Polygonal-spotted forms of microrelief - so-called spotted tundras, small hillock, polygonal, stone circles et al. - were referred to zonal forms of Arctic and Subarctic microrelief long ago and indisputably. There are no less than thirty hypotheses, explaining polygonality and spot of high latitude microrelief. The analysis of these hypotheses and our own researches testify that the main and most general reasons for formation of these microrelief forms are deep freezing and the following melting of the grounds and thin soil-plant cover, that does not cover the Earth's surface fully, or its absence. When there is an undisturbed soil-plant cover from 5 to 7 and more sm thick, polygonal-spotted forms of microrelief are not formed. The reason is that the plant roots as an all-round net fasten the soil and prevent the ground from freezing the stones out and frost cracking. But as soon as a thin layer of soil-plant cover is disturbed (fires, caterpillar transport, trampling-down by domestic deers), the formation of polygonal-spotted relief of different types begins. To the point, in Murmansk region and Northern Karelia, with no permafrost, in the ploughed up fields the processes of pushing the stones out (freezing out) of the ground's freezing-melting layer are intensive. These stones are "growing" on the field's surface, they are annually gathered and put along the ploughed field border. It goes on until all the stones have been pushed out of the freezing-melting layer (1.5 - 2.0 m).

In autumn freezing of the melted very damp soil-grounds begins. At the same time the melted ground between the two freezed surfaces (freezing - above, permafrost ground - below) is exposed to greater hydrostatic pressure. This often causes the break of the upper freezing crust and pouring out the deluted ground on the soil surface, i.e. the formation of microrelief of spotted tundras. In the grounds, homogeneous by mechanical composition, that are saturated with moisture in autumn, in winter frost cracking of grounds and formation of polygonal microrelief take place. Anthropogenic human activities in the North cause tree retreat to the south and expanding tundra-like forestless territories. At the same time zonal forms of Arctic and Subarctic microrelief are moving to the south.

Vasiliy Kryuchkov
Institute of Economic Problems
Kola Science Center, RAS
184200, Apatity, Murmansk Region, RUSSIA
Phone: +7-815-55-306-72
Fax: +7-815-55-306-72
E-mail: luzin@ksc-iep.murmansk.su