Physical properties of peat and palsa formation

This work considers the physical properties of peat and their effects on the formation of palsas under cold environmental conditions. Peat samples were taken in winter from the surface of a palsa in Finnish Lapland and from its frozen core and the material characteristics were determined. The thermal conductivity of the peat samples, measured with a thermal needle probe, varied between 0.23 and 0.28 W/mK with natural water content and between 0.43 and 0.67 W/mK in frozen peat. The thermal conductivity of saturated peat samples ranged from 0.41 to 0.50 W/mK and after freezing from 1.48 to 1.49 W/mK. Unfrozen water content in frozen palsa sample was measured by the TDR method. Water in the studied peat freezes at temperatures of 0 to − 0.8 °C, which is considerably a higher temperature range than in high frost-susceptible soils like silts. The frost susceptibility of the peat was measured in the laboratory with a frost heave test, but no frost heave was observed, which means that these peat forming palsas have no potential to form segregated ice lenses. The formation of a palsa is based on the thermal properties of peat.