Permafrost

Permafrost forms when the mean annual temperature is approximately 27° F (-3° C).

The mean annual temperature in Fairbanks is just 27° F. Consequently, Fairbanks is a region of discontinuous permafrost. In areas of south slope, good drainage or little vegetation cover, the soil temperature will generally be above average and no permafrost will exist. On the other hand, north slopes or heavily vegetated areas often contain permafrost. The type of soil also is a factor; the wind-deposited silty soil on many of the hills around Fairbanks is prone to permafrost and lenses of nearly pure ice.

Serious problems have occurred when houses have been built on frozen soil containing a high percentage of ice. When the ice melts due to heat from the house, damaging collapses can occur. Unless special precautions are taken, it is unwise to build on permafrost.

Though it may not cause any special problems, permafrost is now forming on the north side of large buildings constructed on previously unfrozen ground. The buildings shield the soil from sunlight and thereby allow the average soil temperature to fall below 27° F.