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[MIS11-08] Evolution of DGSD reconstructed from the formation and growth ages of multiple gravitational depressions: A case of Mt. Wakamaru-yama in the Etsumi Mountains, central Japan
Keywords:Deep-seated gravitational slope deformation, Deep-seated landslide, Etsumi Mountains, Mt. Wakamaru-yama, Neodani fault, Humid and tectonically active region
Some mountain ridges display microtopographic features such as double ridges, uphill-facing scarps, and linear depressions, and these features are interpreted as the result of deep-seated gravitational slope deformation (DGSD) formed due to their weight. Although at least some of these DGSD features are considered to be precursors for large-scale deep-seated landslides, there are few cases in which the evolution has been elucidated based on empirical geochronologies.
Mt. Wakamaru-yama (1286 m), located in the central part of the Etsumi Mountains straddling Gifu and Fukui prefectures, has more than 100 uphill-facing scarps and about 30 associated gravitational depressions (bogs), and the possibility that these features were formed and have been grown by past activities of the Neodani fault, which runs near the ridge, has been reported. In this study, core drilling using a hand auger and a portable percussion coring system was conducted in 11 depressions on the east ridge of Mt. Wakamaru-yama to reconstruct the evolution of DGSD based on the formation and growth ages. The results indicate that the Mt. Wakamaru-yama site experienced the first depression at 20,100-7800 calBP, followed by six to four growth events. The uphill-facing scarps are presumed to have formed first at the ridge top and then spread to both sides of the slope. On the other hand, several studies report that in high-latitude, high-elevation DGSD terrain, such as the European Alps, uphill-facing scarps first form in the middle of the scarp, and then the formation of the scarp gradually move to the top of the ridge. The reason for the difference in the evolution of DGSD between humid and tectonically active regions, including our study area, and high latitude and high elevation regions is the difference in the cross-section of valleys due to the difference in incision style, as represented by V-shaped and U-shaped valleys.
Mt. Wakamaru-yama (1286 m), located in the central part of the Etsumi Mountains straddling Gifu and Fukui prefectures, has more than 100 uphill-facing scarps and about 30 associated gravitational depressions (bogs), and the possibility that these features were formed and have been grown by past activities of the Neodani fault, which runs near the ridge, has been reported. In this study, core drilling using a hand auger and a portable percussion coring system was conducted in 11 depressions on the east ridge of Mt. Wakamaru-yama to reconstruct the evolution of DGSD based on the formation and growth ages. The results indicate that the Mt. Wakamaru-yama site experienced the first depression at 20,100-7800 calBP, followed by six to four growth events. The uphill-facing scarps are presumed to have formed first at the ridge top and then spread to both sides of the slope. On the other hand, several studies report that in high-latitude, high-elevation DGSD terrain, such as the European Alps, uphill-facing scarps first form in the middle of the scarp, and then the formation of the scarp gradually move to the top of the ridge. The reason for the difference in the evolution of DGSD between humid and tectonically active regions, including our study area, and high latitude and high elevation regions is the difference in the cross-section of valleys due to the difference in incision style, as represented by V-shaped and U-shaped valleys.