N2: Naeba Volcano Ejecta
C1: Collapse Deposits
Kt: Ketto Formation
K2: Ōiwa and Byōbu Rocks
Based on the surrounding topography, it is inferred that the area consists of the Ketto Formation, andesite, and other sediments. There is a scarcity of gravel from the Shimizugawara and the area is characterized by a significant presence of angular debris and rock fragments with little friction. It is believed that andesite pyroclastic rocks from the surrounding area have become sediment and deposited in the riverbed. This has resulted in changes to the watercourse and water volume due to landslide debris from both banks.
Ketto Formation:
Distributed along the Nakatsugawa River, from Koakasawa to Sakasa, primarily consisting of submarine volcanic ejecta.
Andesite Outcrops:
Seen at locations such as Sakasa Riverbank, Sarutobi Bridge, Shimizu River’s Byōbu Rock, Sekiganita in Ketsuto, and the Kiriake Hot Springs.
Naeba Volcanic Deposits:
The pyroclastic flow deposits are characterized by poor (slow) water removal due to the inclusion of fine particles, rock fragments, and pumice.