[H-GM03] Geomorphology

[HGM03-P03] Development of fluvial terraces and moutainous hillslopes as part of the landscape evolution in the Koma Mountains, central Japan

*Ryoga Ohta^1,2, Yoshimasa Ota^3,4 (1.Chuo University, 2.JSPS Research Fellow PD, 3.Kyoto University, 4.JSPS Research Fellow DC)

Keywords:mass-movement, Shimotsuburai-Ichinose Fault, tephrochronology, longitudinal profile of rivers, tectonic geomorphology

Sediment yielded from hillslopes in response to tectonic and climatic events provides clues for reconstructing the landscape evolution, which archives as Quaternary strata within the mountainious watershed. The authors performed geospatial analysis and field investigations in a tectonically active mountainous watershed, where mass-movement and river incision are the dominant processes. This study area, the Koma Mountains in central Japan, develops fluvial terraces classified into eight treads, which are constrained their ages by tephrochronology. The middle and higher terraces develop on the eastern piedmont areas facing to the subsiding Kofu Basin and the Shimotsuburai-Ichinose active fault. The lower terraces distribute increasingly to the upstream, subdivided into four treads. On the eastern side of the Koma Mountains, fine-grained sediments that sandwiched Ontake volcano-derived tephras (e.g., On-Pm1) were buried by landslide deposits. These reflect the sediment yield in the watershed and the deformation of the hillslope morphology in the late Pleistocene, which should capture essential processes in shaping the landscape. This study will discuss the development of the fluvial terraces and changes in the hillslope morphology with respect to the landscape evolution in the mountainous wastershed.