Survey of Myozin-Syo using the radio controlled buoy(Manbou).

Abstract

Since the violent submarine eruption of 1952 to 1953, the survey for the submarine configulation of Myozin-syo has not been carried out because of its danger. On May 1989, the Hydrographic Department of Japan (HDJ) could do in details the survey of Myozin-syo using the radio controlled buoy (MANBOU) which was developed for the research in dangerous waters such as above submarine volcanoes. According to the results, Myozin-syo is a conical mountain of which slopes incline about 20 degrees, the shallowest depth of the top is 43 m, and the diameter of the crater is about 500 m. It is considered that Myozin-syo is still active on account of high temperature measured at the crater. Up to the present, topographic features of Myozin-syo and its adjacent areas have been recognized as a double volcano which is composed with Beyonesu as west-side of the somma and Myozin-syo as the central cone. Previous survey results by Geological Survey of Japan revealed a ring shaped deep inside the somma with a central high (depth 300～350 m) , and our HDJ survey confirmed that Myozin-syo situates at the northeast part of the somma. Previous papers reported basaltic rocks from the somma (Beyonesu), and dacitic rocks from Myozin-syo. These results lead to a conclusion that the central high (depth 300～ 350 m) is a central cone which has been called Takane syo in the previous papers, and Myozin-syo is a dacitic high on the northeasten somma.