Physical stratigraphy in relation to collapse mechanism at the Aira caldera wall in Ryugamizu area, Kagoshima Prefecture

Research Project

Project/Area Number	07458246
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	Natural disaster science
Research Institution	Kagoshima University
Principal Investigator	IWAMATSU Akira Kagoshima Univ., Fac. Sci., Professor, 理学部, 教授 (80018663)
Co-Investigator(Kenkyū-buntansha)	YOKOTA Shuichiro Shimane Univ., Fac. Sci., & Eng., Professor, 総合理工学部, 教授 (60211653)
Project Period (FY)	1995 – 1996
Project Status	Completed (Fiscal Year 1996)
Budget Amount *help	¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1996: ¥400,000 (Direct Cost: ¥400,000)
Keywords	Aira caldera / Collapse / Debris flow / All core boring / Hydrogeology / 地下水
Research Abstract	Large debris flows frequently occur at the Aira caldera wall near Ryugamizu. But detailed geological succession is not surveyed because of their steep dangerous cliffs. All core drilling was carried out in 1995. The lithology and cracks of the cores are described in 1996. Results of the study are summarized as follows. 1. There are Yoshino ignimbrite, Kekura formation, basaltic lappilli tuff and Ryugamizu andesite in descending order. 2. Many joint planes are well developed in Yoshino ignimbrite, basaltic tuff and Ryugamizu andesite. Therefore these rocks are good aquifer because of high crack porosities. 3. Kekura formation has low permiability. 4. Yoshino plateau gently dips to the oposite direction against the caldera wall. 5. Underground water usually flows on the top planes of Kekura formation to Yoshino. 6. In case of heavy rainfall, underground water overflows to the direction of wall. Then debris flows occur due to overflow water.