In this paper, seasonal freezing and thawing of an active layer near a power transmission tower foundation are investigated experimentally with a metal rod buried in an enclosure filled with soil. The measured soil temperatures are used to examine thermal effects of the tower footing and snow cover on seasonal freezing and thawing cycles. it was found that the metal tower has significant thermal effects on the local region around the tower footing. This increases the thaw depth of the active layer and lengthens the freezing/thawing cycle, which adversely affects the foundation stability and safety. These results provide useful new insight of practical utility in the design and maintenance of power transmission line foundations and other infrastructure in northern regions. (C) 2008 Elsevier Ltd. All rights reserved.