Regularly spaced submarine rhyolitic-calderas on the Tokara volcanic ridge, northern Ryukyu arc, Japan

(1) Earth & Environ. Sci. Kumamoto Univ., Kumamoto, Japan (yokose@sci.kumamoto-u.ac.jp), (2) Nature System Science, Kagoshima Univ. Kagoshima, Japan (madhaj2004@yahoo.com), (3) Earth & Environ. Sci. Kagoshima Univ., Kagoshima, Japan (koba@sci.kagoshima-u.ac.jp), (4) Center for Marine Environment Studies, Kumamoto Univ. (akimoto@sci.kumamoto-u.ac.jp), (5) Faculty of Fisheries, Nagasaki University, Nagasaki, Japan (yasu-m@nagasaki-u.ac.jp)