GEOTHERMAL SURVEYS ON SUBMARINE HYDROTHERMAL SYSTEMS USING SUBMERSIBLES IN JAPAN

The present status of geothermal experiments using the Japanese submer sible Shinkai in hydrothermal areas is briefly reported. Although exte nsive diving investigations have revealed metal-rich deposits in hydro thermal fields, they are valuable only from a purely scientific standp oint and are obviously not economically cost-effective mainly because of the deep water depth of the sites. The long-term measurement of hea t flow using submersibles can be a powerful tool to uncover the therma l regimes in a hydrothermal system. Usage of submersibles is inevitabl e to deploy such instruments, because of the need to have sufficient a ccuracy in positioning and flexibility in the placement of instruments or sensors. In 1994, three long-term heat flow monitoring systems wer e successfully deployed at the TAG active mound of the Mid-Atlantic Ri dge at 26 degrees N and on the ridge crest of the East Pacific Rise at similar to 18 degrees S, using the submersible Shinkai 6500 and its s upport vessel Yokosuka. The systems are presently working, waiting for recovery in 1995.