Valley formation initiated by ice wedge polygonal nets in terrace surfaces

Abstract

Based on observations of present-day valley formation through thermokarst processes in river terraces of Spitsbergen, some mainly fossil valleys (gullies) in marine terraces of the Varanger peninsula are analysed. Their connection with a fossil pattern of ice-wedge polygons is still visible, and the formation of the valleys was evidently initiated by thermokarst processes in the polygonal furrows.

A more developed, dry valley pattern in another former periglacial area situated in southern Sweden is also discussed. The valleys are situated in a raised coastal area and formed in loose material, mainly sand.

The former presence of a well-developed polygon pattern in ice-rich permafrost (evidenced by distinct crop markings due to former ice-wedge polygons) is considered as the basic factor for the morphogenetic interpretation of the valleys. Meltwater, collecting in flat depressions and polygon furrows, started a thermo-erosive process and initiated the valley formation.

When the gullies had developed and were growing deeper, the amount of water present may have increased by the seeping of interpermafrost water from taliks connected with the adjacent river. The presence of icings further contributed

to the development of the fiat valley bottoms.