九重火山群,松の台岩屑なだれ堆積物の地質学的研究(＜特集＞火山噴火史解明のための露頭データベース構築の検討(3))

抄録

We investigated geology of the Matsunodai debris avalanche deposit (MDA) and its adjacent area in Kuju Volcanic Group, Kyushu, Japan. Based on the eruptive history, the source of the MDA should be inferred to be the Mimata-Gairinzan lava. Volume of the collapsed part of the lava is calculated to be ca. 0.3 km³ . On the other hand, volume of the MDA is estimated as ca. 0.2 km³ , which is almost consistent with collapsed volume. The MDA can be divided into three terraces on the surface. Debris avalanche rushed down 6 km to the north, and spilled over the gentle slope at least 40 m above the lower land. We could not find any evidence for high-temperature deposition from previous reports on rock-magnetism of the MDA.