Actual situation of forests after the Taisho mudflow in the Biei River, Tokachi Mountain, Hokkaido

Jounghyen KIM, Hitoshi ASANO, Hiroki HONMA, Tadashi IKEGAMI, Takashi YAMADA, Mio KASAI, Tomoyuki NANRI and Tomomi MARUTANI

Abstract

In 1926, due to snow melting caused by the eruption of Mount Tokachi, volcanic mudflow flowed down to the Furano River and Biei River. In Biei, within the area of volcanic mudflow, two areas were found. 1) Forest area which was not washed away by the  volcanic mud flow. 2) Forest area where trees were washed away by the volcanic  mudflow. It is important that a buffer zone be establish of mudflow with forest and to evaluate the capture effect of volcanic mudflow sedimentation and the depressor effect of woody debris of vegetation. In this study, It was analyzed that the actual situation of volcanic mudflow sedimentation and trees survival/loss in Biei River through deciphering aerial photographic and field survey. Based on aerial photograph, volcanic mudflow down/sedimentation area and tree survival/loss area were interpreted. As a result, it is determined while many trees were washed away in the area of volcanic mudflow flowed down, trees survived in some area of volcanic mudflow sedimentation. Moreover, existence and nonexistence of sediments were surveyed by pit-investigation and the age of trees was estimated by the result of diameter at breast height survey and tree-trunk graph analysis. Based on these two results, the volcanic mudflow and the mudflow sedimentation range were clarified in detail by interpreting the distribution of the space of original trees and after flow event trees.

Key words

the Taisho mudflow, the Biei River, tree survival/loss area, diameter at breast height survey