Dear Tom,
In general, how far south does the permafrost line run?
Troy Clark, Fairview, N.C.
Dear Troy,
Permafrost is surprisingly extensive, but we’re hardly aware of it because it is found mainly in sparsely inhabited polar regions. It underlies one-fifth of the Earth’s land surface.
Geologists define permafrost as soil or rock, at some depth below the surface, that remains continuously at or below freezing (32(degrees)). Lying above permafrost is a surface layer (the active layer) 2-12 feet in thickness that alternately freezes in winter and thaws in summer.
In the Northern Hemisphere, permafrost occurs in a circum- Arctic belt varying from a few to several hundred miles in width. It underlies 85% of Alaska, 88% of Siberia and most of northern Canada, and it extends south as alpine permafrost in the higher elevations of the Rockies all the way into the U.S. Lower 48.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
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