近畿・山陽地方の花崗岩土壌中のテフラ起源粒子と母材の堆積状態
1990 年 34 巻 2 号 p. 104-118
詳細
1990 年 34 巻 2 号 p. 104-118
In Kinki and Sanyo district there are only a few volcanos and so it is said that volcanic ejecta is distributed only on terrace or flat plain on the summit. But even on slope a few tephra-origin particles are intermixed in the soil. Then in the Granite low-reliefed mountain areas mineralogical and tephrochlonological study was made to make clear mode of deposition of forest soils. The results are as follows. 1. There was no tephra-origin particles in eroded immature soils in this area. Contents ratio of volcanic glass in brown forest soils were generally 1〜10%. 2. In many soil profiles contents ratio of volcanic glass of B horizon was more than that of A horizon. In C horizons there were no volcanic glasses. 3. Volcanic glasses in the soils were classified to at least 3 types according to figure and refractive index. The distribution of volcanic glasses sujested that they were mixed into the soil because of mass-movement. 4. It is considered that volcanic glasses were mainly originated from AT-tephra (erupted from Aira caldera about 22000〜25000 yrs. ago) and Akahoya-tephra (erupted from Kikai caldera about 6300 yrs. ago).
