秋田県八幡平トロコ地すべり地における地熱水の地下水への混入

抄録

Groundwater from bore holes penetrating into the sliding debris are studied with respect to isotopic and anion compositions. The groundwater from individual bore holes has characteristic isotopic and chemical features. The Cl^- and SO₄^2- contents and also the δD and δ¹⁸O show two mixing relationships, respectively, though these relationships are only partly accordant between anion and isotopic one. These relationships and the HCO₃^- contents can be interpreted as the result of 4 components mixing, i. e. (1) shallow groundwater similar to the surface water, (2) thermal water of NaCl-type and of meteoric water origin similar to the Zenikawa hot spring, (3) steam separated by boiling from the thermal water of NaCl-type, and (4) thermal water of SO₄ type, the origin of which is not obvious, but may be the same as the Sumikawa hot spring of volcanic steam origin. Different mixing manners occuring within a close distance suggest that these two thermal waters are individually coming up through separate vertical fissures. Temperature and pH of the groundwater seem to be controlled by interaction with rocks.