Periglacial phenomèna and the laws of their distribution in the U.S.S.R.

Abstract

The elucidation of the most important active factors of frost lithogenesis constitutes the base of the system proposed for genetic types of frost-caused geologico-morphological or so-called periglacial formations.

Three cryo-morphological genetic groups are here distinguished - a macrostructural one, comprising forms predetermined by frost-cracks; a microstructural group comprising forms predetermined by fissures of desiccation with subsequent alternate congelation and melting along the fissures and between them; an astructural group, uniting forms not predetermined by the formation of fissures.

Leading factors of frost-caused morphogeny under conditions of arctic countries and of periglacial environments are frost cracks; in a lesser degree - desiccation fissures in grounds. Other factors are less significant and occur only locally. Differences in processes of frost-caused morphogeny in three regions, unequal in exogenetic develop ment, determine also the most characteristic differences in the general aspect of the periglacial landscape. Less important are climatically controlled provincial differences of the frost-caused morphogeny, and also the differences, provoked by an unequal historical development of diverse regions.

Throughout the USSR territory the following regions can be distinguished: (a) regions of accumulation, syngenetic with the development of periglacial forms. Characteristic is the formation of polygonal ice veins that grow upward together with the sediments. On the surface are clear polygons as a result of the ever-recurring growth of ice veins due to accumulation of sediments and formation of fissures; (b) regions of relative stabilization in accumulation and discharge with epigenetic development of periglacial forms. Characteristic is the formation of polygonal ground-veins, the transformation of upper rock horizons within fissure zones into a secondary product i.e. covering loam. On the surface, there are reduction of polygonal blocks. The formation of a stable sheet of covering loam is possible only in the absence of sedimental accu mulation and denudation; (c) regions of prevalent denudation with epigenetic development of periglacial forms. Characteristic is the ,,eating up" of big polygonal blocks (altiplanation terraces) during the process of nivation and solifluction, along the network of epigenetically formed fissures. Nivation-solifluction products upon the slopes, are very dynamic. The enumerated regions are distinguished for both the present-day stage and for that of the