PERIGLACIAL ENVIRONMENTS

Environments characterised by cold nonglacial conditions. There are two broad categories: (1) those that experience frequent freeze-thaw oscillations and/or deep seasonal frost [Page 821](seasonally frozen ground) but lack permafrost and (2) those that experience both frost action and permafrost. The permafrost zone of the Earth is sometimes termed the cryolithozone. These environments range from polar deserts and tundra to boreal forest and alpine zones, all of which are most extensive in the Northern Hemisphere. Around one-quarter of the Earth’s land surface experiences periglacial conditions and up to another quarter experienced similar conditions during the pleistocene. In the Northern Hemisphere, about 24 per cent of the land area experiences permafrost, almost half of which is continuous permafrost (defined as covering >90 per cent of the landscape), while about 58 per cent experiences seasonal frozen ground.

[See alsoperiglacial landforms and processes, periglacial landscape evolution, periglacial sediments]