Present-day periglacial phenomena in northern Finland
DOI:
https://doi.org/10.26485/BP/1982/29/20Keywords:
discontinuous permafrost, seasonal frost action, palsas, periglacial forms, Finnish LaplandAbstract
The northernmost part of Finland is located at the southern edge of the zone of discontinuous permafrost. The mean annual temperature of this region is somewhat below -1°C and during the coldest season in January and February the temperature can fall down below -40°C. In some favourable localities permafrost survives over the thawing season in mires under dry peat layers. Local permafrost concentrations raise the peat above the surface of the mire forming so called palsas which are frost cored peat hummocks rising up to 7 m in height in Finnish Laplapd and the diameter can be some hundred metres.
In detailed palsa studies it has been found that their cyclic development is not caused by climatic changes. An experimental study of the formation of an artificial palsa has been carried out. This study has confirmed the hypothesis of the origin of palsas according to which the critical factor is the thickness of snow cover which is controlled by wind drift.
Many other periglacial phenomena occur in northern Finland, but all, with the exception of palsas, are connected with, and formed by seasonal frost. Such are turf hummocks, string bogs, patterned grounds of different types, sand and soil wedges, stone stripes, gelifluction terraces, frost weathering, deflation and dune formation, and phenomena produced by river and lake ice.
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