Underground water in Kawazu-dani region

Abstract

I carried on a series of investigation as to temperature of underground Water, and as to distribiltion of pH and C1^-content, in Kawazu-dani region, southern part of Izu from March 3 till 5,1068, and again from April 3 till 4 in the same year; add I gave some consideration to their origin.
The region I investigated is a place where there springs up hot water in such parts as Yazu and Mine it is noted, too, for its intensive cultivation of flowers by the use of thermal water and the heat of the earth. Kawazu-dani region is a narrow place,3.4 km from north to south and 1.0-0.5 km from east to west, with the Kawazu River flowing through the central part of the valley. As to the geology there, the basis is made up of layers of Yugashima groups (andesitic lava, tuffaceous breccia, and tuffaceous sandstone), on which are formed Shirahama groups of layers (a deposit of quartzous andesite). In this region, especially, there are tuffaceous sandstone and basalt so well developed that they are are found everywhere and have a complex distribution. On the right bank of the Kawazu River there is a terrace,110 m or so in relative height, which is chiefly made up of andesitic big gravels; and on the left bank is a enountainous area,110∼ 120 m in relative height. As to the geological structure, many investigators presume that there happened a fault from north to south along the Kawazu River. After this fault, it seems, there occurred another fault from east to west, which caused the layers to be cut into pieces.
(1) It can be deduced, from topography, geology, Cl^- content, temperature of underground water, that flow from thermal water in the central part (the spa of Mine) runs out into the right bank of the lower stream and into the plain of the left bank.
(2) It seems that hot water of the spa of Mine flows down, underground at the depth of 200∼ 300 m, along the Kawazu River, raising the subteranean temperature and that of underground water of the plain on either side of the Kawazu River.
(3) The hot spring areas contain a vary large amount of Cl^-, and this amount becomes lower, according as we go downstream. Judging from topography and geology, the high amount of C1^- content in Tanaka area cannot be considered to be due to fossil sea salts. So this is perhaps because of thermal water flowing, along the crack of the layers, and staying in the hole.
(4) The relation between underground water and hot spring water could be traced by investigating the distribution of pH a little more minutely. According to the result of investigation, pH of the underground water is 5.0-6.8, showing slight acidic reaction; while pH of water in the Yazu hot springs is 7.0-8.6, and pH of water in the Mine hot springs is 7.3-8.7, showing alkaline reaction.