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学術研究成果リスト

Detail of Grant Awarded Academic Researches

Project

Geomorphological and geological study of deep-seated gravitational slope deformation and large-scale landslides on mountain slopes in the upper Tama River basin, west Tokyo

Academic
Research
No.310
Principal
Investigator
Yoshihiko Kariya
Affiliation Professor, School of Letters, Senshu University
Research
Summary
Deep-Seated Gravitational Slope Deformation (DSGDS) as a precursor of landslide and large-scale bedrock landslide (LS) are often developed in mountain areas composed of sedimentary rocks. Although sedimentary rocks of the Chichibu and Shimanto Belts are widely present in the upper Tama River basin, little is known about DSGDSs and LSs. This study attempted to identify DSGSDs and LSs in the upper Tama River basin by using airphoto interpretation (geomorphological classification), GIS analysis, field geological survey and dating analysis with tephras and 14C measurements.

DSGDSs often occur on the northeast facing valley side slopes with buckling and toppling. Especially, typical examples are found in Mount Kurato, Mount Mitou and Hounose Dendeiro Ridge. DSGSDs are confined to the specific river basins such as Tarusawa Valley of Nippara River and Tamagawa Valley of Kosuge River. Chronological data show that linear depressions related to DSGSD on Hounose Dendeiro and Mount Kurato were already present at 95 ka and 10 ka (or before), respectively. The LS in the Tamagawa Valley was caused in the Kamakura Period or before, forming with a small dammed pond.

Although LSs are limited to occur in the upper Tama River basin, DSGSD and its related landforms (e.g., linear depression and valley side bulging) are common. This fact suggests that DSGSDs have affected on geomorphic development in this region. Based on the geomorphological and geological information obtained by this study, Quaternary landscape evolution connected to DSGSD and LS in the upper Tama River should be reevaluated. In addition, elucidation of spatial distribution and geologic deformation of DSGSD will help to new evaluation of erosion control and soil and water conservation problems. This study also revealed that fallout tephra grains and plant fossils are well preserved in the landslide-dammed lake deposits (e.g., Tamagawa Valley) and in the slope material filling a linear depression (e.g., Hounose Dendeiro Ridge). Erosion processes are more generally in mountain areas and thus it is difficult to obtain preferable materials for dating and paleoenvironment reconstruction. However, it seems that these depositional environments will provide good opportunities for Quaternary studies in the upper Tama River.
Collaborators Go SATO Kuniyasu MOKUDAI Chosei SHIMIZU
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