[H-QR04] Quaternary, Diachronic dynamics of human-environment interactions

[HQR04-P02] Landform development of the alluvial plain in the west part of the Kazo Lowland, Saitama Prefecture, Japan

*Masanori Murata¹, Takayuki Takahashi², Kaori Aoki¹, Junichi Sato³, Takehiko Suzuki^1,4 (1.Research Center for Volcanic Hazards and Their Mitigation, Tokyo Metropolitan University, 2.International Research Institute of Disaster Science, Tohoku University, 3.Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 4.Faculty of Urban Environmental Sciences, Tokyo Metropolitan University)

Keywords:Kazo Lowland, Volcanic products, Saitama Prefecture

In the central part of the Kanto Plain, Alluvial lowlands such as the Kazo Lowland, Nakagawa Lowland, and Tokyo Lowland are widely distributed. The sedimentation by the Tone River before changing of the course in the early Edo period affected the landform development of these alluvial lowlands. Volcanoes in the northern Kanto region located in the upper reaches of the Tone River, have repeatedly erupted. The reworking of volcanic products had a great impact on the formation of the alluvial plain in the lower reaches of the Tone River. We investigated the landform development by radiocarbon dating and tephrochronology at three points along the Moto-arakawa River in the eastern part of Saitama Prefecture. In this meeting, we will present the results of underground geological survey at the alluvial plain in the western part of the Kazo Lowland, which is upstream of those points. Based on the lithological observation of the boring core, the sediments from the surface to a depth of 6.7 m consist mainly of medium-grain sand. Sediments deeper than 6.7 m are mainly silt. Rounded white pumice with a maximum grain size of 10 mm is concentrated together with carbonized plant pieces in a sand layer at a depth of 6.5 m. This white pumice is a tephra originated Haruna Volcano, because it contains hornblende and orthorhombic pyroxene. Therefore, in the western part of the Kazo lowland, the backswamp was transformed into a natural levee due to the increase in sediment caused by the eruption of Haruna volcano. In the future, we plan to reconstruct the age and paleoenvironments of sediments in the western part of the Kazo Lowland using radiocarbon dating, and to assess the spatial and temporal impacts of the reworking of volcanic products in the central Kanto Plain.