Tundra ecosystem fragility
Permafrost is rock and soil material that has remained below zero centigrade for two or more years continuously. Much permafrost is composed of silty soil with a high frozen water content. Any disturbance to the thin vegetative cover which insulates the permafrost from warm air and sunlight, causes it to thaw into an unstable slurry of watery, oozing mud. This thawing can cause differential settlement of the ground surface, erosion, drainage problems and subsequent frost action. Once the equilibrium has been upset, the whole process continues irreversibly. It can be initiated simply by the passage of a tracked vehicle which destroys the vegetation mat and erodes into gullies many feet deep. This instability makes economic exploitation difficult (for example, road construction, oil pipelines with oil at temperatures of 160 fahrenheit) and is a threat to the fragile tundra ecosystems.
The distribution of the permafrost is not precisely known but more than one fourth of the Earth's surface has it in some degree. It is a phenomenon of high latitudes in both hemispheres and of high altitudes of major mountain systems.