ABSTRACT

As already noted, permafrost is defined as ground that remains below 0°C for more than two years. Determining this is difficult without actual temperature measurements since by merely looking at the ground surface, the temperature regime cannot be determined. Again, fluctuations in weather from year to year can change the status of frozen ground. Using actual temperature measurements and relevant observations, Brown & Péwé (1973) divided the factors affecting the presence or absence of permafrost into climatic and terrain factors which interact together to determine the actual distribution of permafrost. The climatic factors control the level of heat (temperature) and amount of heat (duration) applied to the surface of the Earth. Altitude, latitude, longitude and type, timing, and amount of precipitation are involved. Their combined effect is modified by the terrain factors, e.g., local relief, aspect, vegetation, hydrology, nature of the substrate and fire. In addition, environmental changes over time and the activities of humans further affect the distribution of permafrost. The climatic factors are dominant in areas of continuous permafrost, whereas the terrain factors increase in importance as the percentage of ground underlain by permafrost decreases. Each of these factors will be discussed in turn in this chapter.