제주도 서귀포지역 용천수의 기원 대수층 및 용출 유형

Abstract

In order to clarify the aquifers and seepage patterns of springwater in Seogwipo area, we examined the surface geology around springs and the geological cross-sections based on the boring cores for the development of groundwater. The water sampled from springs and wells were also analyzed for its SiO2 concentration. Trachybasaltic and trachyandesitic rocks are underlain by Seogwipo Formation, suggesting the existence of multi-layered aquifers. Nine springs are situated at the bedding plane between trachybasalt and trachyandesite, while two springs are located at the pyroclastic bed within trachyandesite. Because impermeable trachyandesite occurs thickly in the zone of unsaturation, groundwater does not percolate the rock and then migrates laterally at a relatively shallow depth. As a consequence, springs are well developed at valley bottoms, sea cliffs, and feet of trachybasaltic lavas overlying trachyandesite, in the coastal region where the rock is broadly exposed. The SiO2 concentration of springwater in the coastal region is higher than that in the upstream region where the altitude of springs is higher than that of water table. By contrast, the altitude of springs in the coastal region is nearly equivalent to that of water table. It indicates that the coastal springs are likely formed by the seepage of groundwater rising from a main aquifer.