• The Journal of Engineering Geology
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• v.34 no.2
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• pp.207-216
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• 2024

This study clarified the flow path of Choosan Spring, Nari Basin, Ulleung Island, South Korea. The orientations of faults and fractures developed on the inner edge of the caldera were identified as major factors affecting the flow path. The main flow paths include fracture zones oriented N-S and E-W. The spring also flows in a NE or NNE direction under the influence of the irregular shape of the caldera, which slopes to the NNE. Using Entrobacteriaceae species as tracers, it was found that Nari groundwater flows toward Choosan Yongchulso. However, the small number of water samples used in the analysis limits our understanding of the flow path from Sungin Valley to Nari Basin and Choosan Yongchulso.

• The Journal of Engineering Geology
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• v.34 no.1
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• pp.13-24
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• 2024

The purpose of this study is to identify the geology, geologic structure, hydrogeology and geomorphic characteristics of the Nari Basin and establish the controls on the discharge of water 20,000~40,000 m³/day from the Choosan Yongchulso, Ulleung Island, South Korea. Pumice and lapilli tuffs showing well-developed stratification are the predominant rock types surrounding the spring. The spring shows a structure whereby discharge occurs along a lens-like erosion cave formed by differential erosion of strata comprising tuff or pumice tuff. The Choosan Yongchulso is located at the point where the planation surface of the Nari Basin' ends and steep slopes begin. The basin is bounded on all sides by these steep slopes, except in the north, where the Choosan Yongchulso is located. Given these geomorphic characteristics, the Choosan Yongchulso is regarded as the ultimate outlet of the basin catchment area.