Large Nonsorted Polygons in Padjelanta National Park, Swedish Lappland

Abstract

Large no nsorted polygons in tundra areas underlain by discontinuous permafrost occur in Padjelanta National Park, northern Sweden (67° 16′ N; 16°52′ E). Excavations in those of the polygons developed in silty till show only vague subsurface structures beneath polygon trenches, and crack fillings present are less than several millimeters thick. Such polygons may be contraction-crack polygons developed by seasonal frost cracking. Pits across trenches where polygons are developed in sandy outwash display obvious wedge-shaped casts predominantly more than several centimeters thick; these polygons are interpreted as tundra polygons originally developed in permafrost. The possibility of differential preservation is recognized; structures in silty till may have been more susceptible to destruction than forms in sandy outwash.

Both types of polygons formed after the last major deglaciation, which ended approximately 8 000–9 500 B. P. They are now either fossil or largely inactive Frost cracking in the surface polygon trenches occurred between the summers of 1963 and 1967; possibly during the severe winter of 1965–1966 which was accompanied by thin snow cover.

Outside the Puolejokk polygon sites in Padjelanta, similar surface features and subsurface casts have been. reported from other localities in Swedish Lappland and northern Norway by other authors.