Geological and geochemcical studies on the slope failures and debris flows in the Ura river basin, Nagano Prefecture : part 2

This second paper as continued first paper (AOKI et al 1982) deals with the results of research in the Ura river basin carried out in1981. The results can be summarized as follows: 1. Pyroclastic deposits exposed along the Kanayama river were hitherto recorded as the sliding mass from mt. Hieda in 1912. From our studies, these deposits are not the sliding mass but are the lowerest part of the andesite group exposed at the cliff of mt. Hieda, (Fig. 1) 2. From the water content and consistency of soils, three types of soil can be recognized in this area. The soil of sliding mass occurred in 1981 (Fig. 10 and Photos 11～16) belongs to the A-type as shown in Fig. 3. 3. From the chemical analyses of spring water, the servyed area is divided into 9 zones as shown in Fig. 6. 4. During about 50 days in 1981, we could observe several debris flows by T.Ⅴ. as shown in Fig. 7, Table. 2 and Phot. 1. The observed data clearly shows the interrelation between the features of rain fall and occurrence of debris flows (Figs. 8 and 9.) 5. In 1981, abnormal change of patterns of electrolyte of river water was observed during rain fall or before occurrence of debris flows as shown in Fig. 11 to 16