The gradual heating of the soil began in mid-July Within several weeks, a clearly defined 

 zone of warmer soils appeared at 10-cm depth and thickened downward as heating continued. Input 

 temperatures into the 200-m loop were generally about 10 to 12°C. Temperatures in the alcohol- 

 water mixture at the outlet were in the 8 to 9°C range. Increased soil thaw became evident in 

 August as ice-rich permafrost began to melt and differential subsidence began. By the end of the 

 summer, average thaw due to artificial heating was 15-20 cm greater than on adjacent control plots. 

 A distinct thaw bulb had developed beneath the center of the plot where input pipe temperatures 

 are greatest (Fig. 23b). At this time, one-half of the pipe was shut off and the soil in it permitted 

 to refreeze. Figures 23c and 23d show the temperature conditions in the plot for early September 



Figure 22. Close up of heated soil experiment. Pipes 

 are buried beneath strings. 



To Data Acquisition 



System and Troilar 



^ 



a. Plot 112 

 Figure 23. Idealized section of heated soil experiment and plot of 

 temperature fields at selected sample periods. Diagrams c and d 

 illustrate the freezing of half the section after heating was termi- 

 nated in it. 



62 



