Source area of heat and NaCI for hot springs in Gora region, Hakone

Abstract

This study determines the source areas o f the heat and chemical components at a hot spring from a hydrological viewpoint. The study area, in the Gora region of Hakone, Kanagawa Prefecture, is one of the most famous hot spring resorts in Japan, locates upon the northeastern slope of the central cone of Hakone Caldera. High-temperature NaCl-bearing water -the presence of NaCl is one of the representative chemical properties of hot springs in this region- is formed by the mixing of groundwater with magma-derived thermal fluid (Oki and Hirano,1970).
The spatial distribution of the hydraulic head to a depth of several hundred meters was estimated using measurement data collected from 1960 to 2000. The data reveal that the groundwater flow has a downward component. The high-temperature NaCl water shows a WNWESE zonal distribution that does not correspond to the direction of groundwater flow and does not related to the boundary of the hydrological basin. It is therefore concluded that this zone is the source area of the heat and chemical components of the hot spring. The Gora region lies within a stress field marked by NESW extension; therefore, the source area is inferred to have formed under the influence of tectonic stress.