[H-GM22_30AM2] Geomorphology

[HGM22-P06_PG] The characteristic of roots distribution on the slopes in Izu-Oshima where landslides were occurred by Typhoon No.26

3-min talk in an oral session

*Wataru MURAKAMI¹, Akiho OGAWA¹, Yasuhiro OGAWA¹, Hiromu DAIMRU¹ (1.FFPRI)

Keywords:Izu-Oshima, Typhoon No.26, landslide, roots distribution

Large-scale landslides were occurred in Izu-Oshima by Typhoon No.26 on October 16, 2013. By the urgent investigation after the disaster, it is reported that the landslides were occurred in the part within about 1m from the slope surface and the few rhizomes were on the slip surface. We surveyed the distribution of the fallen trees (species, height, the root depth, and the extensions (widths) of the roots) on the slope near the landslide. The surveyed fallen trees were a lot of Eurya japonica, and were the order of Ilex crenata var.hachijoensis, Prunus lannesiana var. speciosa, and Camellia japonica. Most of the surveyed fallen trees were about 5-7m in height, and the high one was 10m or less. The root depth of most fallen trees was 60-80cm; however, the root depth had the difference by the tree species. The Camellia japonica and the Prunus lannesiana var. speciosa had comparatively deep roots. On the other hand, the Eurya japonica and the Ilex crenata var.hachijoensis tended to be distributed shallowly the root systems. As a factor to which the root systems are not deeply distributed, a peculiar properties of soil situation of the volcano is pointed out. In this survey, the difference of characteristics of the tree species on the surveyed slopes was guessed as a cause, too.