periglacial

Originally referring to the processes and landforms of areas bordering on ice-caps, this term has been extended to refer to any area with a tundra climate, such as mountainous areas in mid-latitudes, or where frost processes are active and permafrost occurs in some form. In consequence, as much as 20% of the earth's surface falls into this category.

Periglacial climates are arid, with temperatures below 0 °C for at least 6 months, and summers warm enough to allow surface melting to a depth of approximately 1 m.

Periglacial deposits include

1. those formed by fragmentation due to freeze-thaw: blockfields, scree, stone streams;
2. those formed through solifluction: solifluction gravels, lobes, and terraces;
3. those formed through aeolian deposition. See loess.

Periglacial processes include abrasion, freeze-thaw, nivation and solifluction, and are responsible for three processes: the formation of new deposits, the modification of the structures of existing unconsolidated deposits, and the modification of existing landforms by mass movement. It is suggested that mass movement accelerates under periglacial conditions, and solifluction can give rise to turf-banked terraces and turf-banked lobes. In each case, the turf limits the extent of solifluction. The crucial factor in periglacial weathering is snow fall, which may protect ground against weathering processes.