Formation Processes of Karst Landforms in the Nansei Islands: An Approach from Field Measurements and Field Experiments

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K01160
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 04010:Geography-related
• Research Institution: University of the Ryukyus
• Principal Investigator: Hada Asami 琉球大学, 国際地域創造学部, 准教授 (70508746)
• Co-Investigator(Kenkyū-buntansha): 青木 久 東京学芸大学, 教育学部, 教授 (30423742) ; 廣瀬 孝 琉球大学, 国際地域創造学部, 教授 (40305181)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 円錐カルスト / コックピット / 石灰岩堤 / 野外実験 / 溶食速度 / 岩石強度 / ケースハードニング / 亜熱帯島嶼

Outline of Final Research Achievements

The purpose of this study is to clarify geomorphic processes in a subtropical karst on Okinawa Island using field measurements and field experiments. Penetration tests showed that a soil layer of more than 3 m was formed in the middle of the cockpit, and the shape of the basement was ship-bottom shaped. The solution rates ,as determined by the percentage weight loss of limestone tablets, were 3 to 10 times faster in the soil than in the air, and the higher the water contents of the soil, the faster the solution rates. Rock strength results from Schmidt rock hammer test on limestone walls along faults indicate that the strength at the surface of the fault cliff is higher than the internal strength. Case-hardening at the surface of the fault cliff increases the resistance to erosion and causes the formation of limestone walls.

Free Research Field

地形学

Academic Significance and Societal Importance of the Research Achievements

熱帯・亜熱帯におけるカルスト地形研究は，分布や形状的特徴を述べた定性的な記載に留まっており，その形成プロセスは未解明な点が多い。本研究において，熱帯～亜熱帯に分布する凸型カルストの形成について，石灰岩の溶食速度の大きさや地形の内部構造（風化層の厚さ），石灰岩表層でのケースハードニングの実態把握をおこない，従来ない，実測による定量的アプローチにより解明を試みた点に学術的意義がある。