[H-GM03] Geomorphology

[HGM03-P12] Infilling rates in the valley head areas of granodiorite mountains in Marumori, Miyagi Prefecture, Japan

Rikuto Sekine², *Tsuyoshi Hattanji¹, Takahisa Furuichi³, Yasushi Tanaka⁴, Shoji Doshida⁵, Takuro Ogura⁶ (1.Institute of Life and Environmental Sciences, University of Tsukuba, 2.College of Geosceince, School of Life and Environmental Sciences, University of Tsukuba, 3.Forestry and Forest Products Research Institute, 4.Faculty of Letters, Komazawa University, 5.National Research Institute of Fire and Disaster, 6.Graduate School of Education, Hyogo University of Teacher Education)

Keywords:hollow, shallow landslide, radiocarbon dating

Infilling rates in the valley head areas with shallow landslide scars were estimated in the granodiorite mountain of Marumori, Miyagi Prefecture, Japan. Many shallow landslides occurred in the study area because of the heavy rainfall by the typhoon in October, 2019. Infilling rates were estimated by combining radiocarbon dates of charcoal samples collected from deposits remained in the landslide scars and elevation data from 1-m DEMs taken before the landslide event. The deposits in the valley head areas were composed of an upper black soil layer with granitic sand and a lower brown soil layer consisting only of granitic sand. The age of the upper black layer was approximately 600 to 1200 cal yBP. Assuming that the burial continued without any interruption after these ages, the infilling rate estimated from depth of upper black layer and pre-event ground surface elevation ranged from 2.5±0.4 to 3.2±0.3 mm/y. The infilling rates in Marumori were smaller than the maximum infilling rate in Hofu, where bare lands had been widerly spread by intensive human impacts, and larger than those in Hiroshima, where human impacts were limited.
In addition, the infilling rates estimated from two charcoal samples with the different sampling depths ranged from 0.9±0.1 to 2.3±0.2 mm/y for the upper black layer, and 0.3 mm/y for the lower brown layer. The infilling rate of the upper black layer was significantly larger than that of lower granitic sand layer. These results suggest that the environment around the investigated valley head areas in Marumori changed after 1200 cal yBP, and that the infilling process progressed rapidly with the formation of the black soil layer.