Periglaciation

Periglaciation (adjective: 'periglacial', also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures. 'Periglacial' suggests an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner.Periglaciation became a distinct subject within the study of geology after Walery Łoziński, a Polish geologist, introduced the term in 1909. Łoziński drew upon the early work of Johan Gunnar Andersson. According to Alfred Jahn, his introduction of his work at the 1910 International Geological Congress held in Stockholm caused significant discussion. In the field trip to Svalbard that followed the congress participants were able to observe the phenomena reported by Łoziński, directly. Łoziński published his contribution to the congress in 1912. From 1950 to 1970, periglacial geomorphology developed chiefly as a subdiscipline of climatic geomorphology that was current in Europe at the time. The journal Biuletyn Peryglacjalny, established in 1954 by Jan Dylik, was important for the consolidation of the discipline.Albeit the definition of what a periglacial zone is not clear-cut, a conservative estimate is that a quarter of Earth's land surface has periglacial conditions. Beyond this quarter an additional quarter or fifth of Earth's land surface had periglacial conditions at some time during the Pleistocene. In the northern hemisphere larger swathes of northern Asia and northern North America are periglaciated. In Europe parts of Fennoscandia, Iceland, northern European Russia and Svalbard. In addition Alpine areas in the non-arctic northern hemisphere might also be subject to periglaciation. A major outlier in the northern hemisphere is the Tibetan Plateau that stands out by its size and low-latitude location. In the southern hemisphere parts of the Andes, the ice-free areas of Antarctica and the sub-Antarctic islands are periglaciated.Periglaciation results in a variety of ground conditions but especially those involving irregular, mixed deposits created by ice wedges, solifluction, gelifluction, frost creep and rockfalls. Periglacial environments trend towards stable geomorphologies.Many areas of periglaciation have relatively low precipitation—otherwise, they would be glaciated—and low evapotranspiration. which makes their average river discharge rates low. However, rivers flowing into the Arctic Ocean adjacent to northern Canada and Siberia are prone to erosion resulting from earlier thawing of snow pack in the upper, more southerly reaches of their drainage basins, which leads to flooding downstream, owing to obstructing river ice in the still-frozen, downstream parts of the rivers. When these ice dams melt or break open, the release of impounded water causes erosion.