| |
| ||||||||||||||||||||||||||||
Proactive disclosure Print version   | |  Environmental Atlas of the Beaufort Coastlands Permafrost
Permafrost is a thermal phenomenon occurring in rocks or soils in which the temperature remains at or below 0°C for long periods of time. According to the former Permafrost Subcommittee of the National Research Council of Canada, the minimum period extends from one winter, through the following summer, and into the next winter. At temperatures below 0°C, most of the moisture in the soil occurs as ground ice. Because this ice usually exists at temperatures close to its melting point, thawing is likely to take place as ground temperatures rise. This ground ice occurs as structure-forming ice, namely, segregational ice, intrusive ice, reticulate vein ice, ice crystals, and icy coatings on soil particles. Ground ice occurs also as large bodies of more-or-less pure ice, of which three main forms are recognized. All three forms - pingo ice, wedge ice and massive ice - occur within the Beaufort Coastlands. Controls on Permafrost Temperature is the main control on the occurrence of permafrost. Permafrost can exist only in areas where the equilibrium temperature, between the amount of heat lost from the ground in winter and that gained from the atmosphere in summer, plus geothermal heat, remains continuously below 0°C. Other controls on the distribution of permafrost and the nature and extent of associated ground ice include variations in latitude, altitude, climate, topography, geology and vegetation. Colder climates prevail at higher altitudes and more northerly latitudes. Topographic features, such as slope aspect and slope angle, affect insolation, depth of thaw, runoff, and moisture content. Extent of Permafrost
The geographic extent of permafrost in Canada includes almost half of the nation's landmass, primarily in the northern regions and at higher elevations in the western mountains. Certain undersea areas, such as the southeastern part of the Beaufort Sea, are also underlain by permafrost. In the accompanying map, almost the entire land area of the Beaufort Coastlands and the Beaufort Shelf are underlain by permafrost. Exceptions are those areas of taliks or unfrozen ground beneath large lakes and rivers, and beneath the Mackenzie Trough. The distribution of permafrost is described in terms of four distinct classes, as follows:
Environmental Problems On land, permafrost and, more particularly, ground ice pose special problems regarding activities for engineering and economic development. Implications of Global Warming Continued global warming, with even a moderate rise of a few degrees of temperature, is highly likely to have far-reaching effects on permafrost throughout the world. A general warming will probably lead to the widespread disintegration of permafrost, particularly in those regions where ground temperatures are warmer than about -2°C. In the latitudes of subarctic areas, the sporadic discontinuous permafrost will be the first to disappear. As the mean annual ground temperature rises and its thawing isotherm progress in a northerly direction, increasingly greater areas of permafrost will vanish.
Such effects of global warming would create many alterations to the existing landscape, particularly in areas of abundant ground ice, lying in the zone of discontinuous permafrost. The ground would undergo subsidence and dislocation, thus leading to failure of foundations and other engineering structures. Drainage would be altered such that while some lakes emptied others would form. Thermokarst topography would develop in areas of ice-rich permafrost, because of the thawing process; also, landslide activity and erosion of river banks and coastal features would accompany the thaw. With increased global warming, however, the concomitant destruction of permafrost and subsequent alteration of the landscape would continue. Another factor of permafrost disintegration to consider is the release of so-called greenhouse gases (methane, carbon dioxide, water vapour, etc.) to the atmosphere. Very large volumes of these gases are presently trapped beneath the permafrost or are stored within it. They commonly occur in frozen peatlands and other wetlands; and may exist also as shallow accumulations of natural gas hydrates. In any case, they pose a hazard in the event of global warming because of their capacity to hold heat and to inhibit the latter from escaping the upper atmosphere. As global warming increases, so would the rate of release of these gases which, in turn, would worsen the situation.
Author: J.A. Heginbottom
|
