[M-IS11] Mountain Science

[MIS11-07] Stratigraphy and age of topsoils in a DSGSD linear depression on Mount Cho, the Northern Japanese Alps

*Yoshihiko Kariya¹, Sadao Takaoka¹, Yusuke Shimizu² (1.Department of Geography, Senshu University, 2.Kankyo Chishitsu Co. Ltd)

Keywords:Linear depression, Montane aqueous slope , Environmental changes in the Holocene epoch, 14C age, Deep-seated gravitational slope deformation

The main ridge between Mount Cho and Tokugo Pass in the southern part of Northern Japanese Alps is composed of Jurassic accretionary sedimentary rocks, which have undergone gravitational slope deformation of the bedrock. This has led to the development of characteristic micro to meso-scale topographies such as linear depressions and scarplets lines. In fiscal year 2023, we excavated soils at the shore site of Yoseino-ike Pond on the southern side of the summit of Cho. As a result, a 60 cm long core (YOS-2023) was obtained. Most of the core consisted of debris with little humus, but near the ground surface and at a depth of 40 to 60 cm were slightly rich in humus. The ¹⁴C age of soil sample obtained from the 40-50 cm depth of the core ranged from 5,901 to 5,730 cal BP. It is possible that vegetation existed near the bottom of depression during the mid-Holocene, supplying humus to the soil fill, but that the vegetation temporarily declined and debris movement on the slope became more active after that period. This would be related to climatic cooling in the late Holocene. During this period, a water level of Yoseino-ike Pond would also have changed.