Thermal ice core drilling to 700 m depth at Mizuho Station, East Antarctica

As part of the Glaciological Research Program in East Queen Maud Land, Antarctica in the Japanese Antarctic Research Expedition (JARE), thermal ice core drilling to the depth of 700.63m was conducted at Mizuho Station, East Antarctica (70^o41'53"S, 44^o19'54") in 1983-1984. For the operation, an improved version of the drill was designed and manufactured by Geo-Tecs Co. Ltd. in Japan. With the aid of a micro-processor, the drill could send to the surface analog data (converted to 8 bites) on the temperature of the main-heater, water tank, etc. during drilling. Drilling of the first borehole started on April 22,1983 and terminated on July 22 at 411.5m depth. Drilling was stopped because closure of the borehole became so rapid that the drill might be come stuck. This drilling was conducted by a five-man team during 499 working hours. On March 11,1984 reaming of the drill-hole was conducted. The core drilling of the second borehole was started from the depth of 133.5m on June 11,and finished on August 1,1984. At that time the drilling was conducted with larger clearance between the drill and the hole. A drill 168mm in diameter was used for drilling to 633m and another drill 142.6mm in diameter was used up to 700.63m depth. A six-man team spent 1014 working hours to reach that depth.