Distribution and Chronology of Relict Polygon Patterns on the Laholm Plain, the Swedish West Coast

Abstract

Earlier observations of relict patterns of ice-wedge polygons in a coastal area of southern Sweden were followed up by photography from a small air craft during dry periods of the summer. The polygons showed up very distinctly as crop marks in the cultivated area and could easily be mapped. The stratigraphical characteristics of the polygon lines were studied in test pits, all of which revealed clear ice-wedge casts.

The distribution of polygons and their connection with shore levels from the Late-Glacial time is analysed from the map of polygon marks, combined with field data. A maximum age of polygon formation can be established from dated shorelines.

In the innermost, highest part of the plain the ice-wedge polygons may have begun to form at the end of the Oldest Dryas phase. The elevation of the land continuously brought ground surfaces into the realm of frost activity during cold phases of the deglaciation period.

The lowest observed polygons are situated in surfaces which were elevated above sea level as late as the Alleröd phase.

Topographically and geologically the Laholm plain was well suited for the formation of ice-wedge polygons during the Late-Glacial period. Also in recent time with its temperate climate, frost cracking accompanied by earthquake-like shocks and sharp sounds from the ground may occur in the area, when north-east winds bring intense cold in late winter.