Permafrost

Permafrost, In the periglacial zones of North America and Asia (beyond the areas of permanent ice and snow), the lower layers of the ground never thaw (permafrost). Only a few patches of unfrozen land provide deep water circulation, connecting the water table to the surface. As the temperature rises in the spring, the top layer of the ground (the mollisol, or active layer) thaws. The thickness of this layer, which varies from a few centimeters to a few meters depending on the latitude and temperature, determines the type of vegetation that grows on it: tundra (moss, lichens, grass, dwarf shrubs) or taiga (conifers). (Photo by: QAI Publishing/Universal Images Group via Getty Images)