The town of Kamisuwa, Nagano Prefecture is situated at the eastern shore of Lake Suwa, which occupies the Suwa Basin; a long trough runing SE to NW and practically surrounded by high mountains, including the volcanic groups of Kirigamine (1925m) and Yatugatake (2899m). The place is celebrated for its great number of hot springs in the town itself. About five hundred springs are being operated at present, chiefly in the alluvial plain of the Suwa basin. These hot springs have been investigated by D Satô (I) and K. Misawa (2).
At the request of the Municipality of Kamisuwa, the author investigated the physico-chemical, properties of some of these springs. He examined in all 118 springs including some cold springs outside the town, during the period between Nov. m Dec., 1930, and in Aug., 1931.
The temperature and pH were 'determined on the spot. The following were determined by analysis, either at the laboratory of the Kamisuwa Municipal Office or at that-of the Geographical Institute., Tokyo Imperial University: H₂S, free CO₂, carbonate, Ca, Mg, . Na, Fe, Mn, SO₄, Cl, SiO₂, N₂O₃, N₂O₅ P₂O₅, the amount of KMnO₄ consumed, the total residue, etc.
Excepting for total residue and sodium, volumetric and -colorimetric methods were employed, because of their rapid determinations. Sodium was determined by the uranyl zinc acetate method of Barber and Kolthoff (3).
From data obtained by these analyses, many maps of temperature distribution and some of chemical composition were drawn. These distributions show two quite different types:
(1) Water temperature type. As is seen in the distribution of the water temperature, large amounts of Cl, and SO₄ are found in several zones arranged en échelon, and slightly oblique to the trend of the fault scarp bordering the eastern side of the Suwa Basin. A temperature of 85°C, and Cll and SO₄ in amounts respectively of 300 and 150 mg/l are observed here.
(2) Water colouration type. This type of distribution has no relation to the echelon distribution of the preceding kind. As is shown in the distribution of carbonate, organic matter, and water colouration, we find a zonal arrangement parallel to the fault scarp. The amounts of these ' substances increase. toward the west, but a rapid rise takes place on the N-S line, which nearly coincides with the trend. of the railway. Both the hot and cold springs that are situated at the western side of the town are coloured yellowish-brown, while those at the eastern side are colourless. At the middle part of the Suwa Basin the carbonate amounts to 200mg/l.
Total residue and other constituents, such as Na, Ca, etc. show a mixed type of distribution between those of water temperature and water colouration.
The underground water systems of Kamisuwa are believed to comprise the following three systems:
(1) Cold-water system of the alluvial fan. This system occupies the eastern margin of the basin, its origin being the sinking of river water down the gravel beds of the alluvial fan. Its temperature is 10°C, colourless, weaky acidic (pH =6.0), and poor in dissolved substances (about 100mg/l).
(2) Cold-water system of the Suwa Basin. This occupies the, greater part of the basin and is chaiacterised by the yellowish tint of the water. Such. hot springs are . therefore called Akayu or Tetunoyu meaning red or iron hot water, due to abundance of CO₂ and alkali earth ions extracted from the basin deposits. The yellowish colour is derived from the humus layer lying between. the basin deposits The water is weakly acidic (pH=6.2) and rich in dissolved substances (about 600 mg/l).
(3) Juvenile water system. This is colourless and hot (90°C). Dissolved solids: amounts to 1.3gr per liter.