Permafrost can be continuous (covering a whole area) or it can occur in discontinuous patches throughout a region. Which ever way it appears, permafrost presents a barrier to development and infrastructure, agriculture, and life in general for the peoples of the locations in which it exists. In addition, permafrost is becoming a world issue due to climate change and its resultant melting.
Permafrost Basics and Global DistributionPermafrost generally occurs in areas where moisture seeps through the soil but because of cold temperatures, it freezes and over time, a layer of frozen soil or subsoil develops 3 to 3,280 feet (1 m to 1000 m) below the ground's surface. Permafrost is not determined by the moisture content in the soil; it is instead defined by its temperature. Therefore any rock or soil that is at or below freezing for two years (including spring and summer), is considered permafrost.
Because permafrost is determined by temperature, certain areas of permafrost can have different types of ice beneath the soil and even ice content itself - from nearly 0% to 50%. This ice is typically called ground ice and it can occur in two forms. The first is a large, solid piece of relatively pure ice, located deep in the ground. The second type is closer to the surface and appears in a veined pattern, or sometimes as ice wedges.
In addition to temperature, permafrost is also characterized by its inherent instability. This is because the permafrost itself is covered by a layer of soil (the "active layer") that freezes and melts following seasonal patterns. The permafrost itself also hovers around the melting point and is consequently instable and vulnerable to melting.
In general, permafrost mainly occurs at latitudes higher than 60°N and is most abundant and continuous throughout Alaska, the northern portions of Canada, parts of Greenland, and a large portion of Eastern Russia and Siberia. It also occurs sporadically in alpine regions in lower latitudes such as the Himalaya, the Alps, the Rockies, and even in the tropics in portions of the Andes and on Mount Kilimanjaro above 16,404 feet (5,000 m).
Permafrost also occurs in Antarctica but it is different from that found in the Northern Hemisphere. It is older and there is less actual ice in the soil. Much less is known about this area however, due to limited research.
The Importance of PermafrostPermafrost is important in the areas in which it appears because the rigidity of solid ground causes barriers to development and infrastructure. Roads, for example cannot be successfully paved in these areas because the freezing and thawing of the active layer causes expansion and then compaction of the ground, making pavement crack. Therefore, gravel is largely used in building roads.
Plumbing and acquisition of water with wells is also a problem because the ground water is either frozen or developers must dig through the permafrost to get to the water. In addition, pipes underground are more prone to freezing because of ground temperatures.
Building structures is a more difficult process in areas with permafrost as well. Due to a building's warmth seeping through its foundation, frozen land under the structure can melt and cause subsidence. As a result, homes and other buildings must be lifted off of the ground using stilts, which are planted below the permafrost - increasing the cost of building.
Permafrost is also a barrier to development and transportation of natural resources. The Alaska Pipeline for example, transports crude oil from Prudhoe Bay in the northern portion of the state down to Valdez, in the south. Since the oil is hot when it is extracted, the pipeline had to be built on stands raised above the ground to avoid melting the permafrost throughout the area, which could have caused the pipeline to break with the shifting ground.
Finally, permafrost is a problem in areas where agriculture is possible in that it limits what types of crops can be grown because of the short growing season when the land is actually thawed on the top few feet. In addition, the plant must have shallow roots to avoid hitting the frozen portions.
Continue to Page Two for Permafrost and Climate Change