THE CONCERNTRATION OF BICARBONATES IN GROUNDWATERS PASSING THROUGH A HYDROTHERMAL FIELD

Abstract

Groundwater of about 60°C flowing through the alluvial fan area in Beppu hydrothermal field has been considered as the result of mixing of usual groundwater, NaCl-type thermal water and subsurface steam originating from it. However, these chemical qualities are not uniform over this field, and two kinds of water are characterized according to the difference of their HCO_3^- contents. The geographical distribution of these waters shows a distinctive feature. One of them has about 500 mg/l of HCO_3^- content, and another more than 1000 mg/l. Such figures have been quantitatively explained by visualizing the difference between depths where groundwaters encounter the subsurface steam in relation to the observed geologic, geothermal and hydrologic conditions of the field.