When we look at landscapes in Canada we always look at the majestic Rocky Mountains and the coastal mountains of British Columbia. Living in Manitoba we also know the wide prairies of the Country or some of the beauty of the Canadian Shield. But living in the southern part of the prairies, we tent to forget about the periglacial environment of Canada′s north. And with over 50% of this country definitely the biggest area of Canada. The most important feature of the periglacial region is permafrost. This region might not be as magnificent then the coastal mountains of British Columbia, but we can find some unique features, that are only found in Canada′s northern Territories. With this paper I will try to visualise some of the features found in the periglacial environment and explain their formation.
Permafrost
1. What is permafrost
2. The distribution of permafrost
3. The freezing process
4. The effect of permafrost on the landscape
1.Introduction
When we look at landscapes in Canada we always look at the majestic Rocky Mountains and the coastal mountains of British Columbia. Living in Manitoba we also know the wide prairies of the Country or some of the beauty of the Canadian Shield. But living in the southern part of the prairies, we tent to forget about the periglacial environment of Canada’s north. And with over 50% of this country definitely the biggest area of Canada. The most important feature of the periglacial region is permafrost. This region might not be as magnificent then the coastal mountains of British Columbia, but we can find some unique features, that are only found in Canada’s northern Territories. With this paper I will try to visualise some of the features found in the periglacial environment and explain their formation.
1. What is permafrost?
A long winter freeze and a short summer thaw may lead to the formation of a layer of soil which stays frozen (below 0°C) throughout the year. If this condition remains for two or more years we term this frozen ground a permafrost (Bone, 2000). Soil and rock do not automatically freeze at 0°C, especially if percolating groundwater is highly mineralised or under pressure. As a result, unfrozen porewater may continue to exist at temperatures well below 0°C (French and Slaymaker, 1993). The atmospheric climate is the main factor determining the existence of permafrost. However, the spatial distribution, thickness and temperature of permafrost are highly dependent on the temperature at the ground surface. The temperature at the ground surface, although strongly related to climate, is influenced by several other environmental factors such as vegetation type and density, snow cover, drainage, and soil type (Nat. Res. Canada, 2000). Thus permafrost includes ground that freezes in one winter, and remains frozen through the following summer into the next winter. During this time limit the permafrost may only be a few centimetres thick. But permafrost may be thousands of years old and therefor several meters thick. Above the permafrost is the so-called active layer. This layer is the surface layer of the soil, in direct contact with the atmosphere and therefor subject to thawing in summer and freezing in winter the thickness of this layer depends on the climatic surface conditions (Brown, 1970). Between the Active layer and permafrost we will find the permafrost table. It is important to know that the permafrost table is not associated with the water table.
It has been realised that permafrost is not always permanent. Changes in climate and terrain can cause permafrost to thaw and even disappear. Permafrost thins and the active layer thickens when ground temperatures increase. Permafrost thickness is also a function of a number of factors, including ground surface temperatures and the rate of temperature increase at depth. Because rock deep beneath the earth's crust is hot and molten, the temperature beneath the earth's surface increases with depth. This change of temperature is known as the geothermal gradient (Nat. Res. Canada, 2000).
Fig 1:
Abbildung in dieser Leseprobe nicht enthalten
Source: http://sts.gsc.nrcan.gc.ca/permafrost
Fig. 1 is an example of ground temperatures within permafrost in the Yellowknife region. The warmest and coolest temperatures occurring at depth show the annual range in ground temperatures. With increasing depth in the ground, the ground temperature does not vary as much as on the surface. The point at which there is no notable change in temperature is termed the "depth of zero annual amplitude". Below this depth, temperatures may stay the same year around.
Ground ice is a major component of permafrost. In the arctic region of Canada, ground ice counts for up to 50% in volume of the upper 1 - 5m of the permafrost. Pore ice, segregated ice and wedge ice, are the most significant in terms of volume and occurrence (French and Slaymaker, 1993)
2. The distribution of permafrost
Abbildung in dieser Leseprobe nicht enthalten
Fig 1.: Distribution of permafrost.
Source:
http://sts.gsc. nrcan.gc.ca/p ermafrost
Permafrost is underlies in around 20% of the earth surface area. It occurs mostly in Canada and the Soviet Union. Both countries have around 50% of their land area underlain by permafrost (Brown, 1970).
Permafrost is divided into four types (Fig 2)(Bone, 2000), alpine/mountain permafrost, continuous permafrost, discontinuous permafrost and sporadic permafrost. Alpine permafrost is found in mountainous regions and has a vertical pattern with increasing latitude, unlike the other types of permafrost. Continuous permafrost can be found in high latitudes of the arctic climate zone. Continuous permafrost occurs everywhere in the ground except in the newly deposited unconsolidated sediments (Brown, 1970)
Thickness and distribution of permafrost along a north south transact from the Beaufort Sea to the Alberta border. Source: http://sts.gsc.nrcan.gc.ca/permafrost
The thickness of permafrost varies. Fig.3 shows the thickness of permafrost at the Beaufort Sea. At high latitude the continuous permafrost reaches to depth of 700m. The depth of the permafrost Slowly decreases with decreasing latitude (Nat. Res. Canada, 2000). Continuous permafrost is associated with very low mean annual air temperatures of -15°C or less (Bone, 200) In the discontinuous permafrost zone, frozen and unfrozen layers are found together (Fig. 3). In the southern area of this zone, permafrost is distributed in scattered islands of a few square meters to several acres in size and is confined mostly to peatlands. Between 30 - 80% of the ground is permanently frozen. The average mean air temperature varies from -5°C in the southern latitude to -15°C in the northern latitude (Bone, 2000).
Sporadic permafrost is found at the most southern part of the permafrost area. During harsh winters this kind of permafrost can reach down to Manitoba’s northern Interlake region. Sporadic permafrost is associated with a mean annual temperature of zero to -5°C (Bone, 2000) The most southerly extend of permafrost in Canada is between 51°N and 52°N in the James Bay area. West of the Hudson Bay, permafrost extends northwards through the northern parts of British Columbia and the south-west corner of Yukon (Brown, 1970)
3. The freezing process
The only source for this part of the paper is “The permafrost environment” by Stuart A. Harris (also see reference list). Therefor I will not make any citations in this part of the paper.
Frozen ground consists of a least four materials: mineral/organic matter, air, ice and liquid water. Water is found in two areas of the soil. Some moisture is filling in the pores between and soil Grains and a film of molecular water is found around individual soil particles. Water can reach up to 30% of the dry weight of the soil. The porewater is held in the soil by gravitational and electrostatic forces between the water and the minerals in the soil. Since water contain two positive hydrogen molecules and one negative oxygen molecule, the water molecules interacts with the minerals and its charges in form of hydrogen bonds. Some water is also being held due to capillary forces between soil grains.
When the soil is cooled below 0°C, the porewater will start to crystallise. The exact temperature when this water will start to freeze depends on pressure and mineralogical composition, for example water in saline ground conditions will start freezing well below 0°C because of the salt contains in the soil.
Under normal conditions, the ground will start freezing with the very top layer. At first needle ice will form with the crystals growing at an 90° angle to the freezing plane. This will prevent a supercooling of the underlying soil moisture. If the underlying soil is too dry, supercooling will occur until the force of crystallisation is stronger than all other forces.
After a freezing plane has been created, liquid water from underlying layers will move upwards to the freezing plane. The freezing plane will stay at the same level until the latent heat produced by the freezing of water is less than the heat loss at the surface, then the freezing plane will slowly move downwards (Harris, 1986).
5. The effect of permafrost on the landscape
Unlike other regions, the freeze thaw circle of water plays the most important role in the creation of different geomorphic features. When a permanently frozen layer exist below the surface, water is unable to drain downwards. Therefore the active layer is often saturated. In this active layer, frost breaks up boulders and rocks. These are constantly moved by gravity and the freeze/thaw circle, which results in landforms that are unique to this region (de Blij and Muller, 1996)
The most widespread landform of the periglacial region is large-scale thermal contraction
cracking of the ground, which leads to the formation of polygonal patterns (Fig. 4) (French and Slaymaker, 1993).
Abbildung in dieser Leseprobe nicht enthalten
Fig. 4: Polygons and blown sand, Prince Patrick Island. Source: http://sts.gsc.nrcan.gc.ca/clf/landscapes.asp
Figure 4. Shows a network of patterned ground that is developed by the action of permafrost in fine-grained floodplain deposits. Ice wedges force up ridges which create depressions for small ponds (Nat. Res. Canada, 2001). The depressions formed may be as deep as four to five meters and the polygons may be as large as 15 - 30 meters in diameter. If water at the ground surface trickles down the fissure and cracking is repeated, an ice wedge will form (French and Slaymaker, 1993).
If the ice wedge grows wider, a peaty ridge develops a polygonal, saucer shaped depression called a low centred polygon (Fig. 5)
Abbildung in dieser Leseprobe nicht enthalten
Fig. 5: Low-centred polygons,
Blacktop River area.
Source: http://sts.gsc.nrcan.gc.ca/ clf/landscapes.asp
The most recognisable landform created by permafrost are pingos (Fig. 6) and palsas (Fig.7). Pingo is an Inuit word and simply means hill.
Abbildung in dieser Leseprobe nicht enthalten
Fig. 6: Pingo near Tuktoyaktuk, NWT
Source: http://sts.gsc.nrcan.gc.ca/ permafrost/general.htm
Pingos can grow to 50 meters or more in height and 30 to 600 meters in diameter (Trenhaile, 1998). A pingo is an ice-cored hill, which may be produced by injection of groundwater under pressure from below or by water freezing in cracks. Pingos have been classified into two types.
Close system pingos are found in continuous permafrost regions, where there is little relief. Here they occur in flat poorly drained terrain such as old lake bottoms or river deltas. The water from the underlying thaw basin is forced upwards to the permafrost. The unfrozen material is trapped between freezing surface layer and the advancing permafrost. The doming of the surface happens when the water freezes and expands (Trenhaile, 1998).
Open system pingos are found in the discontinuous region of permafrost, where groundwater in unfrozen zones is forced to the surface and creates an ice mass which causes an uplift of the surface. (Brown, 1970).
Abbildung in dieser Leseprobe nicht enthalten
Fig. 7: New and mature palsas in fen, Tadoule
Lake, Manitoba.
Source: http://sts.gsc.nrcan.gc.ca/ permafrost/general.htm
Figure 7 shows palsas, which are low hills or knolls of perennially frozen peat. Palsas can be between 1 - 10 meters high and 10 - 50 meters in diameter. Palsas form as a result of peat accumulation and the segregation of underlying mineral soils (Brown, 1970). Another periglacial landscape is patterned grounds (Fig. 8). In patterned ground we will find rocks and soil debris, shaped and sorted that they form regular pattern like rings, polygons or stripes. Patterned grounds are a result of frost shattering of the underlying bedrock and than due to the frost heaving forces like gravity (de Blij and Muller, 1996).
Abbildung in dieser Leseprobe nicht enthalten
Fig. 8: Stone polygons, Bjorne
Peninsula, Ellesmere Island
Source: http://sts.gsc.nrcan.gc.ca/ permafrost/general.htm
Thermokarst is a term used for one more distinctive landform, which is found in either continuous or discontinuous permafrost. Thermokarst resembles the karst topography like we are used to find limestone areas where sinkholes provide a landscape of many small lakes. The hummocky and uneven ground is formed doe to melting of the ground ice (Brown, 1970).
References
de Blij, H.J. and Muller, P.O.1996. Physical geography of the global environment. New York, John Wiley & sins, Inc (p. 491 - 497)
Bone, R.M.2000. The regional geography of Canada. Oxford University Press (p. 76 - 77) Brown, R. J. E. 1970. Permafrost in Canada,its Influence on the Northern Development. University of Toronto Press. (p. 2 - 20)
French, M.H. and Slaymaker, O. 1993. Canada’s Cold Environment. McGill-Queen’s University Press. (p. 150 - 159)
Harris, S. A.1986. The permafrost environment. Totowa, New Jersey: Barnes & Noble Books Trenhaile, A.S. 1998. Geomorphology:a Canadian perspective.Oxford University Press. (p. 162 - 174)
Natural Resources Canada. Permafrost, at the Geological Survey of Canada, http://sts.gsc.nrcan.gc.ca/permafrost/index.html. Oct. 19, 2000
Frequently asked questions
What is Permafrost?
Permafrost is ground (soil or rock) that remains frozen (below 0°C) for two or more consecutive years. This frozen layer can vary in thickness from a few centimeters to hundreds of meters and is often mixed with ice.
Where is Permafrost Found?
Permafrost underlies approximately 20% of the Earth's surface, primarily in high-latitude regions such as Canada and Russia. It is divided into alpine/mountain permafrost, continuous permafrost, discontinuous permafrost, and sporadic permafrost zones, each with varying characteristics and distribution.
How Does Permafrost Form?
Permafrost forms due to a combination of long, cold winters and short, cool summers. The atmospheric climate is the main factor determining the existence of permafrost, but vegetation, snow cover, drainage, and soil type also play a significant role. Porewater in the soil starts to crystallize when the ground cools below 0°C.
What is the Active Layer?
The active layer is the surface layer of soil above the permafrost table that thaws during the summer and freezes during the winter. Its thickness varies depending on climatic conditions.
What is Ground Ice?
Ground ice is a major component of permafrost, and in arctic regions, it can account for up to 50% of the volume in the upper layers of permafrost. Pore ice, segregated ice, and wedge ice are the most common forms.
What are the Different Types of Permafrost Distribution?
Permafrost is classified into four main types based on distribution: alpine/mountain permafrost (found in mountainous regions), continuous permafrost (occurs everywhere except in newly deposited sediments), discontinuous permafrost (frozen and unfrozen layers exist together), and sporadic permafrost (found in the most southern parts of the permafrost area).
How Does Freezing Process Work in Permafrost?
The freezing process starts with the formation of needle ice on the top layer. Liquid water from underlying layers migrates upwards to the freezing plane. The freezing plane will stay at the same level until the latent heat produced by the freezing of water is less than the heat loss at the surface, then the freezing plane will slowly move downwards.
What Effect Does Permafrost Have on the Landscape?
Permafrost significantly influences the landscape by preventing water from draining downwards, leading to saturated active layers. The freeze-thaw cycle breaks up rocks and boulders, creating unique geomorphic features such as polygonal patterns, ice wedges, pingos, palsas, and thermokarst.
What are Pingos and Palsas?
Pingos are ice-cored hills that can grow to significant sizes and are formed by the injection of groundwater or water freezing in cracks. Palsas are low hills or knolls of perennially frozen peat, resulting from peat accumulation and the segregation of underlying mineral soils.
What is Thermokarst?
Thermokarst is a landscape characterized by hummocky and uneven ground, formed by the melting of ground ice in permafrost regions, resembling karst topography.
- Arbeit zitieren
- Schwark, Carsten (Autor:in), 2001, Permafrost. Verteilungsgebiete und Einfluss auf die Landschaft, München, GRIN Verlag, https://www.hausarbeiten.de/document/105466
