A Studty of the Phreatic Caves : the origin of the Hiura-do Cave and the Kyusen-do Cave and on the phreatic features in other Caves

In Japan, before or after 1970, for the origin of limestone cave, the water table or the shallow phreatic theory were maintained by many researchers, because the levels are remarkably concentrated at the same altitude in several regions. The phreatic features of caves are hitherto not paticularly researched in our country. But, in the last several years, the members of the Circle of Cave Study of Yamaguchi University and its old boy have surveyed and investigated the phreatic features in many caves. In this paper, the typical phreatic caves of the Hirua-do Cave in the Shikoku karst region and the Kyusen-do Cave in the Kuma Mountainland, Kyusyu, and the phreatic features in other caves are described and considered. The process of the development of the Hirua-do Cave is divided into four stages, and its model is shown, and the Kyusen-do Cave is presumed to be a phreatic cave developed at a depth not less than 120 meters beneath the contemporary water table. We found frequently the phreatic features even in the cave situated within the vadose zone, so we can not sufficiently explain the origin and development of their caves without the phreatic theory. The phreatic features and the phreatic theory require further examination.