Pingo problems in the Scandinavian countries

Abstract

The northern part of Scandinavian peninsula reaches such high latitudes that permafost occurs, especially in peat bogs. The most typical and frequent form of permafrost in these northern regions is the palsa, a frost mound a few me tres high and covered with peat. The interior structure of the palsa is mostly built up of segregated ice. The palsa does not require such hard climatic conditions for its formation as does the pingo. In northern Scandinavia palsas appear in different stages of degeneration and have been sometimes confused with pingos. True pingos in active formation do not exist in the Scandinavian peninsula. Further northwards, in Spitsbergen, however, pingos can be found in different stages of development. In aerial photographs of plateau areas in northern Norway, terrain features have been observed that from the geo morphological point of view show the characteristics of both the palsa and the pingo group. A type of circular lakes form ed in minerogenic soil is interpreted as a fresh collapse stage of-frost mounds that have originated as palsas or pingos. Ring-ridged depressions of a more stable character propably have the same origin but are of an older date. In southern Scandinavia pingos may be suspected to have formed (1) in the periglacial environment of the retrea ting ice sheet of the last (Vistula) glaciation or (2) outside the margin of the ice cap, e.g. in wester,n Jutland, Denmark. During the deglaciation, periods of climatic deterioration occurred, as it is manifested by t)le vast areas of fossil ice-wedge polygons in southern Sweden. Some circular depressions filled with peat occur. However, as they lack a bor dering ring wall, these depressions cannot be geomorphologically classified as collapse forms of ringos. Western Jutland was not covered by the last glaciation and was for a lbng time exposed to a periglacial climate. In aerial photographs, low relief features of circular to oval shape have been observed in cultivated areas of Jutland. From the geomorphological point of view, their origin is hard to explain, except in terms of thermokarst processes in former frost mounds.