Thermal regimes beneath coarse blocky materials

Monitoring of air and ground temperature at Plateau Mountain (South-Western Alberta) at short intervals (20 minutes) for two years shows vastly different thermal regimes in and beneath coarse blocky materials as opposed to mineral soils and rocks lacking substantial interconnecting voids. The dominant process of heat transfer in the upper layers is by rapid air movement through the voids to at least 50 cm depth as compared with slow conduction through the individual grains. Thermal response to a change in air temperature (positive or negative) is immediate and substantial, so it is not merely the result of the Balch effect. Rain and snow can also penetrate more deeply. These blocky materials are called kurums in Russia. Mean annual ground temperatures are 4-7 degrees C cooler in the blocky materials than in the adjacent mineral soils in cold climates, but this would be different in warmer climates. The ground temperature envelope is cone-shaped rather than bell-shaped, and this difference also occurs in mineral soils under a thin cover of blocks. There is also a smaller geothermal gradient within the zone affected directly by cooling/heating due to air movement. These processes appear to explain the occurrence of permafrost and substantial ice bodies in block fields such as rock glaciers below the limit of regional continuous permafrost in adjacent rocks and mineral soils. They also affect permafrost mapping and heat flow modelling, but offer a means of cooling near-surface soils. (C) 1998 John Wiley & Sons, Ltd.