The power of permafrost

Permafrost is made up of two layers: a thin “active” upper layer that melts in summer, and a thick underlying base of frozen ground that never melts. The Arctic and the Taiga lie within zones of continuous, discontinuous, or sporadic permafrost. (Alpine permafrost, another type of permafrost, is found primarily in the Rockies and the Coast Mountains.) The permafrost varies in depth and extent from zone to zone. In the eastern Arctic, where 80 percent of the ground is frozen, permafrost is continuous and half a kilometre thick. In the northern Taiga, where frozen ground ranges from 30 to 80 percent, discontinuous permafrost occurs. In the southern Taiga, permafrost is sporadic, reaching depths of only a few centimetres below the active level. Permafrost is formed when annual mean ground temperature — determined by air temperature, soil, drainage, and snow cover — remains below zero. The thawing of the “active” layer creates boggy conditions because the unyielding frozen layer hinders water drainage. Permafrost impedes mineral exploration and extraction. Thawing permafrost can undermine road surfaces, which require insulating layers of sand and gravel. Buildings must be steadied by supports capable of withstanding ground shifting. But thawing permafrost can be beneficial for it provides the mix of soil and water essential for the brief outburst of summer vegetation in the Canadian North.