Soil frost from the winter 1941-1942 was of a special form. To create such a strong soil frost there need to be capillary soil form and long period of permanent and intense cold, meaning minus temperatures. The frost layer was thicker than normally.
Such a frost causes many problems on the fields and roads when the soil rises because of the frost and then falls unevenly back when the frost melts.
The PDF contains a summary in Finnish.