[HQR05-P09] Sedimentological features of Fuji-Sagamigawa Lahar deposits from the upper reaches of Sagami River, central Japan
Keywords:lahar deposits, Fuji-Sagami River Mud Flow, Katsura River (Sagami River)
Lahar is a general term for a rapidly flowing mixture of rock debris and water (other than normal stream flow) from a volcano (Smith and Fritz, 1989). Fuji–Sagamigawa Mud Flow (Lahar) originated from the Fuji Volcano (Older Fuji) around 22 ka (Machida, 2009) distributes along the Sagami River Valley. The lahar deposits have been reported from Tsuru City, Yamanashi prefecture to Zama City, Kanagawa prefecture which apart ca. 90 km from the present Fuji Volcano summit. At least 3 events have been recognized based on field surveys by Geographical and Geological Research Group in Sagamihara City (1990).
Detailed description of outcrops of the lahar deposits in the upper reaches along the Shakunagashi River, a branch of Katsura River (Sagami River) revealed that (1) the lahar deposits are divided into 6 or more units with less than 3m thick, (2) the units do not show characteristics of hyper–concentrated flow deposits, and (3) the units often intercalate parallel–cross bedded layers. These features imply that the lahar deposits in the upper reaches are formed by multiple flow events.
Detailed description of outcrops of the lahar deposits in the upper reaches along the Shakunagashi River, a branch of Katsura River (Sagami River) revealed that (1) the lahar deposits are divided into 6 or more units with less than 3m thick, (2) the units do not show characteristics of hyper–concentrated flow deposits, and (3) the units often intercalate parallel–cross bedded layers. These features imply that the lahar deposits in the upper reaches are formed by multiple flow events.