This study investigates the thickness of the active layer of palsas in northernmost Finland and temporal, local, and regional differences in the thawing of palsas there. (Seppala 1983). Probes of frost depth were made over a 9-year period, a total of 185 measurements in 17 palsa bogs at sites ranging from 50 - 490 m in altitude. Thermal gradients were also measured ; weather observations were taken at two sites.