Frost-sorted block concentrations in Western Inari, Finnish Lapland

Abstract

Frost is capable of breaking up the plant cover on the steep slopes and in the depressions with ground‑water conditions favoring frost action in the area investigated. In the pine‑forest zone there are boulder depressions in which the ground frost to this day sorts the boulders in both horizontal and vertical directions. On the flat summits of the barren fells, the plant cover is broken by block pits, boulder depressions and sorted nets of rock fragments. On the slopes of the fells there occur block streams and sorted stripes. As the slopes become steeper, the extent of ground covered by blocks increases. Block fields are met with in the zone of subalpine mountain birch forests and in tracts of barren fells with gradients of 7 to 25 degrees. On the northeastern and eastern flanks of the fells, the lowest block fields lie at elevations of 275 to 300 meters, on the other slopes at elevations of between 300 and 380 meters. The areas covered by the block fields sloping toward the northeast and the east are broader than the ones sloping in other directions.