is activated only when the air temperature is colder than the ground temperature. 

 The temperature differential can be as small as one degree. The temperature 

 differential starts an evaporation /condensation cycle within the pipe. The material 

 within the pipe is in both a liquid and gas state due to being charged with a 

 refrigerant. Heat is absorbed from the ground through evaporation of the liquid 

 which rises to the top of the pipe. The rising gas meets the colder air temperature 

 and condenses, radiating heat out from the upper half foot of pipe. Gravity pulls 

 the condensate back down the pipe to the bottom and starts the cycle over again. 

 This cycle tends to keep the thermopile at a uniform temperature over its entire 

 length. This will reduce the thermal expansion /contraction effects and result in 

 freezing occurring radially about the thermopile. Ice lenses and other associated 

 pressures will develop radially and therefore not in the vertical direction necessary 

 to cause heaving. See Figure 1 1 . 



Three thermo bench marks were installed in Port Moller in 1 987 to supplement 

 five standard Class B deep-rod bench marks installed in 1984. Three of the Class 

 B deep-rod marks are steadily being jacked out of the ground by frost heave. To 

 date, after three years of seasonal freeze and thaw, the three thermo bench marks 

 have not shown any movement. 



It is recommended that thermo bench marks be incorporated into NOS' 

 accepted bench mark types and be used at remote sites with suitable conditions, 

 where appropriate. 



4.0 CONCLUSIONS AND RECOMMENDATIONS 



4.1 Conclusions 



The conclusions of this report are essentially the same conclusions reached 

 by the various workshops held on making water level measurements in polar 

 regions. The problems are associated with ice scouring on the near-shore sea 

 bed, the destruction of support structures by sea ice, the logistics of gauge 

 installation and maintenance, the lack of ice free locations, and the necessary 

 power requirements of the site. But, on the other hand, it appears that these 

 problems are not insurmountable and, with proper planning and resources, are 

 definitely solvable. The consensus of the experts is that the technology needed 

 to make sea level measurements in polar regions exists today and is considered 

 affordable. However, the technology needed and the techniques used for 



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