters across can result over long periods of time. This phenomenon of excess or segrega-tion ice in turn catalyzes most periglacial geomorphic processes. Frost heave is a direct result. The slope-normal heave and the vertical subsidence upon thaw result in downhill frost creep. Upon thaw, the excess ice in near-surface materials melts, and the impermeable nature of the underlying frozen material prevents this water from escape. The resulting very weak soil can flow downhill on slopes of only a few degrees. Frost heave also results in jacking of larger clasts upward through the soil over repeated thermal cycles.
eBook - PDF- E. Derbyshire(Author)
- 2019(Publication Date)
- Routledge(Publisher)
E. Sugden and B.S. John (1976). Awareness of the nature and extent of the cryergic (frost) and nival (snow) processes dawned early but application of the knowledge to geomorphological problems was slow to develop. Certainly, knowledge of the extent and thickness of perenially frozen ground existed in the seventeenth century. Establishment of the study of cryonival processes on a scientific basis was delayed until after the first World War, fundamental contributions being by Taber (1929, 1930) and Beskow (1935). Application of these principles to the understanding of landform and sediment genesis was relatively slow, however, and had to await the growth in awareness of the strategic and economic potential of the polar lands during and following the second World War. Steady but notable progress has been made in the past thirty years, as may be judged from the major contribution by Washburn (1973). 188 Cryonival and Glacial Processes 5.1 FORMS OF ICE IN THE LANDSCAPE At the present point in geological time, atmospheric temperatures regularly fall below the freezing point of water at some time in the year over more than one quarter of the land area of the globe. Sedimentological, organic and geomorphological evidence suggests that this was true of between one third and one half of the land surface during the cold phases of the Pleistocene epoch (2.5 million-10 000 years ago). Water in the solid phase is an important geomorphological agent. It exists in the landscape in two major forms: as finely segregated aggregations in soil or rock and massive, essentially pure bodies of ice, the generic term for which is ground ice; and as large tabular or elongate masses of polycrystalline ice variously mixed with rock debris resting on the land surface and extending locally into standing water bodies and known as glaciers. Ground ice includes a wide range of forms (Table 5.1).
eBook - PDFGeomorphological Processes
Studies in Physical Geography
- E Derbyshire, K. J. Gregory, J. R. Hails, K. J. Gregory(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
E. Sugden and B. S. John (1976). Awareness of the nature and extent of the cryergic (frost) and nival (snow) processes dawned early but application of the knowledge to geomorphological problems was slow to develop. Certainly, knowledge of the extent and thickness of perenially frozen ground existed in the seventeenth century. Establishment of the study of cryonival processes on a scientific basis was delayed until after the first World War, fundamental contributions being by Taber (1929, 1930) and Beskow (1935). Application of these principles to the understanding of landform and sediment genesis was relatively slow, however, and had to await the growth in awareness of the strategic and economic potential of the polar lands during and following the second World War. Steady but notable progress has been made in the past thirty years, as may be judged from the major contribution by Washburn (1973). 188 Cryonival and Glacial Processes 5.1 FORMS OF ICE IN THE LANDSCAPE At the present point in geological time, atmospheric temperatures regularly fall below the freezing point of water at some time in the year over more than one quarter of the land area of the globe. Sedimentological, organic and geomorphological evidence suggests that this was true of between one third and one half of the land surface during the cold phases of the Pleistocene epoch (2.5 million-10 000 years ago). Water in the solid phase is an important geomorphological agent. It exists in the landscape in two major forms: as finely segregated aggregations in soil or rock and massive, essentially pure bodies of ice, the generic term for which is ground ice; and as large tabular or elongate masses of polycrystalline ice variously mixed with rock debris resting on the land surface and extending locally into standing water bodies and known as glaciers. Ground ice includes a wide range of forms (Table 5.1).
eBook - PDF- Timothy Foresman, Alan H. Strahler(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
They are characterized by cold temperatures, low snowfall, and limited vegetation. • Permafrost is ground that is perennially below freezing. Permafrost is continuous in the highest latitudes, as shown on the map. In lower latitudes, discontinuous permafrost includes areas of unfrozen ground called taliks. Distribution of permafrost • Figure 14.12 • Above the permafrost is an active layer that undergoes a seasonal cycle of freezing and thawing. • Water that freezes in the ground is ground ice. Cycles of freezing and thawing of ground ice cause frost action including frost heaving and frost thrusting. In the process of gelifluction, saturated soil can flow slowly downhill on a bed of permafrost. • Ice wedges are a form of ground ice found in permafrost terrains. Freezing pockets of water in lake beds push up hills called pingos. • Patterned ground occurs when freeze–thaw cycles distrib- ute rocks into patterns. • When the permafrost thaws, the ground can collapse to form a landscape of shallow lakes and trenches called thermokarst. Increased permafrost thawing results from global warming as well as human development on permafrost terrain. • As shown in the photograph, glaciers can erode bedrock by removing fractured blocks and using embedded rock frag- ments to chip or grind the bedrock. They leave depositional landforms, constructed of glacial drift, when the ice melts. Glacial abrasion • Figure 14.6 Glacial Landforms 433 • Alpine glaciers erode and enlarge the heads of mountain valleys to form cirques, leaving peaks called horns and sharp ridges called arêtes. • Through erosion, glaciers shape stream valleys into glacial troughs, which can become fiords if later submerged by ris- ing sea level. • Moraines of rubble and debris mark the sides (lateral mo- raines) and ends (terminal moraines) of glaciers, as shown in the diagram. When two tributary glaciers come together, they form a medial moraine down the middle of the trunk glacier.
eBook - PDF- Alan H. Strahler(Author)
- 2013(Publication Date)
- Wiley(Publisher)
Ice lenses form under other conditions as well. During the short summer season, when ice in the active layer thaws, the soil and regolith becomes satu- rated with water that cannot escape downward into solid permafrost. In a process called gelifluction , the saturated soil can slump or flow down shallow slopes and take shape as terraces or lobes. (Figure 17.23). With the return of cold temperatures, water in the active layer freezes. Recall from Chapter 10 that water expands when it freezes, and ice accumulation in the soil can cause the ground to shift horizontally through frost heaving, or vertically through frost thrusting. In areas that contain coarse-textured regolith, consisting of rock particles in a range of sizes, this shifting and thrust- ing can give rise to some very beautiful and distinctive features. These include rings and stripes of coarse frag- ments called patterned ground (Figure 17.24). Another remarkable ice-formed feature of the arc- tic tundra is a conspicuous conical mound called a pingo (Figure 17.25). Pingos emerge when pockets of unfrozen ground under a lakebed freeze after a lake is drained. As the unfrozen groundwater is converted to ice, its volume expands and pushes upward into a dome shape. In extreme cases, pingos reach heights of 50 m (164 ft), with a base diameter of 600 m (about 2000 ft). HUMAN INTERACTIONS WITH PERIGLACIAL ENVIRONMENTS Permafrost is now thawing at an accelerating rate, and the periglacial environment is feeling the effects. Localized thawing occurs as a consequence of construc- tion and industry, while regional thawing is a result of human-induced climate change. Permafrost thaw further contributes to global warming by releasing greenhouse gases into the atmosphere. The frozen ground contains vast amounts of carbon, in the form of peat, which decays to release CO 2 more rapidly under warming temperatures. Also abundant is methane, held within ice as methane hydrate.
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