9:00 AM - 9:15 AM
[MIS23-01] Stratigraphy and ages of cores recovered from three linear depressions on the landslide bodies of deep-seated gravitational deformation slopes in the Kamikochi Valley, northern Japanese Alps
Keywords:deep-seated gravitational slope deformation, landslide, Holocene epoch, peat, Yakedake Volcano
In the Kamikochi Area of the northern Japanese Alps, deep-seated gravitational slope deformation (DSGSD) is common on mountain slopes and ridges of various types of bedrocks. On the slopes around Mount Nishihodaka-dake (2909 m ASL), Quaternary granodiorite is wide-spread, and slopes are well-deformed by DSGSD with characteristic features such as depressions, antiscarps, and bulges. We conducted drilling surveys using a hand-corer at two ponds and a bog on DSGSD-derived depressions and was successful to recover cores: 1) Kinugasano-ike pond (KNG2017 core), 2) Nishiho-ike pond (NSH2018 core), and 3) Nishihosanso Minami A bog (SMA2019 core). Three cores gave geological and chronological information beneficial for reconstructing environmental changes and natural history during the Holocene epoch.
All the depressions were formed in the period from the latest Pleistocene (~ 20 cal ka for KNG2017) to early Holocene (~ 8 ka for NSH2018 and SMA2019) during which global climate had drastically changed. In the study slopes, full-scale DSGSD would begin by this period and caused depression features. Subsequently, accumulation of humic silt and peat had started in the depressions with or without an aqueous body, suggesting onset of vegetation cover around each coring site. Timing of early accumulation of humic silt and peat were around 8 cal ka (KNG2017), 4.2 cal ka (NSH2018), and 6.3 cal ka (SMA2019). Differences in onset time of soils between three sites are thought to be affected by global to local climate and micro-scale topographic situations. The study slopes also received thin volcanic ash layers supplied from nearby Yakedake Volcano around 4 cal ka and 2.3 cal ka, respectively, useful for key beds. In this presentation, we show columnar sections of cores, calendar-calibrated 14C ages, and time-depth diagrams for all sites.
All the depressions were formed in the period from the latest Pleistocene (~ 20 cal ka for KNG2017) to early Holocene (~ 8 ka for NSH2018 and SMA2019) during which global climate had drastically changed. In the study slopes, full-scale DSGSD would begin by this period and caused depression features. Subsequently, accumulation of humic silt and peat had started in the depressions with or without an aqueous body, suggesting onset of vegetation cover around each coring site. Timing of early accumulation of humic silt and peat were around 8 cal ka (KNG2017), 4.2 cal ka (NSH2018), and 6.3 cal ka (SMA2019). Differences in onset time of soils between three sites are thought to be affected by global to local climate and micro-scale topographic situations. The study slopes also received thin volcanic ash layers supplied from nearby Yakedake Volcano around 4 cal ka and 2.3 cal ka, respectively, useful for key beds. In this presentation, we show columnar sections of cores, calendar-calibrated 14C ages, and time-depth diagrams for all sites.