Frost heave, frost and snow depths on two earth hummocks ( pounus ) were monitored from 1992 to 2002 in Finnish Lapland. Frost heave was measured with motometers, frost depth with Gandahl's frost tube containing methylene blue, and snow depth with frost tubes above the ground surface. The annual range of frost heave was from 1 mm to 94 mm. The mean annual frost heave on a peat pounu was up to twice that on a mineral-cored pounu . Frost heave values on the pounus did not differ much from those from the surrounding mire. During the early summer, slow thawing of frost keeps the surface of pounus higher than the surrounding mire surface and this supports the formation of earth hummocks.