The chemical composition of spring waters from Mushigame landslide and its neighbourhood. : The chemical composition of ground water in landslide area 4

Spring waters (54 samples) were collected from the landslide area and stable area in Yamakoshi village and its neighborhood (Fig. 1, 2) and analyzed for major ion constituents (Ca^<2+>, Mg^<2+>, Na^+, K^+, SO^<-->_4, HCO^<-->_3, and Cl^- ion). The distribution of each elements was discussed reffering to geologic nature of sampling location and summarized as follows. 1. Electrical conductivity of spring waters from study area was 40～510 μs/cm. It correspond to the ion concentration 0.82～3.6 epm. As the class frequency distribution of total ions is not normal or log-normal distribution, it is concluded that the origin of chemical constituents of them is prural (Figs. 4, 5, 6). 2. Sodium ion is a dominant cation in many samples (Fig. 3, Table. 1) and its concentration is high in Shiiya formation. As chloride ion concentration of the most samples from Shiiya formation is higher than that of rain water and average river water in Japan, it is assumed that chloride ion originated from gas-bline like water distributing in this formation (Figs. 7, 8, 9). 3. Concentration of hydrogencarbonate and sulphate ions are high in samples from springs in Shiiya formation area. The hydrogencarbonate ion may also come from carbondioxide gas dissolved in gas-bline like water. Sufate ions are produced by bacterial oxidation of pyrite found in mudstone (Figs.10, 11). 4. Calcium and magnesium ions also rich in Shiiya formation area. Generally Ca/Mg ratios are low comparing with average river water in Japan. High Ca/Mg waters were found in springs in volcanic rock area and Shiiya formation (Figs. 12, 13). 5. The characteristic nature of the spring waters from Shiiya formation area suggests the vigorous weathering of the mudstone and should be related to the frequent occurrence of landslides in this formation area